stinky

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Oh. I think thats what those A-cat dudes in Michigan do, right? Sounds like a good way to go.

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397201_262703477116004_100001290620607_615442_87191535_n.jpgThis is a pic of a mates canoe here i393508_262229773830041_100001290620607_613748_775870787_n.jpgn Airlie.He doesn't know much about it but believes it has been modified.Still loks like a great ride.

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This is a one of a kind boat tat once started life as and International Canoe, the hiking plank dropped for wings and I believe about an extra metre or so added to the mast as well as the kite. The few times I've sailed against it up wind well off the pace as the extra weight and drag slow it down significantly compared to a nethercott and lacked height also. Downhill the big kite works but not enough around the cans to be worth while... But a good joy boat to have so great downhill slides on I suspect... The new rules minimalist approach so far appears the way to go in Canoe's Steve and others did a good job creating the current rules...

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This is a one of a kind boat tat once started life as and International Canoe, the hiking plank dropped for wings and I believe about an extra metre or so added to the mast as well as the kite. The few times I've sailed against it up wind well off the pace as the extra weight and drag slow it down significantly compared to a nethercott and lacked height also. Downhill the big kite works but not enough around the cans to be worth while... But a good joy boat to have so great downhill slides on I suspect... The new rules minimalist approach so far appears the way to go in Canoe's Steve and others did a good job creating the current rules...

 

Cheers mate shits and giggles it is.No one else to play with anyway.

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We've been working on a method for the home builder to build a carbon/foam IC using really simple tooling.

 

The goal is to build a light, stiff boat to any one of the fastest designs without the use of a solid mold.

post-16686-097885300 1325439904_thumb.jpg

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Briefly, the method involves laying up carbon/foam panels on a smooth table. The side panels are skinned with carbon cloth on both side. The bottom panels are only skinned on one side.

 

Like a female mold, the table gives the panels a smooth, fair surface on one side. This side is the outer surface of the boat.

post-16686-086560300 1325440910_thumb.jpg

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The jig is reconfigured and the hull is pushed into it.

 

The inside of the bottom panels is now covered with a layer of carbon cloth.

 

The foredeck and dancefloor are built in a similar fashion. Maybe the seat too.

 

This model is 1/4 scale. We haven't built a full scale boat. I'm reasonably confident the method will scale up nicely but there are always surprises when you take an idea into the real world.

 

I think this could also be a slick way to build Moths, A-cats and maybe I-14s, though 14's may have too much shape. What really surprised and pleased me was that I could push the shape into any reasonable configuration - more rocker, finer bow, rounder sections, whatever.

post-16686-039595400 1325441900_thumb.jpg

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The jig is reconfigured and the hull is pushed into it.

 

The inside of the bottom panels is now covered with a layer of carbon cloth.

 

The foredeck and dancefloor are built in a similar fashion. Maybe the seat too.

 

This model is 1/4 scale. We haven't built a full scale boat. I'm reasonably confident the method will scale up nicely but there are always surprises when you take an idea into the real world.

 

I think this could also be a slick way to build Moths, A-cats and maybe I-14s, though 14's may have too much shape. What really surprised and pleased me was that I could push the shape into any reasonable configuration - more rocker, finer bow, rounder sections, whatever.

 

Good work, certainly appears logical. Keep us updated on how the real world fares with this :blink:

 

Happy sailing,

 

Fish :)

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Chris,

 

That looks awesome...I'd be interested in either a Moth or A Cat version of this build technique.

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I'm not sure I'll take this project any farther. I mean, I already have an IC mold. Mainly I wanted to prove what I think is a really cool idea. Jake (he built the model above) may build a Moth this way.

 

I guess I'm hoping someone will pick up the idea from this point and turn it into a boat. I'm happy to help out with advice and maybe with building panels.

 

One thought I had was that the panels could be built on a 10' long table, rather than full length. It's no big deal to join the panels together full length.

 

If there's enough interest I could see making some kits that could be shipped cheaply in a box. It always a question of how much time and money I'm willing to lose on these propositions. Good thing my profession is also my hobby.

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amazing project ! I can see you're not suffering from cabin fever, at least in your shop !!

 

 

 

I'm not sure I'll take this project any farther. I mean, I already have an IC mold. Mainly I wanted to prove what I think is a really cool idea. Jake (he built the model above) may build a Moth this way.

 

I guess I'm hoping someone will pick up the idea from this point and turn it into a boat. I'm happy to help out with advice and maybe with building panels.

 

One thought I had was that the panels could be built on a 10' long table, rather than full length. It's no big deal to join the panels together full length.

 

If there's enough interest I could see making some kits that could be shipped cheaply in a box. It always a question of how much time and money I'm willing to lose on these propositions. Good thing my profession is also my hobby.

 

 

 

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I wondered when somebody would apply the stressed ply method to foam sandwich. Particularly like the outer skin being prelaminated. There could perhaps be some mileage in using contour foam to increase the compound-ability.

Pretty sure that the old gougeon book says that the method is more suitable to narrower and fuller forms (higher prismatic)

Currently I14 is 1040mm beam at midships RoF points giving l/b as high as 4.1 (although I think most are a bit wider aft.

Certainly they should be high cp.

This could be a very cool way of building a 14 on the cheap (kind of an oxymoron once you've put over £10k of kit on it) but anyhow my question is - how "designable" do you guys see it as being? I.e you could make a chined powerboat form without compounding and it'd be very easy to take something off the drawing board and develop onto the lofting floor. However with the stressed approach with a lot of compounding, is it just a case of making a shit load of models and guessing somehow if they meet the design intent?!

Dan

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Oh yeah - and I guess how you install bulkheads is important too - I seem to remember Phil s design doc for the hollow log suggested that anything other than polystyrene would distort the skin. I guess that he was using 3mm ply though, or thinner?

I certainly wouldn't want to use polystyrene as major structure to triangulate best part of a tonne of rig tension! Although I guess that 5mm foam is a bit stiffer once it is laminated both sides.

Dan

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After 3 ICs built out of tortured plywood I concluded you need to have a jig in order to build consistent stuff.

Like that's a huge surprise, right?

Maybe that the monster I designed is overkill, but if you are just paying for plywood and laser cutting, it probably pays off if you eliminate one bump in the hull.

The best way for this to work is if several people go in on the cost of the jig and help each other building several boats.

 

I have wanted to do a plywood 14 for a few years, the modern shape seems like it would be fairly easy to generate out of 3mm plywood and then get a 6mm core with an inside skin of Kevlar and carbon.

SHC

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There is a chap on your side of the pond building a very impressive ply 14. More trad method over frames, but looks really nice in any case. On the 14 forum.

But I guess the full length "chine" makes things more do-able.

It'll be interesting to see how he does on weight.

Trouble is, whilst even when the weight goes down to 70 kgs (Inc racks) the weight is pretty achievable, the nature of the tfoil means that there is a massive gain to be had in having a heavily corrected boat - all correctors in the gantry.

This in turn places a premium on exotic build techiques and risky scantlings, which is kind of a shame.

If there was some limit on placement on correctors, or a Finn style swing test then medium tech home build would be far more viable.

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I wondered when somebody would apply the stressed ply method to foam sandwich. Particularly like the outer skin being prelaminated. There could perhaps be some mileage in using contour foam to increase the compound-ability.

Pretty sure that the old gougeon book says that the method is more suitable to narrower and fuller forms (higher prismatic)

Currently I14 is 1040mm beam at midships RoF points giving l/b as high as 4.1 (although I think most are a bit wider aft.

Certainly they should be high cp.

