stinky

DC Designs

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1. Chris,

Comparing speed to Allister? Its hard to say. In the northerlies Allister seemed to go off by himself upwind when the rest of us were going inshore where we could see wind. His boat looked like something from 1960, but he most often cane out ahead of a lot of us. I seemed to spend moretime with Steve and Oliver.

One race I remember well with Allister and Phil was H1 of the WC with a reasonable southerly. They were faster upwind which I balanced it downwind. It ended up close depending on who swam or messed up tacks. They both messed up the last one and I beat them.

 

2. Seabag:

My mast is about 6kg but most of that is in the bottom section, and 2ft of that is in the boat.

 

3. Danny,

My sail has a Zip almost all the way up to satisfy the rule. It is a heavy zip the light one failed while first rigging it.

 

I do not think there were any canoes faster than the Log deep reaching or running. It was also very impressive beam reaching which is against the theory agaoins the sloops. I passed so many boats downwind every day it made the poor upwind performance feel better. I even passed Chris on at least one occasion. And the sail is 0.6sqM small while I am 86kg..

 

I think a lot of my great downwind speed is because the sail is not stuffed up bt leeward stays and spreaders. It can go out square or over square with no distortion to the sahpe. This tallies with Andy's lack of downwind speed.

 

So I am reluctant to leave the unstayed Una rig yet. Adding forward raked diamonds will stiffen the mast considerable. I might be able to lighten the mid section and reduce its diameter, but the pocket has to go unless I fit 3 separate Zips?

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My impression was that Andy had a bigger reaching advantage than upwind last year. Square running, well I dunno, there seems to be a lot of technique about that in Canoes I don't have judging by the way everyone goes past me... I'm not that happy about releasing the leeward shroud on the runs and don't do it: Phil is probably right about that. Hopefully a DC will be able to be sailed with a bit of heat in most conditions.

 

Gust response seems to me important in Canoes, judging by how much easier and faster my boat seems with a more-flexible-than-conventional plastic stick against the previous tin ones. I'd hate to sail the boat with a telegraph pole.

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Jim, you may have openned another can of worms. What is gust response?

 

The physics of sailing say that the load on the rig, the sail leach etc is a function of the righting moment applied by the weight of the crew and boat. It really has nothing to do with variations in wind strength if the boat is sailed upright or at a constant heal angle, with no lateral changes in crew position.

 

A lead mine boat does get higher loads as it heals over because the lead moves further off centre, a wide dinghy can gain a little if it heals more and the centre of bouyancy moves to leeward. But a narrow boat like a DC , moth or cat on one hull can not gain any significant RM by healing, so in a gust the rig can not gain any extra loads, the leach can not get any extra tensionn, so the mast can not bend any more, So there is no gust response. UNLESS the crew eases the sails or the skipper feathers the helm.

 

Multiple Moth, 18 and 12 champions, the "professor", Emmet Lazich wrote this up very well in a long forum thread on the Aust 12ft skiff site, its worth a read.

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I would expect that when a gust hits there will be some hysteresis (time delay) between when the mast flexes and the leech lets go and the hull starting to rotate to leeward. This would be a function of the rotational inertia (in this case righting moment) and flexibility of the rig.

Geoff Harman

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The hysterisis is the supposed gust response.

Geoff Harman

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So there is no gust response.

I'll have to do a lot of thinking about that... can you provide a link to the Emmet L post? The transformation in the behaviour and manageability of my Cherub when I switched from a telegraph pole stiff tin rig to a nice responsive C-tech plastic one was like getting a new boat.

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Andy P – I can understand that an actual windsurf rig, even stayed, would be far too bendy and the sail shape all wrong for the canoe, which has orders of magnitude more RM.

Absolutely hear you re: the mast weights – my belief is that an unstayed canoe rig would have to be proportionally stiffer than the finn rig, therefore weigh, say, 10+kg. Obviously this is not a trivial amount of weight in the context of a 50kg canoe, nor is the cost of 10kg of carbon/epoxy…

Just to illustrate, I reckon that a finn and moth with appropriate sized sailors would generate similar sized RM, so a unstayed moth mast designed to the same concept would be approx 7 or 8kg!!

On the flipside the benefits, if done well, would include no windage/cost/complication from stays, and poss slight structural simplification of the boat, as well as the obvious ability to square the boom downwind with no interference on sail shape from stays.

I do believe that technology has moved on enough since the 70s that an unstayed rig would be far less compromised by a lack of staying than it would have been back in the day, particularly on such a skinny boat. The luff curve would be so much less that cunningham to prebend the mast would be uneccesary.

 

K76 – the IC has a max mast height that practically limits the aspect ration one can achieve. Also the canoe, esp DC has a very narrow shroud base, especially compared to the huge base of the A class and large base of the moth.

If the shroud base issue is extrapolated to the natural conclusion of zero, then we have, in effect an unstayed rig but with huge compression, hence why an unstayed rig might work well on this kind of boat.

 

Phil S – I can well believe you were dynamite downwind – I’d wager that the sloop rig becomes less efficient anything lower than a really broad reach. I’m sure diamonds would def improve the side stiffness lower down and thus pointing. The rig would still be wobbly around deck level but the lower leech would be more controlled. Another point is that the una upwind will suffer from having a high foot and losing out on endplate effect – maybe a longer foot, nice and low on and forward of the carriage then cranked up to give the helm space would work, although this would require some funky boom action, prob impractical.

 

Amati - A shorter mast would not need to be so stiff to maintain a similar ratio of midspan deflection to cantilever length at sailing righting moment so sawing the relevant amount off the top of a finn mast would be a good start.

One of the better finn lofts would be able to have a stab at this I reckon – North dominate at the moment I think, but I think Quantum, or WB in finland might help.

A very rough order of events would be: shorten finn mast, add material to stiffen approx 30% while maintaining the distribution of f/a and athwartships bend.

Do some static bend testing, measuring tip and deflection at bands at quarters. This can be nondimensionalised by the guys at the loft for the RM and mast length.

Ask them to take their best Finn mould shape (predicted flying shape under sailing loads) and adapt it to an IC planform (much shorter foot, roach, full battens) and the bend data that you’ve supplied for the luff curve.

This would prob give a respectable first stab. Ideally you’d get someone to run an aeroelastic simulation using the flow/membrain software or whatever the Quantum equivalent is, which would speed up the prototyping no end. This ain’t cheap though so would prob rely on having friends on the inside. It would be unlikely to get any development cash as the captive market isn’t that big.

 

Dan

 

Right, Gust Response.

I’ve not seen Emmit Lazich’s prose, but my take is that “gust” response is a bit of a misnomer, and that “dynamic response” would be a more appropriate term. Gusts, apart from at the onset, really aren’t particularly dynamic events.

 

In the non existent steady state, then dynamic response would be irrelevant, but in the real world, the boat is subject to motions from 1) the seaway and 2) the movement or inputs of the crew.

The effect of driving the boat through waves, or the crew moving about is to subject the boat to accelerations in the 6 degrees of freedom – heave; pitch; yaw; sway; roll and surge. In the context of sailing upwind, coupled heave and pitch are by far the dominant motions.

As anyone who has jumped up and down on scales will know, accelerations magnify a static force, therefore any of the equilibrium forces acting on the boat can be affected by motions in a seaway, or crew kinetics.

Imagine sailing along with a completely stiff rig. Hit a bit of chop which instantaneously imparts acceleration onto the boat, and suddenly the heeling force multiplies by the magnitude of the acceleration. This will require corrective action from the crew, whether steering, sheeting or kinetic, to maintain the equilibrium heel angle, course ect. Liken this to driving a F1 car over rough ground.

With a bendy rig and or foils (which, to one extent or another, all foils and sails are), the sudden increase in load will result in the mast bending more, the mainsail leech twisting open ect ect which will serve to lessen the effect of the overpowering force, and reduce the amount of input necessary from the crew to keep the boat sailing on an even keel. Liken this to driving a rally car over soft ground. (N.B not all aeroelastic effects work in the right way to shed or gain power dynamically – i.e under greater loads, badly supported masts will bend between the hounds, increasing jib luff sag, which is opposite to what is required, hence sloop masts are kept pretty rigid below the hounds, and all the dynamic response comes from the topmast)

If a mast is changed to one that is lighter for the same stiffness, the dynamic force caused by the mast whipping about aloft will be less, and also reduce the amount of corrective input required from the sailor – (think rally car on rough ground with lighter wheels/suspension components, or my previous post for the windsurf mast analogy.) This is what Jim C describes as manageability. The mast will recover its undisturbed shape sooner too (higher natural frequency).

 

Finn evolution over the last 30 years has basically been use of material improvements to increase and increase the stiffness of the mast within an acceptable level of manageability (corrective sailor input), allowing sails with less luff curve and consequently more control on shape. Another variable to consider here is that a fitter sailor of the same weight will be able to maintain corrective input for longer than a less fit sailor, thus allowing a stiffer rig with less luff curve.

Dynamic response can also be provided by other factors, such as sailcloth stretch (if it is in the right place!) Apart from planform aero factors, the square top mainsails currently in vogue will help out here – the area outside the straight line between the clew and head will stretch dynamically and depower the rig. This is why the threadlines on the 3DL sails on 18 footers and AC boats are generally pretty sparse in this area, allowing stiffer masts and more genoa (or spinnaker in the 18ft case) luff control, decoupling dynamic response from the mast alone.

 

I have writers cramp now and will have to work a bit later. Ah well.

 

Dan

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A lot of this is over my head but I have to say that this is a great thread. Dan - what do you sail?

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I used to be a pretty serious Laser sailor, that most technical of classes. I mostly windsurf now but dabble a bit in other stuff.

I believe one of my best mates is your cousin Tim..

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I used to be a pretty serious Laser sailor, that most technical of classes. I mostly windsurf now but dabble a bit in other stuff.

I believe one of my best mates is your cousin Tim..

