"Classe 10"

[Doug Lord]

Marco, can you tell a little about this class and some of the boats in it. Stuff like sail area, weight and more on rigs would be fascinating...

[casavecchia]

Hi Doug,
Classe 10 is not an official sailing class. We are just a group of friends, about 40 people, that like to
build cheap boats and race together informally.
Except length , ten feet maximum, and sail area , 8 sq. meters, everything is free.
So you have monohulls, multihulls and even strange things in between!
Marco.

[tspeer]

Interesting that you have a class measured in feet, and we have a 3 metre class!
http://www.nwmultihull.org/3meter/3mtr.htm
http://www.nwmultihull.org/3meter/images/2002tmw03.jpg

[Andy P]

An int moth (with a 'normal' 8m² sail ) but shortened by a foot to 10 feet would be a very fast option here! Without foils for < 10kts breeze, and with foils for 10kts +. However it would probably kill the class!

[casavecchia]

Hi all.
My next 10 feet boat will in fact be Moth inspired. But being 54 and much less agile than I used to be it will have two outriggers. I am interested in Andy Paterson opinion about rocker for such a small trimaran (main hull and outriggers). We normally sail in less than ten knots winds.
I’d like to know Tom Speer opinion on my canting unstayed mast.
And Doug Lord opinion too.
Thanks.
Marco.

[Andy P]

The moth hull shapes are now double-enders, with sharp bow, and very narrow V or U transom. max w/l beam at about 2/3 aft at ~ 300mm. The very narrow transom combined with low rocker gives ( just ) adequate displacement, and the drag of the narrow immersed transom is acceptable at low speeds.
At higher speeds, the aft support for the hull comes from the T foil lift, and when driven very hard, the t foil gives down force, resisting nosediving. ( narrow transom helps here )



The hull shapes are fairly rectangular section - best for maximising volume with some wetted surface penalty.
Rocker is 50 - 75mm.

For a double ender, a T foil reduces pitching dramatically. A light mast would make pitching less. More rocker eg hobie 16 pitches a lot!

However the very low moth displacement of < 100kg inc crew makes it relatively easy to design all the features - displacement, wetted surface, planing hull form as well as slender hull form that exceeds hull speed easily.

Adding outriggers may help to learn to sail the boat,
In very light winds the outriggers could be used for support, however it would sail much faster balanced on the centre hull moth style, with outriggers clear of the water.

Adding weight and reducing length means the beam will have to increase, and may also increase the pitching. ( add a T foil ! )

I gave my opinions of the bent rig earlier on aus moth site - in summary - not suitable for moths.

Andy P

[Doug Lord]

I think it was really interesting that Tom pointed out that the US has a metric class and Italy has a class based on the foot-didn't know we had a 3 meter class. Unfortunately, whether it is for cost or what, the framers of the rule put built in brakes on the boat by limiting beam and with such a high weight. Is there a beam restriction under your rule ,Marco?
I think, as I said before, that the kinked mast is real interesting but I am not convinced it is necessary or maybe even desisrable for a high speed small multi or foiler. But I definitely think it has merit in slower boats.
The rig that has realy turned me on is the rig Rohan and others are using on the Moth-made by a Windsurfing company and using camber inducers.The shape looks real good for high speed but I'm not sure how good it is in light air. I think probably it can be tuned for any condition but Stevo would know better.
Marco , I think for a small boat that you want to go really fast you can't touch a foiler-"buoyancy" pods with whatever RM makes you comfortable would work well as long as you sailed with them out of the water.
I'm going to experiment with a tri/foiler configuration where the main hull would be as skinny as possible and a double ender and would have a main foil about half the size of a Moth and a rudder foil about the same size. It would be 12' LOA by 12' wide and the ama's would be planing hulls. The sail area to planing area would be slightly better than on a windsurfer and the foils are there to stabilize the boat in pitch.
In light air you would keep the amas out of the water and as the wind picks up more and more of the weight of the boat would be carried by the ama allowing a huge righting moment-way more than a standard Moth foiler. So sail area on my 12 footer would be around 130 square ft,; weight of the boat 100-120 pounds and crew weight from 160-220 with a weight equalization system(for a marketable version); light crew for ultimate speed. Just to clarify: at speed the boat would fly the main hull with most weight being supported by the plaing hull on the ama. The main foil will use a wand to keep the main hull at just the right height and would control pitch in concert with the rudder t-foil.
If you don't have a beam restriction you could experiment with both the foiler and a tri with planing ama's -just use the same "main hull" for both. But give serious consideration to getting a high speed rig like the KA-even if you use it with the canting mast.

[casavecchia]

Hi all,
maximum beam allowed is 3 meter, so a perfecly square tri
could be built.
Another question:
I noticed that Moths and A Class centerboard are now using a section that has a slight hollow near the tail.
What's for?
Thanks.
Marco.

[casavecchia]

And here is another.
If the outriggers are designed with enough volume to float the whole boat, is there anything against having three identical hulls?
Marco.

[Andy P]

Hollow in trailing edge is a NACA 63 variant section, giving low drag at low angles ofg attack. This is fine for high speeds, since leeway is small.
A slower boat needs the NACA 000x sections.

3 hulls = lots of surface if you've got 2 or 3 in the water - and flying 2 hulls on a 3 m wide boat with only 8 m² sail would not happen in 10 kts!

[Doug Lord]

Marco, Andy is right: forget the tri if you want real speed; I hadn't seen the 8sq. meter sail area limitation on your boats-thats way too little power to make the tri I suggested work.
For real speed do a (bi)foiler.
------------------
Since you have no beam limitation you could consider an over square(12' or so max beam) scaled down Rave foiler but the Moth type bi foiler would probably beat it.
The Rave requires two forward foils which equals two surface penetrations and more drag. It would be easier to sail than the Moth type slightly and maybe have a faster top end since it would generate it's own righting moment.
But at your size I'd go with the Moth type foiler with whatever size "buoyancy pods" that make you comfortable-just so they are out of the water when you're sailing.

[Skippy]

... is there anything against having three identical hulls?
I can think of three issues you would need to deal with: weight, windage, and the fact that you'd need three keels and three rudders (if you're talking about flying the center hull), along with the long connection between the rudders, and of course some way to adjust the keels if they're adjustable.

[John Perry]

With wide beam and large floats on a small trimaran you have to think about what is going to happen when you capsize!

When I built a small bifoiler hydrofoil with outrigger floats I kept the floats small so that their bouyancy was within the limit of what I could pull down under the water by hand while swimming, so that I could get back onto the main hull. It also helps to have a lot of mast bouyancy so that the boat does not go right upside down. Once you get back on board with the mast floating flat on the surface righting the boat was easy because you can use the outrigger as a lever.

John

[Doug Lord]

For a really high performance 10 -12' tri if you don't fly the main hull any higher than a typical Moth foiler or even half as high you wouldn't need three rudders and three dagger/centerboards-one will suffice. In my experimental planing ama/foiler tri(described above) you don't need much buoyancy in the ama at all; lift is provided from planing. But you would need around 130 sq. ft. of sail to make it work. And the wand on the main foil controls heeling angle....
A boat like that is much more likely to pitchpole than it is to capsize but both the foils and the placement of the center of lift of the planing hulls relative to the CG of the boat will combat that. With low buoyancy ama's coupled with mast head flotation-at least until you get used to it-it will certainly be easier to right.
I think it's an interesting idea but it doesn't fit the "Classe 10" rules; under those rules a straight out foiler would probably be pretty quick....

[Skippy]

... if you don't fly the main hull any higher than a typical Moth foiler or even half as high you wouldn't need three rudders and three dagger/centerboards-one will suffice.
All right. Sounds like it might drift a little, but maybe not. I share the concern about pitchpoling.

[Doug Lord]

On the boat I described earlier a wand (like on a Rave or Moth) would be used to keep the boat at a more or less precise angle of heel when flying the main hull. That makes it easier to design the rudder and daggerbaord for the correct upwind area. Using this system also means that in light air both the rudder and daggerboard will have to be partially retracted to reduce wetted surface. But with so much SA and so little weight she'll be flying the main hull pretty early-6-8mph....