I think this is a “problem” with deep V shaped tri and catamaran hulls, compared to deep V proa/walap vakas.
The walap and proa needs for and aft symmetrical hulls, and they have a lifting sail keeping the vaka from pitching to much in waves. The tri and catamaran has two or three hulls that can excite pitching, and with the right (wrong) wavelength they will hobbyhorse and behave badly.

A catamaran or trimaran can not use the same amount of rocker due to excessive pitching and hobbyhorsing, whilst the proa can and should use more rocker. The cat and tri has two or three hulls in different parts of the waves, with will excite much more unwanted (non forward) motion. The proa is inherent more pitch-resistant due to having the sail far forward on the hull, acting like a wing. I believe the low aspect delta wing sail effectivly transforms pitching motions into forward thrust like a dolfins tail-fins. The deeper V shaped hull (or asymmetric ASP) with pronounced asymmetry and deep rocker will push the forward bow upwind each time it is lifted up on a wave, and similarly it will push the forward bow downwind into the wave each time it is lowered down between waves, keeping it tracking straight and with a good “contact” with the water. When the forward bow is lifted up on a wave, the aft bow is pushed down into the wave. the asymmetry will push the different amounts of water aside on the two sides. The aft bow will have more submerged lateral area then the forward bow, due to being in a trough. Without asymmetry this will not happen. This property will help to keep the low aspect lifting body on a straight course through a confused sea. This will not happen on a Wharram, due to the symmetry and two hulls fighting each other going through different parts of the wave.

All these aspects add up to a greater synergy.
Thinking about this makes me very very impressed by their advanced design.

Cheers,
Johannes

TINK - 10 May 2013 10:19 AM

Mal and Rob,
On TP01 which had an asymetric hull I found the CLR move to about 1/4 the hull length from the bow, I wonder if with a symmetrical hul it will remain nearer the centre. 

If anything, the CLR should be further aft on an asymmetrical hull. 25% to 30% from the bow is fairly normal.

johannes - 12 May 2013 01:41 AM

I think this is a “problem” with deep V shaped tri and
I believe the low aspect delta wing sail effectivly transforms pitching motions into forward thrust like a dolfins tail-fins.

That’s an interesting thought Johannes.

I’ve been a catamaran sailor for many years, starting out on the asymmetrically-hulled Hobie 16. These boats have a good amount of rocker and are also well-known for being able to be sailed in high winds and rough conditions (by very experienced crews). I despised the boat for its low-volume hulls and willingness to pitchpole. A 130lb 15-year-old boy doesn’t have the weight to keep the bows up in 20 knots of wind… with full sail, anyhow.

After a year of learning to sail on the Hobie 16, I sold it to purchase a G-Cat 5.7M (18’8”), which has symmetric, deep-V shaped hulls. These also have a good amount of rocker to maintain maneuverability. They handle the waves, especially chop, better than any other hull shapes. They also had enough volume to have over 1,000 pounds of people aboard and still float plenty high. The forward trampoline allowed me to spread the load out evenly and maintain full control of the boat. I once took 8 people out in 15 knots of wind and 6’ rollers and we had a blast! On another occasion, I launched the boat with the rudders still tied up for trailering, and steered it using only the sails. This included backing it up from head-to-wind, turning onto a reach, tacking, and sailing upwind to a mooring buoy where I tied it off and casually freed the rudders.

Both the Hobie 16 and G-Cat 5.7M hove-to very well, even under full sail, a tactic I was fond of using for many situations.

They both went upwind just fine, but neither of them pointed as high as a boat with boards. The “trick” to getting the most out of them (any catamaran, for that matter) is called “footing”. Shifting the weight forwards to get the bow down and move the CLR forwards. The lighter the wind, the more we would foot. In high winds, of course, everyone was hanging off the back of the boat as much as possible, trying to keep the bow from going under.

Thank you all very much for all your brilliant thoughts. The reason a posed the original question was that I was considering using an asymmetric vaka with my lug rig with adjustable CE.

There seams to be some very convincing arguments and positive attributes to an asymmetric or deep v’ed hull.

However in my particular application I have two concerns
1) ultimately such a hull will have a lower prismatic coefficient and grown in both length and depth compared to my box section proposal. This increase in size goes against the grain on the minimal ideals.
2) the other concern is the CLR movement, though I could have lots of rocker this would further exasperate number 1 above. This is likely to require the swinging arms to increase in length and result in more movement away from the minimal proa ideals.

For the moment I am going the park the idea of an asymmetric or deep v’ed hull. I will carry on the model development of the rig

Thanks again for all your input

TINK

It is very easy to build light and strong H-beams. Just laminate several pieces of hardwood to the desired shape and cover the top and bottom with flanges of wider plywood. All the fillets are on outside.

Cheers,
Johannes

Is it not normally the other way around - ply webs & solid flanges? 
Softwood is generally better structurally,  though is normally less rot resistant.
H-beams win hands down on ease of construction and can readily be maintained. 
That said they are not so good in resisting torsion, which is important.  A tube or box section is better.
Mark

lack of torsional stiffness could be a good thing in a proa!

I posted this in the wrong thread..
I will repost it in the right thread when i get home from work.
Cheers,
Johannes