This could be a very cool way of building a 14 on the cheap (kind of an oxymoron once you've put over £10k of kit on it) but anyhow my question is - how "designable" do you guys see it as being? I.e you could make a chined powerboat form without compounding and it'd be very easy to take something off the drawing board and develop onto the lofting floor. However with the stressed approach with a lot of compounding, is it just a case of making a shit load of models and guessing somehow if they meet the design intent?!

Dan

 

Well the topsides are easy to design anyway. At least on boats like the IC and I14.

 

For this model I had a great starting point by scaling down my full size hull foam patterns. I don't know how you would - accurately - design the bottom panels from scratch without a physical model. But once you have that first model - and who doesn't like to build models?- it looks like an easy thing to make modifications to the design without making a new model each time.

 

There doesn't seem to be a need for any bulkheads to push the hull into shape or hold it there once the carbon inner skin is on.

 

Structurally the stressed foam boat is no different than my mold built ICs and should use the same internal structure.

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Ah the reverse engineer - nice! I've templated core before by taking a quick splash from a mould, cutting it up and moving it around flat sheet until the entire boundary has been captured. Similar thing I guess.

I know that you can "unroll" developable surfaces in rhino, but there must be a way of doing it with compound surfaces. Will have a think...

 

Pretty sure that most of the 14s that bieker built himself were largely from flatstock - the topsides anyhow, the lower hull was stripped in foam over a male frame. Pretty low cost approach!

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Rhino 5 has some cool mash and smash features, but there is a program called TouchCad which for wrapping a d unfolding to flat panels with ability to alter panel shapes and have it affect the folded shape is pretty hard to beat. Unfortunately it's $1300, but you have to pay to play as the saying goes.

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Daniel, the Holllow Log was built from 3mm ply with a layer of 200gsm carbon on the diagonal inside. I would use kevlar if I did it again. There were 3 ply bulkheads as well as all the foam ones. But the ply ones showed on the outside.

 

About 20 years ago I built an NS14 hull from foam/glass panels without a jig. The stress and hence the compound component were minimal and the shape was not up to speed but it did build easilly. I think I may have had the glass on the inside which would have limited flexure, probably not a good option. I had previously built a Sabot by the same method but that is all flat panels.

 

I like Chris' approach and think that foam/carbon panels would work better and accept more flexure before skin failure.

 

The panel shapes are not that hard. Have a look at the Hollow Log article for a starting point. The shapes will be the same for ply or foam. You can widen the stern to suit current fashion but I am not convinced its the best way to go for an all round boat. The 45deg cut off transom design makes it simpler than wrapping the topsides to the canoe stern. I actually did not wrap the sides all the way back until I formed the hull shape (pulled the gunwales into design beam) because the chine edges make interesting S shapes as they follow the bottom curve to the CL.

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So Phill what would have happened if you put a 40mm wide doubler under the bulkhead with a 10mm bevell on each side to diminish the hard spot under the Bulkhead?

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So Phill what would have happened if you put a 40mm wide doubler under the bulkhead with a 10mm bevell on each side to diminish the hard spot under the Bulkhead?

That works, its what I used to do with stitch and glue ply 12s in the 70s. I dropped the idea from the moths to save weight. I did not do it with Hollow Log as I had skinned the inside with carbon first and thought that would do the job. It was strong enough but the BHs showed on the outside after a while.

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So Phill what would have happened if you put a 40mm wide doubler under the bulkhead with a 10mm bevell on each side to diminish the hard spot under the Bulkhead?

That works, its what I used to do with stitch and glue ply 12s in the 70s. I dropped the idea from the moths to save weight. I did not do it with Hollow Log as I had skinned the inside with carbon first and thought that would do the job. It was strong enough but the BHs showed on the outside after a while.

 

Of the 9 cherubs i Built and The first 12 Tejin Sailcloth which had ply topsides we never encountered this problem although we were using 4.5mm plywood (although it was sold as 4mm) but I have seen s/tape boats with hardspots (mainly early Tornados) when i spoke to the LKate Chris Tims of Adhesive Technologies here in NZ about it he said that it was from forcing the bulkhead in rather than just putting it in loose and coving it in place with a bit of glue .Is this also your opionion Phil

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Rhino 5 has some cool mash and smash features, but there is a program called TouchCad which for wrapping a d unfolding to flat panels with ability to alter panel shapes and have it affect the folded shape is pretty hard to beat. Unfortunately it's $1300, but you have to pay to play as the saying goes.

 

The free version of Delftship will develop plates....

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Maxsurf, rhino or many more will let you design in 3d. Then develop. The advantage with max surf over many others is it will tell you how much stress is in the plate once formed. There is a big difference between what can be formed mathematically and what can be done physically. What Chris is doing here is basically an at home version of DuFlex from which we have built cats up to 60ft.

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Of the 9 cherubs i Built and The first 12 Tejin Sailcloth which had ply topsides we never encountered this problem although we were using 4.5mm plywood (although it was sold as 4mm) but I have seen s/tape boats with hardspots (mainly early Tornados) when i spoke to the LKate Chris Tims of Adhesive Technologies here in NZ about it he said that it was from forcing the bulkhead in rather than just putting it in loose and coving it in place with a bit of glue .Is this also your opionion Phil

I think the thicker ply helps but weighs too much and does not bend enough.

I never force BH in, they always need a fillet of bog to hold in place.

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My approach for a plywood hull is to use closely spaced 3mm plywood frames (say 150mm spacing) bonded in with glue fillets. The hull panels would be stitched together and the frames inserted and bonded in prior to taping the panel seams. As long as the hull panels are developed accurately, this method provides an accurate hull shape with no jig required. Although there are a lot of frames, they can of course be laser cut to reduce labor.

 

post-3095-015656200 1325606238_thumb.png

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What Chris is doing here is basically an at home version of DuFlex from which we have built cats up to 60ft.

 

I'm not seeing how you can form DuFlex sheets into a compound curve though, short of cutting it into strips. Am I missing something?

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My approach for a plywood hull is to use closely spaced 3mm plywood frames (say 150mm spacing) bonded in with glue fillets. The hull panels would be stitched together and the frames inserted and bonded in prior to taping the panel seams. As long as the hull panels are developed accurately, this method provides an accurate hull shape with no jig required. Although there are a lot of frames, they can of course be laser cut to reduce labor.

 

post-3095-015656200 1325606238_thumb.png

I have built very nice wood boats by the "stringer frame' method.

3mm bulkheads on 300 mm centers.

4mmx 18mm stringers notched in.

Cover with 3mm ply.

Cut into strips about 150-200mm wide, 90 Degrees to face grain (i.e. the bendy way)

I put a bevel on each edge so they can overlap and then plank at 90 degrees to center

line.

post-738-038957100 1325628311_thumb.jpg

A cathedral shot of Patient Lady 5 showing what it can look like.

Skip and Terry at their best.

This was done the old fashioned way before Auto CAD and Laser cutting.

Structural band aids are visible, after 5 years of almost continuous use she was losing it.

Hulls weighed about 45 kg complete.

IC hull built the same way would weigh about 30 kg.

SHC

 

SHC

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My approach for a plywood hull is to use closely spaced 3mm plywood frames (say 150mm spacing) bonded in with glue fillets. The hull panels would be stitched together and the frames inserted and bonded in prior to taping the panel seams. As long as the hull panels are developed accurately, this method provides an accurate hull shape with no jig required. Although there are a lot of frames, they can of course be laser cut to reduce labor.

 

post-3095-015656200 1325606238_thumb.png

 

 

That would be a shame to cover up with a deck.

 

Do you know what that hull alone would weigh Mr. Nutter?