 

Ha. My estimation of Tim has just gone up, didn't realize people that knowledgeable would hang out with him ;)

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Danny Boy,

 

Why wouldn't a UNA rig be faster in light air? I've always pictured a fast UNA rig for an IC as something A class like (like the rig Steve found didn't really work although it looks good).

Anyway, based on a rig like that: (all upwind)

 

In really light air the benefit of having more sail area up high surely would outweight any advantage from the two sails having a higher effiency?

In light to medium wind the two sail boat has the jib sheeted so tight that you are in marginal territory with the slot anyway. Once the slot gets too narrow you might as well not have the jib. You just end up with a very flat main to stop it backwinding. In this wind range you are still benefiting from more wind and better apparent wind angle up high too.

 

Once you start to depower the two sail rig is conceptually better with a lower center of effort and the slot is in the effective range.

 

I understand a triangular finn style sail would have a lower center of effort so all of the above doesn't apply. But is that the right way to go remembering that the canoe has relatively much more righting moment/sail area than a finn?

 

 

kz- but Steve's una rig mast isn't a Class A mast, which are really really really thin, which would conform more to the advantages of curved plate airfoils at lower re numbers (say, below 100,000 re for sure). Could it be that the jib serves this function, among others, at lower speed regimes?

 

Danny Boy, thanks for the reply. As usual, it's only money.....

 

Paul

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I would expect that when a gust hits there will be some hysteresis (time delay) between when the mast flexes and the leech lets go and the hull starting to rotate to leeward. This would be a function of the rotational inertia (in this case righting moment) and flexibility of the rig.

Geoff Harman

 

 

I think Geoff has got this right. In harsh gusts, when it is difficult to sheet out fast enough, flex in the mast top does give you a delay in heeling due to the inertia of the boat and crew.

 

So that is gust response. Dynamic response is a little different?

 

I almost understand what Dan says about dynamic response - I think. In an IC we might be encountering a wave upwind at what, say one wave every second or less? Dan's analogy about the F1 on a rough surface was helpful. So as we are blasting along over these waves and the top of the rig is gyrating all over the place the stiffer rig somehow imparts more heeling moment than a softer rig? Would'nt there be a balance between almost immediate and oppositing forces as you travel though the waves? Sorry if this is a stupid question.

 

Bill Hansen (Hanse Aerosports) told me that the end plate of the sail and board on a windsurfer was not effective if the gap got to be more than 25mm. Any thoughts?

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I think we're all singing from roughly the same hymn sheet. Dynamic reponse is just response to anything dynamic, whether gust or seaload. Like you say most wave encounters are pretty "transient" or quick - often too quick to trim to. Gusts are usually slower, although a decent rig will soften the effect of the gust, "automating" the rig.

 

The stiffer mast whipping about imparts more force back onto the boat if it is stiffer due to higher sectional weight (i.e same material, same diameter, thicker wall). If the mast is stiffer due to either a different section shape (larger diameter, thinner wall) or higher modulus material, then provided the sectional weight is the same it will feel the same to the sailor, only it will respond quicker (higher natural frequency - proportional to the root of the stiffness to weight ratio)

 

I think Hysteresis is maybe not the right term - I think strictly speaking hysteresis is a difference in the magnitude of one variable depending on whether its dependant variable is increasing or decreasing. I think its seen quite a lot in woven sailcloths - strain being less when load is being applied as compared to when the load is reduced.

Quite a lot of examples in electromagnetism but forgot all that as soon as I could.

 

As for the endplate stuff - I did a wind tunnel project at University about the boom/deck gap. Like most of university I can't remember much of it (blame Nige's cousin) but between my dodgy experiments and proper papers I read, it seemed that the gap was pretty important and its effect less absolute than the 25mm gap Bill Hansen talks about.

Some good stuff out there somewhere on theoretical optimal spanwise lift distribution for maximising driving force/righting moment ratios for varying endplate gap. Like I say though, lots of water under the bridge since then, time and beer addled my memory.

 

Dan

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Jim, you may have openned another can of worms. What is gust response?

 

The physics of sailing say that the load on the rig, the sail leach etc is a function of the righting moment applied by the weight of the crew and boat. It really has nothing to do with variations in wind strength if the boat is sailed upright or at a constant heal angle, with no lateral changes in crew position.

 

A lead mine boat does get higher loads as it heals over because the lead moves further off centre, a wide dinghy can gain a little if it heals more and the centre of bouyancy moves to leeward. But a narrow boat like a DC , moth or cat on one hull can not gain any significant RM by healing, so in a gust the rig can not gain any extra loads, the leach can not get any extra tensionn, so the mast can not bend any more, So there is no gust response. UNLESS the crew eases the sails or the skipper feathers the helm.

 

Multiple Moth, 18 and 12 champions, the "professor", Emmet Lazich wrote this up very well in a long forum thread on the Aust 12ft skiff site, its worth a read.

 

Phil,

 

I both agree and disagree with what you are saying. I think Geoff's point with inertia about the heel axis is important as it will be the trigger for something to happen. For a properly set up rig that something shouold be the topmast flexing &/or square top flexing out, twisting out the top in gusts, lowering the centre of effort of sails and increasing the drive force for the same righting moment. That is something you can't achieve to the same extent just by sheeting out or feathering, and you certainly can't match the reaction time. It won't last very long, in longer gusts you have to take manual action. Maybe we are discussing different timeframes for our gusts?

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K76 – the IC has a max mast height that practically limits the aspect ration one can achieve. Also the canoe, esp DC has a very narrow shroud base, especially compared to the huge base of the A class and large base of the moth.

If the shroud base issue is extrapolated to the natural conclusion of zero, then we have, in effect an unstayed rig but with huge compression, hence why an unstayed rig might work well on this kind of boat.

Dan

 

You're right Dan, I was thinking more sailplan than stick. Looking at the stick I agree that the finn mast is a highly developed piece of equipment. I hope we don't go there though, I think that kind of stick lends itself too well for professional analysis and advanced construction techniques. The Finn and the Europe has shown itself to be classes where you pay someone to develop stuff and that's no fun. But if its fast I'm sure we will go there eventually, me included.

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As for the endplate stuff - I did a wind tunnel project at University about the boom/deck gap. Like most of university I can't remember much of it (blame Nige's cousin) but between my dodgy experiments and proper papers I read, it seemed that the gap was pretty important and its effect less absolute than the 25mm gap Bill Hansen talks about.

Some good stuff out there somewhere on theoretical optimal spanwise lift distribution for maximising driving force/righting moment ratios for varying endplate gap. Like I say though, lots of water under the bridge since then, time and beer addled my memory.

To clarify what Chris Maas has mentioned, we did some CFD analysis with a NA student at UC Berkeley in the mid-late 80's to study the endplate effect relative to boardsailing (where the sailor feels a dramatic increase in power as he closes the gap.) The reason for the study was to clarify the contention by some that the gap need not be completely closed and the effect had more to do with mast rake and other bio-mechanical factors. Our findings showed a dramatic increase in benefit as the gap approached zero. Clearly 25mm is an arbitrary dimension given the many other variables such as foot chord length, aspect ratio and AOA. But, for our theoretical study of a 5sq-m high-aspect semi-elliptic windsurfing sail with a foot dimension of about 100cm, the benefit of a sealed endplate was clearly obvious relative to a gap on the order of and exceeding 25mm.

 

On the other interesting topic being discussed here, a compliant rig definitely is better in the realm of Formula boardsailing for a number of reasons including time-averaged effectiveness of the sail/rig based on energy storage and release in gusty winds and rough water as well as smoothing out the ride allowing the sailor to maintain a correct and more advantageous sailing position. To this end, I filed a patent application entitled "Sail with Selectively Compliant Surface" in July of 2007. Attached are pics of a Formula sail using this technology. The leech has 'flex panels' (black triangles) which allow the sail to compliantly and progressively automatically flatten and twist under increasing dynamic loads. The sail then returns to a fuller and tighter membrane as the loads subsequently decrease. The rig also involves a somewhat flexible mast which contributes to the dynamic response. An aeroelastic wing of this nature can react much more quickly and with an improved 3D profile than a non-compliant or mismatched rig/sail system. We did some preliminary tests with the Hoot which were less dramatic because the Formula sail flex panels were not up to the increased leech tension and stiffness of the rig. Whether it would work on a DC is unclear at this point but I think if properly executed, it would show promise in higher winds and rougher water where control becomes an issue.

Bill Hansen

Hansen Sails, LLC

hansensails.com

hansenaerosports.com

post-9717-1203636958_thumb.jpg post-9717-1203636925_thumb.jpg

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You're right Dan, I was thinking more sailplan than stick. Looking at the stick I agree that the finn mast is a highly developed piece of equipment. I hope we don't go there though, I think that kind of stick lends itself too well for professional analysis and advanced construction techniques. The Finn and the Europe has shown itself to be classes where you pay someone to develop stuff and that's no fun. But if its fast I'm sure we will go there eventually, me included.

 

To be honest I reckon that the finn/europe masts are so constrained by their rules that the external dimensions are pretty much fixed and there isn't much difference between the top guy's kit - I believe the europes post '96 tried to word their mast rule to create a 1 design (female) mould situation in order to control development costs, but I think a certain nation applied the sledgehammer approach and made its own tooling at vast expense, making a bit of a mockery of the rule.

From these same moulds different sailors can specify different layups to suit their required bend characteristics, which isn't too hard to do for those in the know.

 

I don't think that the IC would need to go that specialised - you'd get 99% of the performance for a fraction of the cost and hassle if the basic characteristics were remembered.

 

The OK class is a good case in point - after carbon sticks were legalised, contemporary europe/finn thinking was applied to the bend curves - normalized for mast length and RM. Most of these masts are circular made on male mandrels, just with modern bend characteristics. Sure, the aero performance compared to a moulded wing section will be a little poorer, but this is almost a secondary concern, even less so if a sleeve luff were to be used.

