Jump to content

Recommended Posts

Ok I'll spill some beans- one way to keep things light with a fat boy hull (~40" beam :)) and keep the shaping and gluing of foam and wood inside the realm of sanity is to have an external chinelog :o . MUCH easier to build myself. The lines are exceedingly fair- no weird bumps, unless chine runners are bumps. Sure, I'm also channelling Matt Leyden..... ;). Just a bit.

 

Which would put the resulting concavity outside of the 1000mm athwartship tape, at BMS. But the concave won't be outside of the 1000mm string's reach if that tape is slid fore and aft, centered, on the 2000mm tape centered on BMS.

 

5e says "A 1000mm tape centered on the keel at BMS and pulled tight transversely against the outside skin of the hull, shall bridge no hollow in excess of 1 mm in depth." But it seems measuring practice is to slide the 1000mm string (longitudinally) centered on the 2000mm string to check for concavities? Which means the whole 2000mm line is BMS? Or is there another rule intersecting here?

 

When 5e says "a 2000mm tape centered on BMS and pulled tight fore and aft against the outside skin of the hull, shall bridge no hollow in excess of 1mm in depth." Does that mean the 2000mm tape slides centered on the BMS line laterally, turning around the bilge etc. as it goes forward? Kind of like cutting vertical longitudinal lines in the hull?

 

There's really only 1 BMS, isn't there?

Link to post
Share on other sites
  • Replies 3.7k
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Popular Posts

First weekend I have been able to race since building this ride over a year ago. It was great to line up against boats especially more canoes :).

Mean while in a shed in rural Australia another IC is being built 90% complete the fun task of paint prep and paint left to do. Only 2 weeks until the OZ nationals no time to waste....

DCrazy Ivan,  my latest. Old Sails

Posted Images

Never ever heard of external chine logs or chine runners... [hits google]. Hmm, no wonder I haven't heard of them. Not often used on my style of boat. Maybe is US terminology too.

 

I'm pretty confident, I'm afraid, such excrescences would not be legal. I don't really see how you could write a rule that allowed for such things without also allowing all sorts of hull shape distortions that the rule is attempting to prevent. I'm also not at all sure why they should make building the boat easier. On Phil's style of tortured ply boat, for instance, the same task is done by a layer of carbon tape.

Link to post
Share on other sites

 

There's really only 1 BMS, isn't there?

 

There is really only one BMS, but you can nominate where it is (i.e. find one that works for the beam measurement, 1000mm transverse tape test) anywhere between 1300mm and 2600mm from the stern. But I would suggest that to be confident the hull should be able to pass the 2000mm longitudinal tape test at any BMS that works for the transverse tape.

Link to post
Share on other sites

Never ever heard of external chine logs or chine runners... [hits google]. Hmm, no wonder I haven't heard of them. Not often used on my style of boat. Maybe is US terminology too.

 

I'm pretty confident, I'm afraid, such excrescences would not be legal. I don't really see how you could write a rule that allowed for such things without also allowing all sorts of hull shape distortions that the rule is attempting to prevent. I'm also not at all sure why they should make building the boat easier. On Phil's style of tortured ply boat, for instance, the same task is done by a layer of carbon tape.

Phil can use epoxy. I can't, so I use chine logs, TB3 and screws/annular ring nails. But I've found a way that satisfies the infinite BMS rule. Billions and billions of BMS's.....

Link to post
Share on other sites

Del and Jim, I really appreciate your clarifications-

 

Only one more- 5e is a bit vague about where the 2000mm tape is placed, depending how you define "centered on BMS":

 

In practice, is it only placed on the longitudinal centerline of the hull? Or does it slide sideways on the BMS like the 1000mm tape slides lengthwise on the 2000mm tape?

 

SEZED, I think from what Jim and Del are saying, spray chines would have to be pretty high on the sides of the hull and curved up, so as not to run afoul of the 1000mm tape, unless you go for more of a scow/surfboard/wide body shape. Unless they were less than 1mm high.

Link to post
Share on other sites

No matter what the rules say or how you interpret them, I think that putting any hollows in a boat so long and narrow and an IC is asking for trouble. Basically 750mm wide is so small that you need all of the volume you can get to lift the boat as high as possible and maybe even keep the chines out of the water, so go for convex not concave sections. Concave waterlines are a disaster anyway, unless its a rule cheat.

Steve has created a good set of rules which strongly discourage distorted shapes and hollows, there are no options to cheat the rule with ugly distortions.

Link to post
Share on other sites

 

Only one more- 5e is a bit vague about where the 2000mm tape is placed, depending how you define "centered on BMS":

 

 

 

Half the tape each side of the centre...

Link to post
Share on other sites

You slide the 1m athwartships tape fore and aft for 1m each way.

and you slide the logitudinal 2m tape sideways 0.5m each way.

(starting centred at BMS.)

No hollows etc like it says.

 

My boat originally was 750 at the chines, with vertical sides, so the deck was also 750mm beam - too narrow!

I made deck extension platforms so it was about 1000mm wide, it measured OK with the reverse chine/hollow outside the tape measuring position.

post-2679-0-99765300-1390556460_thumb.jpg

post-2679-0-45645300-1390556655_thumb.jpg

Link to post
Share on other sites

Finally! The longitudinal tape slides sideways .5 m centered on the BMS.

 

So within the dimensions generated by the BMS the hull must 1m wide by 2 m long and 275mm thick.

 

Somwhere.

Link to post
Share on other sites

This seems very like the discussion we had some time ago. Page 9 of the thread, I think.

 

To change the topic somewhat. A question for Andy P

 

When Tin Teardrop was modified by chopping the stern off, was there much of a change in performance?

Link to post
Share on other sites

Finally! The longitudinal tape slides sideways .5 m centered on the BMS.

 

So within the dimensions generated by the BMS the hull must 1m wide by 2 m long and 275mm thick.

 

Somwhere.

 

and the sideways tape slides 1m fore/aft.

 

The circumference skin is 2m x 1m, but the actual hull can be smaller ;-)

 

Only at BMS is the required 275mm depth.

The 2m x 1m tape etc is for the 'no hollows'.

Link to post
Share on other sites

This seems very like the discussion we had some time ago. Page 9 of the thread, I think.

 

To change the topic somewhat. A question for Andy P

 

When Tin Teardrop was modified by chopping the stern off, was there much of a change in performance?

Mmm I changed a lot. Downwind was much faster - but that might be the kite ;-)

Upwind was much slower - but that might be the reduced righting moment :-(

 

The original stern was very narrow and pointy, but definitely at low speed, the longer hull was less burbly and smoother wake.

Planing speed was not much difference I would say.

Link to post
Share on other sites

The design panic thread is around post 3987781

 

So nowhere within the BMS box can the hull be less than 750mm in beam, and no weird shit inside of the 1000mm by 2000mm BMS box at all?

