High Performance MPX Foil/Self-righting Trimaran-The Test Model

I meant what if for example foils were suspended 2 feet outside ama? So instead of in line and under 2 foot outside. Imagine hydoptere with them facing out. Would that act like a larger phantom beam stretch?

Barry

 

If you took a surface piercing foil like on Hydroptere and made it point out instead of in , it wouldn't work very well. Greg Ketterman, designer of the Hobie Trifoiler, tried "L" foils pointed in and out-the boat was noticeably faster with them pointed in. He was also convinced that "L" foils were faster than T-foils, because the problem is leeway which can cause the outward facing foil to have high pressure and low pressure on the same side of the foil-very draggy. Again, your description sort of left me guessing-so if this isn't what you meant draw a sketch.

Here's a boat- "SYZ"- that has the foils mounted in the right direction but hanging off the side:

 

Yeah last pictures was exactly what I meant! Same as you have but just suspended further out. Like faking making your boat wider when on foil. Although I'm sure that's not what they were aiming for, or where they? Thanks again

Barry

 

Are you implying there's something unethical about attaching foils this way ?

 

Hahaaha no! Lol. I just made observation as some of these boats seem to be going with more beam, is there any advantage of having a thin boat for slow turns, parking in harbor and such, but when at speed they are actually wider.


Barry

 

Hello
There are two issues concerning foils pointing outwards. Yes they can add stability, but if you are sailing at a proper rc sailing club you will have problems on grounds of safety. Most monohull sailors will frown at the thought of their boats getting caught up by the foils.
The second is class rules. The Mini40 class has maximum dimensions of 122cm x 122cm (4feet x 4feet, as it a 1/10 scale of the Formula 40 class that used to race in Europe in the late 1980s). We make our trimarans at maximum beam, so no appendages can protrude beyond the outer side of the floats. Some of us are probably strictly out of class since the foil controls stick a few mm outboard of the outer skin at deck level but.....

The kinked foils I am using on the Mini40s help to get the foils further outboard. The white boat has foils 9mm thick which everyone tells me is too thick but seems to work OK.

On my one metre cat I am experimenting with 3 sets of different foils - 2 of them and controlled and one with fixed v foils that come off the bottom of a vertical fin. You can see these in the attached photos. Currently the fixe foils are working best but that is because I do not yet understand how to use the wands. New learning curve for me. Will keep on experimenting

 

One more photo - shows the outboard v foils

 

Ian, two things:
1- I've been told that with an uptip foil the radius between the vertical portion and the uptip portion is important-should be fairly large.
2- Greg Ketterman a long time ago told me that having "L" foils pointing outward is really draggy because you wind up with high and low pressure on the same side.(one of the reasons he claims his "L" foils are faster than Bradfields T-foils)
----
I might be able to help you with wands since I'm using them(dual wands to a single axis) on the test model and I built several production F3's using the Bradfield wand system so I'm pretty familiar with what it takes to make them work. One problem you have to consider is whether or not to allow the two main foils with independent wand systems to develop downforce on the windward foil. Generally, for that to work well, you need a square or ,preferably, an oversquare platform otherwise the foils have to work too hard creating too much drag. One solution is to neutralize the windward wand or use movable ballast.
I'd be glad to help.... you can e-mail me.

Pictures-Left-showing pressure on the "Vampire" version of outward facing uptip foils, Center, Dario Valenza's sketch showing the pressure on a "normal" uptip foil. Keeping the same pressure on each side is the key, Right- the Flying Phantom UptiP foil: (just in case you don't get the leeway arrow: it shows that the boat and foil are moving in the direction of the arrow due to leeway)

 

Ian, the active foil cat looks promising, does the wand pivot the bottom of the T foil or is the bottom fixed and the wand pivots the whole T foil??
The wands look too short for leverage but I am sure you will get it setup.

 

Fire Arrow Foiler / MPX Foil System Testing and Development

We ought to start a class or at least a version of a class like Mini 40 NBL(no beam limit). The beam restriction is artificial and stops(in some cases) designs that could maximize the potential of some foil systems. If I build a smaller version of the Fire Arrow it will definitely be much wider than "legal" for a 48" tri(wider with more SA and possibly an adjustable rudder gantry).
Artificial restrictions on beam just don't make sense to me-at least for a foiler design.

 

Very cool stuff, and informative. Also I can see peril you mention when things to sea are problems when your docking! Although I suppose in rc format at least, am expanding beam system wouldn't be too hard.


Barry

 

This, theoretically, to a number of experts, cannot work - but I call BS, it works fine; boat carries a daggerboard as well (for bite) in the main hull. This on a full sized 11 metre (37 foot) boat, not some toy in pond or backwater.
The only negative point is that you must realize your boat is wide (this one is 11 metres plus the angled out foils which totalled around 12) - so one has to be aware rounding buoys, marks etc. There was zero wrong with the boat's performance ... although I've since changed to inverted Y's, then half Y's (because of curiosity) but can't tell the difference in performance from any of the combinations. Maybe the last is the best, similar to the C foils on Sid. Boat goes to windward like a witch.
Groucho Marx anchored at beautiful Otata Island, Noises, Hauraki Gulf, 2008.

 

Fire Arrow Foiler / MPX Foil System Testing and Development

This is an e-mail I got a few years ago from Greg Ketterman in answer to a question about why his "L" foils didn't point out, instead of in:
Hi Doug,
Forgive me if I am too condescending but I am amazed at how many people do not get this. ***** argues that it would provide more righting moment. Imagine how ineffective a curved daggerboard would be if it curved out. I would have expected you to understand.
The boat in the attached photo did not perform well at all.

My senior project report explains it here: http://picasaweb.google.com/gketterm...57835053693858

A simpler way to look at it is the aspect ratio of the horizontal foil adds to the aspect ratio of the vertical foil when the foil points in. Aspect ratio is everything with hydrofoil sailboats.
All the best,
Greg Ketterman
VP Engineering Hobie Cat Co.
==================
He didn't only postulate this theoretically he built two identical boats and tested his theory. He found that the Trifoiler with the foils pointed out was slower than the trifoiler with inward pointing foils. It's the effect leeway has on the pressure distribution of the immersed foil.Anyone looking at the boat sailing would have said that it was going pretty well-but Ketterman knew better and proved it.
Here's the picture of the outward pointing trifoiler with the foil circled-click for best view:

 

Fire Arrow Foiler / MPX Foil System Testing and Development

Dan, my Fire Arrow "crew", gave me a camera tripod that was useless to him. I found a way to mount my camera to the thing and will get it done today. It's extremely simple and should work well for Sunday.
UPDATE: Done. Simply required removing the spring loaded retention mechanism(that wouldn't work on my camera) and adding a 1/4" fastener plate(bolt with attached plate). This thing expands to 6+' tall!

 

Congratulations on finally getting the thing sailing, and up on foils. However, I'm not sure what you mean by "the next long all foiling video", since the use of "next" would imply there has already been a "long all foiling video". All that seems to be available is video of the boat getting up on foils for short spurts.

Instead of running around like a headless chicken building a smaller version, why not just develop the one you have until it will foil around a course? If you can do that, you will have something really interesting.