Does anyone know the angle of attack for foils? And how is this figured. I'm sure its similar to an airplane wing, more chord more lift/drag. Is there some way of making a more educated guess-timate on size? I've been fantasizing about building a plywood trimaran, and as soon as I move my cabinet shop into a larger location, (which has to be done regardless) I'm going to start on one. One that foils would be just plain cool.

Start with the third chapter of the (free) online book "See How It Flies" (http://www.av8n.com/how/htm/airfoils.html). It will give you basic indispensable information.

Afterwards, talk to Dave Carlson (dacarls@gmail.com - http://www.fastsail.com/catcobbler)

Good luck!

If you want to get even more keen...

Fluid Dynamics Textbook

Karl,
How about one of these?

http://www.hydroptere.com/accueil/images/videos/var/lang/FR/rub/19/movies/67.html

go to 1:14 into the video.

Thats pretty crazy. More R+D than I probably have the patience for, or money, or supplies, or time, or......

I'm thinking more tri than whatever that thing is. But it is plenty cool. The smaller one looks a little unstable, and hard to control. Do most of the foiling boats use a t-rudder? What got me hooked on this was watching Int Moths on youtube. I think for what I'm thinking most of the load should be carried by the center hull and less with the ama's. There would have to be something substantial I suppose just to keep from submergeing the ama's.

Alot of things to think about and consider.

What boat size you are dreaming with?

I've come up with the "magical" number of 23ft long, 20 wide. Why? I don't know, it's what has been in my head. I'd like to use a H20 rig and sails. Probably have a bigger reacher jib made as well. The 20 rig is just based on availability and price. I don't want to have rediculous amounts of money wrapped up in this when it becomes a colossal flop.

I have a couple of Dave Keiper's book Hydrofoil Sailing. Look up International Hydrofoil Society's references to foiling.
Williwaw was a homebuilt 1/4 inch Fir plywood trimaran the size you describe: It survived San Francisco bay, a trip to Hawaii then to New Zealand and back to Hawaii. There are tapes of it with the skipper sailing standing up, running at 20 knots in SF Bay with a lousy Catalina 25 rig, if I remember right. This was 1972. Dave built all the parts- surface-piercing ladder-style aluminum foils.
Usually the major lifting foils ran at +4 degrees: Dave and I argued about this when I was trying to make his Hobie 18 foiler work properly: he wanted the aft section of the cat to drag like on his Stormy Petrel 14 foot foiler. I showed him that it would not work that way, that the stern had to fly too.
We compromised- I put a positive angle on the stern lifters and it finally worked pretty well in 2000, even with poorly made Clark Y-foil extrusions as the lifting elements.
I had to clean everything up to make it work.

As Luiz says, look at my pix at www.fastsail.com/catcobbler
Foiling is a real blast. Unfortunately, few Americans are willing to innovate anymore. Very strange....
Dave

I have been designing, sailing, building commercially, multihulls for over forty-five years and for longer than that I have been studying foils of every description. It has only been over the last few years that I have felt confident enough to design and start to build something similar to what you are proposing. What I am saying is that it is a long hard road when you go down the path of "foiling" and no one that I am aware of, is fully there YET. But it WILL happen. The tri foiler shows great promise, the surface piercers on Hydroptere are doing what few expected them to do, as with the moth, and Dr Sam Bradfield has shown a most promising way to explore, BUT as I said, none of them have truly reached the pinnacle yet.

Hydropthere's current record stands at 47.2 knots. (87.32 km/u)

The current outright record over 500 mm is held by a windsurfer (Minian) at 48.70 knots.

But Hydropthere has now broken the highest record ever held by a non-windsurfer craft, Yellow Pages endeavour 46.52 knots.

They are now hunting for the all out record and even the honour to be the first over 50 knots.

And what I find personally so amazing is that they are not doing it on some ultra-light contraption like a moth, windsurfer, trifoiler or Macquarie Innovation who all need well protected waters to achieve their max speeds. Now Hydropthere is as large a battle ship (crew of 7 to 8 persons) and does it in a significant seaway. They could cross the atlantic this way. See the video of their fastest run :

http://www.hydroptere.com/accueil/images/videos/var/lang/FR/rub/19/movies/284.html

What a style, Massively cool.


Here a video of the actual record run.

http://www.hydroptere.com/accueil/images/videos/var/lang/FR/rub/19/movies/335.html

Wouter

It's an advantage for them in challenging the world speed record that they can just go for a long run at the best angle and pick the best 500m. The windsurfers and Macquarie Innovation only have a straight track of maybe 1km to wait for the best breeze, hit the water, build up speed, start at a start line, finish at a finish line (that has been pre-laid hours/years earlier), and then if they didn't get the right conditions on that run, they have to haul it back to the start.

There are pros and cons for all the attempts. First to 50 wins, no ifs'...no buts', I'm betting it will be Macquarie...eventually...