Link to post
Share on other sites

 

Finally! The longitudinal tape slides sideways .5 m centered on the BMS.

So within the dimensions generated by the BMS the hull must 1m wide by 2 m long and 275mm thick.

Somwhere.

and the sideways tape slides 1m fore/aft.

 

The circumference skin is 2m x 1m, but the actual hull can be smaller ;-)

 

Only at BMS is the required 275mm depth.

The 2m x 1m tape etc is for the 'no hollows'.

So depth is not a BMS box but a rectangle BMS.

Link to post
Share on other sites

Is the center of the 1 m athwartship tape always centered on the 2m centerline of the hull, or does the center of the 1 m athwartship tape travel with the longitudinal 2 m tape as it travels .5 m side to side? Which would mean the 1 m athwartship tape would be effectively 3 m long as it wraps around the hull?

 

Say this is the 1 m tape centered on the longitudinal 2m tape located on centerline of the hull

 

post-906-0-02645200-1390628854_thumb.jpg

 

When the 2m tape moves .5m to say the right, looking for weird and forbidden shit, does the 1m athwartship tape move with it, centered on it like this:

 

post-906-0-30724500-1390629199_thumb.jpg

 

Or does the athwartship 1m tape always stay centered on the 2 m centerline, sliding up and down it, as the 2m longitudinal moves .5m to either side looking for weird and forbidden shit, independent of the 1m athwartship tape?

Link to post
Share on other sites

"Or does the athwartship 1m tape always stay centered on the 2 m centerline, sliding up and down it, as the 2m longitudinal moves .5m to either side looking for weird and forbidden shit, independent of the 1m athwartship tape?"

Yes but i think of it like this :

 

Ok start with the 2 tapes as below.

attachicon.gifimage.jpg

then keeping one tape still - taped to the hull ;-)

slide the other one, centred on the stationary tape, from the centre position to the end of the stationary tape, and then to the other end.

now do the same with the other tape.

no hollows etc

 

so it's not a rectangular box as such, because the tapes go round the hull skin, making it a wonky box.

 

at the BMS which is where the tapes cross initially, depth 275mm min, and beam 750mm min.

anywhere else can be anything else, but must comply with the sheerline projection hollows etc rule.

 

the planing fins would be OK, as long as the athwartships tape wraps around the fin without hollows when going up the sides for the required 0.5m from the centreline ( and within the 1m from BMS requirement.) It might be advantageous to push the BMS forward, so the fins are outside the measurement zone.

Is the center of the 1 m athwartship tape always centered on the 2m centerline of the hull, or does the center of the 1 m athwartship tape travel with the longitudinal 2 m tape as it travels .5 m side to side? Which would mean the 1 m athwartship tape would be effectively 3 m long as it wraps around the hull?

Say this is the 1 m tape centered on the longitudinal 2m tape located on centerline of the hull

attachicon.gifimage.jpg

Link to post
Share on other sites

 

But just to be safe,attachicon.gifimage.jpgattachicon.gifimage.jpg :)

But would this be ok? Slab sided with planing wings.attachicon.gifimage.jpg

Starboard phantom styleattachicon.gifimage.jpg

You'll need to be pretty dang spry to get back there to deal with the rudder before you sink! Or is there no rudder?

I'm losing weight as we speak...

 

And I'm over 60, so yes, spry.

 

Swim, stand in water, stern hung rudder. It's supposed to float. Or flip up/down when tired of that.

Link to post
Share on other sites

"Or does the athwartship 1m tape always stay centered on the 2 m centerline, sliding up and down it, as the 2m longitudinal moves .5m to either side looking for weird and forbidden shit, independent of the 1m athwartship tape?"

Yes but i think of it like this :

 

Ok start with the 2 tapes as below.

attachicon.gifimage.jpg

then keeping one tape still - taped to the hull ;-)

slide the other one, centred on the stationary tape, from the centre position to the end of the stationary tape, and then to the other end.

now do the same with the other tape.

no hollows etc

 

so it's not a rectangular box as such, because the tapes go round the hull skin, making it a wonky box.

 

at the BMS which is where the tapes cross initially, depth 275mm min, and beam 750mm min.

anywhere else can be anything else, but must comply with the sheerline projection hollows etc rule.

 

the planing fins would be OK, as long as the athwartships tape wraps around the fin without hollows when going up the sides for the required 0.5m from the centreline ( and within the 1m from BMS requirement.) It might be advantageous to push the BMS forward, so the fins are outside the measurement zone.

 

 

Is the center of the 1 m athwartship tape always centered on the 2m centerline of the hull, or does the center of the 1 m athwartship tape travel with the longitudinal 2 m tape as it travels .5 m side to side? Which would mean the 1 m athwartship tape would be effectively 3 m long as it wraps around the hull?

Say this is the 1 m tape centered on the longitudinal 2m tape located on centerline of the hull

 

attachicon.gifimage.jpg

It's faint, but there is a forward marking for the 2m tape. The planform shape (width) of the planing shoe is defined by the 1m tape, so it's an analogue of the hull planform. I'll have to play with a model to figure out the 2m tape. I take it the seat carriage, tracks etc don't count as concaves as far as the 2m tape is concerned?

 

Thanks Andy

Link to post
Share on other sites

"Or does the athwartship 1m tape always stay centered on the 2 m centerline, sliding up and down it, as the 2m longitudinal moves .5m to either side looking for weird and forbidden shit, independent of the 1m athwartship tape?"

Yes but i think of it like this :

 

Ok start with the 2 tapes as below.

attachicon.gifimage.jpg

then keeping one tape still - taped to the hull ;-)

slide the other one, centred on the stationary tape, from the centre position to the end of the stationary tape, and then to the other end.

now do the same with the other tape.

no hollows etc

 

so it's not a rectangular box as such, because the tapes go round the hull skin, making it a wonky box.

 

at the BMS which is where the tapes cross initially, depth 275mm min, and beam 750mm min.

anywhere else can be anything else, but must comply with the sheerline projection hollows etc rule.

 

the planing fins would be OK, as long as the athwartships tape wraps around the fin without hollows when going up the sides for the required 0.5m from the centreline ( and within the 1m from BMS requirement.) It might be advantageous to push the BMS forward, so the fins are outside the measurement zone.

Is the center of the 1 m athwartship tape always centered on the 2m centerline of the hull, or does the center of the 1 m athwartship tape travel with the longitudinal 2 m tape as it travels .5 m side to side? Which would mean the 1 m athwartship tape would be effectively 3 m long as it wraps around the hull?

 

Say this is the 1 m tape centered on the longitudinal 2m tape located on centerline of the hull

 

attachicon.gifimage.jpg

 

 

Well, that is not the complete interpretation used by the UK measurers Andy. The rules actually state that the measurement is taken AT the BMS which is elected to be ONE position between the positions stated from the transom. The rules state that the string is then run perpendicular to the centreline AT the BMS. Nowhere does it actually state that this string is then run up and down the boat within the 1m box. Suggest you speak to Colin Brown about this if not clear but that is how we have agreed to measure the boats.

