Subject: Re: [harryproa] Pro vs bi-rig cat?
From: "Rob Denney" <>
Date: 4/4/2008, 12:02 AM


On Fri, Apr 4, 2008 at 1:58 AM, gardner.pomper <> wrote:

> After following the discussions on the advantage of proas, and playing
> around with a layout for a liveaboard version, along with very limited
> info about the upcoming charter version of the harryproa, I realized
> that I seem to be missing some basic points.
> The proa has an advantage because all the stresses are concentrated in
> a small portion of one hull. That seems to be mostly due to the
> ballestron (sp?) rig.
A lot of the advantages are from the unstayed rig, not specifically
the ballestron. The unstayed schooner, or even the mainsail only rig
both have far lower loads on the rest of the boat than a stayed rig.

> Weight and cost can be kept down by keeping accomadations out of the
> hulls and putting them on a bigger bridgedeck. That would apply to
> cats too.

Yes and no. You get more drag, and more cost at some ratio of hull
size to bridge deck.
> So, I am wondering, if you design a bi-rig cat with a freestanding
> ballestron rig in each hull and just put everything up on the
> bridgedeck, wouldnt that work pretty much as well as the proa concept?
> It would seem that the weight would be about the same.
> Things would be different; you would have 2 identical hulls to build,
> somewhere near the average of the ww and lw hull sizes. That should be
> easier. You only have to sail in one direction, which would make the
> rudder and wheel designs easier. You could mount inboard diesel
> engines, which would be handy for liveaboard crusing, so you can
> travel when there is no wind. You do need 2 masts, and they would have
> to have shorter booms, so they don't run into each other.
> Can someone give me a clearer picture of the inherent advantages of a
> proa? (not compared to cruising fat cats, but for a liveaboard couple,
> wanting a small level of comfort)

Mike, Nuvaslacker and Robert have covered this pretty well. I would
only add 1) that the hull design of a biplane rig cat needs to be
compromised to make it tack without a jib. The Radical Bay is very
hard to tack, they often gybe and occasionally find even this
difficult. 2) Once you have sailed, and especially shunted a well
sorted proa, you (and especially your wife) will never go back to
tacking, and gybing.

To address your specific points: 2 hulls the same or a long and a
short is a fair swap, but the proa optimises one hull for speed and
load carrying and the other for space and comfort, whereas the cat has
to try and do this with the same shape, and suffers for this
Rudder design would be easier, but you need daggerboards and these are
serious cost and safety items. Two beam rudders and no daggerboards
is a far better solution for a cat than 2 rudders and 2 daggerboards,
although the current crop of cats would need some layout
Inboard diesels are possible on a cat but difficult (not impossible)
on a proa, and if you don't mind the smell, noise, weight, drag and
the constant maintenance are a good option.

Why have two masts? A single mast (and daggerboard) in one hull will
work better in most conditions.

Just like to mention that all the activity on this list is fantastic.
Thanks to all who have contributed. Please keep it coming. If I miss
answering anything, please let me know.

By the way, we have had positive builder responses for the charter cat
from Peru, Trinidad, Latvia and South America so far.



> Thanks

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