Facing out wards foils on a lightweight tri.

Looking at building a very small tri based around windsurfing gear and sails that I have laying around this coming winter. Basically a modified board with foil stabilisers at about 1.5m from the centre line. The intention is to create a skimmer rather than full on flying as I suspect at this sort of technological level a skimmer may well be faster than to try and get full flying capability. Plan is to not be foiling until about 10 knots of speed which with the large windsurf race boards is relatively easy.

My intention is to use a form of J foils rather like the A Class style but to turn them out wards like Gary Bagient did on one of his boats. So the base of the J acts as the lift and the straight part to be set as a Bruce foil to get maximum lift when fully submerged ie when fully heeled.

But I remember reading somewhere that foils set out wards like this have some problems, can you refresh my memory on this.

 

The reason it's a bad idea is that you wind up with high and low pressure on the same side of the foil(due to leeway) which is real draggy.
This is from the High Performance Test Model(Fire Arrow) thread on the same subject:

Here's the picture of the outward pointing trifoiler with the foil circled-and two views of the Trifoiler foil-click for best view:

 

Interesting how the Trifoiler still seems to have been there and done it a very long time ago and still regularly takes the fastest speed at the UK speed week.

On thinking this through then why not turn the J through 180 degrees and use the straight section as a true Bruce foil and use the now downward section to take some of the leeway loading. Remember that I will need a central small dagger board ( perhaps a standard board fin ) and a TFoil rudder.

The optimum would be for the outer foils to simply stabilise the sail at low speeds but to take the full loading of the craft at speed if the central hull did become airborne. This is not a full on foiler but a hybrid that is cheap to make and maintain and yes it will be some ride at speed.

 

My test model system uses a foil on the daggerboard to fly the main hull in light air and UptiP foils on each ama. One ama foil is used at a time-with no adjustment required under sail. Right after takeoff the ama foil begins to take the load from the daggerboard foil so that it carries the majority of the load and the main foil is unloaded except for working with the rudder foil in pitch control and maintaining the designed angle of heel.
It's a simple low drag system that allows an oversquare trimaran to function well throughout the wind range.

 

Hugh Welbourn found a solution to the outward facing foil:
1) shape it so it behaves as a V foil,
2) shape it to be able to act as a high aspect planing surface,
3) design the boat for flying at relatively low altitude.
http://www.boatdesign.net/forums/sailboats/quant-23-foiler-scow-53468.html

 

Interesting to dig this old thread back up as the little foiler is still on my hit list, we'll get the TC601 on the water first me thinks, hard at work trying to get back on track with paid work at the moment and into winter play mode with the ski bikes I play around with.

 

How very strange, deluded and offcourse are the new IMOCAs with new? outfacing foils; someone needs to rush over and tell the poor incompetents that their new fangled foil system is completely, totally and theoretically wrong.
I mean look at their pathetic performance increase; only a miserable few knots faster than with conventional setup.
But strangely, so much faster that the hull structures can't handle the new loads. Some all-knowing believer needs to get over there fast?

 

OUTWARD POINTING FOIL*. Gary, the 60 foils aren't pointing outwards!
And they work great on a reach but are a disaster upwind(mainly because of rule limitations).
And all outward pointing foils aren't bad-like Welbourns Q23 foils-they work great even with the disadvantages pointed out by Ketterman-mainly because the vertical portion is mostly out of the water. And DSS works great because the foil DOESN'T have high and low pressure on the same side. And my Test Model foils work great because they don't have high and low pressure on the same side.
*the words I used in the post you quoted.

Gary, the 60 foils point up(!) :

 

Maybe my eyes are deceiving me ... but these foils appear (to my old eyes) to be pointing outwards? Or maybe the crew can walk on air above the windward foil? And the working leeward foil has the upper section near vertical and the uptip end section closer to horizontal. And this is more emphasized with the boats powered up in high wind and seaway; just look at the videos.

 

Gary, you're so right-it does point out! Right before it points UP!! Geez.......

 

Your images are of a stationary yacht with withdrawn foil; the foil is not being utilized, boat is parked (so what is the point of posting this nothing image?) - the other is an artist's pretty illustration of a 60 in supposedly very light airs - when I doubt the leeward lifting foil would be used anyway.
This is a totally different situation with an IMOCA 60 powered up in heav air and seas and heeling way over, carrying more sail than earlier designs (because of the powerful foil lifting forces) and the "uptip" section would be closer towards horizontal than your celebrated withdrawn foil, parked boat, UptiP position.

 

Now Now Gary,

Don't get yourself in a tizz. You should know by now that when talking to the King of all things foily that you must bow to his greater knowledge.

But keep up the good work and keep building boats that do foil well and not pig jump for a few seconds then claim it a huge successl.

Tony

 

Tony, good advice - and I should (and do know) better. Cheers.

 

Guys, how do you resize pictures when you publish them on this site ?

 

I do it on the computer-right click on the picture in your library then click "edit"-then repost.