 

This does have a relevance with the M2 which has concavity in the side panels above the chine which starts above 500mm line at the BMS but may not do further forward.

Link to post
Share on other sites

 

"Or does the athwartship 1m tape always stay centered on the 2 m centerline, sliding up and down it, as the 2m longitudinal moves .5m to either side looking for weird and forbidden shit, independent of the 1m athwartship tape?"Yes but i think of it like this : Ok start with the 2 tapes as below. attachicon.gifimage.jpgthen keeping one tape still - taped to the hull ;-)slide the other one, centred on the stationary tape, from the centre position to the end of the stationary tape, and then to the other end.now do the same with the other tape.no hollows etc so it's not a rectangular box as such, because the tapes go round the hull skin, making it a wonky box. at the BMS which is where the tapes cross initially, depth 275mm min, and beam 750mm min.anywhere else can be anything else, but must comply with the sheerline projection hollows etc rule. the planing fins would be OK, as long as the athwartships tape wraps around the fin without hollows when going up the sides for the required 0.5m from the centreline ( and within the 1m from BMS requirement.) It might be advantageous to push the BMS forward, so the fins are outside the measurement zone.

Is the center of the 1 m athwartship tape always centered on the 2m centerline of the hull, or does the center of the 1 m athwartship tape travel with the longitudinal 2 m tape as it travels .5 m side to side? Which would mean the 1 m athwartship tape would be effectively 3 m long as it wraps around the hull?Say this is the 1 m tape centered on the longitudinal 2m tape located on centerline of the hull attachicon.gifimage.jpg

Well, that is not the complete interpretation used by the UK measurers Andy. The rules actually state that the measurement is taken AT the BMS which is elected to be ONE position between the positions stated from the transom. The rules state that the string is then run perpendicular to the centreline AT the BMS. Nowhere does it actually state that this string is then run up and down the boat within the 1m box. Suggest you speak to Colin Brown about this if not clear but that is how we have agreed to measure the boats.This does have a relevance with the M2 which has concavity in the side panels above the chine which starts above 500mm line at the BMS but may not do further forward.

I think my head just exploded. "...But MAY not do farther forward."?

 

I will not find fault with Andy for replying to my questions- he has experience building canoes, working with professional designers, working with the class, and has actually taken (a lot of ) time to elucidate-

 

When I hear things like "...that is how we have agreed to measure the boats " I get nervous.

 

I don't want to arrive in California to be told to go home. I don't want to cheat. I wasn't in on the measuring agreement, or it's politics.

 

Perhaps an 'ask the measures' thread would be ok?

 

The first question I have is: do the 2 BMS tapes move?

Link to post
Share on other sites

As AngloSteve says the 1 m transverse tape is placed at a single position, according to the rule, " A 1000 mm tape centered on the keel at BMS and pulled tight transversely against the outside skin of the hull, shall

bridge no hollow in excess of 1mm in depth."

It says nothing about it moving the tape. The part of the rule which causes the problem is the instructions for the 2 m tape. " A 2000 mm tape centered on BMS and pulled tight fore and aft against the outside skin of the hull, shall bridge no hollow in excess of 1mm in depth". The meaning of fore and aft is insufficiently precise, because the hull is a non-Euclidean surface. Further moving each end of the 2 m tape transversely out from the keel by 1 m around the hull will almost certainly not move the centre of the tape to 1 m around the hull. It will depend on the hull shape whether it is more or less than 1 m around the hull. This was my difficulty with the rule way back. I see AndyP's logic, but some definition of what is meant by fore and aft would be helpful. This rule doesn't state that the 2 m tape should only have its centre moved around the BMS by 500 mm from the keel. Thus it would seem that it could be centred on the BMS, just at the deck level. What then is the meaning of fore and aft? For Tin Teardrop, the flairs, deck extension platforms in AndyP's parlance, were outside the region measured by the 1 m tape, but a 2 m tape centred on the junction of the hull and the deck extension platforms at the BMS would need to be placed tangential to the junction to allow the canoe to measure. My guess would be that the ends of the tape were less than 1 m transversely around the hull from the keel, unless the canoe was pretty well parallel sides over the region 1 m either side of the tape. I have and will always push for precision in the rules, so that builders know exactly what is required, even though I will probably never be one of them.

 

 

Link to post
Share on other sites

And this post sounds grounded in experience....

 

(And why I posted the fat boy hull. Post 2936)

 

 

 

 

 

There's really only 1 BMS, isn't there?

There is really only one BMS, but you can nominate where it is (i.e. find one that works for the beam measurement, 1000mm transverse tape test) anywhere between 1300mm and 2600mm from the stern. But I would suggest that to be confident the hull should be able to pass the 2000mm longitudinal tape test at any BMS that works for the transverse tape.

Link to post
Share on other sites

So I'm going to order wood and foam tomorrow: I really need to get going. I think it is only rational to assume both tapes move as Andy has explained. I am assuming that the 2000mm tape moves PARALLEL to the LONGITUDINAL CENTERLINE of the BOTTOM of the hull out either as far as the hull is wide, or 20" max, and the ends of the tape wrap around any hull on that parallel line if there is tape left over. I am assuming the 2000mm tape will be centered and sliding on the initial BMS. I am assuming I can pick my initial BMS as long as it is within 52" and 104" of the stern.

 

I am assuming that the only place the hull needs to be 11" thick is at the initial BMS in 2 dimensions: athwart ships (30") and vertically (11").

 

Speak now measurers, or forever hold your peace.......

Link to post
Share on other sites

I'm sure the way I describe is how Steve Clark SHC explained it to me...

However if the hull is fair it will measure both ways! ( moving the tape or not )

Tin Teardrop measured the slidy tape way, with the hollows outside the meas area.

Link to post
Share on other sites

The best advice I think I can give, having seen a fair few amateur designs in various classesover the years, is "don't bang the corners too hard". You won't often win an event if you bang the corners on every beat, and you're unlikely to do it with a design that does the same thing.

Rule writing is not so finely tuned an art that the fastest boat is likely to hitif every min or max in the rules. As I recall when they were being drafted, beyond beam and length, our main concern was to get a reasonably simple rule set that encouraged elegant fair surfaces and discouraged lumps and bumps to cheat the measurements. As I recall (too late to look it up) there's probably a catchall for the measurer to refuse somethingvreally weird. My advice FWLIW isto build a sweet fair smooth shape and don't try to bust holes in the rule,

Link to post
Share on other sites

The reason I was asking about the beam and the rules wrt chines etc is that I have in my shed a boat in pieces in ply and moulds to build a jig from. Way back in 2005, before the whole new rules development came about, my research was limited to what I could find on the web. Which at that time, on dial up was not much. And I was living on the west coast so there was no IC within 2800km.

