RE: Capsize ratio

From: Judith Franklin Blumhorst (drjudyb@pacbell.net)
Date: Tue Feb 15 2000 - 09:32:04 PST


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Alan,

The classic primer on traditional boat design is Ted Brewer's book
"Understanding Boat Design" is easily understood and very educational.
Covers hull design, rig design (a little), construction, layout. A ton of
knowlege in just 125 pages or so. The 4th edition, 1994, is very good.
about $15 at amazon.com.

Also, Dave Gerr's book, The Nature of Boats, is good essay-stlye foray into
quantitative analysis of boat design. More math, but it's pre-digested in
the form of charts, without too many equations. Less focused on tradition
ocean going yachts, more analysis of small boats and modern boat design.
goes into more detail than Ted Brewer, but assumes you know the basics.
Read Ted Brewer first. About $20 at amazon.com.

There are many more very good books that others on this list can suggest,
that I'd love to buy and read, but those are two of my favorites on design
for under $30. Most of the other books on yacht design focus too much on
bigger, ocean-crossing yachts than coastal trailer sailors.

Many beautiful books on yacht design just don't really apply to small boats
like our Potters or other trailor sailors. The famous designers that write
and sell those books are experts on ocean-cruising custom yachts. The books
are fun to read, with color pictures to drool over, but you can't always
apply the metrics of big yachts to small trailer-sailors.

The mathimatical reality of "scaling" gets in the way. A small boat must be
fundamentally different than a large boat if the design is to be successful.
If you took the most beautiful 40 footer and scaled it down to 20 feet, it
would be pretty but sail like a dog -- impossible to handle and dangerous.
Dimensions would decrease by 1/2, sail area and lift by 1/4,
weight/displacement/volume by 1/8, heeling moments by 1/8, and righting
moments by 1/16th --- argh!!!! what a nightmare!!! The boat would be totally
out of balance.

These books will help you understand why small boats like our potters are
well suited for their intended use (coastal crusuiing) and why they aren't
suitable for trans-atlantic crossings. Let's face it, our Potters aren't
going to be be as seaworthy or safe in a fierce gale as a well-found 40
footer cruiser, or as comfy in 12 foot rollers a little off shore, but they
sure are damned fine for a boat in the 15-22 foot range, and safer than a
lot of racing boats.

======================

BTW, John Rousmanierre's _Annapolis Book of Seamanship_ is my favorite
all-around book about sailing. I consider it a must-have for any sailor's
library. More useful for the sailor, I believe, than the classic primer
Chapman's Piloting, which is alos very good to have around.

BTW #2, Tom Whidden's book _the Art and Science of Sails_ is my current
favorite on sail construction theory, though he's more interested in racing
than cruising sails. The "slot theory" is dead, dispproved, gone. The
"circulation pattern and starting vortex" explain why sails move boats.
Flat keels provide lift... here's where you learn why.

BTW #3 - for info on rigging, Brion Toss' _The Rigger's Apprentice_ is the
best I've found on punderstanding rigging. There aren't alot of good books
on rigging. Tons of Practical stuff that you can apply to your boat. A
lot of "how-to" stuff, but won't answer all your questions on this
incredibly varied topic -- but better than anything else I've found. Also
good stuff on knots.

BTW #4 - Frank Bethwaite's _High Performance Sailing_ is very technical, but
contains tons of info on reading the wind, weather and water currents, and
finer points of trimming sails. It's for racers, but good for cruisers to
understand. NOt useful for beginners.

Happy reading!
Judy B

> -----Original Message-----
> From: Marilyn Dimson-Doyle [mailto:mddoyle@mediaone.net]
> Sent: Tuesday, February 15, 2000 7:39 AM
> To: potter
> Subject: Re: Capsize ratio
>
>
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> West Wight Potter Mailing List maintainer
> dfarrell@ridgecrest.ca.us
> List hosted by www.tscnet.com
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> Hi Judy,
> This is Alan. Marilyn is my wife. Sorry for the confusion on the
> e-mail address. We have been talking about changing it since I spend most
> of the time using it, just haven't got around to it.
> All that you have said follows exactly what I have been
> reading. What I
> was confused on was the vulnerability to capsizing versus after capsizing.
> Thanks for that clarification. Could you recommend a good text that does
> talk about stability and vulnerability to capsizing? Or just a good text
> about boat construction, particularly within our class of boat? The snow
> and ice isn't melting very quickly.
> Thanks for putting up with us novices.
> Alan
> P-19"?"



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