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My approach for a plywood hull is to use closely spaced 3mm plywood frames (say 150mm spacing) bonded in with glue fillets. The hull panels would be stitched together and the frames inserted and bonded in prior to taping the panel seams. As long as the hull panels are developed accurately, this method provides an accurate hull shape with no jig required. Although there are a lot of frames, they can of course be laser cut to reduce labor.

 

post-3095-015656200 1325606238_thumb.png

 

 

That would be a shame to cover up with a deck.

 

Do you know what that hull alone would weigh Mr. Nutter?

 

As drawn, without centreboard case or any additional reinforcements, the plywood weight is just under 15 kg, based on a wood density of 450kg/m^3, which I measured from some samples of 3mm gaboon plywood. I think it might be possible to come in at around 25-28 kg for the finished bare hull. The design shown has small wings at the aft end to widen the dance floor (as discussed elsewhere), which would add a small weight penalty.

 

I would like to avoid using carbon or glass for panel stiffness (wood is a light structural material, but a heavy core material). I would probably use Dynal to sheath the hull, for durability. I used this method on my existing sliding seat and it seemed to work ok. The seat, which longer than normal at 2500mm, came in at 9kg.

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My approach for a plywood hull is to use closely spaced 3mm plywood frames (say 150mm spacing) bonded in with glue fillets. The hull panels would be stitched together and the frames inserted and bonded in prior to taping the panel seams. As long as the hull panels are developed accurately, this method provides an accurate hull shape with no jig required. Although there are a lot of frames, they can of course be laser cut to reduce labor.

 

post-3095-015656200 1325606238_thumb.png

 

So I see the leeboard idea is catching on.

 

 

:lol:

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Chris, if the sheets are going into developable shapes then they can be formed (assuming they are not to stiff). In some cases we used to kurf cut the inside skin then re-apply which results in a similar panel to yours.

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My approach for a plywood hull is to use closely spaced 3mm plywood frames (say 150mm spacing) bonded in with glue fillets. The hull panels would be stitched together and the frames inserted and bonded in prior to taping the panel seams. As long as the hull panels are developed accurately, this method provides an accurate hull shape with no jig required. Although there are a lot of frames, they can of course be laser cut to reduce labor.

 

post-3095-015656200 1325606238_thumb.png

 

So I see the leeboard idea is catching on.

 

 

:lol:

 

Well, that wasn't quite what I meant. I just haven't gotten around to designing the CB case yet. However, a leeboard might be lighter. :D

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Something along the same lines from SUP land, if you haven't seen it before, 3 mm ply I think

 

 

What's kind of cool is the freedom in planform and rocker at the beginning without a mold or strong back. Try it with a model- even rectangular shaped sides are fun to develop. Slab sides, but not vertical might be slow? Light frames. Would need massive beefing up to resist twisting.....

 

Sent from my iPad

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cid:745E9134-9A27-4FEE-B47C-06657D37472A/photo.JPG

 

Here is a 14' try. 4mm ply. If you look at the bottom middle you'll see the stick I used to keep the top sides apart. Tape across bottom was not really necessary.

 

A nice serendipity is that with 4 mm ply, you get very close to b spline tension #1 on Vacanti:

 

Dammit, my iPad still won't put pics on SA. I'll get some pics on here when I get to the laptop. About 4 months ago I was spending a lot of time with this.

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OK, lets try this again-

 

There is no curve cut into the panels in the the 1st pic (just rectangles of straight 90 degree cuts), and the bow is initially @ 90 degrees, which gives it a very fashionable reverse bow when stressed. You can see the stick I used to separate the top (deck side) of the panels. That's on the bottom of the 'hull' in the pic here. You can see butt scarfs at the 60% point, which I used also to give a bit more flatness longitudinally in the middle. 4mm ply. With the 4mm, you can add backing plates that can also change how the panel bends- since there will be bend with two thicknesses, just less. This side panel approach also works with chine logs and sheer clamps attached- I did one with cypress 1/2" by 3/8", and it worked nicely- i could bend things by hand (barely), and still use masking tape or duct tape. You have to be a bit careful- the plywood would not take the stresses without the sheer clamp/chine log backing all the way to the bow and stern. If you work at it, you only need one BH to establish the shape- just like the B Splines. Then add where you need support. This approach is a real PITA to do without epoxy. Or a LOT of power woodworking tools. I wonder if 6mm would work even better, as it would be stiffer, and require less internal support.

 

post-906-071214600 1325696943_thumb.jpgpost-906-006572100 1325696974_thumb.jpg

 

and here are some numbers from Vacanti to give you an idea of what the shape might give you. I entered the shape from the panels in pic #1 into the Vacanti, and found that the shape fit well into the B spline tension 1 setting with just one set plane. I went with 14' because that is what I had around that was expendable.

 

post-906-006572100 1325696974_thumb.jpg

 

post-906-081920600 1325696999_thumb.jpg

 

post-906-054731100 1325697017_thumb.jpg

 

Not too bad, at least in computerland.

 

This approach seems a good one for epoxy fillets, tape/stitch 'n glue. It also gives a way to make it up as you go. An interesting part of this was that if you had the computer next to the two side panel setup you can see what the wood wants to do, and model it on the computer as you go. It gives you some feedback during the setup, so it's a lot like shaping with a computer. And yes, I was going for straight lines longitudinally near the bow and sterns in this instance. IOR, baby!

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With B splines (NURB) showing

 

post-906-020989400 1325699510_thumb.jpg

 

You can add other support NURB points in the computer and then correspondingly inside the initial panels to get more shape. They relate closely (digital and analogue), so at worst you get a good guestimate with the computer of a good position to start. As I mentioned above, you can use thinner/thicker ply, layers, initial shape cuts in the panels etc. Plywood is not very consistant in bend, though, even the Joubert I was using here, so get a feel for each piece of ply and what it WANTS to do before you commit. You can see the difference on the Starboard panel at the bow. Even twists the bow off vertical a bit.

 

Paul

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I should have mentioned that the wider the single spreader bar (aka the stick) at the deck level, the more rocker. The more you narrow the bottom, like with tape, once you have the top spreader in, the more rocker. The two do not have to be at the same point, but it does make it easier for the computer.

 

I assumed that was obvious, but maybe not. The things I assume....

 

Paul

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Any Idea how? I might be abnormally dim (most likely) but I cant work it out

 

When you download Delftship it comes with some examples. One is a chined tug. To see the developed panels, go to the view task.

 

As for designing a chined shape, I have not done it....but I would start with the tug example and work backwards.

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Heh heh. That's the 13er. All of 'em. Even the pic.

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OK, lets try this again-

 

There is no curve cut into the panels in the the 1st pic (just rectangles of straight 90 degree cuts), and the bow is initially @ 90 degrees, which gives it a very fashionable reverse bow when stressed. You can see the stick I used to separate the top (deck side) of the panels. That's on the bottom of the 'hull' in the pic here. You can see butt scarfs at the 60% point, which I used also to give a bit more flatness longitudinally in the middle. 4mm ply. With the 4mm, you can add backing plates that can also change how the panel bends- since there will be bend with two thicknesses, just less. This side panel approach also works with chine logs and sheer clamps attached- I did one with cypress 1/2" by 3/8", and it worked nicely- i could bend things by hand (barely), and still use masking tape or duct tape. You have to be a bit careful- the plywood would not take the stresses without the sheer clamp/chine log backing all the way to the bow and stern. If you work at it, you only need one BH to establish the shape- just like the B Splines. Then add where you need support. This approach is a real PITA to do without epoxy. Or a LOT of power woodworking tools. I wonder if 6mm would work even better, as it would be stiffer, and require less internal support.

 

post-906-071214600 1325696943_thumb.jpgpost-906-006572100 1325696974_thumb.jpg

 

and here are some numbers from Vacanti to give you an idea of what the shape might give you. I entered the shape from the panels in pic #1 into the Vacanti, and found that the shape fit well into the B spline tension 1 setting with just one set plane. I went with 14' because that is what I had around that was expendable.