 

I ended up deciding to attempt to build a stitch and glue IC put of ply. I ordered some plans from Selway Fisher in Uk, and I had a company called Capeboatworks cut out the ply and the jig-mould using a cnc router, then shipped over to me in WA, cost about $1100 all up. When it all arrived, they'd used a "B class" hull, the plans came with two, and the b class is one of them. The max beam is 1200mm, the stern does not quite fit the 45 degree rule and there are spray chines. I was obviously out of my depth, and the boat didnt fit the rules way back in 2005.

 

So all the pieces have been following me around the country as I move for work. I am finally in a good position to have a crack at building it, and it seems it would fit in the new rules better, maybe with a few mods. I fully acknowledge it wouldn't be up to speed, or even close to a skinny hull, but this would be my first build so I am not to fussed. Plus I already have a skinny fast boat, AUS 21.

 

I don't want to post up the designs as they are copyright to selway fisher. Anyone out there interested in a PM with some pics of the areas I am concerned about that may be able to provide some advice on a way to alter what I have to fit within the current rules?

Link to post
Share on other sites

As far as I remember, the idea of the static tape is to get a fair hull, and the idea of the slidy tapes is to prevent hollows ( and therefore bumps ) similar to those seen on i14s at one time.

The hulls are narrow enough not to need 'rule cheat' bumps to artificailly narrow the hull even more.

The planing wing things weren't considered during rule writing, but even with the stricter measurement system they could be made legal ( whether they work is another matter entirely! )

Link to post
Share on other sites

Hi Sezed,

For what it's worth the B class plans you've got were drawn up by Alan Powell who is also responsible for designing and building the skinny pointy IC "Asbo". See.......

 

http://www.intcanoe.org.uk/gallery/thumbnails.php?album=23&page=1

 

http://www.intcanoe.org.uk/gallery/thumbnails.php?album=31.

 

PM me if you want his contact email details.

 

Ian McP

Link to post
Share on other sites

As far as I remember, the idea of the static tape is to get a fair hull, and the idea of the slidy tapes is to prevent hollows ( and therefore bumps ) similar to those seen on i14s at one time.

The hulls are narrow enough not to need 'rule cheat' bumps to artificailly narrow the hull even more.

The planing wing things weren't considered during rule writing, but even with the stricter measurement system they could be made legal ( whether they work is another matter entirely! )

Puts the D back in Development! A lot of wetted surface too-

 

But given enough width on the bottom, they are a no brainer.....

 

Wonky Box!

Link to post
Share on other sites

The best advice I think I can give, having seen a fair few amateur designs in various classesover the years, is "don't bang the corners too hard". You won't often win an event if you bang the corners on every beat, and you're unlikely to do it with a design that does the same thing.

Rule writing is not so finely tuned an art that the fastest boat is likely to hitif every min or max in the rules. As I recall when they were being drafted, beyond beam and length, our main concern was to get a reasonably simple rule set that encouraged elegant fair surfaces and discouraged lumps and bumps to cheat the measurements. As I recall (too late to look it up) there's probably a catchall for the measurer to refuse somethingvreally weird. My advice FWLIW isto build a sweet fair smooth shape and don't try to bust holes in the rule,

Not to be a martinette but there is such a rule. Naturally it's on the last page, under Adminertration, the " spirit of the rules clause" ; 14b.

" The National Federation may refuse to issue a Certificate, even if the specific requirements of the rules are met, if a canoe departs from the spirit of the rules."

Every measurer is loathe to go there, but in the final analysis they are the police for every Sailboat Class I am familiar with.

Someone has to hold the keys to the asylum !

DWO

USA

253

Link to post
Share on other sites

So, what wouldn't be in the spirit of the class?

 

Helium filled kite powered 16 by 30er with hydrofoils on the end of the seat and rudder?

 

Can anyone channel Paul Butler? Heeeeeeeeeeeee'd knooooooooooooooooooow...............:)

Link to post
Share on other sites

 

 

 

 

"Or does the athwartship 1m tape always stay centered on the 2 m centerline, sliding up and down it, as the 2m longitudinal moves .5m to either side looking for weird and forbidden shit, independent of the 1m athwartship tape?"Yes but i think of it like this : Ok start with the 2 tapes as below. attachicon.gifimage.jpgthen keeping one tape still - taped to the hull ;-)slide the other one, centred on the stationary tape, from the centre position to the end of the stationary tape, and then to the other end.now do the same with the other tape.no hollows etc so it's not a rectangular box as such, because the tapes go round the hull skin, making it a wonky box. at the BMS which is where the tapes cross initially, depth 275mm min, and beam 750mm min.anywhere else can be anything else, but must comply with the sheerline projection hollows etc rule. the planing fins would be OK, as long as the athwartships tape wraps around the fin without hollows when going up the sides for the required 0.5m from the centreline ( and within the 1m from BMS requirement.) It might be advantageous to push the BMS forward, so the fins are outside the measurement zone.

Is the center of the 1 m athwartship tape always centered on the 2m centerline of the hull, or does the center of the 1 m athwartship tape travel with the longitudinal 2 m tape as it travels .5 m side to side? Which would mean the 1 m athwartship tape would be effectively 3 m long as it wraps around the hull?Say this is the 1 m tape centered on the longitudinal 2m tape located on centerline of the hull attachicon.gifimage.jpg

 

 

Well, that is not the complete interpretation used by the UK measurers Andy. The rules actually state that the measurement is taken AT the BMS which is elected to be ONE position between the positions stated from the transom. The rules state that the string is then run perpendicular to the centreline AT the BMS. Nowhere does it actually state that this string is then run up and down the boat within the 1m box. Suggest you speak to Colin Brown about this if not clear but that is how we have agreed to measure the boats.This does have a relevance with the M2 which has concavity in the side panels above the chine which starts above 500mm line at the BMS but may not do further forward.

 

 

I think my head just exploded. "...But MAY not do farther forward."?

 

I will not find fault with Andy for replying to my questions- he has experience building canoes, working with professional designers, working with the class, and has actually taken (a lot of ) time to elucidate-

 

When I hear things like "...that is how we have agreed to measure the boats " I get nervous.

 

I don't want to arrive in California to be told to go home. I don't want to cheat. I wasn't in on the measuring agreement, or it's politics.

 

Perhaps an 'ask the measures' thread would be ok?

 

The first question I have is: do the 2 BMS tapes move?

 

 

Amati,

 

OK, I shall be more precise.....for the avoidance of any doubt, the instructions given to UK measurers is that the transverse tape test is only required to be taken at the BMS.

 

It is fair to say that the rules may require an overview at Richmond as with the benefit of 5 years of experience there is likely to be some clarifications and improvements which should be made for the next revision.

 

If you are still concerned about this, I would have thought it best that you discuss this directly with the Class Measurer in the US and also direct these questions over the official IC class forum.

