I'd like to add some small points. The Harry ww hulls are not really
that heavy. Traditional canoes hulls would be a fair bit heavier, so
it would be difficult with traditional materials. By the time some of
the Pacific Proas add their ballast, they are getting up to a
significant proportion of the Harry ww Hull. For a cruising Harry a
Ballestrom makes more sense than a una as the proportion of the weight
of the ww hull can be greater. Windage is a big factor when the winds
are strong enough to need to reduce sail, as the relative windage of
the ww hull increases, though this is somewhat balanced by the windage
of the lw hull

If you are a bit wary of loading up a rudder that can reverse, you
could always have a dagger board set up towards the ends to take some
of the LWR and have a smaller rudder
-- In harryproa@..., "k_s_oneill" <K_S_ONeill@...> wrote:
>
> --- In harryproa@..., "gardnerpomper" <gardner@> wrote:
> >
> > Hi,
> >
> > I was searching for info on proas, other than the harryproa website
> and this forum, and I
> > came across an old message (from 2003) that mentioned that the
> weight to windward proa
> > design was new and had traditionally been ignored because it was
> believed that it would be
> > unable to shunt properly.
> >
> > Does anyone know if this really was the assumption and why? The
> harry's obviously shunt.
> > Did Rob do something special to make that work, or was this just
> another case of "everyone
> > knows that a heavier object will fall faster" ?
>
> I can't find the message you're referring to. Can you copy the
> message number to your reply?
>
> Without seeing the specific statement, I can say that I was dubious
> they would shunt quickly or reliably when I first saw one. Rob can
> explain better than I how his boats work, but perhaps I can explain
> why I thought what I thought.
>
> In general, the CLR of a symmetric hull is at about 25% of the way
> back (from the bow). So a proa often has the CE of the sail moved way
> forward to match that, more or less. If the CE is way back, as it is
> on a ballestron rig, or worse on an una rig, the boat will often 'not
> shunt', which is to say when you try to shunt it will spin up to
> windward very hard, and often tack and go aback. That can happen even
> if you have a rudder, the sail's aft CE can just overpower the rudder
> and around you go. That's bad. I'm not saying that's what Harrys do,
> mind, I'm just saying that's the sort of general thing that people
> who've had frustrating days on lakes with amateur-designed proas tend
> to think about.
>
> Weight in the ama makes this worse. The ama is shorter than the main
> hull, so it doesn't want to go as fast anyway, and it's often made too
> small on the first iteration of a boat's design. So if you put weight
> on the ama you sink it, and if you do that during a shunt there's no
> way the boat will shunt, if you're lucky you just sit there, if not
> you tack. Again, some of us have done this, so some of us thought
> about weight in the ama during a shunt as an inherently bad idea.
>
> So that's what people were thinking about when they looked at Harrys
> at first, perhaps. I think it's more or less what I was thinking.
> The CE is well back, compared to a Gibbons rig or a crab claw. The
> ama is loaded up. One would tend to wonder if it's going to shunt,
> wouldn't one?
>
> As I said, Rob can no doubt explain his boats better than I can, but
> having said what I was worried about with respect to Harrys, here's
> what I've come to think, and he can correct me where he thinks I'm
> mistaken; the CLR is still at about 25% of the way back from the bow.
> Harrys aren't magic, nor is a lack of rocker in the lee hull really
> an answer to where the CLR ends up. The CLR of the lee hull is where
> it is, it's way forward. But Harrys have rounded hulls rather than
> traditional sharp proa hulls of whatever cross section, which makes
> the magnitude of the hull's lift fairly small when compared to the
> lift of the rudder, much smaller than you would get with a
> sharp-keeled hull and smaller rudders, for example. So the shape of
> the hull and the size of the rudders lets Rob dominate the CLR of the
> whole system with the rudders. That's the key, to me. It's also nice
> that he can keep the front rudder down during the shunt and have it
> push to lee for a second as the boat gets going, I think that could
> save the day every once in a while.
>
> In a secondary sense, the weight in the windward hull of a Harry isn't
> the problem it would be if you loaded up a traditional proa ama;
> you're not going to sink a Harry 'ama'. The windward hull's drag may
> be more than the lee hull, but again it's small enough to be dominated
> by the rudder.
>
> This also explains, to me at least, why people haven't copied Harrys
> much. I actually thought about what Rob had done and built a set of
> big-assed 5 ft long rudders to put on my boat, but I'm scared to try
> them, I really think they might tear the boat in half or something. I
> went back to a big long leeboard on a hefty mount in the middle of the
> boat and beachcat sized rudders. Engineering steering foils that size
> that have to steer, kick up, spin 180 degrees to shunt, and not break,
> it's not an easy thing, and once you draw them you have to have the
> materials expertise to make them strong enough.
>
> Kevin
>