 

post-906-006572100 1325696974_thumb.jpg

 

post-906-081920600 1325696999_thumb.jpg

 

post-906-054731100 1325697017_thumb.jpg

 

Not too bad, at least in computerland.

 

This approach seems a good one for epoxy fillets, tape/stitch 'n glue. It also gives a way to make it up as you go. An interesting part of this was that if you had the computer next to the two side panel setup you can see what the wood wants to do, and model it on the computer as you go. It gives you some feedback during the setup, so it's a lot like shaping with a computer. And yes, I was going for straight lines longitudinally near the bow and sterns in this instance. IOR, baby!

 

Are you giving up "planing surface" with the pinched stern? I liked what I saw in the RYC parking low, I think it was a Maas design, with the chopped off stern, looked like more "planing" surface aft - but I don't know much about ICs other than I'm going to give one a go soon.

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Richard Feynman said when he got to heaven he wanted to ask God what the controlling equations for fluid dynamics were. Maybe the planform shape of skinny planing surfaces too?

 

This method also works for a transom hull. The Maas hull gets tricky. You have to beef up the tail stiffness laterally, or it goes weird. Not as easy as a smooth pointy stern. But you can get higher prismatic hulls Thames my sub .50. Order some .8mm or 1mm birch aircraft ply and make models. You can even use thicker file folder paper to get the idea ( the creamy stuff) but it helps to limit the length to 6" or so.

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The fat versus pointy stern is one of the things this class is going to sort out.

That's at least half the fun.

SHC

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Why I am not convinced wide stern canoes are best:

 

Boats plane on the area under their centre of gravity, thats the laws of physics. Boats which plane on their stern either have their bows lifted by spinackers (on long poles) or low thrust line propellers. Canoes have neither so they obey the laws of physics. In fact like most sailboats the thrust is high up so there is a bow down pitching moment and hence centre of the planing surface needs to be forward of the centre of gravity.

 

Wide sterns add wetted surface, stability and somewhere manageable to work the boat. They also move the static centre of bouyancy aft and reduce the moment available when the crew moves aft to counteract the inevitable bow down pitch from aft CoB. In extreme, if the volume is too far aft no matter how far back the crew goes the boat will still nosedive. 18s, 12s, 49ers all have wings aft of the transom but still go down the mine on extreme bear aways, so they are very close to the limit.

 

They need wide sterns for stability because they carry large rigs. Canoes cary relatively small rigs and are proportionally long for their weight, width and area.

 

So if a canoe can have a narrower stern with adequate stability and work space, it will have less wetted surface and hence go better in light winds, and it will be easier managed in tough downwind conditions because moving crew weight aft will have greater remedial affect on any nosediving.

 

I though that the Hollow log was probably only slightly deficient on the stability and space quota but I could always get it downhill with only a little aft body weight.

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Mr Nutter, you just may have helped me out here.

 

Your density number, is that for epoxy coated ply? I had the numbers written down somewhere from a previous boat for plain ply then one and two coats either side. Hopefully you've solved my bad memory issues.

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Why I am not convinced wide stern canoes are best:

 

Boats plane on the area under their centre of gravity, thats the laws of physics. Boats which plane on their stern either have their bows lifted by spinackers (on long poles) or low thrust line propellers. Canoes have neither so they obey the laws of physics. In fact like most sailboats the thrust is high up so there is a bow down pitching moment and hence centre of the planing surface needs to be forward of the centre of gravity.

 

Wide sterns add wetted surface, stability and somewhere manageable to work the boat. They also move the static centre of bouyancy aft and reduce the moment available when the crew moves aft to counteract the inevitable bow down pitch from aft CoB. In extreme, if the volume is too far aft no matter how far back the crew goes the boat will still nosedive. 18s, 12s, 49ers all have wings aft of the transom but still go down the mine on extreme bear aways, so they are very close to the limit.

 

They need wide sterns for stability because they carry large rigs. Canoes cary relatively small rigs and are proportionally long for their weight, width and area.

 

So if a canoe can have a narrower stern with adequate stability and work space, it will have less wetted surface and hence go better in light winds, and it will be easier managed in tough downwind conditions because moving crew weight aft will have greater remedial affect on any nosediving.

 

I though that the Hollow log was probably only slightly deficient on the stability and space quota but I could always get it downhill with only a little aft body weight.

 

 

Exactly.

 

Phil, have I ever asked about your thoughts on pressure recovery? Ballpark CP on hollow log? Just curious- once the hull has risen on it's bow wave, things get different. Converging straight buttocks aft do kindof beg the question of pressure recovery as a function of speed. Although seaplane floats tend to be very straight and somewhat converging behind the step.

 

What would a 1 mm step do?

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Why I am not convinced wide stern canoes are best:

 

Boats plane on the area under their centre of gravity, thats the laws of physics. Boats which plane on their stern either have their bows lifted by spinackers (on long poles) or low thrust line propellers. Canoes have neither so they obey the laws of physics. In fact like most sailboats the thrust is high up so there is a bow down pitching moment and hence centre of the planing surface needs to be forward of the centre of gravity.

 

Wide sterns add wetted surface, stability and somewhere manageable to work the boat. They also move the static centre of bouyancy aft and reduce the moment available when the crew moves aft to counteract the inevitable bow down pitch from aft CoB. In extreme, if the volume is too far aft no matter how far back the crew goes the boat will still nosedive. 18s, 12s, 49ers all have wings aft of the transom but still go down the mine on extreme bear aways, so they are very close to the limit.

 

They need wide sterns for stability because they carry large rigs. Canoes cary relatively small rigs and are proportionally long for their weight, width and area.

 

So if a canoe can have a narrower stern with adequate stability and work space, it will have less wetted surface and hence go better in light winds, and it will be easier managed in tough downwind conditions because moving crew weight aft will have greater remedial affect on any nosediving.

 

I though that the Hollow log was probably only slightly deficient on the stability and space quota but I could always get it downhill with only a little aft body weight.

 

 

Hmmm, well, maybe if someone were to build a wide stern boat and win a bunch of races we'd know that wide sterns, at least, weren't slow!

 

Phil you have some good points. But I have a few reasons why I like the wide stern:

 

I can't see a way to design a pintail stern whose chines don't drag in the water at slow speed, unless I have more round in the buttock and/or rocker than I want to see. If the chine is submerged and the pintail is fine then at slow speeds the water can flow along happily as on a double ender like a rowing shell. As speed increases though the water will break clear at some speed, but there is a sucky time - in technical jargon - when the water is still attached to the top sides.

 

For me the added stability of the wide stern in maneuvers is important and until I become younger and more nimble it's going to stay that way.

 

In light air with weight forward and a little heel I don't think my hull has much, if any, more wetted surface than a pintail.

 

You are right that the wide stern adds little lift for planing. As I understand it most of the lift comes from the forward third of the submerged surface.

 

It makes sense that the wide stern hull would be easier to nose dive. However, Steve and David Clark's boats at the last Worlds were the widest stern, narrowest bow IC's I have seen and they didn't seem to have any problem on the windier downwind legs, to put it mildly.

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fwiw, my rational for the pintail centers on when it breaks or rises to a plane, and what happens in the non planing forced mode just before then.

 

And that is not information available easily digitally.

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Re my post a couple of pages back about stressed foam construction that met with such deafening silence - This is what you can do with 6mm foam that is skinned on one side.

 

Can you see the possibilities?

post-16686-051328400 1325822358_thumb.jpg

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Foam is so cool.

 

If you aren't allergic to epoxy.

