Some thoughts on the ‘ideal’ cross section.

If the essence of a proa can be said to be -  keep it simple, and spend on length.  So no fancy steps, perhaps not even a lee-pod.

My requirements, for the central section are:

Standing headroom, say 1.9m.

Cosy double berth, 1.2m wide.

Sitting headroom over berth, 1.5m.

Assume made of plywood, a simple dory shape, so best if faces are 1.2m or about 0.6m.

Looking at sketch (sorry, got scanned as a mirror image):

- No need for symmetry.

- The windward side more vertical, ,so will not catch the waves as much & reduce spray.  When heeled has less wind resistance.  The lower face a half panel, a full 1.2m above.

- The lee more flared,  giving more interior space and more righting moment when heeled. Panels stacked the other way to the windward, with the first panel at a full 1.2m, and half above.

A lee pod is still desirable, and so is a solid dinghy.  So combine the two, in the form of a removable lee-pod / dinghy.

The hull length ideally about 11m,  giving a l/b of 1:12 so not that slippery, but still ok.

Flipped….

I’m certainly of similar mind on dory shape, though lean towards more symmetry, but each to his own. The only comment I’d make is regarding weight/displacement. Based on first guess at mid-section area (.45 sq. meters), 11 meters long and a moderate pc of .66 you have a displacement of 3.25 metric tons and a D/L near 70.

Of course if the boats lighter it’ll just float higher but if you narrowed the wl beam a bit you’d have a bit less wetted surface.

Cheers,
Skip

Mark,

Presumably, all the hull sections are (or could be) symmetrical below the weather chine????

If you are going to use a solid (sit in) dinghy as a safety lee pod, presumably it will also have to be double ended??? I would hate to dig it in stern first or shunt it each time otherwise ....It could also fill up and become a disaster pod. All the fixings / lashings and their points would also have to be pretty robust and rigid to withstand sudden uncontrolled dunking at 15 plus knots??

I am a big fan of cross sectional asymmetry above the water plane…...Don’t over simplify it, get as many advantages out of it as you can.

Good Luck. PM me if you want.

Rob

Thanks for comments.

Displacement:  I was expecting about 2.5T,  giving a immersed depth of about 0.4m.  Slimmer is no good as it looses the 1.2m wide berth.

Pod / dinghy:  Definitely designed as a pod, so double ended,  more of a canoe with small, easily sealed cockpit(s), and strong enough and very well secured.

Asymmetry:  The different angles to the lower panels give this, though not the correct way around in plan.  whether this is sufficient to adjust the plan, with a less curve to the lee, perhaps.  There was a design I saw a while back (German?) which had this form, though with curved cross sections.  Also had a small separate hull to lee, rather than a pod - Perhaps my inspiration.

Mark - 09 April 2014 05:46 AM

There was a design I saw a while back (German?) which had this form, though with curved cross sections.  Also had a small separate hull to lee, rather than a pod - Perhaps my inspiration.

Very interesting concept, using the pod as dinghy. Or if it fits one’s worldview better, call it a demountable lee “safety” hull, structurally divorced from the main hull. Now, whether it nests snugly into a purpose-built niche or rides alone, 2’ away as a counterpoise becomes completely optional, depending on your tastes.

Dave

here is an old thread talking about dingy lee pods

http://proafile.com/forums/viewthread/59/

Thanks for the link.  Interesting to see Helmut’s ME2 with dinghy fitted tilted on edge, good idea, did not think of that.
Any news of what happened with ME2?