I suggest you look at the videos of 'Rare Bird' to see how comfortable a Visionarry can be in a bit of a sea.
Multihulls with flared bows and overhanging stems lack of bridge deck clearance will have problems moving at any speed in a sea. The more you can keep the boats sailing flat, without hobbyhorsing or bouncing off waves, the more comfortable it will be and less stress on the boat as well as much faster. The time of impact with the waves needs to be as long as possible and sudden changes in buoyancy reduced. An overhanging bow with a flare will hit the wave all at once, the flare will cause the bow to rise rapidly, turning forward motion into vertical, and then will come down again. If the frequency starts to match that of the waves it gets right out of hand. Rocker reduces the ability to damp the motion. This motion also causes a sudden increase in bow resistance, and if the waves are that little bit bigger the bow can go right under with a wide flat area on top resisting the ability to rise again.
A deeper forefoot with high prismatic coefficient and no flare on the bow allows the bows to meet the wave early, have sufficient low down buoyancy to give hydrostatic lift early and gently, and if it does penetrate the wave, can shed water and rise gently.
I can see a deep V working below the waterline or near the centre of the hull, but if allowed above the waterline near the bow, will induce hobbyhorsing. A deep V below the waterline at the bow with a rockerless hull, going to a shallow V and vertical topsides and chine below the waterline, should work and be made easily from flat panels.
I see the extra value of a Harryproa for sea kindliness is that; it has two different length hull that reduces the racking forces when working to windward as the two hulls meet the waves closer together; the two different length hulls reduce harmonic matching with the sea as they have different frequencies of motion; the lack of rocker and lack of flare damps motion; the skinny hulls allow shedding of water off the bows when they do penetrate; the bridge deck is in the lee of the ww hull which reduces wave impact.
The ability to work to ww is also improved by the lack of windage of the lw bows and subsequent induced drag, and the bridge deck being in the lee of the ww hull
What I am doing differently for my Harry is for the the lw hull to increase the time of impact of the bows meeting a wave by having a reverse stem above the waterline and a V at the bow to allow coming off a wave without slamming. I am also having a flare at the beam, to allow some accommodation in the hull, increasing the bury of the beam and reduce the wave impact on the beam. This flare finishes well back from the bow to avoid hobby horse problems
For the ww hull I am going skinnier with a bow bulb going to slightly reversed stem with spray rails to improve comfort. The bow bulb is partly to give a step allowing easy access from the water
--- In harryproa@yahoogroups.com.au, barrie lyall <protocomposite@...> wrote:
>
> Extremely interesting comment Paul, As a somewhat recent multihull convert I think this is a very important topic. Could we venture to say that less of a planing and perhaps a more V form hull would be something to consider for blue water sailing?
> --- On Sun, 7/25/10, Paul Wilson <opusnz@...> wrote:
>
>
> From: Paul Wilson <opusnz@...>
> Subject: [harryproa] Swells in open ocean
> To: harryproa@yahoogroups.com.au
> Date: Sunday, July 25, 2010, 11:01 PM
>
>
>
>
>
>
> I have found the recent threads very interesting and thanks to all for
> their contributions. One thing has been bothering me though. Talk has
> been of large proas at high speeds. I assume these are designs for open
> ocean. 12m, 15 m and speeds of 25 to 30 knots have been mentioned.
> This seems unrealistic to me and would be designing for an ideal of high
> wind with flat water and no waves. Having sailed offshore, I know that
> a 10 to 15 knot trade wind that has been blowing for a few days normally
> kicks up a 2 to 3 meter swell. Going 25 knots on a 3 meter swell with a
> light boat could launch you into the air. These waves are what limit
> your speed as their tops crash into beams, superstructure, or you. If
> one is designing an offshore cruising or racing boat, wouldn't it be
> better to design for max efficiency at a more realistic speed? Say 10
> to 15 knots for a fast, offshore multihull? This seems more realistic
> to me and may result in a boat that was more all round, easier to keep
> "in the groove" and possibly faster.
>
> As an illustration, I have a friend currently sailing from Galapagos to
> Marquesas. His average speeds have been between 6 and 7 knots on a 35
> foot catamaran that in the same conditions in flat water would probably
> be 12 knots or better. The pounding and smashing if he pushes the boat
> is always so bad that he has to limit the speed. On my heavy 36 foot
> monohull, I have made passages in the same conditions in less time, due
> to the fact that I can push the boat harder without beating myself or
> the boat up. Everything says the multihull should be much faster than
> my heavy monohull, yet I know offshore, the reverse is true.
>
> Something to think about.
>
> Cheers, Paul
>