Small Tri Test Platform

[P Flados]

Ok, I guess it is time that I admit to actually doing some boat building / sailing.

However, understand that so far I consider everything as more of learning exercises rather than building anything that I plan to keep.

This summer I got tired of messing with the small Proa test platform I had been sailing for about a year, and decided to take a Geko Moth hull that was laying around and make a small tri out of it. A photo of the boat just before a launch and a photo of a planing ama in action are included

Background / Details:

A few years ago, I did my first hull build mainly just to try my hand at building something. I chose the offsets from the Geko Moth (https://www.sites.google.com/site/chrismiller49/). I did a strip build with thin (~0.1” x 1.5”) strips of mostly scrap lumber from construction site dumpsters . Most was labeled SPF for Spruce, Pine or Fir. The hull looked ok, but the truth is that I learned a lot of what not to do. It was light, but only the bottom has glass on it.

I used a 10' cross beam I made for the proa. It has a hollow wood core and lots of carbon tow for strength.

I started by mounting my old sunfish rudder with a home build kick up conversion. Later I built a T foil rudder.

I started with an aft-mast for the main that I would get later with fore-mast for a Hobie 16 jib that I have. After several sails with jib only, I got rid of the 2-mast config and went with a single mast and the Hobie 16 jib as a main.

I started out with 4" thinwall PVC amas and straight NACA 0012 ama foils (~3.5' x 4: chord) angled at 45 ° off of vertical.

So far, I did not get the vertical lift I wanted from the ama foils. I got rid of the PVC tube floats, and went to small planing surfaces with just enough styrofoam to keep the sail up when the trying to get on it and away from shore. I also added full length tabs (thin flat extension to the rear of the foil that are like fixed position flaps) to the foil that are about 1/2" wide and give the foil a small amount of under camber (I think this is the term for having a concave surface on the back half of the underside).

The planing surface amas are better than the floats when responding to a gust without enough speed for the foils to provide the needed righting moment and the foil mods probably helped too.

Not being satisfied with lift, I added a ~1' horizontal extension to the bottom of the port foil.

On my last sail, the extension seemed to help, but I still want more lift. Late in the sail, I overloaded the foil and it broke up close to the kick up pivot. Since then I have added 6 layers of tow on the top and added more tab surface (3/4" added at max) on the lower half of the 45 ° angled portion and extending across the horizontal section. The planform that started as square, is now much closer to elliptical.

Build info:

Until I can put together something that I am confident will perform like I want, I will continue to do all of my building at the “super cheap” end of the spectrum. Other than some limited raw materials, I do not buy much of anything. Most of my cash outlays for my boat building include:

I just ordered my second 1.5 gallon epoxy kit. The second order included some micro balloon filler.

Early one, I ordered glass cloth and carbon tow:
------------------------------------------------------------------------
25 Fiberglass Cloth 3.6 oz., 30"25 yd. pkg.S-G15223-30 $1.95/yd $48.75
5 12k Carbon Fiber Tow, Bolt Pricing Standard ModulusCF706-B10 $16.00/lb $80.00
------------------------------------------------------------------------

Since then I bought a roll of 24k carbon tow that I saw on Ebay for $16. Dirt cheap by any standard. The 24K tows are ~3/8” wide which makes flat surface buildup easier.

Some saw blades (table saw and band saw) and some sandpaper
A used set of rather worn Hobie 16 sails for $50.

I have probably used less than 15 linear feet of the glass and so far and about half the carbon tow.

 

[P Flados]

Here are a few more photos. One is the planing ama on the hard with the original square planform foil behind it (rotated to about 1/2 way kicked up), the other is the modified foil ready for the next trial run.

 

[Doug Lord]

Very interesting! Thanks for posting... Are you trying to fly the whole boat or are you going for some lift fraction with foil assist?

 

[P Flados]

Foil assist and full foil are both on the table.

As a test platform, I expect to change configurations a lot to see how various things work.

 

[rcnesneg]

Woa! That is cool! I like it!

 

[Doug Lord]

Foil assist and full foil are both on the table.

As a test platform, I expect to change configurations a lot to see how various things work.

------------------
How about trying a lifting foil with wand(?) on the daggerboard and an UptiP foil on the planing ama(because of its intrinsic altitude control)?

 

[P Flados]

I want to see what kind of performance I can get without moving flaps first.

The port foil extension is slightly "up tip", around 3.5° with the boat flat.

A big desire is to maintain kick-up foils and rudder that do not require on the fly AOA adjustments.

 

[Doug Lord]

I think you could fly the main hull using something like a t-foil-no wand, no flaps with manual control of rake. I want to try that with the model sometime. I'm convinced it will work because the model sails with the main foil flap in neutral a lot. The wand helps to get the thing up in light air but after its up
it's not doing a lot. Just a thought.....

 

[Doug Halsey]

So far, I did not get the vertical lift I wanted from the ama foils.

Is there any indication that the foils are stalling, or are they just set at too small an incidence angle to give the required lift? I see no mention whether or not you can adjust that.

I can't resist pointing out that a V foil of the same depth would have twice the horizontal span & much more rigidity than the inclined foils you're using.

Finally, your use of a Moth as the main hull caught my interest. I've recently gotten back into the Moth class (after a 45-year vacation). My new boat is a Mach2 foiling Moth, which is a great boat, but maybe too nice to experiment with, so I'm toying with the idea of building something in wood. Do you have a rough estimate how many man-hours you put into building this one, & about how much it weighs?

