I just red the thred on "Smiple questions", having dun a search for "canted hulls" :
As usual, lots of interesting opinions, mostly diametrically opposed.
-Bill says it might not be advantageous, I can understand the theory he puts behind his opinion, which is a first for me. I would tend to agree with him based on what I`v seen, especially going downwind with the kite up - I can push the boat much harder if it`s heeled over quite a bit, the daggerboards provide lift, as does, I believe, the fact that the leeward hull is pressing it`s leeward side into the water, and since the side of the hull is curved it acts as a lift-producing device itself.
-Darryl says it works, especially for barges, and cats should be the same, as long as the boards cant outward & are toed in to REDUCE DRAG when sailed flat. Makes no sense to me, I`d imagine that when sailed flat daggerboards & rudders that point inward would be like sailing with the handbrake on. I`d be willing to try it, but only if I understood why.
-John Pierce (in a private conversation), says canted hulls work on the Stealth, but for a different reason that would unlikely work on my boat, but that I should try it out anyway. Makes sense, practical testing gives different answers to theory most of the time anyway. Question is, how much of what ?
-Darryn says he sailed against a Mosquito that had canted hulls and it had no problem sailing away from the rest of the fleet. Now I`m interested, but can`t get any more information on that particular incident. (First real-world account based on experience I could find.) Unfortunately Darryn now sails a Laser, probably doesn`t log in here often, and doesn`t answer private messages as a result.

Back to Darryl`s theory : If you cant the hulls by, let`s say 7 degrees, the amount I think I`d need based on preliminary sketches I`ve done. I would keep the hulls parallel, but that`s just me, I reckon if both hulls are pointing at a point one-third of the boatlength forward of the bows, both hulls are trying to get to the same place, so you`d have more drag, not less. (I just drew a sketch of this and it CAN`T work !!)If anyone can explain this in Smiple terms I`d appreciate. Unfortunately the thread then turned direction and became a discussion in Inter 20/17/18 daggerboard design, which, while I found interesting, I`m not likely to apply to my possible experiment, which is why I thought it better to start another one.
My interest would be in canting the hulls, and keeping the daggerboards perpendicular to the hulls, so they are both canted, not in having upright hulls with canted boards, since that would be a costly exercise.
Any suggestions ?

Steve

I can only give you a comment that was shared with me by Pieter Saarberg when we were discussing this. I also convey the content of a post that Jim Boyer posted about this subject a few years ago.

Pieters opinion is that canted hulls do work somewhat on light boats, singlehanders, like the A-cat but not much at all on the heavier boats like doublehanders or F18's. He also mentioned that the F18 class at the time seemed to move away from canted hulls. Right now we can say that this is truly the way the F18 has gone. I'm not sure wether the Capricorn F18 is a canted hull design but all others (newer designs or competitive design) are currently uncanted.

Jim Boyer said that his experience when going from the uncanted Mark 3 A-cat to the canted mark 4 A-cat was that the canted boat showing improved steerage in the middle speed range mainly; there was no noticeable speed range. Of course this improved steerage was welcome on the A's in these conditions due to the wildthing manouvre that seems to pay off here. Jim also stated that the Mark 3 and Mark 4 were largely the same boat with the canting as the exception. This could therefor be regarded as a pretty good comparison test in my opinion.

Some other designer, I forgot who (could be Jim), mentioned that a small payback was found in light weather when both hulls are in the water. However it was stated that since the boat must be wildthinged here that the payback was minimal although the outward canted board on the luff hull still seemed to be less efficient than the less canted normal board.

Wouter

Your right Steve these are not simple questions and I am not qualified to answer them. On one point I may be able to help. I believe the theory on toeing the hulls is the same as toeing rudders. That is, the weather hull will track straight through the water as the result of the boats leeway angle.

If you’re going to experiment your probably wise to only change one thing at a time anyway. Interesting stuff so keep us posted. You might also consider posting your questions on the boatdesign.net forum. There are some brains over there.
Dan

2 cents:

Consider paralel hulls and simetric foils sections. Both rudder and daggerboard are similar to Bruce foils, contributing with a vertical lift which depends only on their angle of attack.

For the daggerboard, the relevant angle of attack depends exclusively on the boat atitude. With the bow up, the lift is upwards (good) with the bow down the lift is downwards (bad).

First conclusion: move your weight back to increase lift, reduce wetted surface and possibly sail faster. This is no news for any catsailor.

(Why "possibly" instead of "certainly"? Because there is an added drag from the daggerboard that may or may not compensate the reduction of drag due to the smaller wetted surface. My experience is that it works, but how much will depend on boat and foils design.)

Now the rudder. Since some weather helm is desirable, its vertical angle of attack will be bigger then that of the daggerboard most of the time, so the rudder's lift will point upwards most of the time.

However, due to the rudder location, its lift modifies the boat atitude, reducing the angle of attack and the positive lift contribuition.

Second conclusion: more weather helm requires more weight in the back to keep the bow up. Highest lift happens with the rudder close to a stall (assuming a fixed heel angle) and the key to benefit from lift is to keep the bow up.

So, with paralel hulls and simetric foils, a bow up atitude is key to obtain a positive lift and a marginal speed advantage. No news.

Now the canted hulls.
Vertical lift disappears. Its advantage is the drag reduction from the hull remaining vertical when flying the other hull and a slight weight reduction due to shorter beams (or slightly larger width with the same beams).

Final conclusion: canted hulls are better in low speed and paralel hulls are better in high speeds - provided that you can keep the bow up.

Cheers,
Luiz

Thanks Dan, Wouter for replies. I guess that if canted hulls had been shown to be truly superior they would have found their way to many newer designs by now. Based on what was written in the original post on the subject, it seems that it would hardly be worth the effort, so it might not happen to my boat at all. I`m just curious as to what developments recently, if any, have been a notable improvement on design. I think you once pointed me towards the boatdesign.net forum on an entirely different subject, I read 2 or 3 posts and then ran away with my tail between my legs. I think the level of discussion is a bit above the average sailor sometimes. Even on this forum the answers are sometimes quite difficult to get my head around.

I was about to add a post asking if anyone had seen or heard of the Ventilo ZipO / Mattia Dynacat F16 in recent times, as since their launch at a boat show (I think in Paris) which Wouter took pics of some time back, I`ve heard nothing of them. They had very different hull shapes from the accepted norm, so I was curious as to how they went, but Wouter recently informed us that the Mattia was discontinued in F16 & F18 format, and I don`t know if many Vetilo`s were ever sold. It`s a pity, since we only learn what works better than the accepted norm when someone tries something completely different, and it works.
Just constantly looking for ways to go that little bit faster !!

Cheers
Steve

I believe the N20s hulls are canted by four degrees. I don't remember anyone saying they are slow.

Hi Brian, would that be the Inter 20 ??
Oh, and well done on fixing the typo - it made it unscathed for 26 posts !!

Steve

Yes, the Nacra/Inter 20. You probably cannot see the angle from looking at the sterns, but a direct view of the bows makes it almost apparent. I got the "Four Degrees" quote from Tom Leobold when I crewed for him recently.

I'm almost anal when it comes to spelling/grammar- I read a lot of books so that helps me some. Then I come online to sailing, jeeping, and photography forums and everything goes to hell. Any errors from foreigners I can completely understand, but I come across a lot of native-English speaking adults who can't spell and have no clue how to properly use a comma

Or a period.

something makes the I20 fast and stable. Its the best boat I've ever sailed, by far.(not that Im the expert)
Look at its track record, I think it speaks for itself.

David
F18

A graemlin at the end of a sentence precludes the use of punctuation.

To stay somewhat on-topic. I'd love to see what a 10 or 12' wide Nacra/Inter 20 could do! At that width a curved traveler track may be in order. Also, at that width would there be less use for canted hulls

Does a graemlin preclude the use of a question mark

Kevin
Prindle 18

Canted hulls are used on the A2 at 7.5' wide and use 7 degrees. I am pretty sure the 8.5' wide N20 is canted at 4 degrees. I have been led to believe that the canted hulls are done so that at ideal state with one hull just out of the water, the leeward daggeboard and hull are vertical.
Then the answer to your question would be that at 10' wide or 12' wide, the amount of canting would be less that at 8.5' wide.