Subject: RE: [harryproa] Harryproa hull length and shape
From: "'Peter Southwood' peter.southwood@telkomsa.net [harryproa]"
Date: 6/8/2018, 5:23 AM
To: <harryproa@yahoogroups.com.au>
Reply-to:
harryproa@yahoogroups.com.au

 

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)

 

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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