 

Dan

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Silly question: Thinking of the end-plate briefly seen on Alpha's wingsail, which I guess supposedly gave them stability issues, has anybody ever considered trying to generate the end-plate effect on the foot of the main? This is the basic principle behind why it's supposed to be fast to drop the foot of your jib so it's just sweeping the deck, no? I can think of plenty of reasons why not, but I'm just curious whether if anyone has ever given the gimmick a go.

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I think a certain nation applied the sledgehammer approach and made its own tooling at vast expense, making a bit of a mockery of the rule.

It was a classic example of how badly framed one design rules can make things really expensive... The rule defined external dimensions that were not what was required for Ms Robertson to be fast. Knowing the bend they required theyhad to reverse egineer a mould and lainate spec that would end up with the right bend, and then finally the mast had to be fine tuned by sanding down the inside of the tube with abrasive on a stick, because doing the tuning on the outside would have broken the one design rule... Europe foils are also viciously expensive because they are sods to construct... Witness the fact that a S glass Europe CB from my favorite foil builder costs 50% more than a carbon International Moth daggerboard...

 

has anybody ever considered trying to generate the end-plate effect on the foot of the main?

That's the reason for the "shelf foot" often seen on classes where loose footed mains are prohibited.

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Wow we are covering some ground now!!

 

Comments:

Re Finn mast option. I suspect that the 10kg weight might be rule controlled. When I was working out the Log mast I discussed with Ginge from CTech the potential of his OK dinghy mast. He said we could do a lot better and more cheaply with parallel tubes because the Ok mast has a heap of glass and bog just to make class legal weight. Maybe the Finn also has an anachronistic weight on masts left overfrom alloy or even timber spars.

Consequently I think an unstayed DC mast can be made stiffer than mine and still be well under 8kg. My mast is not that far off.

 

Link to Emmett's gust response thread:

http://z10.invisionfree.com/12ft_skiffs/in...hp?showtopic=53

Emmett's contribution starts on second page.

 

I think I agree with Geoff and Danny at least that the phenomenon we call gust response is more the rig yielding temporarilly before the inertia induced delay in healing or human reaction delay in easing sail. While I said that gust response does not exist I probably should have said that an automatic rig resonding to gusts is not possible.

 

The elasticity in sails including Bill's inserts still react to gusts like the mast, only due to inertia delays and crew reaction.

 

Now flexibility going into waves is another thiing all together and I know that is an area where my rig was poor, but then so is my sailing.

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regarding TT stern shape request earlier :

post-2679-1203704676_thumb.jpg

and after the flares added

post-2679-1203704707_thumb.jpg

pointy at both ends!

 

and the unstayed mast -

I didn't like the delay between gust/ response, or wave /response of the unstayed rig - a bit like driving a car on flat tyres with a bit of spongy rubber on the pedals. I like the go-cart feel of direct response.

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Speaking of Ass Kicking Canoes, results are coming in on the IC Ballot (One design vs box rule hulls) AUS, NZ, USA and CAN have so far all voted YES to the new rules.

B)

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Speaking of Ass Kicking Canoes, results are coming in on the IC Ballot (One design vs box rule hulls) AUS, NZ, USA and CAN have so far all voted YES to the new rules.

B)

and you forgot about POL! its a yes from poland!

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If we didn't have the pointy ends rule, what would the stern look like?

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I am happy to have a pointy stern. It parts the water really cleanly at low speed and there seems no disadvantage at high speed. It saves wetted surface and weight in the ends too. It makes the hull shape more forgiving to healling without upsetting longitudinal trim, or dragging a corner.

 

I believe the need to wide sterns on fast planing boats is a fallacy. Boats with moderate power lift on the midship area and as long as the buttock lines are straight aft they will plane happilly all day no matter what the stern shape is.

 

The canoe is long enough toget all the benefits without a need to add volume in the ends to carry its weight.

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I am happy to have a pointy stern. It parts the water really cleanly at low speed and there seems no disadvantage at high speed.

There is also some pressure recovery if the back is immersed, which cuts down drag if you tack with the weight too far aft...

As the boat is 17 feet long, easily driven and not short of buoyancy I to have doubts whether a fat posterior is necessary. Its been very instructive to watch how the water behaves round the stern. I'm not sure that the nethercott isn't a little too blunt, but how would I know!

 

In the Cherubs the trend for many years has been to go for smaller sterns. A new design is in build which reverses that trend, I guess maybe to reduce hull aspect ratio whilst riding on a T foil rudder, and I shall be very interested to see how it goes, especially when the wind isn't up.

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This thread has now surpassed 10,000 views!

 

 

 

The quality of the conversations, and the knowledge that is shared here is truly impressive. Thank you to all who have taken the time to contribute & keeping the thread on topic and positive.

 

 

 

John K

 

USA-244

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The world's video was ... SHORT. Could we see more of it? Better quality?

Please.

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The world's video was ... SHORT. Could we see more of it? Better quality?

Please.

 

I could ask everyone to come back and we'll film it again? Sorry, but it was made as an overview of the event.

There is also a class promotional DVD, however that is just a short concise overview of the IC Class.

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I could ask everyone to come back and we'll film it again? Sorry, but it was made as an overview of the event.

There is also a class promotional DVD, however that is just a short concise overview of the IC Class.

 

Could you possibly put any of the promotional DVD on the web Christian. I didn't purchase but I would be very interested to see some.

 

Willy

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Could you possibly put any of the promotional DVD on the web Christian. I didn't purchase but I would be very interested to see some.

 

Willy

 

The Promotional DVD is still in Draft, I've posted a copy out to the UK for review - it will be available online (youtube) via www.onthewater.com.au after they air it on their TV show. Copies will go out to each National Body for class promotion.

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The world's video was ... SHORT. Could we see more of it? Better quality?

Please.

 

 

Hey Gui,

I think you are refering to that short youtube video that there was a link to further back on this thread. The McCrea Yacht Club put together a longer version on DVD. I'll loan you mine if you can't find one. MYC also has an unedited version that is really long. Both Steve and Del have that I think.

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I checked back through some old correspondence, and we will not be getting a result from the international IC/DC ballot untill about 17th March, when the Canoe Sailing Committee meet.

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I checked back through some old correspondence, and we will not be getting a result from the international IC/DC ballot untill about 17th March, when the Canoe Sailing Committee meet.

 

Well shoot... I wanted to start on a new boat next week. I may not wait. There really is not anything I'd rather sail than a DC - whether the new rule is adopted or not.

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Well shoot... I wanted to start on a new boat next week. I may not wait. There really is not anything I'd rather sail than a DC - whether the new rule is adopted or not.

You are a credit to the force old son!

SHC

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Chris,

So how is the new boat different to ST?

My 1/4 scale model Log #2 under construction for Bill's tank has a little less spring up front and lower freeboard.

Phil S

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You are a credit to the force old son!

SHC

 

Quick Hijack: Steve, did you get my PM about the possible need for reinforcing?

 

As you were...

 

TC

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Chris,

So how is the new boat different to ST?

My 1/4 scale model Log #2 under construction for Bill's tank has a little less spring up front and lower freeboard.

Phil S

 

Lower dance floor; convex foredeck; chines extend further forward with a little more width in the bow; slight flat in bottom of forward sections; 10mm more rocker forward; narrower at the chine aft.

That is pretty much it. I wonder if all of our boats are going to be very similar in a few years? I have certainly been influenced by the other boats I saw at the worlds.

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Quick Hijack: Steve, did you get my PM about the possible need for reinforcing?

 

As you were...

 

TC

TC

Yes, you will want to do something depending on how you do it.

I will send you an email with some Pics

SHC

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TC

Yes, you will want to do something depending on how you do it.

I will send you an email with some Pics

SHC

 

Alright, sounds good. I might come up this Saturday with Mike to pick the boat up with him, so we could probably talk about it more in depth then. Thanks.

 

TC

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Alright, sounds good. I might come up this Saturday with Mike to pick the boat up with him, so we could probably talk about it more in depth then. Thanks.

 

TC

Talk to Mike! It has to be NEXT saturday the 8. There is too much frsh snow in NH to miss this weekend.

I also sent him a message to this effect!!!!

SHC

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Talk to Mike! It has to be NEXT saturday the 8. There is too much frsh snow in NH to miss this weekend.

I also sent him a message to this effect!!!!

SHC

 

Ok, I'll stop by his house today and let him know, next Saturday works better for me as well so I'll see you then!

 

TC

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QUOTE(IC AUS @ Feb 24 2008, 12:50 PM)

Speaking of Ass Kicking Canoes, results are coming in on the IC Ballot (One design vs box rule hulls) AUS, NZ, USA and CAN have so far all voted YES to the new rules.

 

 

and you forgot about POL! its a yes from poland!

 

And now the UK has voted in favour of the new rules - just France, Sweden and the Comittee to go!

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And now the UK has voted in favour of the new rules - just France, Sweden and the Comittee to go!

 

That's great news! Hopefully some of the AC guys decide to get involved with the development boats.

 

TC

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Gents.

The reason that gybing daggerboards work (if done properly) is this:

 

The sideforce that opposes the forces from the rig and propels the boat forwards is provided by the daggerboard, but also the rudder (usually by virtue of a couple of degrees of weather helm, as the rudder operates in the downwash of the dagger), and the hull, which usually has a lateral area of comparable size to the dagger.

Whilst the dagger and rudder are fairly effective lifting devices (high - ish aspect ratio, good section shape) The hull is a highly inefficient lifting surface (very low aspect ratio, dodgy shape) and as such cannot produce anything near as much side force for its area as the dagger or rudder. More importantly, the induced drag penalty of such an inefficient body when dragged at a yaw(leeway) angle is huge when compared to deriving the equivalent amount of lift from the foils.