 

Well, it's still cool. And you can wrap EPP in packing tape.

 

Which someday, I will do around a mast. Yes, it will happen. Oh yes.

 

If truth be known, I was struck dumb. Dumb, I tell you.

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Mr Nutter, you just may have helped me out here.

 

Your density number, is that for epoxy coated ply? I had the numbers written down somewhere from a previous boat for plain ply then one and two coats either side. Hopefully you've solved my bad memory issues.

 

Jethrow,

 

The figure quoted was for the wood only, but I just checked my figures and the actual density I measured was 506 kg/m^3. Seems a bit high. I have done a spreadsheet for this hull which includes an epoxy coating and an allowance for glue fillets (pdf attached). I can send you the Excel file if you want to plug in your own figures. Again, this is just for the 3mm plywood structure.

 

PanelWeight.pdf

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...As speed increases though the water will break clear at some speed, but there is a sucky time - in technical jargon - when the water is still attached to the top sides.

 

 

Sucky time. I like that. I'm going to add it to my vocabulary. :D

 

Regardless of the performance issues, I have a philosophical issue with the truncated sterns in that they are not really canoeish. To me the stern shape of these wide stern boats consists of a transom that is bent at 45 degrees. The term canoe tends to imply hulls that have no transom (canoe sterns in fact) although some paddling canoes do have small transoms. The truncated hullforms of the wide stern ICs have almost full width transoms and to me seem more like narrow skiff hulls.

 

However, the rules allow it, I can see the sense in it and I'm not one to let philosophical musings get in the way of a fast hull.

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... I have done a spreadsheet for this hull which includes an epoxy coating and an allowance for glue fillets................

 

I worked out how to attach the Excel file. You have to zip it first. D'oh.

 

PanelWeight.zip

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...As speed increases though the water will break clear at some speed, but there is a sucky time - in technical jargon - when the water is still attached to the top sides.

 

 

Sucky time. I like that. I'm going to add it to my vocabulary. :D

 

Regardless of the performance issues, I have a philosophical issue with the truncated sterns in that they are not really canoeish. To me the stern shape of these wide stern boats consists of a transom that is bent at 45 degrees. The term canoe tends to imply hulls that have no transom (canoe sterns in fact) although some paddling canoes do have small transoms. The truncated hullforms of the wide stern ICs have almost full width transoms and to me seem more like narrow skiff hulls.

 

However, the rules allow it, I can see the sense in it and I'm not one to let philosophical musings get in the way of a fast hull.

 

As an outsider, I was curious how widespread this thought might be.

 

Mr Maas - what sort of foam?

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Nutta:

That horse left the barn in 1956.

Uffa was the first to do it, Ian Proctor was next and the one design Nethercott has had a "funny shaped transom" since day one.

In creating the new rules, I stuck very close to the original formulas, the "inside 45 degrees" language to type form the pointy stern came down from the mountain with Moses.

SHC

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One thing I have wondered about the wide 45 degreeish hulls is that the stern crossection has to be slightly rounded or v'd to have a long LWL without a sudden corner that the flow has to deal with. But it would seem to demand sailing very flat upwind, because if you heel enough, say 5-10 degrees,that at some point the truncated chine becomes the effective LWL. And that is shorter than the LWL of the point. And the wider the stern, the shorter the chine. So in a sense, the end of the chine has to be pretty high to avoid it's own sucky point at speeds lower than clean planing.

 

So that deadrise would seem to limit early planing? And if heeled, which length governs hull speed, the pointy part or the end of the chine? Is the idea of the corner that is basically limits the sucky point to a smaller area, like a square head sail does?

 

Paul

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...As speed increases though the water will break clear at some speed, but there is a sucky time - in technical jargon - when the water is still attached to the top sides.

 

 

Sucky time. I like that. I'm going to add it to my vocabulary. :D

 

Regardless of the performance issues, I have a philosophical issue with the truncated sterns in that they are not really canoeish. To me the stern shape of these wide stern boats consists of a transom that is bent at 45 degrees. The term canoe tends to imply hulls that have no transom (canoe sterns in fact) although some paddling canoes do have small transoms. The truncated hullforms of the wide stern ICs have almost full width transoms and to me seem more like narrow skiff hulls.

 

However, the rules allow it, I can see the sense in it and I'm not one to let philosophical musings get in the way of a fast hull.

 

 

To my eye, in the dinghy park, the pointy stern on my IC definitely sets it apart from the skiff type hulls.

 

I guess the rules could have been written to require a pointier stern, like say 30 degrees instead of 45. And a 200mm radius on the corner instead of 60mm. I don't think it would have made for a better boat though.

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...As speed increases though the water will break clear at some speed, but there is a sucky time - in technical jargon - when the water is still attached to the top sides.

 

 

Sucky time. I like that. I'm going to add it to my vocabulary. :D

 

Regardless of the performance issues, I have a philosophical issue with the truncated sterns in that they are not really canoeish. To me the stern shape of these wide stern boats consists of a transom that is bent at 45 degrees. The term canoe tends to imply hulls that have no transom (canoe sterns in fact) although some paddling canoes do have small transoms. The truncated hullforms of the wide stern ICs have almost full width transoms and to me seem more like narrow skiff hulls.

 

However, the rules allow it, I can see the sense in it and I'm not one to let philosophical musings get in the way of a fast hull.

 

As an outsider, I was curious how widespread this thought might be.

 

Mr Maas - what sort of foam?

 

That's Divinycel H80.

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Foam is so cool.

 

If you aren't allergic to epoxy.

 

Well, it's still cool. And you can wrap EPP in packing tape.

 

Which someday, I will do around a mast. Yes, it will happen. Oh yes.

 

If truth be known, I was struck dumb. Dumb, I tell you.

 

So build with vinylester. What's not to like about styrene?

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It outgasses. But I love it so. I'm covered in xps particles as I post. Now I need to vacuum the keyboard. And my hair.

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With regard to Phil's post about being able to sink the stern to get the bow up...

It's really pretty interesting, because you can get further aft on a wider stern.

post-738-068493100 1325884665_thumb.jpg

This is with the helm and seat at the back end of the tracks.

Hull is becoming less stable as the deck goes under, so this is minimum limit of freeboard and volume.

Seems like the bow won't be sticking into many waves.

post-738-066558800 1325884690_thumb.jpg

In light air with the seat all the way forward, stern a center line is just in the water.

Keeping enough section curvature is pretty important for making the boat somewhat tolerant of heeling a bit but there is no doubt that these boats have more wetted area than ones with pointier sterns.

SHC

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I'm just starting to build a Maas design IC for JimC - who has done the hard work entering the design into computerese.

 

post-2679-050218900 1325888523_thumb.jpg

 

The mould will be like this, but the boat has the V-transom chopped off / transom sides added later.

 

It's a bit of an optical illusion that makes the stern looks very wide.

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With regard to Phil's post about being able to sink the stern to get the bow up...

It's really pretty interesting, because you can get further aft on a wider stern.

 

There are all sorts of interesting tradeoffs - that's what makes it fun.

When I put a 45 degree stern on my Nethercott I learned all sorts of things...

You need more freeboard aft with the wide stern - otherwise the deck goes underwater all too readily when heeled

You get a much flatter stern wave at any speed, which I think means more pressure recovery.

You really feel the extra wetted area in the light, especially if you can't heel the boat because the decks go under

I suspect the detail treatment of the corner could be rather significant in the heeled light airs mode.

Maybe with the finer bows of a new design it will be easier to get the stern out of the water in the light

My success rate at tacking in conditions marginal to my ability level improved significantly

I don't sail in waves so I have no idea what changes there will be in waves.

