Interesting paper on the foiling moth

http://www.moth-sailing.org/download/CSYSPaperFeb09.pdf

Thanks for posting that! Very interesting data and I think we can apply it to our cats. The windward rig leaning for one thing. Do you have any contact information for these guys? I have some questions I'd like to ask them.

Contact John Ilett, Perth.
Use International Moth website.

Thanks Dave. Since you have already done some foiling cat work, do you think a V type foil instead of their T foil might work, without all that moveable flap stuff? I was thinking about how the T foil has to be able to shed lift or risk a pop up and crash. A V type foil should self limit as the top of the V comes up through the surface, lift is reduced, right?

Sorry for not replying sooner, new baby is preventing a quick response. I didn't have a contact as I got the paper form the boatdesign.net site.

John Illet can also be contacted through his website http://www.fastacraft.com/contact.html

All the best

Gareth

Thanks for that, and congrats on the new baby! Now, get some sleep.

The Moths use T foils because the V foils (Bruce foils) were virtually prohibited by a rule saying that foils could not be attached to the tramps. Besides providing lift, Bruce foils may also increase stability, so the boat could be faster and easier to sail.
A good thing about those foils is the smoth ride. They dampen roll, yaw and (depending on the setup) pitch.

Interesting,

using their numbers and the back of an envolope..

if you fitted 2 moth rudder foils upside down to an F16's rudders you'd increase the total drag by about 6% but it would be the equivalent of having another crew member trapping off the transom. This would mean a boat sailing single handed would have a similar top speed to a conventional double hander but maintain it's acceleration advantage.

I've been here before; and firmly believe this to be correct. Loss of job prohibited the build of said boat. Initial discussions were already taking place.

Project shelved.

Ok, negative lift in the rudder works just as well as crew's weight to avoid pitchpoles.

I prefer positive lift in a forward placed and smaller area daggerboard, together with a bigger rudder blade, to keep the CLR where it was. Avoid pitchpoles and reduce wet surface, probably with lower total drag.

It's a good argument Luiz, and one I'd be far more likely to use on a boat than the over complicated rudder foil system discussed above. The problem from a practical point of view is that the application is limited by pretty much all the cat classes's rules.

A 20 degree canted dagger board is going to produce approx 30kg of lift at 15 knots but will probably be within 0.5m of the LCF so this is the equivalent longitudinal righting moment of just 7.5 kg at the transom. The 30kg is 20% of an A cats sailing weight, 16% of a one person F16 or 12% of a two person F16 (canted boards are not allowed on F18). The wetted area reduction on the one up F16 will be about 10% however both the dagger boards and the rudders are now bigger than was necessary without canted foil and as a result have increased their drag diminishing the return.

So whats the net result...(on an F16 because there are more options).

Hull and foil drag at down wind (less to more)

one up with canted foils.
one up conventional.
one up adjustable rudder foils = two up conventional.

Resistance to pitch pole (safest to most dangerous)
One up adjustable rudder foils = two up conventional
One up Canted dagger boards.
One up conventional.

The above is supported by the move in A cats to canted and/or curved foils as it shows a definate advantage in that setup.

The next question becomes what is more important top speed or resistance to pitch pole? As that will decide the future direction of the F16 under its current rules.

Well we could always change the rules, just like the Moths did. But I am not in favor of that as it would start an expensive arms race that would only make the F16 class less attractive to any new members, I think.

What if you put two boards in each hull, both canted inward at what ever angle works best, so they form a lifting V type setup, front and rear, and maybe even add the T foils to the rudders, I wonder if all of that would be enough lift to get the F16 solo up out of the water.

Doing the boards would be the easiest, cheapest mod, then adding the T foil lifting rudders, but all of it could be done without the adjustable flaps they use on the Moth, and you could still pull them all up when you approach the beach. I am not a fan of the T foils on a cat, since we already have the width for stability, I think the V would work better.

I am also trying to figure a way we could tilt our masts to windward as they do on the Moth (with heal), we might be able to do it with dyneema shrouds that go from the tang, down through a block, across the tramp (under it?), through another block and back up to the mast. Just need to figure out how to adjust it and keep it from slipping!

AS you say, class rules would need to change, currently only one pair of plates on the platform; so one per hill (or two in one hull):

[i]1.6 Daggerboards and rudders


1.6.1 The platform shall be equipped with a pair of rudders.


1.6.2 In addition to the rudders, the platform may also be equipped with a pair of daggerboards or centerboards.[/i]





Tilting the rig is not too difficult. All you need to do is have multi purchase on each shroud base with stoppers to prevent the rig going over the side. Been done on a few boats overhere, catapault being one.

I've got to wonder why the A cats haven't done the tilting mast thing yet. As you say, it would be easy to do with a simple block system on each side stay, like an adjustable trap, as long as you put a stopper ball at the end to keep it from going too far out, probably that split forestay would also need to be adjusted? But you could also lead those back to the main beam through blocks, so maybe their rules prevent it?