Comments:

- A 23 x 20 tri has twice the width of a Hobie 20 and is considerably heavier. As a consequence, he will carry a lot more sail than the Hobie. Even if you accept less speed, the beach cat rig will collapse in stronger winds.

- If price is an issue, you should stay away from foils. They make the boat more complex to calculate and build = higher cost.

- If you go for an improvised homebuilt 23 ft tri with foils, the best money you can spend is on plans from an experienced multihull designer. Building at home in itself is enough difficulty. Foils add stresses that require reinforcements that increase difficulties in such a way that even professionals have problems.

- Dave Carlson has experience with homebuilt foils in a slightly smaller scale and Tom Speer once started something similar to your plans (http://www.basiliscus.com/index.html).

- If you really want a homemade tri with foils, your best bet is one of Farrier's small folding tris. Lately he added ama foils as an option.

All the best,

Thanks Wouter,
Looks fantastique. And not very fragile either. Small rigs will be torn to pieces in big air and big waves....or is someone gonna surprise me?

"Hydropthere's current record stands at 47.2 knots. (87.32 km/u)"

I think thats 47.6 knots Wouter
A little thing but significant when it comes to speed records
They also have the outright 1 nautical mile record as well

"Small rigs will be torn to pieces in big air and big waves....or is someone gonna surprise me?"

you can't get much smaller than the "Bi" rig on the tri foiler and that held the outright record for a while at over 40 knots.
The windsurfer rigs seem to stand up just fine as well at 48 plus knots?
When it comes to sails, "small is strong"

The weight I figured would be an issue. I tend to over build everything. So this would probably follow the same protocol. Kinda what I had in mind for foils was just having them go down at an inward angle on the ama's. Through a trunk like a center board. And possible something that pulls up flush on the centerboard of the center hull as well. I'd like to make it so the foils would be easily changed out, have them bolt onto the bottom of the arm in some fashion. They wouldn't retract all the way, just far enough to be beached. I'd guess that the rudders would have to take the load in back.

I had plywood construction in mind. Just a wild shot in the dark for weight but hopefully under 600 lbs.

There was a post a while back about a folding tri made in poland. I'd also would need to make this fold. I was thinking that the frame on the center hull would be "solid" and 8' wide, giving me a place to attach the rig to and keep it tensioned regardless of the position that the outter hulls are in. There would have to be a framework internally of the center hull to build a truss of sorts to keep everything rigid as well.

I've been fantasizing about this for about a year. It started when a local sailor hit a submerged tree stump at full speed and destroyed a hull on his H20. Originally I was thinking of using the H20 hull for the center, and a pair of H17 hulls for the ama's. But that would have ended up weighing a ton. With all the modifications required it would probably be easier to start from scratch.

You mean something like this??
I am in the "plug" process with the building of this at the present time, with the main hull only 4.3mts in length and with an anticipated all up sailing weight of less than 60kgs. The beam, without the foils is 8"2" IE trailable without dis-assembly. If successful, it is scale able upwards without any major problems.The main difference with this design is with having a third "adjustable" foil well forward and all the "lifting" foils "raked" aft at 45 degrees (the vertical foils also rake forward 10 degrees to aleviate "ventilation")

Weight and foils are like water and oil. They can't be mixed.




Those are "Bruce Foils". Although Tom Speer has a nice centreboard solution, choose the daggerboard style for more simplicity and less weigth and drag.




Weight is critical.




You probably refer to the Catri. It can't be homebuilt. Period. I am having one professionally built for six years (and counting). By no means go this way. The only safe way to get a Catri is buying an existing boat. There's a builder in the US.




As I said before, Ian Farrier is the name to follow when it comes to folding tris. Just add foils to the amas.




If you hit a tree with a foiler you will either have a broken foil or a broken beam. Not necessarily better than a broken float bow, in my opinion.




Upgrade your dream with Supercat (ARC) hulls. They are wave piercers, have more flotation and are more resistant for their weight. Three ARC 22 hulls (or 20 or 19 or a combination) would make a VERY powerful tri, even without foils. Write me at sysfx@yahoo.com if you want drawings to ilustrate your dreams. Also, the ARC27 and ARC30 rigs are likely to suit your dreams very well.

Keep dreaming,

Luiz's suggestion reminds me of Sam Bradfield's last bigtrifoiler. Hollis Caffee and others raced it to the Bahamas 3 years ago: all 3 hulls were about the same length.

The ORMA Open 60 tris also have three hulls of the same length, probably due to their rules. My boat is this way too. Besides, its amas are low flotation (110%) to pierce waves and reduce aerodynamic drag, aiming to improve heavy weather performance. A tri with ARC floats would have low flotation amas as well - at least compared to the original cats.

Cheers,

a Sydney to Hobart on her would be a blast!!