 

A boat with non gybing daggerboard sails upwind through the water, with the hull and dagger making a course a few degrees lower than the heading (the leeway angle) The yaw angle or leeway is necessary to have an angle of attack over the lifting bodies and produce sideforce. If set up properly, the rudder should have some weather helm, such that it is carrying some of the sideforce, unloading the dagger and hull somewhat. The foils generate lift fairly efficiently, but the hull will have a proportionally massive induced drag for its modest contribution to the total side force.

 

The benefit of a gybing dagger is that, if correctly designed, the dagger gybes a few degrees each side of centreline meaning that the dagger can experience an angle of attack while presenting the hull at zero angle of attack - i.e no leeway.

This means that all of the lift creating the sideforce is generated by the (efficient) foils, and none by the (inefficient) hull, which now has no induced drag.

This net reduction in drag means that the boat can either go faster at the same heading, or higher for the same speed. The latter is usually far more valuable in a fleet racing context..

 

Whilst gybing the board means that the foils are slightly more highly loaded, and thus run slightly higher lift coefficients than if using the same foils fixed, it is inconsequential in the context of the reduction of induced drag from the hull

 

For this system to work well, the amount of daggerboard gybe has to closely reflect the leeway angle, which varies from class to class.

Furthermore there has to be a mechanism to "centre" the dagger downwind, else it will slop around pointing in a different direction to the heading of the hull, thus creating unecesary induced drag between the two bodies again, not to mention control probs.

 

Obviously there are some tricky things to get used to when first using a gybing board - little or no leeway meaning that conventionally foiled boats "fall away" to leeward Also, where people have had good judgement of their boat's abilities on laylines, the addition of a gybing board will prove tricky at first!

As for the track of boat / sheeting angles - I think that optimum sheeting angles should be made with respect to the track of the boat, rather than the centreline of the boat. This would infer that a boat with gybing dagger should sheet a little freer than the non gybing boat, by an equivalent amount to the leeway angle of the non gybing boat.

However, optimum sheeting angles are generally a function of the efficiency of a boat, with mirror dinghies sheeting far wider than IACC yachts. As the boat with the gybing dagger has improved its efficiency, it could go to a closer optimum sheeting angle, thus negating somewhat the previous paragraph.

Basically, I reckon amidst the general noise and variables oif dinghy racing, the last 2 points cancel out.

 

Dan

 

Respectfully I disagree with this last set of conclusions. Part of the benefit of a Gybing Board is the reduced drag, but similarly it benefits from even SLIGHTLY eased sheets that the higher AoA of the lower tracking hull allows. As anyone who has gotten "nose out" knows - this lets you "lean" on the tell-tales and roll the boat to leeward in fairly short order. So even a slight ease in sheets can result in a fairly dramatic increase in boat speed.

 

The second thing to realize is that an increase in boat speed on a high aspect foil, even a slight increase in boat speed, results in dramatically more lift. 49ers experience this a lot. Off the line it is important to be able to get your nose out so that you can ease your jib sheet about 2" at the lower spreaders. This increases the power to the sails enough and velocity goes up enough that the increased lift on the blade compensates for the lower angle of sail

 

So in practice a gybing board boat goes forward a bit faster and sails a bit higher. But how should we think about this

 

Another way to think of a gybing board is that it is effectively an assymetrical foil. Low speed foils that do not have to operate symmetrically have long used assymetrical foils to optimize lift. STOL aircraft, Gliders that don't have to fly inverted all use Assym foils. For a boat, if we only have to go fast on one board, Assym foils would be the way to go (Bilge-boarders do this all the time). But of course we can't. Except when we can. A gybed daggerboard essentially creates an assymetrical foil that automatically deforms on each tack appropriately. This is the same general theory and mechanism of the "flapped" boards - and is the same mechanism that Dennis Connors' (its hard to read DC without thinking Dennis Connors) AC Cat used.

 

The benefit of this is so great that This Paper estimates that a properly shaped assymetrical rigid wing has a 50% lift/drag improvement over a symmetric foil.

 

So the Reynolds numbers on water and air are dramatically different. Lets say that the lift/drag improvement is only 5% (because the gybed blade isn't a fully shaped assym foil, but instead the aft 80%-90% of the full foil), it still gives me the option of having the same lift and decreasing my drag by 5%, or increasing my lift by 5% and leaving my drag the same. Or I can compromise and decrease drag by 2.5% and increase lift by 2.5%.

 

Ok, decreased drag means more speed. In fact drag is 2nd order of magnitude effect of speed so a boat with 97.5% of the drag of Boat A will go roughly 11% faster. Means on a .5 nautical mile course with a stock boat doing 10knots, The decreased drag boat will gain 3-4 seconds which at 10 knots is 30-40 feet or 3-4 Boat Lengths.

 

Similarly 2.5% more lift reduces the distance you need to sail to weather because you will be sailing a better VMG. Net net, with only a 5% improvement in lift/drag you will see a benefit of probably 8-10 seconds, which at 10 knots translates into roughly 80-100 feet at the weather mark.

 

Now if you can lock your board going downhill, you don't pay any price for this other than some added complexity in the boat. For weight regulated classes, there isn't even any weight penalty for the additional hardware.

 

Note that looking a gybing board as part of an assymetrical/cambered foil also explains why its so important for the foil to be high aspect ratio and built by a top builder. A thick chord blade or a blade with its max chord too far aft will not do a good job of conforming to the aft 75% of a cambered foil, whereas a thin high aspect ratio blade will.

 

Now I don't know about you, but anything that gives me 160' for every weather nautical mile sailed, is damn well going to make a difference.

 

Note that if this was only about the induced drag of the hull, you could combat this by starting to leeward of a gyber and go into massive pinch mode. Massive pinch mode would put both boats into a mode where hull drag is in play, but the air drag of the sails and then AoA drag on the blades trumps any hull drag benefits. Yet in "pinch mode" is where the gybing board REALLY kicks butt. Its not optimal VMG, but relative boat to boat the Gybing board boat will trounce the normal bladed boat.

 

Now if gybers are sailing against gybers, there is going to be an optimal upwind angle that trades off reduced drag vs. increased lift, and you will have lanes that are as narrow as you see in that fleet based on speed and rig.

 

The big difference occurs when gybing boards are sailing against non-gybing boards. ONLY THEN will you see a difference in performance. And what you will see is a boat that can "climb out" from other boats, hold narrower lanes, or in some cases have noticeably better forward boat speed.

 

so I disagree that you don't get better forward speed with a gybing board.

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A gybed daggerboard essentially creates an assymetrical foil that automatically deforms on each tack appropriately.

I don't understand how you're drawing that conclusion at all.

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I don't understand how you're drawing that conclusion at all.

 

Ok, look at the flow around a board with 0deg AoA. You get symmetric lift, so net net you only get drag. So you increase the AoA to generate more lift to one side of the blade vs. the other. But we know that symmetric foils are less efficient than assymetric foils (why else would you use an assymmetric foil in situations in situations where lift/drag is critical) So now look at the SA 7035 foil. If I were to overlay the symmetric blade with the SA 7035 foil it would essentially conform to the top after 80% of the foil shape.

 

If we look at the flow around a symmetric blade with a positive AoA, its going to be very similar to that of an assymetric with its leading edge blunted.

 

Does that help?

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Ok, look at the flow around a board with 0deg AoA. You get symmetric lift, so net net you only get drag. So you increase the AoA to generate more lift to one side of the blade vs. the other. But we know that symmetric foils are less efficient than assymetric foils (why else would you use an assymmetric foil in situations in situations where lift/drag is critical) So now look at the SA 7035 foil. If I were to overlay the symmetric blade with the SA 7035 foil it would essentially conform to the top after 80% of the foil shape.

 

If we look at the flow around a symmetric blade with a positive AoA, its going to be very similar to that of an assymetric with its leading edge blunted.

 

Does that help?

 

Nope. On the minimal hull resistance types of boats I tend to have sailed I think that no matter what the hull is doing the symettric foil will be operating at the same positive angle of attack to the water whether or not its angled n degrees in the case and producing the same L and D. I am completely in agreement on the advantges of asymettric foils, but think the only way to get that with a single board is with a flap.

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Another way to think of a gybing board is that it is effectively an assymetrical foil. Low speed foils that do not have to operate symmetrically have long used assymetrical foils to optimize lift. STOL aircraft, Gliders that don't have to fly inverted all use Assym foils. For a boat, if we only have to go fast on one board, Assym foils would be the way to go (Bilge-boarders do this all the time). But of course we can't. Except when we can. A gybed daggerboard essentially creates an assymetrical foil that automatically deforms on each tack appropriately. This is the same general theory and mechanism of the "flapped" boards - and is the same mechanism that Dennis Connors' (its hard to read DC without thinking Dennis Connors) AC Cat used.

 

 

I agree with Jim here. Both gybing and non gybing boards will be operating at roughly the same angle of attack. And are therefor both 'assymetrical'. The gybing board might be operating at a slightly greater AoA because the hull is not contributing resistance to leeway. At the same time, when you put the bow down, the gybing board will be operating at a lower angle of attack because, even though the two boards are loaded the same, the gybing board is traveling faster and AoA will be less. Do I have that right?

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BalticBandit,

I'm not completely down with some of the stuff that you're saying here.

 

I agree that generally you'd possibly sheet freer on a gyber, as if you take the AOA as the angle of the sail to the track rather than the centre of the boat then this would be consistent.

 

 

The second thing to realize is that an increase in boat speed on a high aspect foil, even a slight increase in boat speed, results in dramatically more lift. 49ers experience this a lot. Off the line it is important to be able to get your nose out so that you can ease your jib sheet about 2" at the lower spreaders. This increases the power to the sails enough and velocity goes up enough that the increased lift on the blade compensates for the lower angle of sail

 

I think you have this a little wrong - naturally the amount of lift that can be achieved before stall increases with speed - who hasn't ended up going sideways after a crap tack? Or getting hiked/trapezing before getting the boat moving from standstill? Basically Trying to generate full RM without enough speed and stalling the foils.

