-I am very much on the side of no rocker on the lw hull. As soon as there is sailing load on the boat the bow becomes depressed. I do not see how there can be significant hydrodynamic lift from the lee bow unless it is made fairly wide with flare and the boat is prevented from immersing the lee bow by some other mechanism such as very buoyant ww bows, high weight transfer to the new stern on every shunt, or foils. Generally the leeward bow gives no lift, hydrostatic ot hydrodynamic, until it is in the water. Therefore you want it in the water as soon as possible to avoid building up angular momentum and subsequent hobbyhorsing. Also getting that hydrostatic lift early helps keep the cog down and reduces the chance of pitchpoling
It also allows a skinnier hull overall for the same displacement and depth and a higher prismatic coefficient. I have rabbited on about keeping the bow buoyancy low in my raves on reverse bows.
I can see some reason for some rocker on the ww hull to reduce the spray, but I feel this is at the expense of extra resistance, fore/aft stability and ww/lee stability. The less pitching, heaving and rolling, the better for stability of drive over the sails. Rare Bird is fairly heavy compared with Blind Date but is still traveling very nicely for the wind strength. The spray is mainly a nuisance. I think this is still a matter for argument as there could be some hydrodynamic lift arrangement that could work quite nicely, possibly with foils. It could be argued for sailing at higher speeds that the ww hull should be made up of two small power catamaran hulls, back to back with a dihedral of 160-170 degrees. The hull planes on the forward section.
Personally, for the ww hull, I am going for no rocker as it allows skinnier and less draught for the same displacement. The boat will be reducing spray by having a reverse stem with a couple of spray rails to deflect the water back down and provide some marginal hydrodynamic lift with little increase in drag. The first spray rail angled at about 8 degrees to the horizontal down to just above the loaded waterline at mid length, may also pick up some lift off the chop as well as damping roll and possibly heave.
-- In harryproa@yahoogrou
>
> Which shape is better for lw hull?
> Many people think a hull is faster without rocker, as on trimaran hulls. Many racing trimarans have rocker on main hull and straght side hulls.
> But... straight hull does not give much hydrodynamic lift when the nose is pressed as well designed rocker hull does , or does it??
> On a proa to have some hydrodynamic lift on forward of the mast would be an advantage, or would it? any comments.
> I am not 100% convinced about having main hull without rocker.
>
> Regards,
>
> Arttu
>
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