Alternative to marvelous Buccaneer 24

Sid

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Great! You've done a tremendous job. One question: can you adjust the angle of incidence of the ama foils while you're sailing?

 

I'm thinking later, once I get the basics working okay, to run lines to the foils and be able to lift the unloaded windward one - but shifting angle of incidence, no, that is pretty well fixed at 2.5-3 degrees positive. However, if I don't do the lifting adjustments, the foils could be differently wedged at slightly (only .2 -.3 degrees) differences - as they are at the moment.
But on such a fine, low displacement main hull, you can easily alter trim foil angles by shifting your own *** fore or aft.
Yesterday I cleaned the rust marks off the main (looks almost presentable) shortened the battens to quit/reduce runner fouling and also added shock cord, and increased the main sheet purchase to a staggering 5-1. Which sounds like too little but way better than 3-1 I had to just get going.

 

Call me an idiot, as I know nothing of aerofoils - but surely the windward ama foil must be providing some lift while it remains in the water?

And isn't that lift just increasing the heel angle by transferring load across the beam to the leeward ama???

And could that then be increasing drag by depressing the leeward ama and increasing it's displacement somewhat????

Remember, I'm an idiot.....so be gentle....

 

I may be wrong, but it may be a case of the windward foil reducing lift as heel increases, and the leeward one ends further immersed generating more lift.

It is an area I am following with interest.

 

That assumes that there is lift being generated along the entire length of the foil, rather than just at the curved foot..??

So as the foil comes pregressively out of the water as the boat heels, it would generate less lift...??

Makes sense.

my assumption was basewd on the lift coming largely from the curved foot of the foil only, hence it still provides lift (heel pressure) until it comes out of the water.

Might be an interesting experiment for Gary once he can rig up a lifting mechanism for the foils..??

I forget...did Gary install a main hull daggerboard or centreboard??

I recall the rudder had a horizontal foil at its base, but was there any other lift-generating foil on the main hull..?

 

Buzz, this argument(?) can reveal a can of worms similar to whether multihulls plane.
From my observations on inclined foils, the windward foil, flying mostly out of the water, is set at around 2-3-4 degrees angle of incidence, same as the leefoil, and because the platform/boat is making some leeway, the windward (non-lifting) foil is pretty near passing through water at close to zero angle of incidence, so is providing very little lift, a little drag. This is beating to windward. Also it is mostly out of the water, flying through air. Conversely the hard working leeward foil is doing all the lifting ... BUT some foiling multihulls like those from Ketterman, Bradfield and others have articulating foils working from wands passing over waves - and they put a negative angle of incidence on the windward foil - which pulls down. Doug is an advocate to these types ... but maybe he is changing his mind a little after observing the incredible ETNZ 72.
The lift up/pull down Bradfield/Ketterman types have pretty near flat beams, almost anhedral, no dihedral, (I like dihedral because it leans the boat and lifts the windward foil out - less to no drag) - also by having negative and positive angles on the B/K types, you end up lifting the boat twice, one foil fighting the other ... which has to be slower, more drag than one clean working leefoil, again just imo.
All the true foiling boats have inverted T or L rudder setups, set at zero angle of incidence. It is easy to lift the sterns.
Sid has no central dagger, just the inclined, curved L or J's. So far seems to go to windward okay. Actually I've built a very high aspect ratio dagger and case if Sid's performance to windward was not good enough - but I'd rather not fit it. More weight.

 

Hey Gary
Yeah, cool, that makes sense.

Seems the only advantage to the B/K type adjustable foils would be to keep the boat flatter on the water, and maybe thereby increase the righting moment?

Or is it more to getting the entire main hull to fly by generating more lift?

Hence why I was asking about a foily daggerboard that would provide lift to the main hull...

But if the foils in the amas plus the rudder foil provide enough lift to fly the main hull - theoretically making the boat much faster (??) - then I can see a daggerboard might then be needed for stability.

But could it be an inverted T as well? I think the flying Moths have an invert-T centerboard don't they?

And what about L'Hydroptere and such big foily boats? Do they have a foil on the centerboard?

Just curious, really...not expressing an 'opinion'....like I said, I know jack.

I think I hear what you're saying is - if it ain't broke don't fix it?

 

Gary, is sid intended to be foil assisted, to or get fully air borne or would that be a by product as with the AC 72s.

 

Warwick, Sid is meant to be foil assisted in lighter winds and fully foil borne in the fresher stuff; a compromise but with the main concept aimed towards fully flying. A true foiler is always trying to lift anyway in light winds and although the lifting foils create some drag, this can be compensated by the hulls being also lifted somewhat ... which also reduces drag. Sid is an attempt to achieve the best of both worlds.
Buzz, a dagger in the main hull is only to hold the boat from making too much leeway while beating; that is if your foils are not doing the job.
Yes, you could have a T foil dagger like a Moth ... but at this stage, I'm aiming for the lee ama foil to do the work. If you're not careful you could end up with your boat looking like a hedgehog of foils; sure we're foiling ... but far too much drag.

 

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One of the big problems with small trimarans(under 20') is that they develop so much RM(righting moment) if they are near square that it makes it difficult to fly the main hull. I've designed a system that uses a lifting foil on the daggerboard controlled by a wand and set to hold a specific angle of heel-say 10-13 degrees). There is a rudder t-foil as well. The ama could be set up with a single curved lifting foil or "L" foil. The advantage is that the main foil+ wand allows the main hull to fly way before it would w/o the foil(in 6-7 knots of wind). A unique characteristic of this system is that as soon as the main hull flys the main foil begins to unload and the ama foil begins to load up. At a certain point most of the load will be on the ama foil with the main foils virtually unloaded(reducing drag) except in their continuing role in pitch control for the whole boat. This system hasn't been tested on a trimaran yet but a variation has been tested on the cat "Happy Feet"-which is what inspired my system.

 

Thanks Gary, for the insight into Sids concept.

Do you mean a boat looking like a hedgehog the open 60s and volvo boats, with 2 dagger boards, a canting keel and 2 rudders.

 

Yes, and the Mini-Transat 6.5m boats started it off. Also if you check out the old AYRS journals, some of the early pioneers studded their craft with foils all over the place.
And David Keiper's famous and historical foiling tri Wiliwaw was covered with ladder foils. They worked/work well ... but not in light airs.

 

That is the first time that summin named Sid has had that effect on me

 

That is one hot looking boat! Good Job!

 

Cox's Bay triumvirate: Tennant 16 metre cat Power of 2, Sid and Crowther B24/27 Miranda - plus a centreboarder hidden away. Going sailing first thing tomorrow on the tide; weather is incredible here at the moment.