In the context of actual sailing, for the 49er example, you'll be twin stringing in upwards of say 7 kts breeze. At this full righting moment condition the actual lift itself remains constant. If you put the bow down a few degrees and put on a couple of knots, the RM is the same, therefore for athwartships equilibrium your sailing sideforce will be the same. The lift coefficient actually reduces (with the square of the speed at constant lift). Because your lift coefficient reduces, the lift is generated at a lower AOA (leeway) and therefore your induced drag coefficient reduces (although this is tempered by the fairly linear increase with speed of the frictional drag). So max VMG occurs when the sum of the induced component (reduces with speed at constant lift) and the frictional component (increases with speed) is at a minimum.

Naturally there are plenty times on the course where you're forced to sail a few degrees high of optimum VMG, and similarly on a quick boat like the 9er if you can nudge forward enough you'll usually foot off over the boats to leeward to neutralise them. This is obviously tactical suicide on most keelboats where you'll barely go faster as you bear away.

In the pinching mode, whilst you are sailing a bit high with a higher induced drag component, and the lesser speed means you'll be making more leeway, you're very unlikely to get near the ultimate stall angle (about 20 deg) and thus the ultimate lift producing characteristics of the foil.

I'd respectfully say that if you're pinching so hard and going so slow that you're approaching 20 degrees leeway that you should have tacked off or footed out a bit earlier..

 

 

So in practice a gybing board boat goes forward a bit faster and sails a bit higher. But how should we think about this

 

Another way to think of a gybing board is that it is effectively an assymetrical foil. Low speed foils that do not have to operate symmetrically have long used assymetrical foils to optimize lift. STOL aircraft, Gliders that don't have to fly inverted all use Assym foils. For a boat, if we only have to go fast on one board, Assym foils would be the way to go (Bilge-boarders do this all the time). But of course we can't. Except when we can. A gybed daggerboard essentially creates an assymetrical foil that automatically deforms on each tack appropriately. This is the same general theory and mechanism of the "flapped" boards - and is the same mechanism that Dennis Connors' (its hard to read DC without thinking Dennis Connors) AC Cat used.

 

The benefit of this is so great that This Paper estimates that a properly shaped assymetrical rigid wing has a 50% lift/drag improvement over a symmetric foil.

 

I agree that a decent assymetric foil section is far superior to a symetrical ones, provided it is being used at the intended Cl, Rn ect, but without reading this paper I don't follow how an unflapped central dagger that needs to perform on both tacks can be assymetric, unless some pretty interesting flexibility has been built in. IACC yachts have flapped keels whereby when the flap is deflected, the low pressure (windward) side is completely fair. IACCs typically run enough flap to actually make a couple of degrees of negative leeway - this is because the assymetry of the heeled shape of a yacht, even a narrow cup yacht means that it will still be creating sideforce (and therefore induced drag) when it is at zero yaw angle.

 

So the Reynolds numbers on water and air are dramatically different. Lets say that the lift/drag improvement is only 5% (because the gybed blade isn't a fully shaped assym foil, but instead the aft 80%-90% of the full foil), it still gives me the option of having the same lift and decreasing my drag by 5%, or increasing my lift by 5% and leaving my drag the same. Or I can compromise and decrease drag by 2.5% and increase lift by 2.5%.

 

No problem with this - have the option of higher speed at same track or higher track at same speed.

 

Ok, decreased drag means more speed. In fact drag is 2nd order of magnitude effect of speed so a boat with 97.5% of the drag of Boat A will go roughly 11% faster. Means on a .5 nautical mile course with a stock boat doing 10knots, The decreased drag boat will gain 3-4 seconds which at 10 knots is 30-40 feet or 3-4 Boat Lengths.

 

Not always - depending heavily on the hull shape and length/displacement ratio, hull drag is only roughly proportional to speed - this is due mainly to "humps" and "hollows" in the residuary resistance (made up of mostly the wave making drag) due to alternating constructive and destructive interference between the bow and stern waves as the speed increases. Also there is the famous "displacement hump" at about Fn = 0.3 (about 4.5kts on a 16ft 49er) where the boat starts sailing uphill on its own bow wave, and a heavy boat's resistance will start to increase at a much higher rate. Obviously 49ers ect have been designed to minimise the effect of the displacement hump, furthermore a 9er rarely sails as slow as 4.5kts.

When a boat is planing (true planing is Fn greater than 1.0, about 14kts on a 16ft 49er) then the drag starts to rise at a lower rate more linearly proportional to speed for most boats.

Something like a speedboat hullform is horrendously inefficient below planing speed - many of us will have had to fairly bury the throttle on a RIB or dory to get it onto the plane, then to back loads while staying on the plane. Here the resistance actually reduces with speed for a while after hullspeed has been exceeded.

Luckily this effect is rare in sailboats as most need to be efficient over a broad range of speeds, mostly spanning the difficult semi-planing range.

 

Similarly 2.5% more lift reduces the distance you need to sail to weather because you will be sailing a better VMG. Net net, with only a 5% improvement in lift/drag you will see a benefit of probably 8-10 seconds, which at 10 knots translates into roughly 80-100 feet at the weather mark.

 

I think you've made a few big assumptions here, and you may be using the term VMG wrongly - if "better" VMG was gained by sailing higher, then sure less distance travelled. However if optimum VMG was achieved by higher speed at the same heading or even at a lower heading then you'd be sailing the same distance or even more.

Now if you can lock your board going downhill, you don't pay any price for this other than some added complexity in the boat. For weight regulated classes, there isn't even any weight penalty for the additional hardware.

 

Agreed.

 

Note that looking a gybing board as part of an assymetrical/cambered foil also explains why its so important for the foil to be high aspect ratio and built by a top builder. A thick chord blade or a blade with its max chord too far aft will not do a good job of conforming to the aft 75% of a cambered foil, whereas a thin high aspect ratio blade will.

 

I don't really understand this statement.

 

Now I don't know about you, but anything that gives me 160' for every weather nautical mile sailed, is damn well going to make a difference.

 

Still think you've assumed a lot with this value, but sure any racing sailor will take any advantage however small - we've all lost plenty of races by sub - boatlength margins, right?

Note that if this was only about the induced drag of the hull, you could combat this by starting to leeward of a gyber and go into massive pinch mode. Massive pinch mode would put both boats into a mode where hull drag is in play, but the air drag of the sails and then AoA drag on the blades trumps any hull drag benefits. Yet in "pinch mode" is where the gybing board REALLY kicks butt. Its not optimal VMG, but relative boat to boat the Gybing board boat will trounce the normal bladed boat.

 

Sure pinching is limited by the induced drag "AOA drag" of the hull/foils. I guess that if the hull of the gyber is being dragged sideways at a slightly less ruinous angle then it will suffer less. On the flipside, if boats are footing, going faster, less leeway for constant lift, then the dagger may actually be set at too high a gybe angle and the hull may be making a slightly negative leeway angle, thus losing out a little against its optimum. Bearing in mind leeway angles or board gybe angles are typically circa 3 deg then being able to accurately set the angle, and having everything aligned is pretty crucial.

 

Now if gybers are sailing against gybers, there is going to be an optimal upwind angle that trades off reduced drag vs. increased lift, and you will have lanes that are as narrow as you see in that fleet based on speed and rig.

 

This holds true for any type of upwind sailing.

 

The big difference occurs when gybing boards are sailing against non-gybing boards. ONLY THEN will you see a difference in performance. And what you will see is a boat that can "climb out" from other boats, hold narrower lanes, or in some cases have noticeably better forward boat speed.

 

so I disagree that you don't get better forward speed with a gybing board.

 

Whilst I don't want to appear chickenshit, this'll prob be my last post on this thread as I think fellas disagreeing on matters of sailing physics is probably not all that pertinent to "Kick Ass Canoes," and there are plenty other threads on this forum for that kinda chat!

I'm unkeen on just talking the talk when my circumstances mean that I'm not going to be in the market for a DC for some time.

 

Dan

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Thanks for the commentary Danny, I'll think about some of your points and see how they fit in my head. I was trained as an engineer/discreet mathy, so I look at models that map rather than ones that are inherently obvious or which seem "natural". And thats were the assym foil model comes from. I don't have the tools to draw it online, so perhaps I'll just draw it by hand, scan it and post it, but not in the next few days.

 

I too am not going to build a DC, but I am in the process of building a Swift Solo, and I am thinking of incorporating a gybing blade in that and have been doing my best to understand the physics of how that would work.

 

the conclusion I have drawn, and I'll try it out, is that for a gybing board to work optimaly, its max chord, needs to be further forward than for a non-gybing board.

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Speng is right about the sloop rig and the higher Cl due to it being a "slotted wing" but this only really applies upwind where the jib can be sheeted correctly with the slot working. Much lower than this and the jib cannot be trimmed efficiently, especially on a narrow boat like the canoe thereby negating this effect.

Down towards the dead run the jib is both blanketed, and a horrendously inefficient shape, hence the relative superiority of the una when sailing deep.

 

That's why I mentioned outboard sheeting. The further outboard you can sheet the jib is the deeper you can carry it properly. Since the ICs sail reaches downwind (and would probably do so on a W/L) you should be able to carry the jib. There are some other options for increasing the Cl downwind but my thinking is they involve some sort of mast rotation that nobdy seems to want to get into right now. Perhaps a Moth style rig's the way to go for an Una.

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That's why I mentioned outboard sheeting. The further outboard you can sheet the jib is the deeper you can carry it properly. Since the ICs sail reaches downwind (and would probably do so on a W/L) you should be able to carry the jib. There are some other options for increasing the Cl downwind but my thinking is they involve some sort of mast rotation that nobdy seems to want to get into right now. Perhaps a Moth style rig's the way to go for an Una.

 

I have been using a jib boom on my IC this last year. I recently added a tweaker so that I can keep it goosewinged downwind. Unfortunateley there are no other IC's at my club, so I can't quantify the benefits precicely, but judging by my performance agianst other classes, and from general impressions, there is a significant improvement in speed. Wind tunnel tests by One Metre designer Lester Gilbert suggest that goosewinging the jib will be beneficial at angles up to 120 degrees off the wind (onemetre.net).

