Subject: [harryproa] Re: Pro vs bi-rig cat?
From: "nuvaslacker" <>
Date: 4/3/2008, 7:44 PM

--- In, "gardner.pomper" <gardner@...> wrote:
> Mike,
> Thanks for the reply. I guess I wasn't clear enough in what I was
> asking. I am not talking about a "regular" cat. I mean a bi-rig cat,
> where there is a freestanding mast in each hull, just like the harrys
> have in the leeward hull. Then there is no stress anywhere on the
> bridgedeck, no rigging, no strengthening of the hulls. Just like the
> harryproas, the cat can be built VERY light.
> The bi-rig cats I have seen on the web all have dual mains, but I
> would think you could have the same balleston rig as the harry's,
> although it would have to have a higher aspect ratio to keep the booms
> from hitting each other when perpendicular to the hulls.
> I guess my question boils down to, if a cat can be built as light as a
> harry (due to the rig), and the displacement is the same from 2 45'
> hulls, instead of 1 40' hull and 1 60' hull, is the proa still going
> to be faster? They would have the same payload capacity, so that evens
> out the "liveaboard" issue. It seems to me that Rob has mostly been
> successful because of the rig. Even the reefing seems to be a function
> of the rotating, unstayed mast.
> Of course, I am assuming that removed of the rigging, and with proper
> motivation, you can build a cat and a proa with the same displacement
> and payload.
> I can see some advantages in being able to go directly backwards, but
> there are also advantages in being able to have engines and rudders
> set for a single, forward direction. That seems to be pretty much even
> on both sides.
> - Gardner

I may be wrong but.......

(My understanding of the Harryproa is purely from the website and this

What has impressed me about the Harryproa from the two movie clips is
the lack of pitching. True, the swell is not great but the vessel
seems to be much more steady in pitch than other multihulls.

If you look at the Harryproa hullforms there is no rocker in the
hulls, which must give a very high prismatic coefficient (hence little
tendency to pitch). If you try this with a catamaran, it will track
straight as a die, but refuse to come about or change course (see AYRS
Cruising Catamarans, and other publications from the early days when
various hull forms were being tried).

I presume it is something to do with the unbalanced drags from the
hulls and drive from the leeward rig that allows the Harryproa to be
reasonably manoeuverable whilst still having a zero rocker hullform.

For me this is the most impressive feature of a Harryproa, having
experienced hobby-horsing on all of the cruising catamarans I've
sailed on (not a great many, I'll admit!).

Nuvaslacker (UK)

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