 

Steve

Link to post
Share on other sites

Thanks Steve! Good thing no suppliers returned my calls yesterday.

 

I'd like to argue that this sort of conversation seems more efficient to do here- the US site, at least, is usually pretty quiet. I was asking Del in PM's & emails last year, but that seemed a bit like keeping things secret (and I could see it leading to some duplications of our efforts). And this is 99% a polite thread. :)

 

But maybe this is a traditional premise that I don't appreciate? Kind of like a certain keelboat class that keeps it's rule secret? Keeping a new canoe design under wraps for competitive reasons?

 

Rules are going to get pushed. Nature of the beast I suppose. Putting more things out in the open seems fun and fair: might even inspire more joining the party. The class is small and very spread out- transparency can only help?

 

I don't think anyone wants someone to show up and be told 'no'.

 

On the other hand, I can understand not wanting the job of measurer to expand. I've been on a few boards and non profit executive committees....

Link to post
Share on other sites

Thanks Steve! Good thing no suppliers returned my calls yesterday.

 

I'd like to argue that this sort of conversation seems more efficient to do here- the US site, at least, is usually pretty quiet. I was asking Del in PM's & emails last year, but that seemed a bit like keeping things secret (and I could see it leading to some duplications of our efforts). And this is 99% a polite thread. :)

 

But maybe this is a traditional premise that I don't appreciate? Kind of like a certain keelboat class that keeps it's rule secret? Keeping a new canoe design under wraps for competitive reasons?

 

Rules are going to get pushed. Nature of the beast I suppose. Putting more things out in the open seems fun and fair: might even inspire more joining the party. The class is small and very spread out- transparency can only help?

 

I don't think anyone wants someone to show up and be told 'no'.

 

On the other hand, I can understand not wanting the job of measurer to expand. I've been on a few boards and non profit executive committees....

The final point I was making is that this site is not really viewed by many in the class outside the US, well certainly not in the UK anyway and we do have by far the biggest IC fleet ...er hum... You are therefore missing out on a very large pool of resource from people who have a lot of experience over a very long time in the fleet. The IC Forum was set up as a central knowledge base for airing this sort of question and outside the UK appears not to be used much - why?
Link to post
Share on other sites

Just build a nice simple boat which looks like one of the successful new rules boats. Keep it fair, light, and rig it conventionally, and you will have the best chance of learning to sail it (maybe even fast) in time for the September regatta. Development classes have ben around long enough that almost all the weird ideas have been tried, failed and discarded, so unless you are already good enought to get the most out of one of the modern, conventional boats you are probably going to waste a lot more time, money and effort if you attempt anything which tries to challenge the measurement rules. This advice from someone who does not alway abide by these rules and knows the consequences.

Link to post
Share on other sites

 

Still waiting......

I'll look into it. Ed might be away.

 

Phil's bang on the money on boats if my opinion is worth anything. I remember a clever idea of mine back in the 70s that sent a mast through the foredeck twice in three days and left me finishing not one race in the championship...

Link to post
Share on other sites

Phil Jethrow and Jim-

 

Having built 30 windsurfers I know these particular lessons very well. What I am looking for with all these apparent

Machinations is a simple elegant boat with a simple non epoxy building method that won't sink. There's a thread somewhere

around here about epoxy sensitivity. I'll edit it in. But internal space frames are not simple.

 

alternatives to epoxy with wood

Started by Gregzore, Dec 10 2013 08:26 PM

Over on fix it anarchy. I'll refresh it to make it easier to find.

Link to post
Share on other sites

Paul, what is your mast build strategy? There is a fair amount of work required to make a mast intended for an IC from a carbon fibe tube into a complete mast - the base needs reinforcement, the spreaders need gubbins, the headstay and shrouds need attachment points and the tip needs some modification. The carbon fiber tube is epoxy based and usually the mods are all done in epoxy too. A cf mast is 9 pounds, any other material is going to be enough heavier to make the boat more challenging to sail and to sail fast.

 

I know you want to design, build and sail your boat, but if you are serious about sailing the worlds in San Francisco your timetable would be pointing your towards buying a Nethercott and sailing the bejesus out of it between now and then. Unless you are an incredibly gifted sailor, your finish at the worlds will be better on a Nethercott with lots of seat hours than a new rules boat with relatively few hours. There are lots of parts on a Nethercott that can transfer to a new boat - blades, spars, sails and hardware that offset the cost too. But maybe that isn't the goal.

Link to post
Share on other sites

Already have a tin mast and boom, complete CF mast from Forte arriving 1 week or so. 2 sails already finished. Other cf spars 90% done. Foils on hand and finished. Seats 80% done. 3 possible hull designs. Sending offsets to Flying Foam in the next couple of days so they can cut foam out. My goal is to have the hull done when the ice breaks up up here (probably early April) and train every day if I have to to try get to that mythical Elvstrom level of playing with the boat in as many different conditions as possible. My last effort was easy and fun to sail, but I'd like to fix some flaws with the next (4th) one. My minimum goal is to finish every race within the time limits.

 

I'd like to build a hull that is basically a big lowrider moth hull, no flares, minimum IC dimensions. 1.5 lb EPP foam, plywood. I'm going to follow Mr Maas's advice of long ago. and just go ahead and build something and see if I meet the rules. I figure if she doesn't, you all won't send the committee boat after me or shun me if I stay out of the way and tag along. The planing shoe design was a desperate measure to have an easy build that met the rules. (Shape foam to lowrider shape, install bulkheads and spine, glue on top and sides, slap on planing shoe, glue and screw everything together with an exoskeleton. Massive Wetted Surface!)

 

Main goal? Always wanted to do this. See how it stacks up. Don't expect to win.

 

I used to build and race D2 windsurfers, so my theory (and I'm sticking to it) is that I might be able to pull this off. :rolleyes:

Link to post
Share on other sites

For people who would like to race at the the top end of the fleet, building your own boat with self imposed restrictions that will make it non competitive would seem pretty silly. But for some people, the challenge of designing and building your own boat is most of the fun and racing it is only secondary. If you are one of those people, if you actually get it built and make it to the start line, then you have already won your race.

Link to post
Share on other sites

This is why I did it. Unfortunately it was the only winning I've done for a while :(^_^:D

the challenge of designing and building your own boat is most of the fun and racing it is only secondary. If you are one of those people, if you actually get it built and make it to the start line, then you have already won your race.

Link to post
Share on other sites

This is why I did it. Unfortunately it was the only winning I've done for a while :(^_^:D

 

 

the challenge of designing and building your own boat is most of the fun and racing it is only secondary. If you are one of those people, if you actually get it built and make it to the start line, then you have already won your race.

For people who would like to race at the the top end of the fleet, building your own boat with self imposed restrictions that will make it non competitive would seem pretty silly. But for some people, the challenge of designing and building your own boat is most of the fun and racing it is only secondary. If you are one of those people, if you actually get it built and make it to the start line, then you have already won your race.