 

I suspect how the tradeoffs work may be quite different for classy sailors like Phil, Steve and Chris as they will be for a very ordinary middle of the fleet hack like me. They have a lot less trouble actually making it round than I do... Sailing where I do I should probably have had something like the Morrison, which seems astonishingly slippy in the light, but sailing like I do I hope that the Maas will give me a bit more help with the more powerful stern.

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The thread has some interesting points.First in response to IC nutter, sailors have been discussing what defines a canoe since the 1870, so you are in good company. Refer to Dixon Kemp 'A Manual of yacht and boat sailing' 2nd edition, I think published 1880. Over the years there seems to have been a feeling that a wide stern pushes the bow down. The development of the IC In the 1950/1960s went from Uffa's Spindrift through the Proctor mark 2 to the Nethercot. At each stage the main aim was to reduce the volume of the stern. The Nethercot definitely looks as if it has a wrapped around transom, but this is only because it is not faired into the rest of the hull in the way that Uffa did with Spindrift. The element which, in my mind, is important is the chine, as this is what delineates the transom from the bottom of the boat. A chine was first introduced to canoe design in 1914 by Linton Hope in Trittonelle. She was reported to outclass all the other canoes of the time and the chined form was outlawed by the Royal Canoe Club, and that followed over into the International Rule in the 1930s. My own feeling is are that the wide stern has little to do with nose diving. Recently I have been investigating lift during sailing. To do this I developed a simple spreadsheet using the planing theory of Savitsky. The model is very simple and assumes the hulls can be adequately approximated by four chines and that the lift calcs can be done assuming no deadrise, and gives results which may be in error numerically but I would think probably give the correct form of the lift-speed curves. I would be interested if a navel architect in the fleet would redo the calculations and confirm, or otherwise, the results. For my Nethercot approximation I found that lift was only achieved above a speed of about 17/18 knots. Below that there was a suction which at a maximum was equivalent to about 60lbs At about 14 knots. At this speed the bow was out of the water for around 20 inches, so looked very much as if planing was occurring. The reduction in wetted area was about 7%. This amount of suction could be reduced by moving the C of G back towards the stern. The cause of this large suction was the rocker of the Nethercot. In general lift occurred at the front of the boat and suction occurred at the stern, this would suggest that a wider stern might help to keep the stern down and so the bow up rather than the converse. Even for the case of no rocker the lift is higher at the front of the boat as the lift depends on the way the WL beam increases, as well as the WL beam. This is high at the bow and low (maybe negative) at the stern. I found that reducing the rocker reduced the suction and lowered the speed at which positive lift was achieved. I think Chris is correct not to introduce too much rocker. Steves new boat looks as if it is quite low rocker. I should be interested to know how much rocker these canoes have.

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Which is why race boards of the 80's had some intentional reverse curve to the last foot or so of the rocker. My Sailboard Race comes to mind. Not the apparent s curve. Had to sail nose down in the light to lift them out of the drink. More prevalent in squash, diamond and pintails. But these tails were mostly v'd in cross section and usually came out of a double concave, which in turn came out of a single concave at the nose, which wouldn't be legal for a canoe. The idea IIRR was to keep the water constantly accelerating.

 

But if oil canning is happening at the bottom of the hulls of the ply canoes anyway, you might be able to exploit this flexibility at speed, and have longitudinal concavities forming under pressure. Might be happening already? Between the strongbacks and chinelogs? At least on the flattish hull bottoms.

 

I wonder though if the easily movable seats fore and aft aren't making bigger sterns more viable. The 44" beam limit is wider than a formula board, and if you get the weight back enough, like one of the pics of Chris's canoe shows, a year or more ago, and enough of the bow is out of the water, you've effectively got a really heavy early type formula board, complete with the diamond tail. Although with a sloop rig.

 

I think Savitsky would agree with Prandtl that higher aspect planing surfaces are more efficient when planing.

 

Kind of begs the question about speed boards though.

 

And this vid is really cheesy but it has some good glimpses of the skinny speed boards that have always seemed to me to have some things in common with canoes

 

Check out this video on YouTube:

 

 

 

Sent from my iPad

 

Paul

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My objection to the wide stern boats was really only an aesthetic one, and concerns the introduction of the knuckle aft, which runs from the deck line down to the chine. It gives the appearance of it being the side of a transom, albeit a transom that angles back at 45 degrees. I've always appreciated the simple lines of the IC hull (minimalist tendencies) and the extra knuckle line just seems to complicate it up a bit. I'm sure I'll get used to it. Others may think the transom effect looks better than the more traditional shape, more 'edgy', so to speak.

 

Regarding the chine, I agree that it is absolutely necessary to have a chine aft to promote separation at higher speeds. I certainly wouldn't suggest that an IC hull should have round bilges all the way aft. That would be silly. IC's are not paddling canoes, at least, not nowadays.

 

ARE, I would be interested in having a look at your Savitsky spreadsheet. I did some work using Savitsky may years ago (on trim tabs I think), but I've forgotten it. I'll trade you a copy of my HullCalc spreadsheet if you like, then we can all be totally confused. :lol:

 

The primary way in which planing reduces resistance is due to wetted surface reduction. In my opinion, if you can reduce wetted surface whist maintaining clean flow separation aft, you can assume you are planing, regardless of what the net lift situation is.

 

The other thing planing does is to virtually change the shape of the curve of areas. Planing usually results in a stern down trim, and separation off the chine or transom creates a cavity in the water behind the boat. If you could analyse the volume of the immersed curve of areas of the hull and the cavity behind the hull (the virtual curve of areas), you should find that the total mass of water displaced is equal to the mass of the boat. Hence, the reduction in displacement of the hull due to planing should be equal to the volume of the stern cavity. And further hence, if you really want to plane, you need to load the back end of the boat and dig the stern in. In essence the faster you go, the more stern trim you need so that you can go faster. If you the dig stern in too early (i.e. at lower speeds), you will loose the ability to benefit from "pressure recovery", which others have mentioned. The ability to recover pressure from the inward flow of water aft of the maximum cross section (the peak of the curve of areas) rapidly diminishes to zero as you approach "hull speed".

 

The shape of the virtual curve of areas of a hull which is planing, compared to the static curve of areas, is that of a longer hull with the same displacement. So not only does frictional resistance reduce due to wetted surface reduction, but wavemaking resistance is also be reduced.

 

All in my opinion.

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With regard to Phil's post about being able to sink the stern to get the bow up...

It's really pretty interesting, because you can get further aft on a wider stern.

 

There are all sorts of interesting tradeoffs - that's what makes it fun.

When I put a 45 degree stern on my Nethercott I learned all sorts of things...

You need more freeboard aft with the wide stern - otherwise the deck goes underwater all too readily when heeled

You get a much flatter stern wave at any speed, which I think means more pressure recovery.

You really feel the extra wetted area in the light, especially if you can't heel the boat because the decks go under

I suspect the detail treatment of the corner could be rather significant in the heeled light airs mode.

Maybe with the finer bows of a new design it will be easier to get the stern out of the water in the light

My success rate at tacking in conditions marginal to my ability level improved significantly

I don't sail in waves so I have no idea what changes there will be in waves.

 

I suspect how the tradeoffs work may be quite different for classy sailors like Phil, Steve and Chris as they will be for a very ordinary middle of the fleet hack like me. They have a lot less trouble actually making it round than I do... Sailing where I do I should probably have had something like the Morrison, which seems astonishingly slippy in the light, but sailing like I do I hope that the Maas will give me a bit more help with the more powerful stern.

Hi Jim

Whats the programe you use for your design?

I am looking at a Dragonfly MK II (very long term project), I think Dragonfly is not extreame enough, prob more pointy needed at the front.