 

Mal.

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On the sloop vs una question, is there any reason the jib size can't be reduced down to say a 1m2 blade to bennefit from the slotted wing effect and increase the main size to improve downwind performance?

 

It would take a bit of jggery pokery when sorting out a way to rig it i'd imagine but could be an interesting take on the sloop.

 

Cheers

 

AP

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On the sloop vs una question, is there any reason the jib size can't be reduced down to say a 1m2 blade to bennefit from the slotted wing effect and increase the main size to improve downwind performance?

 

It would take a bit of jggery pokery when sorting out a way to rig it i'd imagine but could be an interesting take on the sloop.

 

Cheers

 

AP

The old IC rule had a 2 sqM min, but the DC does not.

In other classes (like Aust NS14) which allow mixed sizes, 2sqM seems to be the min for performance.

It also might have something to do with how stiff a smaller sail becomes if it is made strong enough to last a strong wind regatta. The sail will not fall into shape in light weather.

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The old IC rule had a 2 sqM min, but the DC does not.

In other classes (like Aust NS14) which allow mixed sizes, 2sqM seems to be the min for performance.

It also might have something to do with how stiff a smaller sail becomes if it is made strong enough to last a strong wind regatta. The sail will not fall into shape in light weather.

 

 

interesting phil,

 

i know that it has been commented that a swing rig (a type of slotted main?) has been tried on the canoe but was found wanting. it seems to work on the R.C. Marblehead. Would it be improved do you think, if instead of being fixed to a simple rigid extension of the main boom, the boom could 'break its back' so to speak, in order to allow the jib to hang off more to leeward and open the slot for windward work?

 

bit of a beast of a sentence i fear. hope you can untangle the stream of consciousness .......

 

Frank

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interesting phil,

 

i know that it has been commented that a swing rig (a type of slotted main?) has been tried on the canoe but was found wanting. it seems to work on the R.C. Marblehead. Would it be improved do you think, if instead of being fixed to a simple rigid extension of the main boom, the boom could 'break its back' so to speak, in order to allow the jib to hang off more to leeward and open the slot for windward work?

 

bit of a beast of a sentence i fear. hope you can untangle the stream of consciousness .......

 

Frank

 

I have had quite a bit of experience with swing rigs on models. I'm pretty keen to try a swing rig on an IC, and I've spent a bit of time thinking it through. I have considered the break back style boom. Not only can you let the jib fall off to leeward upwind to open the slot, you can also crank it to windward when sailing downwind, which gains you a heavily cambered slotted airfoil, a bit like a C class wing on a downwind setting, so some potential for a higher CL from soft sails.

 

Having said that, such an arrangement might cost a bit of weight, and there could be issues with the jib flopping about during a tack, which could be disasterous on a narrow IC (I've considered sheeting from the jib end of the boom to address this problem).

 

If I do get around to building my new IC / DC I'll probably try a swing rig, but the first iteration will most likely have a rigid boom for lightness and simplicity.

 

Mal.

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FYI - The IC sailing community has surpassed the required 75% in support of the International Canoe class replacing their current measurement rules (Appendix 2 2005) with the current development rules (Appendix 4 January 2008). The final decision now rests with the committee, but we're one step closer :)

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I have had quite a bit of experience with swing rigs on models. I'm pretty keen to try a swing rig on an IC, and I've spent a bit of time thinking it through. I have considered the break back style boom. Not only can you let the jib fall off to leeward upwind to open the slot, you can also crank it to windward when sailing downwind, which gains you a heavily cambered slotted airfoil, a bit like a C class wing on a downwind setting, so some potential for a higher CL from soft sails.

 

Having said that, such an arrangement might cost a bit of weight, and there could be issues with the jib flopping about during a tack, which could be disasterous on a narrow IC (I've considered sheeting from the jib end of the boom to address this problem).

 

If I do get around to building my new IC / DC I'll probably try a swing rig, but the first iteration will most likely have a rigid boom for lightness and simplicity.

 

Mal.

PM rlm. Pretty sure he tried it, in what specific form I cannot say.

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The result of the 2008 Ballot is as follows:

That the International Canoe Class should replace their current measurement rules (Appendix 2 2005) with the current development rules (Appendix 4 Jan. 2008). The AC rules remaining unchanged.

78.6% in favour. Carried by the membership

Scoring 22 block votes out of 28 cast.

That Electronic equipment, which monitors and records the heading, position and performance of the canoe is permitted. Electronic equipment used for communication must not be used during racing and must be secured in the 'off' position from te preparatory signal until the finish of the race.

75% against Rejected by the membership.

Scoring 21 block votes out of 28 cast.

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What follows is RLM's written account of the short lived but exciting experiment with a swing rig on an IC.

 

Great Moments in Canoe Lore

 

by Rod Mincher (RLM)

 

This text was originally published in the International CanoesLetter November 1995

and re-printed here with permision

 

Steve Clark once remarked that I just had to be different from everyone else. Certainly, I have had my share of IC Experiments; some successful; some not so. One IC experiment was such a total disaster that I have been regaling the local fleet with the story ever since. The tale is of unforeseen consequences; the tale of "The Swing Rig and the First Race at Lewes Delaware"

 

The simple swing rig (1) consist of a "Megaboom"(2) that encircles the mast and continues forward, encircles the mast and continues forward, ending just short of the jib tack position. A jib boom is attached to the forward end of this megaboom. The main clew is attached to the aft end of the megaboom as in a normal rig. The megaboom is allowed to slide up and down on the mast and a powerful tackle to the boom creates a dynamic bow. With the tackle taken up hard, the tension up the main leach is balanced against the jib luff tension. Jib leach tension is determined by positioning the attachment point for the jib boom to the megaboom, a further aft attachment gives more leach tension and less luff tension

 

The attraction for using a swing rig on an international canoe is two fold; ease of tacking and increased downwind speed. The downwind speed comes from the rig automatically booming the jib away from the main's wind shadow off wind (the whisker pole effect) and secondly, the optimal main jib slot is maintained at all angles of attack.

 

In the spring of 87, the swing rig concept beckoned. Tacking without worrying about the jib plus a turbocharger for off wind speed; the combination proved too irresistible. I enlisted boat builder and newsletter editor Bill Beaver into the project (the first of several in our continuing collaborations) and set about building a mock up of the megaboom using my current rig, two by fours and clamps. With the dimensions finalized, Bill made up the megaboom as a box section using plywood sides and a pine top and bottom. Solid wood bored and shaped to accept the mast provided the juncture between the fore and aft parts of the megaboom. A jib boom tied onto the forward end of the megaboom completed the construction. A forestay taken to the stem-head was added to keep the mast upright since the jib luff was no longer part of the staying base.

 

Sailing trials took place out of SSA in Annapolis on Memorial Day weekend. I had two concerns. Was the megaboom strong enough to handle the loads without folding up? Would windward performance be abysmal? I expected that this rig would not provide the jib luff tension of a normal stayed rig. Bill in his Phoenix (Pre-Nethercott IC Design)with a rotating rig would be the trial horse: a potent pointing combination. Winds were light a 3-5 knots northeasterly, building to around 8 knots later on. Pointing was not stellar, but not a killer either. My standard jib was not ideal on the swing rig; the luff sag resulted in a full forward shape and the outside dimension did not match the triangle allowed by the swing rig, making it tough to get enough leach tension. Tacking was easier and downwind speed seemed to be faster, though not devastating. It was mindbending to have the jib right smack in front of your face as you reached along. All in all, at the end of the day the swing rig seemed to hold promise. The Megaboom held with no sign of distress, and a new jib would be all that was needed to make this a credible rig. Since I was working at Shore Sails at the time, a new jib was no problem. It looked like I could spring this on an unsuspecting IC fleet at the Nationals at Lewes Delaware the following week.

 

Lewes Delaware is tucked up just up the Delaware Bay from the Atlantic Ocean. Saturday of the regatta brought a onshore northerly of 15-20 knots with a nasty wave break. Launching and coming home were going to be a chore. The rig went up. The new jib looked to be an improvement. Now came the most fun of any IC experiment; racking up Shore Points. One point for everyone who comes up and after eyeing this contraption says "what the heck are you doing here?" More points for every explanation of the grand theory on why this will work. Unfortunately the time to collect shore points was short lived as everyone rushed to get ready. The wind whipped the sand across the beach and the lumpy seas forebode some exciting sailing.

 

I launched behind the main group. Bob Blomquist was helping everyone through the waves and holding the IC's in chest deep water while skippers sorted things out and climbed aboard. At least Bob wasn't laughing while he held US-163. "Do you think it will work?", he asked. "I'll find out", I replied. I climbed aboard and drifted slowly while I checked for any telltale signs of disaster. The jib was weather cocked straight to windward and the IC was noticeably docile with the swing rig "parked". Time to get this show on the road, for the start was not too far off. I tentatively trimmed the mainsheet and the IC immediately swung head to wind. PROBLEM! I couldn't use the jib to kick the bow around to one tack or another; the rig just tracked straight into the wind. I had the perfect rig for traveling backwards, witch I was doing at a good rate of speed. If I steered backwards onto a course that was abeam of the wind, the leach of the main would fill and US 163 would be right back into the wind again. BIG PROBLEM! Not only was the rig ideally suited for sailing backwards, it resisted any attempt to put it on any other course. This rig liked to be parked and going backwards! after casting about in my brain for sailing experiences with some historical precedent to get me out of this predicament, I resorted to jumping overboard and swimming US 163 abeam in the wind. For the next attempt to go forward, I kept the hull flat, even helled to weather to counteract heading up. I carefully jimmied the sheet. No dice! US 163 slowly but inexorably came up into the wind. I could see the problem. On the swing rig the main leach of the IC full battened main would always fill way before the jib could get powered up.