That's my thoughts too, I can't wait to build mine, I know it won't be competitive, but if I can get something that will float and sail, I am happy, for everything else, there is Aus 21! (Once I tame the beast)

Link to post
Share on other sites

In post 2912 Sezed asked does anyone consider there could be a place for a wider hull?". So far that question has not been answered. I would suggest that the answer is yes there is a place for a wider hull. I have been looking at the so called Added mass theory which is commonly used in the design of planing power boats. Working through the theory suggests that beam will only be of secondary importance, with the main factor influencing drag is the displacement for a given length of boat. In the theory the effect of beam only appears through the effect of deadrise, as shown below.

h5da.jpg

From Contributions to Planing theory, Peter Payne in Ocean Engineering Vol 22 No 7

All the papers I have seen are of studies of chine boats with constant deadrise, rather than boats with rounded bottoms and variable deadrise, but one might expect similar effects. A reduction in the added mass with increasing deadrise is what reduces the wave drag of the hull. My own view is that the added stability and easy of handling could well offset any increased drag (wave plus viscous) for a wider hull. I don't think that I will be building a canoe to prove this, but would love to see a wider hull built. Does anyone know of a University student looking for a project? A study of drag for similar hulls with different draft/beam ratios for the same displacement would produce fascinating results.

Link to post
Share on other sites

In post 2912 Sezed asked does anyone consider there could be a place for a wider hull?". So far that question has not been answered. I would suggest that the answer is yes there is a place for a wider hull. I have been looking at the so called Added mass theory which is commonly used in the design of planing power boats. Working through the theory suggests that beam will only be of secondary importance, with the main factor influencing drag is the displacement for a given length of boat. In the theory the effect of beam only appears through the effect of deadrise, as shown below.

h5da.jpg

From Contributions to Planing theory, Peter Payne in Ocean Engineering Vol 22 No 7

All the papers I have seen are of studies of chine boats with constant deadrise, rather than boats with rounded bottoms and variable deadrise, but one might expect similar effects. A reduction in the added mass with increasing deadrise is what reduces the wave drag of the hull. My own view is that the added stability and easy of handling could well offset any increased drag (wave plus viscous) for a wider hull. I don't think that I will be building a canoe to prove this, but would love to see a wider hull built. Does anyone know of a University student looking for a project? A study of drag for similar hulls with different draft/beam ratios for the same displacement would produce fascinating results.

 

The only problem with that theory is that it doesn't apply for most of an IC's performance envelope. IC's aren't really planing boats.

Link to post
Share on other sites

IC Nutter: "The only problem with that theory is that it doesn't apply for most of an IC's performance envelope. IC's aren't really planing boats."

 

Although we spend some of our time sailing at hull speed or less, the canoe has the capability of sailing with a Froude number of 1 (or maybe more) Uffa Fox claimed in the 1950 that he was clocked at 16 knots over the measured mile, which is a Froude number of 1.1. We spend some and, I would guess, maybe much of our time in the Froude number range 0.4 to 0.7 ( about 6 to 10 knots). This would put the hull firmly into the semi-planing category, if not the planing category. The theory is applied to the hull, and does not require any particular speed. It predicts drag as a function of speed, from the hull characteristics.

 

The characteristics taken into account are

1). waterline beam at each point along the hull, and its variation along the hull.

2). Draft of the keel line at each point along the hull, and its variation along the hull.

3) length of the hull

 

The added mass theory is just a way of trying to take account of the way the water flows around or under the hull and calculate the forces needed to make this flow happen. It thus seems to me that the theory should be as applicable to a sailing boat as to a planing power boat. However, I could well be wrong which is why we need research. Certainly there are restrictions to the hull shape which the simple theory, as applied to power boats, imposes, but these can, I think, be overcome by extending the ideas.

 

My interest in the theory started as I wanted to find some way to compare hulls. I do not have a CFD suite at my disposal, and the methods based on Mitchells theory are too simplified to be of great use. I was thus drawn to a theory which uses simple mathematics, and I can use to produce calculations using Microsoft Excel. I found data on Dinghy Anarchy(?) by Steve Clark (USA) for Mayhem and String theory (left graph) and compared these with data from the simple added mass theory (right graph). Mayhem was easy as it fitted the criteria for the added mass theory, but string theory needed some corrections as both the bow and stern were below the static waterline. Below are the results which I obtained. They compare well, but that could just be serendipity which is why I would like a to see a proper study done.

 

cyjx.jpg

Link to post
Share on other sites

FWIW, here's a link to my resistance calculation spreadsheet. It's based on Newtonian mass flow. Seems to work OK, but it's very general. Don't ask me to explain it :). It was derived based on data for semi displacement hull forms. Maybe there are some useful ideas in it, maybe not.

 

https://dl.dropboxusercontent.com/u/99666108/HullCalc5-120101.xlsx

Link to post
Share on other sites

In post 2912 Sezed asked does anyone consider there could be a place for a wider hull?". So far that question has not been answered. I would suggest that the answer is yes there is a place for a wider hull. I have been looking at the so called Added mass theory which is commonly used in the design of planing power boats. Working through the theory suggests that beam will only be of secondary importance, with the main factor influencing drag is the displacement for a given length of boat. In the theory the effect of beam only appears through the effect of deadrise, as shown below.

h5da.jpg

From Contributions to Planing theory, Peter Payne in Ocean Engineering Vol 22 No 7

All the papers I have seen are of studies of chine boats with constant deadrise, rather than boats with rounded bottoms and variable deadrise, but one might expect similar effects. A reduction in the added mass with increasing deadrise is what reduces the wave drag of the hull. My own view is that the added stability and easy of handling could well offset any increased drag (wave plus viscous) for a wider hull. I don't think that I will be building a canoe to prove this, but would love to see a wider hull built. Does anyone know of a University student looking for a project? A study of drag for similar hulls with different draft/beam ratios for the same displacement would produce fascinating results.

I did a 36' beam quick and dirty (I had dual knee surgery that killed all of the the summer) and it had 1 1/2" bow rocker and 1/2" stern rocker, both measured from the midpoint, flat hull (no deadrise). She never felt like she was rising up on a plane- even when I was literally standing on the stern to get the bow up. Although she was scooting nicely at times. Maybe little rocker works better with narrow(er) hulls? Overweight- like I weighed 220-230 instead of 175. Mainly water in the wings. Did I mention quick and dirty?

 

Anyway, so you all do not need to find the Youtube I posted pages and pages ago, here it is again, in all its primitive glory, with a Formula skeg for a DB. She was really easy to sail. I could not detect the stern wave detaching. Ever. Not much wind in the vid though.....