Very intrested but slightly baffeled by all the tech talk, but to answer one recent question my rocker is 100mm

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...

The primary way in which planing reduces resistance is due to wetted surface reduction. In my opinion, if you can reduce wetted surface whist maintaining clean flow separation aft, you can assume you are planing, regardless of what the net lift situation is.

 

The other thing planing does is to virtually change the shape of the curve of areas. Planing usually results in a stern down trim, and separation off the chine or transom creates a cavity in the water behind the boat. If you could analyse the volume of the immersed curve of areas of the hull and the cavity behind the hull (the virtual curve of areas), you should find that the total mass of water displaced is equal to the mass of the boat. Hence, the reduction in displacement of the hull due to planing should be equal to the volume of the stern cavity.

...

The question I have here is for the transitional, or semi-planing region. So the flow has cleanly detached from the stern but there is no dynamic lift. Here, the hull is displacing the same volume of water AND some virtual amount. Thoughts?

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Okay,

 

It's great to see so much interest in this thread. I played for awhile in a development class in RC boats so I know how much fun the process can be. I also know how daunting it can appear to an outsider with no experience in building a boat that doesn't come in a kit or at least with plans and a fairly detailed bill of materials. I'm definitely curious about building a hull using either wood or foam as in Giajin or Chris's method with the pre-laminated foam.

 

What kind of materials do I need to have on hand to make a hull? Just get me in the ballpark. How many sheets of what core, how much cloth of what type, how much resin etc. This way I can have the lion's share of the stuff on hand to proceed. Any sourcing guidelines would be great too.

 

From a complete outsider's perspective this general info would be very beneficial. It would also be possible to get an idea of the budget for the hull at least. Thanks in advance for any help.

 

Maybe a rough bill of materials will result in more boats getting built. You've already shown through this thread that the necessary hand holding will be available once a project gets started. I'd just like a little push on the first step down the road (or off the cliff as it may be.)

 

Take care,

 

Brent

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Planing may feel like a break from one regime to another but it isn't. If the hull didn't lift a bit, at least, when the stern wave detaches in the forced mode, it would sink. The reason windsurfer race boards, for example, had some sort of pointy tail was that the faster they go, the less area was needed to support the hull dynamically. If you had a square or big diamond tail, after a certain speed things got bouncy and a bit uncontrollable.

 

So it boils down, at least to me :P that the rocker and the foil fit the anticipated planing speed of the board as well as being slippery at lower speeds. A big squash tail is great at mid dish SLR's. It would be nice if wider was better, but Formula boards are tiny airboats, and canoes may just be too heavy to enjoy the lift from trapped air.

 

One of the reasons big wave boards fascinate me is that they operator in two disparate regimes- paddling out and planing. Granted some of them are shaped not to go too fast and stay on the wave, butvthat just makes it, as Steve says, more fun.

 

So canoes are not that fast? So being able to get right to the back of a skinny tail with progressively less wetted surface is wasted effort? Well, that and it's a bit difficult to get the rig CE back that far quickly. Chris, you were messing around with the seat waaaay back on plane. Any of the rest of you with Maas hulls done the same? Besides lee helm, is there any speed advantage? Or does the speed plateau as WS plateaus?

 

Paul

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1:

BOM for John Kells build 2008.

Building jig and design not included.

Seat materials not detailed accounted for

Mayhem BOM.doc

 

2: You have to consider that the driving force of a sailboat is at the aerodynamic center of pressure not at the deck, waterline or keel. This imparts a significant bow down moment to the hull and affects the trim. This is why almost any sailboat towed from the deck will trim very bow up. Suction aft is one way of dealing with this, and when the eat was pretty much fixed in one position, some suction was very desirable to maintain proper trim as the boats went faster and down wind. However, suction usually also means sinkage, which is counter to the goal of reducing wetted area. As always there are conflicting demands.

The other alternative is to enable the helm to get further aft and bring the LCG with him. To do this the deck needs to be wider further aft, which in turn makes the "corner" sharper.

I guess we are lucky that the general nature of the sailing canoe is attractive, and the boat can wear this and still look gorgeous. Some girls have all the luck.

SHC

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...

The primary way in which planing reduces resistance is due to wetted surface reduction. In my opinion, if you can reduce wetted surface whist maintaining clean flow separation aft, you can assume you are planing, regardless of what the net lift situation is.

 

The other thing planing does is to virtually change the shape of the curve of areas. Planing usually results in a stern down trim, and separation off the chine or transom creates a cavity in the water behind the boat. If you could analyse the volume of the immersed curve of areas of the hull and the cavity behind the hull (the virtual curve of areas), you should find that the total mass of water displaced is equal to the mass of the boat. Hence, the reduction in displacement of the hull due to planing should be equal to the volume of the stern cavity.

...

The question I have here is for the transitional, or semi-planing region. So the flow has cleanly detached from the stern but there is no dynamic lift. Here, the hull is displacing the same volume of water AND some virtual amount. Thoughts?

 

Thanks for pointing out that error. The volume of hull plus cavity should equal twice the static hull volume* and the reduction in displacement of the hull due to planing should be equal to the volume of the stern cavity minus the static hull volume.

 

The typical heave pattern for a semi-displacement hull form with an immersed transom is that the hull will sink at speeds below the typical resistance curve hump (before the separation cavity is fully formed perhaps) and will rise thereafter. we could speculate that the sinkage at lower speeds is due to the inability of the truncated (immersed transom) hullform to recover pressure aft of the maximum cross sectional area point.

 

* This assumes that the transom area is equal to the maximum cross sectional area, as it is on a full planing hull form. Semi displacement hullforms often have a transom area that is smaller than the maximum cross sectional area and in this case the ratio will be less than twice the hull volume. Bear in mind that the trim angle changes the (max. cross section/transom area) ratio.

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I have been off line crashing my way half way through a moth regatta but will try to answer some questions from the last few days:

 

Amati: Not sure about separation theories. When I started making stressed ply boats about 1974 I had a theory that water would flow well around any shape that ply could easilly bend through, After that I found the philosophy that volume down low means less whetted surface and less WL width for a given volume. I also found that minimising keel spring is fast espec combined will low volume. When all that is combined and the boaw is made as sharp as possible then the boats do not go through any transition between displacement and planing, they just go faster. Saw this first with cats, then NS14s, narrow Moths and with two canoes, mine and Chrios Maas boat when we all sailed each others at McCrae. Frank Bethwaite calls it a humpless design but he did not invent it.

 

Chris, I have great respect for you, your designs and your two WCs. But I have never been a design follower so am always looking at other ideas and options. I also like your stressed foam idea and can see me using it if I ever build another canoe.

 

Steve: Also great respect for you, your designs and your history, but slight misunderstanding. I know that you can move teh seat back further on the wide stern boats but what I said was that on the narrow stern boats you do not need to because the centre of bouyancy (or planing area for those who think that way) is already further forward and separated from the crew weight by a greater distance.

 

 

Skiffboy: There does not seem to be a semi planing regime in these new boats.

 

Sorry if I missed soem Qs but I am running out of time on themotel internet connection.. More when I get home in a few days.

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Amati: Not sure about separation theories. When I started making stressed ply boats about 1974 I had a theory that water would flow well around any shape that ply could easilly bend through, After that I found the philosophy that volume down low means less whetted surface and less WL width for a given volume. I also found that minimising keel spring is fast espec combined will low volume. When all that is combined and the boaw is made as sharp as possible then the boats do not go through any transition between displacement and planing, they just go faster. Saw this first with cats, then NS14s, narrow Moths and with two canoes, mine and Chrios Maas boat when we all sailed each others at McCrae. Frank Bethwaite calls it a humpless design but he did not invent it.

