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dopeydriver
27th March 2007, 08:41 AM
I found a good article in Nov/Dec 2000 Wooden Boat by Phil Bolger on this subject , using his design 639 William D. Jochems and 625 St. Valery as examples.
It includes a good commentary of sailing the St Valery.
I've also got articles on the Iain Oughtred Haiku , and plenty of literature on the NIS boats .
Anyone care to comment on these , or any other shoal draft 25-30 footer ?.
Rob J.

Boatmik
10th April 2007, 07:35 PM
Howdy Driver,

This is a very big topic. But in general terms - nobody knows what the limits of stability are for a particular boat unless they do the calculations. Once you understand for a "type" maybe it can be extrapolated to others.

There are two main aspects to self righting. How far over a boat can go before it wants to stay upside down. And how long it takes a perfectly upside down boat to turn upright again.

ALL boats will sit upside down perfectly happily in smooth water. But in the sort of sea that is likely to capsize you there will be enough rocking of an inverted boat to allow it come upright.

So here are some things I think I know

Joshua Slocums "Spray" - not self righting (too wide and not much ballast - so unlikely to come upright again from angles as low as 95deg (though I have only heard this but it looks right from the pics). IT has a similar righting curve to a multihull - once it is past 90deg - that's it!

But a racing multi takes a lot of getting over - even 20 degrees feels somewhat scary so people start letting sails go etc to get it back on its feet.

Thames Sailing barges - same

Cruising multis are more genteel requiring a lot of wind to get a hull out of the water.

Full rigged sailing ships - if they are to be licenced to carry passengers offshore they have to be good to go over to (from distant memory) 70 something degrees and recover

Modern fin keeled ocean racers - the rule requires them to be self righting up to a point where the mast is 115 deg (roughly - it is specific in the rule) from the vertical. Everyone tries to have the minimum possible.

A lot of older production fibreglass boats (specifically from the IOR rule era) are pretty poor - they had to meet the criteria in their lightweight racing versions but then when have steel keels rather than lead and more of an interior fitout they don't even make the somewhat relaxed standard required for ocean racing.

Bruce Kirby's NIS 31 - is self righting through to something like 150 degrees - because of the high dome of the coachhouse - the boat will fall off the narrow point. But this does assume little or no water is inside.

Or in fact ALL the statements above require the hull to be perfectly watertight.

It is a big area.

If you want to really get into it the best tome in the world is
Tony Marchaj
"Seaworthiness - the forgotten factor"

Pages and pages of diagrams and formulae - but he does point out the general thrust for the average reader.

The multi example above is the point - if the boat gives you enough time and warning to do something or you are a sailor of the first order then you can do amazing things in silly boats - much like Slocum.

If you are used to sailing small boats like puddle ducks it will help you keep everything from Slocum's "Spray" to a big offshore multi on her feet. You just get to know the feel and the dynamics - if you open enough to become any good that is!!!

MIK

dopeydriver
10th April 2007, 08:20 PM
Thanks Mik.
Its sure food for thought.Have you read the articles I refered to ?.
Yesterday my US visitors went back home , I've sold 2 wagonettes and a tipping spring cart , so the PDR is finally in the shed !.
And I should be able to go to it now.
Rob J.

Boatmik
11th April 2007, 08:09 PM
:-)

Good Man!