 

Link to post
Share on other sites

I've had a question about this for a while-

 

Granted these curves are only up to forced mode, but,

 

A Maas type hull:post-906-0-82114100-1391456677_thumb.jpg

 

A pintail hull: down at the bottom

 

Both 32" beam, 290 lbs displacement. The red line is wave drag, the blue line friction

 

Joseph Norwood pointed out in "High Speed Sailing" that at higher SLRs drag decreases with a double ended hull and increases with a transom hull. I wish I had my copy, but I lent it to a certain NA, so I can't be more specific than that.....

 

Crap they came out upside down, but usually they flip over when you tap on them.post-906-0-57429000-1391457262_thumb.jpg

Link to post
Share on other sites

Thanks for the spread sheet, IC Nutter. A first glance it seems to give very similar results to the Added Mass theory. There is however a fairly large effect of beam predicted by your spreadsheet. I should like to know more about the way the calculations are done, and where that assumption is built in so that I can see that it is reasonable. As I said for the added mass theory beam comes in as a secondary effect , due to deadrise. I haven't tried to quantify how much difference the theory predicts for different deadrise. I suppose I should have done that before now! Anyway I'm going to have a further look at this aspect. With the speed variations within the fleet, it is impossible to see any effect of beam other than the best sailors all have narrow boats. Controlled trials in a designed study would help to sort the question out or quantify the difference in speeds due to beam.

Link to post
Share on other sites

FWIW, in computer land, the curves in displacement mode for fatter pintails are very similar- a very slight increase in wave friction- the main increase is in surface friction, around 50% from a 30" to a 40" beam hull, for example.

 

So Andrew, and Mr. Nutter (to May I call you I?) what is the role of surface friction? If a hull rises at speed you'd think it loses surface friction, which is good one might think. Is limiting surface friction only useful at low SLR's? Or surface friction just doesn't matter as much as wind speed increases? Because my experience with the 36" beam hull indicating no rising of the hull at speed, which means there was no lessening of wetted surface. At 1 degree of bow up/stern down trim, the computer said there would be a lessening of wave drag. But that was with the stern only lowering in the water, not with the bow rising. I was standing on the very narrow tail. Otherwise it would not squat on its own....

Link to post
Share on other sites

Which is sort of my point. The IC is not really a planing hull. It's a long narow hull which dose not rise a lot even at planing speeds. Generally you sail it utilising the full waterline length. The whole point of planing is to reduce wetted surface area. At high planing speeds, there is a thing called the waterskiers paradox whereby the reduction in wetted surface area due to lift cancels out the increase in frictional resistance and the drag becomes constant over the high speed range. Anyway, the IC doesn't operate in the high speed range, which is why I don't think you can apply planing theories to determine IC resistance.

Link to post
Share on other sites

Thanks for the spread sheet, IC Nutter. A first glance it seems to give very similar results to the Added Mass theory. There is however a fairly large effect of beam predicted by your spreadsheet. I should like to know more about the way the calculations are done, and where that assumption is built in so that I can see that it is reasonable. As I said for the added mass theory beam comes in as a secondary effect , due to deadrise. I haven't tried to quantify how much difference the theory predicts for different deadrise. I suppose I should have done that before now! Anyway I'm going to have a further look at this aspect. With the speed variations within the fleet, it is impossible to see any effect of beam other than the best sailors all have narrow boats. Controlled trials in a designed study would help to sort the question out or quantify the difference in speeds due to beam.

 

I have replied to AndrewE by PM, but I've copied the bulk of the PM below for general information:

 

The spreadsheet grew out of a need I had to be able to ballpark some fast ferry hulls. I had noticed that for a range of hulls we had tested that there was a sweet spot (most efficient operating speed) for each hull which was dependent on the volume distribution/transom immersion. Initially I only wanted a method of estimating where the sweet spot was based on the shape of the curve of areas, however once I had developed a method for determining that it became apparent that I could use it to estimate the residual resistance.
The key to it is the thing in the spreadsheet which I call the resonant velocity (Vr). The idea behind it is that a hull with an immersed transom has the same resistance characteristics as a longer hull in which the curve of areas has been extrapolated to the point of zero transom immersion, except that you then have to add in the transom effects.
I developed the resistance formulas by trial and error, determined to use simple maths with no fudge factors. The residual resistance is broken down into a number of factors, bow resistance (the work required to part the waters, so to speak), stern resistance (pressure recovery), and a couple of components for the transom resistance. These are summed together to give the final residuary resistance value. There is an allowance for thickening of the boundary layer, but there is no form factor added so it's probably an underestimate, particularly for beamy hulls.
The resistance formulas basically use mass flow based on the displaced volume of the bow half of the hull (Stem to Amax) and the velocity determined by the Vr calculation to get a resistance value at Vr, and then use scaling factors for other velocities.
Frictional resistance is determined using the ITTC 1958 method.
In the residuary resistance calculations the shape of the maximum cross sectional area (Amax) is approximated as a semicircular cross section of the same area. So for residuary resistance, the hull beam has no effect on the calculation. I had assumed that there would be an effect but after many attempts to include one, I had to conclude that if there is an effect, it is minor and largely indeterminate for the types of hulls I had data for.
For the frictional resistance calculations I use the actual (approximated) wetted surface area and this is where hull beam comes into it, as for shallow hulls changing the hull beam has a large effect on the wetted surface area.
I tried to set up the spreadsheet to use as few inputs as possible, so the hullshape used in the calculations is an approximation based on the key characteristics of the hull.
The purpose of the spreadsheet is not to get exact resistance values, but to be able to quickly get approximate values for ball parking and investigation.
Link to post
Share on other sites

Which is sort of my point. The IC is not really a planing hull. It's a long narow hull which dose not rise a lot even at planing speeds. Generally you sail it utilising the full waterline length. The whole point of planing is to reduce wetted surface area. At high planing speeds, there is a thing called the waterskiers paradox whereby the reduction in wetted surface area due to lift cancels out the increase in frictional resistance and the drag becomes constant over the high speed range. Anyway, the IC doesn't operate in the high speed range, which is why I don't think you can apply planing theories to determine IC resistance.

I agree with almost everything that is said above. However, I do think that the A(dded) M(ass) T(heory) can be applied to give relevant results. Of course a proper study could well prove me wrong! The theory is NOT a planning theory, but a theory about the forces needed to move the water around the object moving through the water, which has been widely applied to planning power boats, these are two different things. The important factor for my predictions is that the hull is fairly flat over most of its length ( little deadrise). The length/beam ratio is totally irrelevant.

 

The ideas embodied in the added mass theory were first suggested, according to Wikipedia, by Bessel in 1828 to describe the motion of a pendulum moving in a fluid. (For non Mathematicians he was one of the greats in Mathematics.) An application of the theory is as far from planning power boats as you can get(!), demonstrating the generality of the idea, and long before the idea of a planning boat was conceived.

