I've read posts from Rob on this mailing list that the target is ~40% of the weight to windward on cruising proas. But I might have misunderstood something. Might be with an empty boat? So with the crew and gear it has more than 50% to WW?

I guess you can move around gear and crew if you want to optimize for the conditions. 40% would still be a lot more than on other types of proas with the rig to leeward.

To always have more than 50% on the short hull doesn't seems like a good idea. If there is not much heeling force in the sails (light conditions or sailing downwind), that hull will produce a lot of drag (short and heavy). Also, sailing downwind in a strong breeze with a lighter LW hull doesn't seem like a good idea to me, then the boat will have lower margins to pitchpole.

I was in Portugal to have a look at Robin Wardes boat, Kleen Breeze, two years ago, while it was still in the boatyard. He put a lot of heavy gear in the LW hull. Like the battery bank, washing machine, e.t.c. He was also talking about this 40% ratio, while we were looking at all the stuff in the LW hull.

And to me, it makes sense. Let's say we put 50% in both hulls, and targets the same length to displacement ratio on the short hull in light winds, and on the long hull in strong winds. Then the long needs to handle 100% of the displacement, and the shorter 50% of the displacement. Then the ratio of the lengths will be cubic root of 50%/100% = 0.5^(1/3) = 79% of the length. And that is quite a long WW hull. If we assume that there is always some heeling forces in the sails, and also put less weight in the WW hull, the WW hull can be shorter, with the same length to displacement ratio. So let's say 40% WW weight, and 10% of the total weight resists the heeling forces. Then we get 0.3^(1/3) = 67%, which is more or less what Rob is using. Again, this is assuming the target is to have the same length to displacement ratio on both hulls. A cat might not be the best design, considering this, since the LW hull gets more loaded while heeling. So if the boat is light, the WW hull is unnecessarily long (extra wetted surface, friction drag). And if the boat is heavy, the LW hull is short and draggy (wave drag).

Don't see it as an issue with a slightly lighter WW hull than 50%, since you can get both high RM and a light WW hull, by just increasing the beam. If RM is kept constant, the load on the beams will stay the same. But the beam loads are always lower on a Harryproa than on a cat boat with a stayed rig in the middle of the beams.

There is also a difference between the light racing boats, and the heavier cruising boat, imo. For racing, the weight of the crew is large compared to the weight of the boat. The crew is always active, and will move to leeward when the conditions or point of sail calls for it. So the sum of the crew and the WW hull can be more than 50%, and the WW can still be very short, like 50% of length. But I think on a cruising proa, the weight of the crew has little significance, and you need to distribute the gear so you have maybe 40-50% in the LW hull, depending on its length. But if you want to have more margins of safety while sailing into a strong wind, I guess you can move some heavy gear from the LW hull to the WW hull.

That is my thinking, anyway! =)

On Fri, Jun 8, 2018 at 12:34 PM, Doug Haines doha720@yahoo.co.uk [harryproa] <harryproa@yahoogroups.com.au> wrote:

 

Yeah, not sure what Bjorn was meaning there.

50% of total or 50% of movable gear/stores ?

On ‎Friday‎, ‎8‎ ‎June‎ ‎2018‎ ‎06‎:‎32‎:‎25‎ ‎PM‎ ‎AWST, 'Peter Southwood' peter.southwood@telkomsa.net [harryproa] <harryproa@yahoogroups.com.au> wrote:

 

Note that a harryproa is specifically a “weight to windward” proa.  More than 50% in the windward hull is almost a defining feature.

Cheers,

Peter

 

From: harryproa@yahoogroups.com.au [mailto:harryproa@yahoogroups.com.au]
Sent: Friday, June 8, 2018 10:14 AM
To: harryproa@yahoogroups.com..au
Subject: Re: [harryproa] Harryproa hull length and shape

 

 

I think the most interesting lesson here was the fact that the height of the rig has such as an importance if there is a wind gradient. So on boats where the height of the rig increases during heeling, it really increases the heeling moment due to stronger winds higher up. On harryproas or normal keelboats, the windstrength decreases from the first degree of heel. The logic is confirmed with math.

 

I don't think its good design to put more than 50% weight in the WW hull, because then that hull needs to be almost as long as the LW. More beam and a lighter WW hull (Rob says 40%) would be better. But I think this isn't really the point here, to look at the static numbers. It's very easy to change same parameters, which will shift shift either curve up or down. What I thought was interesting was the shape of the curves. It's just like Rick says, the proa has less heeling moment at higher angles of heel, and the cat the opposite.

 

Take this one for example, with a very large gradient (Hellman = 0.6)

https://pasteboard.co/HoUBtOO.png

 

The harryproa has positive righting moment all the way to 45° in this case. I can image that when sailing in an archipelago with islands covered with trees, or in a lake surrounded by trees, the wind has a high gradient. So in this case it would be almost impossible to capsize the proa, but the heeling cat will reach stronger winds which has been less blocked by the trees, and will need a really fast reaction by the crew to stay rightside up.

 

 

 

 

On Fri, Jun 8, 2018 at 6:49 AM, Doug Haines doha720@yahoo.co.uk [harryproa] <harryproa@yahoogroups.com.au> wrote:

 

I would submit that in general, if you can build you hp for say $20,000 and can go out and sail twice as fast as boats that cost similar and only get matched for pace by $100,000 boats then you are the comparitive winner overall.

--------------------------------------------
On Fri, 8/6/18, '.' eruttan@yahoo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:

Subject: Re: [harryproa] Harryproa hull length and shape
To: harryproa@yahoogroups.com.au
Received: Friday, 8 June, 2018, 11:42 AM


 













| It is hard to say: assuming all other things being equal.
Obviously the hp can have most of its total weight in ww
hull, whereas cat has to keep it 50/50.

|So the argument can't really begin on an even keel.



Doug makes a good point. Perhaps i missed something too,
but it looks like you made the HP a cat, to make it fair.



Also, and this might be a language thing, but we don't
want fair. We want accurate, don't we?



Not that the thought experiment was not great. Thanks for
it, and I am still chewing on it. Neat to see a physical
representation of the vectors.



Rob, a few posts ago, said cats use weight, and hps use
width, which is lighter and cheaper. I think it's fair
to object to normalizing weight and width.



Perhaps add a third boat. A typical, non normalized HP?
Still constrained by the same weight/cost?



To visualize the more realistic comparison?











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