 

 

The drag characteristics that have been referred to 'humpless' are really just a function of the displacement to length ratio, which affects the proportion of wave (residuary) drag vs skin friction drag. The friction drag curve is a smooth curve whereas the residuary drag curve has humps in it. Lightweight high performance boats have relatively large wetted surface area compared to their volume, hence the greater part of the drag curve will be made up of frictional drag. Thus the total drag curve will appear to be fairly smooth because the humps in the residuary drag curve are relatively small.

 

Further to this, the modern skiff hull has a very broad transom, often the widest part of the hull or certainly at chine level. The benefit of this is that you need only a small amount of stern trim to greatly increase the transom immersion at higher speeds. This helps to avoid the 'sucky time' (I've so wanted to use that) which occurs prior to planing.

 

Getting back on topic, one of the beauties of the chined canoe hull is that separation can occur well forward, so that the canoe stern is kind of sitting in the separation cavity. I think this also helps with the seamless transition from displacement to planing mode. It also means that you can get the centre of lift further forward than with a standard transom hull. The disadvantage is that you end up with fuller sections forward. I suspect that the top end planing performance of a narrow stern canoe could be better in terms of controlability but the narrower bowed wide stern boats should win out upwind and in lighter conditions.

 

Mal's Law states that the boat on the edge of control is the fastest, so one way of going fast is to design the hull to be as difficult to control as you can, then learn to control it. So what you really want is the narrowest possible bow married to the narrowest possible stern, with as much curvature in the underside as you can get in order to make it as unstable as possible. Then add the straightest possible keel line so that it will nosedive easily.

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The drag characteristics that have been referred to 'humpless' are really just a function of the displacement to length ratio,

I dunno about that. My winged 14foot singlehander had damn all planing hump. My lightened Nethercott, which is much the same weight, has a great big one. One thing I did observe with the singlehander, which had a fine straight bow, was minimal bow wave generation. The Nethercott, OTOH, kicks up a big one.

 

Further to this, the modern skiff hull has a very broad transom, often the widest part of the hull or certainly at chine level.

I would have said they reached a maximum back in the late 70s, then went finer. They've only gone wider again sice the rudder T foils with lift, which changed the game.

 

Mal's Law states that the boat on the edge of control is the fastest, so one way of going fast is to design the hull to be as difficult to control as you can, then learn to control it

 

The trouble with that is that if you are backed off to keep the bow out of the mud at the bottom of the lake, and Fred is driving his boat flat out he's going to go past you.

 

I'd not argue with the general propsition that, all else being equal, the less rocker you have, especially aft of mid length, the faster you go and the sooner you head down the mine. There was a big fashion with some english designers for a while with rocker at the back of the boat. The general observation was that at speed such boats stuck to the water beautifully, both in terms of keeping the bow out of the 'oggin and in terms of dragging half of it round the course with you slowing you down.

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Mal's Law states that the boat on the edge of control is the fastest, so one way of going fast is to design the hull to be as difficult to control as you can, then learn to control it

 

The trouble with that is that if you are backed off to keep the bow out of the mud at the bottom of the lake, and Fred is driving his boat flat out he's going to go past you.

 

 

If you have to back off, you are not in control. If your bow is in the mud, you are not in control. You are only the fastest when you are on the edge of control. If you are no longer in control, you are slow.

 

Regarding the rest of it, I'm making very broad generalisations assuming everything is optimal. There will always be exceptions that seem to buck the trend. A badly shaped boat will be shit no matter how light it is. :D

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Phil:

One thing I have noticed sailing the fat ass boats is that you CAN sail them from further aft, and that it is fast to do so.

I believe that the LCG moves aft with the helm. This makes the bow lighter, and reduces the energy absorbed by wave encounters. You cannot get the LCG as far aft without the volume of the fat stern. In practice the movement of the LCG and reduction of wave encounter losses seems to make up for the additional wetted surface.

In many ways it is similar to what has happened with the T Foil on the I 14. The lift off the T foil is enough to support about 1/2 the displacement of the boat, so the crews all sail as far aft as possible once they are trapping. Dave move his seat aft as soon as the he sees a clean "planing" wake and takes a step ahead.

I'm not sure the next IC shouldn't be pointy aft with a T foil rudder. Thus achieving the low wetted area of a pin tail and the LCG aft of a fat ass.

The fact that Andy P already went down this yellow brick road without getting to OZ is something of a caveat.

SHC

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IC Nutter: "The typical heave pattern for a semi-displacement hull form with an immersed transom is that the hull will sink at speeds below the typical resistance curve hump (before the separation cavity is fully formed perhaps) and will rise thereafter. we could speculate that the sinkage at lower speeds is due to the inability of the truncated (immersed transom) hullform to recover pressure aft of the maximum cross sectional area point.". This seems to be confusing way to describe what is happening. A boat will sink ( that is it's C of G will move downwards) in the water because there is an added downward force on the boat. Conversely it will move upward because of an added upward force. This is the only way it can happen. Also remember that when there is suction due to the rocker the boat will be behaving as a heavier boat.

I have not come across the theory that the cavity in the water behind the boat is equal the submerged volume of the boat. Could you give me a reference that explains the theoretical justification ( And the maths behind the idea).

Phil: the minimum wetted area is easily computed, and will be determined by the waterline plane area And the keel profile. To achieve minimum just ensure that every underwater section is a semi ellipse. Changing either of the above mentioned will, or course, change the wetted area. The very best ellipse is the one where the two foci are at the same point, i.e. the circlular cross section- but that is not very practical except very close to the bow. This is entirely consistent with your comments. What do you mean by keel spring? It is a term I am not familiar with. Do you mean rocker?I don't understand you point about centre of buoyancy and position of helmsman. The position of the C of B Is determined by the positions of the centre of gravity of the boat and that of the helmsman, neglecting all other forces. If you want to alter trim then the helmsman has to move. Moving the helmsmans weight back to stop nosediving will have exactly the same effect on a wide stern canoe as it does on a narrow stern canoe. Differences may come about if waves lift the stern, and these could be more severe for a wide stern canoe, but are not due to differing effects of moving the helms mans weight.

Savitsky defines three speed regimes, displacement, semi planing and planing in terms of the speed of the boat. To say that canoes Canoes show no transitions is just redefining the terms, the canoe has a transition when it's speed changes from that defined as displacement to that defined as semi planing and so on. Phil is obviously not talking of the transition in these terms, so I need to know what he means by transition, for me to be able to make any sense of what he is talking about, Or we will just talk at cross purposes. From my calculations I would suggest that semi planing is associated with bow up but no net positive lift, and planing with bow up and positive lift. Oh! By the way all boats obey the laws of physics all the time!

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Savitsky defines three speed regimes, displacement, semi planing and planing in terms of the speed of the boat. To say that canoes Canoes show no transitions is just redefining the terms, the canoe has a transition when it's speed changes from that defined as displacement to that defined as semi planing and so on.

Well if wanting to define transitions in reference to arbitrarily chosen convenient numbers, such as a multiple of 2.50 times or 3.00 times, then certainly one will at one speed be just below such a number and then at a slightly greater speed be just above it.

 

But the numbers don't necessarily refer to sharp transitions in what is happening physically for a given boat.

 

The contribution of dynamic lift can increase smoothly without any speed point being sharply different from the speed slightly below or above it.

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my head hurts as well, but what's this about a rudder foil? Allowed?

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On the (head falls off) post: IC Nutter, I really do want to understand what you've posted in #2080 and have tried a number of times, but just am not getting there. It is the second sentence, first paragraph in the new explanation that is stumping me.

 

If there's a way to explain it differently without having to write something unfeasibly long, I really would appreciate it! Thanks!

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