Interesting project - keep trying!

Doug

 

[P Flados]

Possible foils stall at low speed in response to a gust, otherwise they are producing decent performance I think.

The need for more lift is not unexpected.

The foils, the original amas and the cross beam were all originally made for a proa with a 10' beam. The 45° incline foil configuration worked pretty good for "foil assist" straight line performance with the Proa.

With the Tri configuration, the up force from the lee foil is only ~4' from the center of mass instead of the ~7' for the proa.

The V foil configuration has advantages and disadvantages. My review of discussions left me thinking that it is not as good in terms of lift vs. drag. Your boat seems to the one of the best performing of the V's in recent years. I would love to see side by side comparison of Broomstick and a fast non-foiling cat.

The ama foils and the the rudder are all mounted with simple high friction kick-up configurations. If I pull up to a beach, I can get out and make AOA adjustments of the ama foils just by not having them full down/forward. The rudder is such that I have a stop to keep it from rotating forward (more AOA) under load.

I can also swing up or swing down the ama foils while one the water. My paddle is just long enough to reach out and make full-up / full down type of adjustments. This has been handy after clipping a sandbar and has allowed some single ama foil sailing.

The main hull was my first experiment in boat building. I put way too much time into it, but it was a learning experience as expected. I remember that the basic ~0.1" thick strip hull was very light when it was just an open hull with no deck and no fiberglass at all. After my first float test, I stood on the inside bottom of the hull for a moment and the wood split. I put a layer of 3.5 ounce glass on the bottom wrapping up ~2" on the sides.

My second build was the proa attempt. The goal was to have all major weight to windward with only a 4" PVC tube ama and foils to leeward. I saw promise in straight line speed, but I never achieved a working configuration where I could reverse directions without getting out and adjusting the foils.

When I gave up on the proa, I kind of slapped together the tri. All the care in making the main hull super light took a back seat and getting on the water became more important. I think it took around three weekends to go from an idea to in the water. Since then, I have changed some aspect of configuration on a regular basis (no more than two sails without some significant change). As previously noted, I consider it a test platform, not a final product.

I did check weights today with:

Main hull and rudder: 36.4 lb
Mast, stays, sail, boom: 14.8 lb
Cross beam, amas, foils: 23 lb
Boat total: 74.2 lb
Loose items (est): 0.8 lb
Crew: 185 lb
Total: 260 lb
Crew percentage: 71%​

Note that the cross beam and ama assembly weight could probably be cut in half if I were to actually find a configuration I like and were to build components to specific design requirements instead of just "make it strong".

 

[Doug Lord]

How much of the Hobie 16 rig(in area) are you using in your tests? Again, good luck!

 

[Doug Halsey]

I think you really need to be able to set the foil incidence more precisely. The way you are doing it, I doubt if you can tell the difference between 3 degrees & 10 degrees. It obviously makes a big difference which it is.

I assume you've worked out what the foil area is at take off & what sort of lift coefficient you would need at your desired take-off speed?

 

[P Flados]

The rig is just the jib (55 sq ft) at this point, and yes it is too little. I had a large wind surfer rig lined up when I started, but it fell through. The mast is also too wimpy - I added an extension to an aluminum sunfish spar.

Part of the whole objective was to use stuff laying around and get out on the water. I sail in the sounds between Wrightsville Beach NC and the mainland. I wanted true hand launch. The public boat ramp close by is suitable only for power boats. There is a terrible tidal cross current that can really ruin your day. My ancient sunfish and Hobie 14 just were not worth the hassle of launching.

As far as AOA, I am at about 4° - 5° at rest, but I have probably at least 3° of adjustment by shifting my weight. It is only 11' long and I am 71% of the total weight.

Calculating foil area requires boat speed. I am still no where near a good boat speed. My recent foil adjustment effectively changed the foils section to slightly increase area but greatly increase max lift. The first objective was just "foil assist" so that I can get the lee ama to fly under load.

Full flight will probably require a rig upgrade to get more boat speed. I am still hoping to acquire that large wind surfer rig that my friend has not used in years.

 

[P Flados]

Got out in some pretty good conditions today. Wind direction allowed reaching across a stretch that had a less wind at both ends, and strong (but gusty) wind on a good stretch in the middle.

With the new port foil extension to the lee side, the boat felt much more in control. It took me a few passes back and forth to get up the nerve to let the boat load up during gusts instead of heading to windward. With the port to lee, I could balance the boat under load with both amas up clear of the water.

I did see the need for some adjustments but also got things dialed in enough such that during gusts, the boat would abruptly surge forward. This response gives me hope of better things to come. I was pushing hard and eventually the rudder mount failed. The rudder will be a quick fix.

On the down side, I was getting more beam twisting with resultant foil AOA changes than I wanted. It kind of makes me want to try mounting the ama float well ahead of the beam and having a setup where I could use the twist for foil AOA control similar to the Trifoiler.

 

[P Flados]

The boat repairs were completed & I got the boat back on the water. Good wind on a few runs gave me a chance to push things. Weather is scheduled to turn nasty soon, but it was great today.

As I was letting the sail power up during gusts, the port foil with horizontal extension would completely handle RM loads and keep the ama clear of the water. It felt fast, but I really need to get a GPS to make sure that changes and tweaks are actual improvements.

Based on how the boat behaved, I think I will start on the extension to the starboard ama foil to get back to approximately matched foils.