Micro-Tri , foil advice??

[Denisesewa]

Hi, I am a new poster here, I've found this site to be very interesting and informative.
This past month I have been building a Micro tri , I started by borrowing a mold for a surf kayak and building the kayak from glass , carbon and divincell then cutting the cockpit out and building in the mast step, CB trunk , cross members ect. Its 9'10" will carry 8.2 sq meter sail and will weigh in the 275LBS range with me onboard, I built it so it can easily be reconfigured as far as crossmembers and ama's are concerned
Meanwhile, I've been reading alot on foils, I am totally undecided on what type of system to use, I'd like it simple( home buildable), early planing and preferably no flaps so have considered the Hobie tri-foiler style or possibly foils which lose surface area as the boat rises, I am pretty much set on having a three point system. ( T-foil on rudder) and dont expect great speed.
Unfortunatly, I have no education in this at all and havnt found any real world advice on how to go about judging required surface area, building methods ect. , any help would be greatly appreciated.
The attached pic is from last week, I am hoping to get it done and in the water by weekend after next in non foil form.
Denise
http://hometown.aol.com/denisesewa/index.html

Denise, these sites will help you: The Hydrofoil Societies site- www.foils.org , google the Internatinal Moth Class and go to the Australian site and then to their forum-look under hydrofoils,also, when you google International Moth Class check out the UK Moth site which has some excellent articles,look on page 2 or 3 of boatdesign.net's "sailboats" forum (or do a search) for the thread "Foiler Design". Also, look on page 2 or 3 of the boatdesign.net "sailboats" forum for the Sportboat thread-there are some ratio's in the first post that might be of interest. Good luck!

[Denisesewa]

Originally Posted by Doug Lord

Denise, these sites will help you: The Hydrofoil Societies site- www.foils.org , google the Internatinal Moth Class and go to the Australian site and then to their forum-look under hydrofoils,also, when you google International Moth Class check out the UK Moth site which has some excellent articles,look on page 2 or 3 of boatdesign.net's "sailboats" forum (or do a search) for the thread "Foiler Design". Also, look on page 2 or 3 of the boatdesign.net "sailboats" forum for the Sportboat thread-there are some ratio's in the first post that might be of interest. Good luck!

Thanks for the leads, I think I have it pretty much worked out for an initial setup.
Denise

Denise, if you feel like it why don't you post some sketchs and /or numbers for your boat-like foil loading, sail area per sq.ft. of main foil area, lb.'s of sailing weight/SA etc. Would be very interesting.....

[Denisesewa]

Originally Posted by Doug Lord

Denise, if you feel like it why don't you post some sketchs and /or numbers for your boat-like foil loading, sail area per sq.ft. of main foil area, lb.'s of sailing weight/SA etc. Would be very interesting.....

Are you testing me??
Lets see if I am even close, the boat will weigh #275 all up with me on board, SA= 8.2 Sq meters. surface area of both main foils 1.3 sq ft with rudder foil at .78 sq ft .
So, I should come out with roughly 31.5 Sq ft of SA per sq ft of main foils and 98.1 Lbs loading per Sq ft main foil area.with 3.18 lbs weight per sq ft SA. I am thinking two main foils with moderate aspec ratio at 24"span x4"cord and the rudder foil of 28" span at 4" cord using a modified ( to account for the lower aspact ratio) NACA 63412, I dont know airfoil numbers well enough to convert. am I in the ballpark?? ( by the way, I did this with pen and paper quickly as I dont own a calculator) anyway, I'd love some constructive criticism.
Denise

Denise-no test! I was curious..
For what it's worth an International Moth foiler weighs about 200lb with Rohan Veal aboard. At that weight with the main foil carring 80% of the load the foil area is around 1.04 sq.ft. for a mainfoil loading of 153.8 lb. per sq.ft.. The boat has 86 sq.ft. of sail area for 82.6 sq.ft.SA per sq.ft. of mainfoil area. The sail loading is 2.32lb. per sq.ft. The Moth will foil upwind up to a little over 2.6lb. per sq.ft. SA according to what I've found researching it.
On the other end of the scale the Rave multifoiler designed by Dr. Sam Bradfield has two mainfoils of 1.77 sq.ft. each and 196 sq.ft. of upwind sail area. It weighs around 528 lb. with a 160 lb crew. Mainfoil loading is around 220lb. per sq.ft.(at takeoff-going up from there) considering not only boat weight but heeling moment as well since the foils on this boat are used to keep it upright as well as to lift it.(independent altitude control systems) It takes off in
10-12 knots of wind compared to 7-8 for the Moth(or less). The Raves SA/sq.ft. of mainfoil area is 55.36 sq.ft. and the boat may be capable of higher top end speed than the Moth...
These kind of details are important design tools and maybe they'll help you analyze your design.
By the way, the foil section used on early Moths and some current ones is the 63412 section.
One of the great advantages of a bi-foiler like a Moth is just two foils-usually surface piercing arrangements have to have a third foil. Another bi-foiler advantage is being able to heel the boat to weather upwind unloading the vertical fin and reducing the chance of ventilation.
Good luck with the boat and please update this thread as you progress....

[Denisesewa]

I already see a couple mistakes in my numbers,one being that I actually have 68 sq ft SA per sq ft main foils, Thank you so much for the comparison as it helps alot, I think I am somewhere between the moth and the Rave and since my design is much more like the rave I am hopefull that it will fly.
Water test this week weather permitting and then start on the foils if all else goes well.
Denise