 

Indeed, as IC Nutter says, the canoe hull doesn't rise much at planning speeds, neither does the AMT predict that it will. For the Nethercot the theory suggests that the C of G will rise only above about 15 knots and that at 10 knot the bow will be trimmed up by about 3/4 of a degree, which is equivalent to a 3 cm rise of the bow.

 

Since starting this discussion I have done some quick calculations on the effect of beam. I will go through and check that they make sense. The initial results suggest the AMT predicts an approximate 5-6% reduction in wave drag for a 10% reduction in beam ( constant displacement), so I suppose it is quite significant.( More significant than I expected). The result depends on the position of the maximum WL beam and the maximum draft, so can vary from this figure.

Link to post
Share on other sites

Some time ago I looked at data for variation of trim with speed. The results are shown below compared with published results which applied to power boats. They looked to me as if they followed the same trends. The prediction of 9 cm at 15 knots seems maybe a bit high, but this would be for a hull driven by a force through the C of G, rather than the C of Area of the sail.

 

y56o.jpg

Link to post
Share on other sites

For some real world info, here's a lap from a reasonably windy race in December sailed by this very average mid fleet Canoe sailor in my lightly modified Nethercott on a reservoir in the UK. It was pretty windy, probably mostly F4: windy enough that I could hit 13 or 14 knots between races on about a 100 degree heading. Windward mark at the top. The lap wasn't in fact windward/leeward, there were other marks in it, but it wasn't far off.

 

As you can see the real world speeds are mainly in the 3 - 9 knot region, and the only times 9 knots was exceeded is in the bear away and on one gust on a reach. And yes, the wind does shift a lot on my reservoir... My feeling is that a Nethercott hull lifts the bow a bit more than you guys are predicting, but its interesting that my wider stern definitely has the effect that the bow lifts significantly less.

post-60-0-64194600-1391516900_thumb.gif

Link to post
Share on other sites

Blimey, this all looks pretty heavy stuff but interesting.

 

My observation having built a lightweight Nethercott and 4 M2 new designs is that the new boats are much more easily driven but they also tend to skim over the surface more readily than a Nethercott which has tends to create a lot of resistance (comparatively) under the mast where the waterline gets much wide until it rises over its own bow wave. This is really noticeable when sailing a new rules boat and then going back to a Nethercott. However both designs do something which may not be planning but they certainly rise above the water and skim on the surface if it's flat. The new designs seem to do it more easily which is why we can pull away easily from a Nethercott and accelerate more quickly but top speed doesn't appear to be that different. There is no noticeable change, like the Bethwaite hump less hulls, between displacement and skimming mode which presumably is down to its skinny shape but something is happening there which is akin to planning.

 

Andrew - I read somewhere that Plymouth University have just bought a new wave tank for testing hulls. Could be worth giving them a call.

Link to post
Share on other sites

Really nice information. How was the boat speed measured?

 

GPS and GPSAR software. I have a Sony smartphone which is waterproof so it is just turned on before the race and put in the halyard bag (on a lanyard!). I don't know how well GPS would work inside a carbon hull. Badly I suspect!

 

Steve, I'd have said that the Nethercott has a bloody great planing speed "hump". As you say I reckon its all to do with all that noise under the mast area. Tin Teardrop on the other hand didn't have much of one, and nor did my one off singlehander, which although rather wider was much more akin to the newer boats in bow section.

 

Bethwaite did some interesting more detailed analysis of the phenomenum, and what he reckons he found was that on modern style wedge hulls like the 49er, that there is still definitely a planing hump (and so the laws of physics haven't been rewritten), but that the speed that it occurs at varies very significantly with trim. What he reckoned was going on was that talented sailors (and Julian was normally steering the towed boat when they did his tests) were subconsciously altering the trim of the boat so it was always in the lowest drag trim for the speed being towed at. That does make sense to me.

Link to post
Share on other sites

 

 

Really nice information. How was the boat speed measured?

GPS and GPSAR software. I have a Sony smartphone which is waterproof so it is just turned on before the race and put in the halyard bag (on a lanyard!). I don't know how well GPS would work inside a carbon hull. Badly I suspect!

 

Steve, I'd have said that the Nethercott has a bloody great planing speed "hump". As you say I reckon its all to do with all that noise under the mast area. Tin Teardrop on the other hand didn't have much of one, and nor did my one off singlehander, which although rather wider was much more akin to the newer boats in bow section.

 

Bethwaite did some interesting more detailed analysis of the phenomenum, and what he reckons he found was that on modern style wedge hulls like the 49er, that there is still definitely a planing hump (and so the laws of physics haven't been rewritten), but that the speed that it occurs at varies very significantly with trim. What he reckoned was going on was that talented sailors (and Julian was normally steering the towed boat when they did his tests) were subconsciously altering the trim of the boat so it was always in the lowest drag trim for the speed being towed at. That does make sense to me.

 

 

Jim,

 

That's interesting as his books don't really suggest that - I suppose its too late now for him to make an official amendment, sadly! His tow tests are also shown with the bows being held in position and don't really represent the real world with all the forces focused in the centre of the hull and so were always a simplification.

 

 

Steve

Link to post
Share on other sites

I think D/L dominates the discussion.

Even though a Nethercott is lighter for it's length than any other dinghy out there, a new rules boat is lighter still.

One thing we have learned over the past half century is that flare forward is slow. The Finns w built at Vanguard were as low and skinny as they could possibly be, and that follows through almost everything else I have tested. In essence the "classic" small boat bow was intended to slow the boat and lift the bow when a wave came along (one in a million, I know) In all cases you want to minimize the energy absorbed by wave encounters and still have enough reserve to go down wind. The New ICs solve this by shifting the CG and LCB aft, essentially making a longer water plane do the work of one that was marginally wider.

Yak Yak Yak

SHC

Link to post
Share on other sites

...his books don't really suggest that - I suppose its too late now for him to make an official amendment, sadly!

 

Higher Performance Sailing (the second book) pp160-162. I didn't spot it the first time I read it. Trouble is the books are so dense its easy to miss stuff.

Link to post
Share on other sites

Jim, Modern technology! wonderful isn't it! All we need now is the wind speed and direction to be recorded at the same time. That would give a lot of information.

 

I am interested to know how you identify the added resistance with "noise under the mast", as opposed to some other region of the hull.

 

Your comment about trim is very apposite and can make a huge difference.

 

Anglo Steve, What do you mean by a lightweight Nethercot? Same hull shape but just lighter? Or hull depths reduced to reduce the displacement?

Link to post
Share on other sites

All we need now is the wind speed and direction to be recorded at the same time. That would give a lot of information.

 

I am interested to know how you identify the added resistance with "noise under the mast", as opposed to some other region of the hull.

 

Wind speed and direction logging: wouldn't that be nice:-) Its technically very achievable, but the trouble is putting an expensive and probably delicate bit of hardware at the top of the mast where its so vulnerable to getting trashed.