Thanks again Mike for taking the time to give a full answer.
The point about pitchpoling is good - I understand that many of the capsizes in small multihulls are due to pitchpoles.
I like the Harry configuration and cannot see a better alternative for an economic small cruiser. However must keep an open mind and probe other options - the French prao kicked off the current train of thoughts plus the discussions about balancing the centre of effort and centre of lateral resistance.
--- In harryproa@yahoogroups.com.au, Mike Crawford <mcrawf@...> wrote:
>
> John,
>
> It sounds like some of the items that are priorities for me wouldn't
> be a priority for you. I'd argue that any safety margin, such as
> capsize recovery and reduction in heeling moment as you heel, are as
> important for cruisers as for racers. But if you're intentionally way
> undercanvassed, it could be a non-issue.
>
> <<Fore and aft loads - good point. How much torsion is there on the
> beams in a cruiser due to the water drag forces on the windward hull in
> a rig to leeward>>
>
> I don't imagine that drag adds much torsion. The larger issue,
> probably in terms of several magnitudes, is that the rigs are going to
> deliver a pitchpoling force that wants to drive the bows down, and with
> the bows in the opposite hull, being driven up by flotation and/or wave
> action, tons of of diagonal forces will need to be transferred from one
> hull to the other.
>
> I'm just a fan of designing forces out of the equation, and have been
> since my engineering days in college. Thus, I like the harryproa
> downspiral design: Eliminating torsional (forces in line) and
> compression forces (unstayed mast) means less weight, which means less
> sail, which means lower forces, which means a lighter structure, which
> means less sail, and so forth.
>
> At the same time, less carbon and epoxy mean a lower cost, as does
> skipping additional structures such as crew pods.
>
> But there's no reason to be dogmatic. If you don't care about the
> weight, you don't care about the weight. It's not the end of the
> world. There are plenty of catamarans and trimarans that deal with
> larger forces using whatever additional structure is required. While I
> can't see myself building an atlantic proa, I can definitely see the
> allure of having both the sail controls *and* the sails in the cockpit.
>
> One question is whether or not moving the rigs to the ww hull, and
> thereby incurring these larger forces and structural weight, is the most
> efficient way of dealing with any tendency to luff.
>
> I'd argue that spreading the rudders as far apart as is practical
> would do the same thing more safely. And if you want additional leeway
> prevention while reducing steering loads, throw in a central
> daggerboard/leeboard that kicks up in both directions. I'm not sure
> it's necessary if your rudders are deep enough, but it's certainly an
> option. (unless you're almost always sailing in shallow water that
> doesn't allow enough foil depth to get the lift you need).
>
> I can't prove that, though. Any boats in the water are worth much
> more than my theories, and I'd love to see an Atlantic design with
> unstayed masts.//
>
> - Mike
>