 

Two more attempts to get out to the race course by swimming the boat abeam of the wind resulted in the same futility. I had done it! I had devised a rig witch made the IC completely un-sailable. That in it's self deserved some kudos', but at the moment I was racking my brain on the best way to get back to the beach. The start had long gone and my graceful swoops and reverses had carried me about 100 yards off shore.

 

Into the water for the fifth time, I managed to get US 163 pointed at the beach. It was a broad reach back to the beach and amazingly, after a water start, the rig filled and we were tracking for the beach. Eureka! I was now planning, nay, screaming toward the beach. BIG, BIG, PRBLEM! An IC at speed eats up 100 Yards in a blink. How do I slow this rig down? Think quick! I can't luff anything; its Full Power Mama, here I come. Do I spin up and do a high speed capsize at the waters edge? Or do I get the board up all the way up; point her at the beach in a full bore kamikaze run? I chose the beach landing, more out of a gut feeling that, right now, I would rather be on terra-firma than anywhere else. I made up my mind to jump ship as soon as I felt US 163 tough ground.

 

Lars Guck had aggravated an old knee injury and had dropped out of the first race. Kind soul that he was, gimpy leg and all, he spotted me returning and waded in to help me dismount. With me gesturing and yelling wildly, he quickly realized that, yes indeed, this train had lost it's breaks and it was time to flee. I hit the beach according to plan, straight on, at full speed. I was even able to jump off, though I chickened out and bailed before contact. I expected US163 to immediately slam onto her side on impact, but she didn't. with the big rig still fully powered up, the stem proceeded to burrow into the sand. Another first, a nose dive into the beach with me standing aside, I watched my IC attempt to become a mole. I was astounded! I was flabbergasted! Slowly, I came out of my reverie as I realized that this was not good, and that something was bound to break. US 163 had managed to burry the stem to within an inch of the foredeck. I ran over, heaved on the and finally laid the swing rig to rest in the sand…..

 

Footnotes

 

1 For my experiment, I used what I called a simple swing rig. The Marblehead RC sailors in their continuing development have some further wrinkles on the basic theme. One interesting wrinkle; they have a break back arrangement where the boom forward of the mast rotates to leeward. This allows the jib to stay on the centerline as the main boom is eased. Such an arrangement would have been useful for the IC experiment.

 

2 The Marblehead RC sailors have a named the fore part of the boom the "Balestron". I am told the Balestron was the battering ram on the ancient Mediterranean warships. I am sure the Marblehead RC sailors will wince at the term "Megaboom"

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What follows is RLM's written account of the short lived but exciting experiment with a swing rig on an IC.

 

Great Moments in Canoe Lore

 

by Rod Mincher (RLM)

 

This text was originally published in the International CanoesLetter November 1995

and re-printed here with permision

.......

 

haha. i have heared bits of this story but never in full! thats so funny.

 

sounds like good times!

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I hadn't read or heard that one before, excellent stuff.

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I hadn't read or heard that one before, excellent stuff.

 

JK let's get those old newsletters up on the website. They are a gold mine.

 

KW

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Thanks John,

I do remember reading that before, maybe when I was fantacising about ICs or maybe whenI was planning a marblehead swing rig.

 

I think a lot of Rod's problem was that his boat had the fin poorly placed for the rig, On a std rig you can get away with it but on a swing rig or even a una rig, excess weather helm means you luff up before enough speed is available for the rudder to work, and overcome that imbalance.

 

The problem of the main leach sheeting first is teh same as with una rigs too, you need some twist in the main to balance this out.

 

The Hollow Log has neutral or even slight lee helm and very rarely gets in irons or rounds up. On the rough days like the last race day at McCrae I sail out through the breakers with the rudder only half in the slot, steering with heal and balancing with mainsheet until in smoother water and less traffic.

 

That being said I only ever made a swing rig for the marblehead as an A or #1 rig because I had seen some others with control problems in bigger C rig winds.

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JK let's get those old newsletters up on the website. They are a gold mine.

 

KW

 

 

The CanoesLetter Archive is about 1200 pages of gold. The most recent letters are easy as I have the electronic files. The older letters in the days before the PC are more dificult. Plenty of crazy ideas were tried and described back in the day.....

 

JK

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The CanoesLetter Archive is about 1200 pages of gold. The most recent letters are easy as I have the electronic files. The older letters in the days before the PC are more dificult. Plenty of crazy ideas were tried and described back in the day.....

 

JK

 

Is there anywhere we can see these online? I am a huge fan of the class, spirit of those involved in it. Would love to spend hours reading about some of the innovations that have been tried.

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On a slightly different note. People asked about a month ago about what shapes might be folded up out of plywood similar to the Stevenson Hollow Log.

Of particular interest was whether or not something similar to Chris Maas' String Theory could be generated,

Well here we are.

Introducing:

post-738-1205427789_thumb.jpg

Log Theory This model built using most of Phil's bottom panel expansions without the taper for a pointed stern and a topside plank that doesn't include the foredeck. It takes a bit of coersion, but the result is pretty similar to String Theory, at least as far as my eyes go.

I tried a different foredeck treatment to make reinforce the shroud wings easier. I don't think its unattractive.

Next Up:

post-738-1205427860_thumb.jpg

Second String

Similar to the concept of Log Theory, but the toposides are more conventional eliminating the need for the shroud wings, which are just a pain in the ass to build strong enough. I also wanted to try to raise the chine forward, so the panels are different. This boat has move V in the forward sections in oart because I used light glass instead of carbon for the tabbing. This indicates that there can be a fair ammount of variability in the stitch and glue process and you have to be willing to make judgements about how your boat is looking independently of what is in the instructiuon book. There are plenty of dirty tricks that can change the shapes around.

And Finally:

post-738-1205427819_thumb.jpg

Hollow Threat.

Much more conventional in many ways.

This is a single chine design that gets warped after the chines are taped. I used a long entry angle and matched it with a fairly pointy stern. This model has much less wetted surface than Log Theory, so it will be interesting to see whether the effect of longer quarter beam butts is better than the reduction in wetted surface.

Some group shots:

post-738-1205427925_thumb.jpgpost-738-1205428040_thumb.jpg

post-738-1205427974_thumb.jpgpost-738-1205429983_thumb.jpg

post-738-1205428156_thumb.jpg

 

Bill has offered to throw these things in the tank at some point and see if there is anything that can be concluded about them. I am not going to do much more here unless there is some interest in building one of these boats. I have enough notes and measurements to get to full size if someone is feeling up to it, and am always willing to be helpful. I just can't spend the next few months building full sized prototypes and testing them in the hope that someone will bite.

I should also advise that these hulls don't mean that I am in any way unhappy with the Josie model. I have a small tweak or two to make to that shape, but I think it is on par with anything ( or any string!)

Anyway if someone wants more info on these shapes, they can PM me.

SHC

post-738-1205427956_thumb.jpg

post-738-1205427993_thumb.jpg

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Similar to the concept of Log Theory, but the topsides are more conventional eliminating the need for the shroud wings, which are just a pain in the ass to build strong enough.

 

All looking good Steve... And why do your models look better finished than my whole d*** boat? Don't answer that...

 

I think I'd like to see head on and stern on upside down photos of the shapes if you have them. Is Hollow threat more rockery than some aft?

 

I do like the look of a boat with the hollow in plan in front of the shrouds, just looks great. Not that one should care of course. I've been looking at boats like that for getting on 10 years now I guess. The angle transom/pointy stern debate is going to be fascinating, I can deceive myself with dodgy arguments for both...

 

Much less wetted surface than String theory is interesting... When I put the ST offsets into a design program in seemed pretty good that way anyway, close to the Morrison, (and I never understand how Morrison gets his shapes to be such low w/a, although I think they suffer for it in other ways). I've been drawing thinnish Nethercott type shapes, hoping for more Jim tolerant handling, but the flat stern seems to be *so* much wetted area they just don't seem right.

 

Right, unthought-through comment coming up...

 

I've not tried a boat with shroud flares in wood, but I've always figured the real mayhem loads are vertical, and get taken by the front bulkhead in a direct line from shroud to mast (which is why I get bemused by the Brit habit of locating the shroud anchor two inches aft of the bulkhead). But giving it some more thought they must be just a pain in wood full stop [How did you manage it?]. I wonder if it would make sense to build a straight topside with the bulkhead tabbed out through it, and just fair in the flare with some light ply before the decks go on. should be more than a few hundred grams... Maybe even styrofoam and a bit of glass, then it goes towards your buoyancy [grin]

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Jim: The camera lies.

Unlike people, paint photographs well, no one ever said anything I built was well finished.

But back to the point.

post-738-1205435500_thumb.jpgpost-738-1205435472_thumb.jpg

Log Theory bow and stern views.

The stern is as square as the rules allow, String Theory actually isn't this blunt, but I thought I would moodel the extreme.

I figure you build the wings out of a stack of plywood bonded to the topsides, then tabb the crap out oof the underside over a generous ( say 12mm fillet.) in the way of the chain plates you would hide a compression strut behind the diagonal bulkhead and figure that the mast compression would also hole the chainplate down. Chris did as you thought and put a diagonal bulkhead through the topsides and then put a fairing over the top. It would be better to have maximum clearance under the wing, so I would be tempted to see if you could do it all with tabbing and compression.

post-738-1205435439_thumb.jpgpost-738-1205435686_thumb.jpg

Second String Bow and stern view. Both this boat and Log Theory have practically straight keels behind where the plate case would be. They have generally less rocker than I have thought normal for an IC, in the 50-65mm range.

As you can see the hull has a more pronounced V section, and I left more flare in the topsides to make the building of shroud flares unnecessary.

The stern is more pointy than String Theory but there is still lots of dance floor back there, and you could run the sliding seat further aft than on a more conventional deck plan.

post-738-1205435386_thumb.jpgpost-738-1205435399_thumb.jpg

Hollow Threat bow and stern views.

