Flight One-a New Kind of Performance One Design Dinghy

[Doug Lord]

Had a bit of a surprise today with a visit by Hugh Welbourn-DSS technology inventor and designer of very fast sailboats. See here for more on the story and pictures: High Performance Self-Righting Trimaran: The Test Model post 154
I discussed the Single Curved Lifting Foil with him and he was impressed saying that it was very workable-and a really neat idea. From one of the modern pioneers in the application of lifting foils to monohulls that meant a lot to me.

Here are the rough sketches of the foil, again:
The foil slides in an athwartship partial trunk and replaces a t-foil for foil assist.
click on image-

[Doug Lord]

I was working on a curved foil for the SRT project and decided to see how the single curved foil would actually work on a real boat.
Boat is 16', 459 lb all-up. The underwater portion of the curved foil was 4' long. The portion of the foil doing the lifting was 1.3sq.'. The aspect ratio of the underwater portion was 7/1. The chord was .57'. The idea was to see what it would take to lift 50% of the all up weight.
The results were:
6mph/ 5.2 k speed,lift= 91lb which was 20% of the all up weight,
8mph/ 7 k speed, lift= 161lb= 35% of all-up weight,
10mph/ 8.7 k speed,lift= 195lb=42% of all-up weight,
12mph/ 10.4 k speed,lift= 241.6lb= 53% of all-up weight,
15mph/ 13k speed, lift= 377.5=81% of all-up weight.
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The foil would be adjustable allowing the angle of incidence to be varied, the area to be varied and the foil to be 100% retracted. As a "foil assist" board
it looks like it should work well.

[Doug Lord]

After thinking about this for a long time I'm thinking that a dinghy application of a curved lifting foil might be considerably improved by using two foils at least in some applications as I mentioned once before.
Using two foils would allow a narrower hull with greater overall beam and would allow the curved foils(or "L") foils to add righting moment in addition to vertical lift.
An "L" foil would be mostly retractable and out of the water when the boat is heeled slightly. The "Flight One" concept, using a single curved lifting foil, still is one of the simplest possible incarnations of "foil assist" for a dinghy.
rough sketches:

[awhapshott]

An interesting design. Most Cherubs are now on the T-foil, and it is very handy; Not only is the upwind speed good, but the stability increase is well worth having, even if it does make things a little boring (I haven't got the daggerboard out the water on a T-foil boat yet)
The SK4 foil is brilliant, its planing ability and speed are amazing, although after collision with some Southampton mud at >20kts she is having some serious repair work done.

With the C-foil, how would the angle of attack be changed? Or would it be fixed?

Also, in one of your posts there was a thin red hull, with boards/floats projecting under the wing, what on earth is it? It looks like an early moth development.

[Doug Lord]

Originally Posted by awhapshott

An interesting design. Most Cherubs are now on the T-foil, and it is very handy; Not only is the upwind speed good, but the stability increase is well worth having, even if it does make things a little boring (I haven't got the daggerboard out the water on a T-foil boat yet)
The SK4 foil is brilliant, its planing ability and speed are amazing, although after collision with some Southampton mud at >20kts she is having some serious repair work done.

With the C-foil, how would the angle of attack be changed? Or would it be fixed?

Also, in one of your posts there was a thin red hull, with boards/floats projecting under the wing, what on earth is it? It looks like an early moth development.

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I must have missed something-what is the SK4?? Found this: http://www.sailingsource.com/cherub/...opic=51.5;wap2
The single curved lifting foil would be adjusted just like any curved foil is: the foil would be angled fore and aft and the trunk on each side would be designed to allow that. It could also be done with a slight pivot of the athwartship trunk-though the more I've considered it the less I think a side to side trunk is required.
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The boat in my last post is based on the Tantra which, I think, is the one you're referring to. It was a prototype using asymetrical, toed-in "leeboards"
for lateral resistance. Each leeboard had a replaceable tip. Wish I had thought using twin curved foils back then!



Pictures: Tantra, with 80 sq. US1 rig, circular cockpit with forward traveler, experimental square top rig designed 1975, built 1977. The Tantra II in my last post would be very similar---

[awhapshott]

Originally Posted by Doug Lord

In fact the only dinghies that do use foil assist are the I-14 and National 12, some Cherubs and the SK4 skiff as best I know now..

(http://www.youtube.com/watch?v=gZHK917eULk) -Shows the effect of the foil, I feel that its definitely a way forwards in skiff development.

Yep, the Tantra based boat is the one. Looked quite cool.

Not sure if you've come across it, but a year or so ago I saw a experimental dinghy (Similar to a laser) which has a V shaped keel configuration, with a small bulb held at the bottom. I've been searching and searching for the video of it, but can't find it. It was similar to your idea, but fixed in all aspects, not at all 'beachable' !!

[Doug Lord]

Yeah I found it-just didn't remember it at all! Here is Kevin Elways "treatise" on rudder t-foils:

[Doug Lord]

Originally Posted by awhapshott

(http://www.youtube.com/watch?v=gZHK917eULk) -Shows the effect of the foil, I feel that its definitely a way forwards in skiff development.

Yep, the Tantra based boat is the one. Looked quite cool.

Not sure if you've come across it, but a year or so ago I saw a experimental dinghy (Similar to a laser) which has a V shaped keel configuration, with a small bulb held at the bottom. I've been searching and searching for the video of it, but can't find it. It was similar to your idea, but fixed in all aspects, not at all 'beachable' !!

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Thanks for reminding me about the SK4 and the Tantra comments! Mal Smith did a rendering and some design work on a surface piercing foil for a Laser: