http://vimeo.com/49863540

someone might get a laugh from this one...

design concept of the platform: 
The idea was to use scrap materials to build a light cat that is suited to easily launching and sailing at a
certain bay, then working up to longer runs down to kanaha and back up to hookipa.
The deep V design has been around for decades maybe millennium. 
A wildly different concept is the big boxy shape that is popular today.  with that shape, the more you push down on the box tail, the more it tries to lift out of the water at speed.  The system acts like the tail of a windsurfer.  The boxy hull shape is used on everything from the straight boarded f18 to the foiling ac72.
So this 9'8" boat is the V type.  Kind of opposite world in a way.
the V shape gives a smooth ocean ride vs, the boxy tail/hull shape which gives a pounding ocean ride.
from experience i can say the V shape seems to rise up out of the water on the fast downwind runs especially.
also when leaned on it's side, a shape similar to the bottom of a windsurfer is presented to the water.  So the outline curve of the hull becomes the rocker of a windsurf board bottom once the hull is leaned over.  This cat is a wave model so curved rocker lines are being used like with boards.
The center of effort of the sail is above the rudders so they act as dagger boards on the upwind.  version 1 rudders are larger than they should need to be for the sake of testing future versions.  error toward the side of being able to tack.
A resistance to pitchpole was at the top of the list of concepts and a very full outline at the bow is used.  The double ended hull outline was used so that leaning back would seriously lift the bows up making the pitchpole save a real possibility in case of nose dive.  A tune up of the outline, and geometry of the rig/platform may be scheduled in future protos.

you wrote:
"The center of effort of the sail is above the rudders so they act as dagger boards on the upwind.  version 1 rudders are larger than they should need to be for the sake of testing future versions."


Because you have deep V shaped hulls, these hulls itself have a considerably lateral resistance. So together with the rudders the total centre of lateral resistance is somewhere halfway the hulls.
You wrote that the centre of effort of your sail is just above the rudders (I couldn't check this on the video).

But that should give your cat a very heavy weatherhelm (wants to go all the time in the wind).

By the way, ther's nothing wrong with Deep V hulls. Almost every aged sailor in this forum has begun his sailingcareer on a small hobie or prindle. And they all had deep V hulls.

On waves there's nothing better

that looks like a lot of fun!

and wet!

Perhaps Hobie 1616 will get to take it out for a spin.

minicat9-12 by ammaui, on Flickr

yes Northsea you have a point about the center of effort vs. lateral resistance. The lateral resistance is spread across a distance. I am more artist and rigger than engineer and shouldn't talk engineering. Call the boat a kinetic sculpture.
The idea was to eliminate boards and trunks which are a source of drag. You are correct that there is a little too much weather helm right now, but hopefully canting the rudders more forward will fix that. it seems to work on the Hobie 14.
This boat is made by eye and no calculations were done except for some scaling of 18' cats for the sake of comparison so there will be evolution.
If nothing else i am getting out on the water, having fun, experimenting, and i only spent around $600 so far. Plus i rescued a bunch of styrofoam, sheetfoam, various board building materials and windsurfing equipment from the dumpster. Also i can carry the platform from truck to beach on top my head which is rare for a catamaran.
btw the hobies and prindles that are V are only V-ish. the asymmetrical V gives lift in opposite directions when both hulls are in the water. Symmetrical V seems to give about the same lateral resistance, but is still fast when both hulls are in the water.
the boat is fairly wet in high wind, but did you watch the AC45 races in Naples an Plymouth? Water everywhere and the boats pound significantly.
My camera filled w/water on the first capsize so i only have footage of the lighter sailing. In the real wind i think i need a smaller sail. Right now it is an 8 sq. meter. Also i had hoped to trap out but the mast is too flexible for that right now. A friend speculated that i will break the beams off if i do trap so i may bail on the trapping out. i do think that a sip. beach cat will be upside down frequently on the down wind runs in the kind of wind and swell that i'm dealing with, and that tends to be wet as well.

hi again minicatman,

Here are some tricks that might suit your non-calculations mind:

Place the cat in a swimming-pool and push sidewards against a hull. You can find with a bit of trying the point where to push so that the cat moves exactly lateral to the side (instead of turning his bow towards or from you). That point on the hull gives you exactly the place of the centre of lateral resistance for the whole combination.

Searching the centre of effort for your (surf-) sail is very easy. I presume you use a surfwishbone as boom; so mount everything like a surfsail and hang on it with your surfharness with just one straight line to your wishbone. The point of the line where the sail stays in balance gives you the centre of effort.

Looking at your photo I'm convinced by the way that this centre is far more upfront then you stated earlier.

And please keep your downhaul much more tight. It will change your sail directly in a much nicer wing. And it will help you coping with the weather helm by moving the pressurepoint of your sail closer to the mast.

Finally: Hanging out with a harness connected to the boom seems to me no problem for your mast fixed on the cat

The G-Cats were the main boats with symmetrical deep V hulls. I would think one of the advantages is that you don't have to try to keep the transoms out of the water. With round bottoms, sometimes it is not always possible to keep the blunt transoms out of the water. The deep V however has more wetted area.

What is the all-up weight of this?

Here is a short video from a waterproof point and shoot taken in the morning before taking the boat into the work shop.
http://vimeo.com/50453375
i already got a replacement on warranty for the original boom cam so some day there will be a new vid.

Northsea, Thanks for the input. i could find out the static center of resistance. i am under the impression that the dynamic center is going to move around depending on where the driver is sitting, how far healed over the boat is, what point of sail the boat is on, speed/angle of attack of the water passing over the rudder foils, etc.
What you my be getting at is the mast looks like it is too far aft. That may be the case, but i want to be able to drop into a wave on an outer reef and not pearldive at the bottom of the wave. Also things get pretty hectic jibing in the full trades, so everything that helps keep the bows up is welcomed. Although the cat could possibly blow over backwards, there is a way to control that. Don't go to the back whilst stopped. Also i will try sailing with the mast raked further forward.
The boat is too hard to tack and jibe with the current rudder and sheeting systems for anyone else to try the boat right now. The alignment, rudder rake, and hold down system need fine tuning, and the mainsheet block is from an 18. The boat is back in the work shop for these modifications now.
Originally i planned on making a scaled down 18' cat mast and sail. When that got changed to using existing windsurf parts the rigging concept didn't change. There is a cat style boom, mast rotator, diamonds, and adjustable downhaul. The hounds are higher up proportionally, than an 18 though, and since the diamonds need re-designing, pulling on a wire connected to the hounds bends the mast rather easily making trapping out impossible for now. Even a big gust overly bends the mast which de-powers the sail. So does high downhaul pressure. The sail seems to develop good power being held upright from near the top when the mast does hold it's shape. Normal windsurf booms hold the mast from very low and the top of the sail falls off, spilling power. i think that is one reason that windsurfers can use such big sails in strong wind. i may re-rig and try your idea though.

DHO, The Gcat is certainly the shape that inspired this hull shape. From my experience keeping the transoms out of the water is a light wind thing. Once you are bookin it you can stand further back, get the bows up and load up the rudders.
The V sits down in the water more than the boxy hull creating more wetted surface, but the V is a slippery shape. Also in a comparison you would need to add the wetted surface of the boards used on the conventional hull shape plus consider the added drag caused by the hole in the hull for the boards.
It is my subjective opinion that a board-less hulled cat would be able to go faster than the boarded cat on the right reach. windsurf boards are that way for sure. This theory excludes hydrofoils of course. Obviously dagger boards offer a more efficient lift for beating to windward, and getting first to the upwind mark really helps in winning a race. Then you can throw up a kite and over power any extra drag. Once you get to a certain wind velocity the kite becomes drag though. Hopefully this boat will be good for wind above that velocity.
i have only checked the weight of the hulls during construction and they were about 25lbs each before the final finishing process. 100lbs. is a good guess for the all up weight.

If I were you, I wouldn't bother about the tacking. When you sail at sea, there is not need for. I cannot tack on my cat also and I don't really miss it.

Looking at your video, I would like to express my admiration for what you have achieved so far. In the past I've done my share with trying to build minicats and mini sailingboats (larks).
So ,I'm one of the few guys who really know how difficult it is to compress all the basic forces of a sailing cat into 10 feet. Moreover sailing with it on waves is only possible when you have invented a stable and balanced design considering the presence of the extra demands the waves are posing.

So, respect.

http://vimeo.com/52061787
Short clip with the boom cam getting some under water footage.
a smaller sail is in the works.

looks like fun

Looks like fun, but for waveriding I will stick to kites

Nice videoclip. Did you compose the music too or just the lyrics?

thanks,
The music is a simple recording off of a Jam Hub that we were using during jam nite last year. it's a standard 5 4 1 blues pattern with Bill on slide, me on bass, and dave t. on drums. Mostly you just hear the slide guitar.

The boat is called a wave cat to distinguish the design from a race cat as in wave board vs. race board. there will be waves on any coast runs that i do. obviously when i do catch a wave i will have to just stay in front of the white water. There won't be any aerial off the lips or tube rides.
i haven't seen many good wave rides with kites. They look too fast compared to a surfboard, although a real shredder guy can get awesome wave rides on a kite board. Also a race kite board that you would use for a return trip coast run would suck for riding waves. Some of them use 3 giant fins with more total area than my rudders.
Anyway the design/build/test process is kind of fun.