Dave has already done a foiling A cat, but now with all the carbon stuff, it could probably be done lighter, and faster, but way more expensive, no doubt. And, would it work on the present courses we sail? Would a foiling A cat point upwind as well as a regular A cat? How well do the Moths point? I've never seen one except on You Tube and that wasn't racing upwind.

This configuration is used downwind by ORMA 60s, BMW Oracle, Hydroptere and the like. I just put the concept in words. My boat is far from their leagues, but the configuration is similar. Note that they are all trimarans, not quite the same as beach cats.

Still, Bill Robert's ARC20 features smaller daggerboards forward of the main beam and slightly larger rudders. He says that both the increased distance between the foils and the smaller difference between their areas result in lower total drag (besides shalollower draft, naturally). Turbulence / interference between daggerboard and rudder are not an issue in trimarans, so I guess a beach cat benefits more from this configuration.

Rules suck. Show up with improvements that result in significant increase in performance or seaworthiness and the rules will follow eventually.

I'm with you Luiz on the rules thing, or we would all still be sailing wooden rowboats. Make it faster, and easier to sail fast, and then make the rules to race it!

The A cats are currently voting on the "hydrofoil" rule- if you look at the"explanation" with the accompanying vote it is stated that at present, with the new rule, allowing canted or curved boards, it is not possible to develop an A cat that will "fly" all the way around the course and this is what the class is trying to prevent.
As for the canting mast- if you are asking about "A"'s- What about "C" class cats? I am sure it's been tried in the "A"'s- they have tried everything else- but currently, as pointed out in the A explanation, all the major championships have been won on fairly standard platforms and rigs.
One thing one must always remember is there is always a price to pay for any "benefit"- ie a particular setup that may be blazingly fast in 10-15 may be unsailable over that and slower in lighter air- this is apparently proving to be the case with the A's. Canting rigs may be quicker in a long straight line, but less reliable, heavier, slower to tack, etc. Look at Ben Hall's "winged" A-cat- much faster in certain conditions on certain points of sail but not faster over all and much more expensive/harder to rig/etc.

Kirt

A lot of "Stuff" on this post!
"V" foils lift the hydrofoiler's lee hull, allowing near vertical mast position. They probably won't go to weather well.

Canting an A-class mast is probably not necessary- they are awfully efficient the way they are today. And who is going to do it by hand? Glen Ashby? Naw.

T-foils are difficult to use to cause lift, needing flaps- hand held at the last best version. I went out last fall with my modern A-cat vs Doran Oster sailing his Rave with hand-held joysticks which did very well in their last National Championship: Fresh breeze- 13-16 mph. I ran all over the Rave while it was reaching on foils. And Raves don't go to weather on foils either. Then I put Rave T-foils on my wooden A-cat- and found the vehicle heavy, but it did come out of the water.

External carbon foils? Interesting idea. You have just described a Palatka-Jacksonville Mug Race boat!
Or Randy Smyth's 2-year old Scissors trimaran built on an 20 foot A-cat hull- that is faster than a Tornado.

What? This seems upside down to me. If you want to lift the lee hull to make better speed- just lift the lee hull with a forward-placed lifting foil. (inward canted or new curved A-cat foil)
But to hold down a lee hull by putting downforce on the rudder? Insanity!

So when the boat is up on the foils, it doesn't go upwind very well? I was wondering about how well it could point if most of the boat is out of the water, and most of the boards/rudders too. Not much left in the water to keep it from side-slipping. Now that leads to the next issue, if a foiling cat were to be developed, would it need a new type of race course? Instead of upwind, downwind, maybe reach back and forth over a longer course?

I'm sure Dave can correct me if I'm wrong, but the difficulty with foiling up wind is an available power issue. As the boat gets faster, the apparent wind comes more forward. As the apparent wind comes forward, less power is available. Except in the case of the uber-efficient moth (with very low windage and extreme lightness) most cats and tri's are going to exhibit a pretty high aero drag profile and find it difficult to take full advantage of foils completely around the race course.

And yet this is what existing cats are doing with T foil rudders.

Some benefits are worth the price. Foiled Moths win championships.

Right, but only because they are not using positive lift foils forward. As you already pointed, negative lift rudder foils make more sense then pumping water ballast into the hull: same displacement with less mass. It does increase stability.

The big tris alternate between using their rudder foils to keep the bow up or to help lift the central hull out of the water, according to the conditions. I am sure that at least Hydroptere and Geant can do both things.

...and this cat too - take a look:

The point was that foiling Moth and SYZ have a lifting foil in front, and do not overload the rudder flaps with a terrible load, or try to exert too much control, causing "dive brakes". Another problem not obvious is that the sailing foiler going to weather may run through a puff of wind and lose effective lift, coming off the foils: This is a real nuisance. Foilers need steady trade winds.