Again the rocker is less than I usually have, but it is more evenly distributed than on either of the above hulls. So I guess that means there is more aft. The chine of this model in plan form has a narrower entry further aft than Josie, Wonk or Lust Puppet. I tried to channel Andy Patterson and some of Phil's Chainsaw Moth into this one. It looks like a nice low risk shape. I would be surprised if it wasn't just fine.

SHC

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On a slightly different note. People asked about a month ago about what shapes might be folded up out of plywood similar to the Stevenson Hollow Log.

SHC

 

Strong work Steve!

Do you think that building method is any more difficult than flat panel stitch and glue?

Will you make a model of the tweeked Josie to send down the towing tank too?

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Steve,

Very nice models. Mine is progressing slowly because I seem to keep breaking hydrofoils and have to repair them. (What do I need to build into the deck to attach the towing gear?)

 

Comments on the three hulls:

LT was made with my bottom panel shape but it seems to be very Veed forward. This is probably due to not enough spread when seaming. My boat and model were seamed with the whole assembly spread out flat, stem is unseamed and the two stem panels are clamped across a batten to keep everything flat. This makes the bottom and chine seams flat and so the boat goes U shaped when bent up. I like the U shape for more buoyancy without a wide bow angle. The very first model I made was from only one piece of ply with the chine darts stopping just forward of the mast. I try to flatten the seams on subsequent boats so that the chine forward of the mast disapears.

The back half looks like my boats but with the wider stern.

 

SS seems to have even more V, but the other differences are too subtle for the photos and my perceptions.

 

HT certainly looks more like Andy's boat, the volume is there down low. It looks a bit like Josie too so it might ride a bit higher and make more noise.

 

My boats have straight spring in the back half. H Log has I think about 100mm spring forward (measured against 0 aft) and I have reduced that on the new model.

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Chris, the only difference is that you stitch and tabb the flat panels together in some intermediate shape and then crank it closed such that all the panels form at least some compound curvature. The problem is that without any fixtures, there is a bunch of improvisation that may make people uncomfortable. It is kind of artistic.

If you get it wrong, the stem comes out crooked, or the whole boat twists in some way that fails to inspire pride of craft.

I have some techniques that make that less likely to happen, but sometimes it feels like, if you will excuse the expression, fucking on the moon.

 

Phil, what I don't understand is how you can close up the center line dart, which has 100mm of taper in 2 meters and still keep the bottom panel flat. I end with some pretty decent angle at the front of the bottom panel, Like maybe an included angle of 90 degrees without doing anything with the very bow.

I also tab the topsides straight to the bottom using battens

I push the boat open at the mid length and also back aft to keep the chine angle as big as it can reasonably be.

I'm sure that over the years you have developed a feel for this that I'm not going to duplicate in a short time.

SHC

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HT certainly looks more like Andy's boat, the volume is there down low. It looks a bit like Josie too so it might ride a bit higher and make more noise.

Mmm, I think I like the look of HT best. I agree the feel of yours and Andy's boats. It took me a long time to understand the subtleties of Andy's bow style: the way it enables you to combine rocker and volume in the end with nice fine waterlines. I figure that a thin shallow bow probably doesn't slam that much more than a wider V'd one, and if you have vertical topsides then once its hit at least it doesn't keep bashing further into the wave... (if you see what I mean, I think that's poor phrasing)If I'd understood it a couple of years earlier I might have put one on my one-off singlehander and I reckon it would have been a better boat for it - easier to tack but no loss of volume forward...

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Steve...

Are you saying no intermediate fixturing or fixturing for the final tortured shape? I have done what you describe with a combination of female and male molds so that I get the shape I want without worrying about twist. Basically, I stitch the panels to the female mold set, and then crank it down to the male molds/bulkheads for the final shape.

-Eli

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"Phil, what I don't understand is how you can close up the center line dart, which has 100mm of taper in 2 meters and still keep the bottom panel flat. I end with some pretty decent angle at the front of the bottom panel, Like maybe an included angle of 90 degrees without doing anything with the very bow. "

Steve,

It will bend out with some help. Support the hull at each end so it sags in the middle or try pulling the two ends of the hull together with a rope, I did not need the rope with the canoes but have needed it with some moth hulls.

 

There is photo of full size log from 2006 on http://www.flickr.com/photos/72192268@N00/...57601502156525/

and one of the new model on http://philscanoes.blogspot.com/

 

Eli, you can see from the photos that there is no jig needed, in fact if two boats are made with the same ply cut out shapes, spread to the same dimensions with similar width and weight taping, and then pulled in to the same beam dimensions, then they turn out very similar. maybe not close enough for one design bigots, but certainly close enough for most people.

 

Thisisnot new science, John Mazzotti did the Unicorn A Cat in about 1966 and they are still sailing them as a one design class. Rod march copied the idea for the Tornado and the first few hundred Tornados were built this way to one design tolerances. I remember helping my dad build one about 1970. The canoe hull is actually easier than the cat hull as the width means the stresses are less and there is considerably less twisting loads.

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Is there anywhere we can see these online? I am a huge fan of the class, spirit of those involved in it. Would love to spend hours reading about some of the innovations that have been tried.

 

If John will upload the pdf files, I will put them on the site and password them so paid class members can use.

 

To join the class, go to www.intcanoe.us and register on the website. Then go here and join the class - $30 if you subscribe on an auto-renewing basis, $35 otherwise. Can make available on reciprocal basis for members of other non-US class associations.

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Thanks Phil. I understand the nature of stitch and glue, and I have built a bunch of boats with the method, with and without jigs. I think at some point people can forget about the logical way of thinking that you point out (not worrying too much about boats being accurate to the CH) and end up polishing turds as I have done on some occasions. The only reason I like a jig is that it is easier to eliminate twist...that said, I have seen some very fast boats that are very twisted.

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If John will upload the pdf files, I will put them on the site and password them so paid class members can use.

 

To join the class, go to www.intcanoe.us and register on the website. Then go here and join the class - $30 if you subscribe on an auto-renewing basis, $35 otherwise. Can make available on reciprocal basis for members of other non-US class associations.

 

Karl, It looks like I need to start scanning.....

 

Mat, I'm looking forward to seeing you in Ottawa again this year

 

Steve, Great job on the models. Second String looks very interesting!

 

Right now I'm trying to get house chores out of the way before the ice thaws and Mayhem needs a little TLC before it's next outing.

 

JK

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Thanks Phil. I understand the nature of stitch and glue, and I have built a bunch of boats with the method, with and without jigs. I think at some point people can forget about the logical way of thinking that you point out (not worrying too much about boats being accurate to the CH) and end up polishing turds as I have done on some occasions. The only reason I like a jig is that it is easier to eliminate twist...that said, I have seen some very fast boats that are very twisted.

 

I have been building boats (mostly models but some full size) using the same method as Phil for many years. More recently though I have begun to model the hull on the computer and generate accurate panel shapes and frame shapes. The lofted shapes can be plotted out full size, or even sent to a laser cutter. The result is a building method which is as fast as the fold up stitch and glue method, but deadly accurate as well, without the need for jigs. The limitation is that the panels should have no compond curvature in order to be developable, but that does not really limit the complexity of shapes that can be built. Of course you have to have the software and the experience to be able to do the original lofting work, but once that part is done, the hull shape is easily reproducable. So for those who are nervous about the free form method, there is an alternative. If there is enough interest, I could be persuaded to do the hack work.

 

Mal.

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Steve...

Are you saying no intermediate fixturing or fixturing for the final tortured shape? I have done what you describe with a combination of female and male molds so that I get the shape I want without worrying about twist. Basically, I stitch the panels to the female mold set, and then crank it down to the male molds/bulkheads for the final shape.

-Eli

Yes and yes.

When I built Wonk I made a jig for assembling the shell and then pulled it into shape around a bunch of bulhhead frames.

post-738-1205503647_thumb.jpg

Planking on the jig. I also wanted radius-ed chines, so the "tabbing" was in fact carbon bog carbon over 3"PVC pipe.

post-738-1205503752_thumb.jpg

The bulkheads were stuffed in and the boat wrapped to that shape.

The bottom panels were compounded about 1" such that they are a sort of arched Vee shape. This is better for stiffness and gets a bunch of displacement with practically no increase in wetted surface.

post-738-1205503854_thumb.jpg

Of course a bunch of this was made necessary by the tumble-home in the bow and what I thought was going to be a slick system for building something which seemed to have round bilges without having to actually build round bilges.

I would have to say that the pipe deal was a bigger pain in the ass than it was worth. Nevertheless the boat was built in less than a month.

SHC

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Very inspiring,

 

This has to be one of the best SA threads ever. No bickering, just smart people messing about with boats!

 

It's lots of fun cutting up bits of cardboard and making boat shapes.

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Indeed. Very refreshing to not have to see yet another douchebag utter "shut the fuck up newbie" Even said in jest, it always comes off as the overcompensating loser who feels that he needs to protect his position in a clique hierarchy... In any case, the discussion on this thread is fantastic on many levels.

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Which is why you should get your ass into a canoe and start sailing with us.

I mean could you hope to hang out with a better looking group of guys?

post-738-1205692145_thumb.jpg

For what is behind Door #2,

CAN YOU identify the anarchists in this photo?

SHC

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Got all of the blokes Steve but not sure about the lady on the right.

 

Who will tell the story of Sam's eye?

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She is a non combatant, innocent bystander, and otherwise person to be held harmless.

SHC

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Who will tell the story of Sam's eye?

 

It was a dark and stormy night. Lets just say it was a night too dark and to stormy for any witness to be able to see what really went on. A tale best told by he who didn't quite see all what was happening around him at the time quick enough :).

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Well... I don't think the night was all that dark and stormy but I have it on good account that the persons involved certainly downed a few dark and stormy's. ;)

 

anyway, I thought the general consensus was "what happens in McCrae stays in McCrae"...

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