Peter Ward wrote:

I guess I was thinking of seaworthiness in the fairly narrow sense of
being able to survive something like 'The Perfect Storm'; &
particularly the ability to quickly self-right in the event of
capsize. According to Czeslaw A. Marchaj
in 'Seaworthiness : The Forgotten Factor' the "point of vanishing
stability" et.al. of most modern yacht designs is woefully inadequate

There are some fairly simple ways to evaluate the relative stability of a
sailboat, and there is a very wide range of boats on the market. To say 'modern
yacht designs' have *any* single factor in common is like saying 'modern motor
vehicles' are all thus-and-so. How about we say 'some popular modern yacht
designs are woefully inadequate'? Then the trick is much simpler, just avoid
these particular ones.



As a natural pessimist, I want to build the 'ultimate-unsinkable'
craft, which will weather the worst that the sea can inflict;

As a natural pessimist myself, let me assure that such a thing does not exist.
The ocean is incredibly powerful, it can tear up battleships & supertankers when
it's in the mood to. The only answer for surviving such conditions in a small
sailboat is.... be elsewhere....

That said, a high ballast displacement ratio and full positive flotation make a
lot of sense for ocean passagemaking sailboats.





"William R. Watt" wrote...
define "seaworthiness"

I thought it meant a boat that would take care of itself in rough
conditions

That is a good quality to have, but it can also include having the right gear
such as a drogue and/or a storm staysail.

.... not a boat that could perhaps outrace the weather. This
outracing the weather is only helpfull along the coast where, given
advance warning of deteriorating weather conditions over the radio, the
faster boat can run for cover. Its not much help mid ocean in a big
weather system.

I disagree strongly. A boat that can make good miles, especially reaching or
close reaching in a seaway, is going to spend a lot less time in a storm system
and will be able to keep further away from the center.



The main indicator of seaworthiness is the displacement to length ratio.
Boats with a ratio over (I think) 300 are the most seaworthy. These are
ocean going cruisers. Because boats are sold by the pound they are
expensive. I know lighter materials can cost more per pound by they don't
have as many pounds. The heavy cruisers also have more room for
accomdation and storage and a better comfort factor. They can make good
time under all conditions but light winds.

And to windward, usually.

The issue here is that a lot of the current generation like heavy heavy boats.
Therefor, since so many of the boats out there cruising are heavyweights, the
statistical evidence that heavy boats make the best cruisers is self
perpetuating.

Heavy boats are good at one thing.... not getting bounced around. Weight conveys
no advantage beyond simple inertia.



Jim Woodward wrote:
Again, I point at Sayula II. Tough boat, but a whole lot faster than a
Colin Archer.

As for outracing the weather at sea, if I have a hurricane forecast in front
of me, with pretty good track guesses from the NHC, I'd rather have a boat
that was a modern, fast, tough, seaworthy design, rather than an old, slow,
tough, seaworthy design. Not extreme, but taking into account modern design
thinking.

For example, there's some evidence that a modern keel and skeg design is
less likely to "trip" on a wave and capsize, than the old full keel designs.
Certainly modern designs with the rudder way aft have more steering leverage
and therefore will steer better in extreme conditions than long keels with
attached rudder.

They will also respond better with less work by either helmsman or autopilot. A
tired helmsman is a poor safety factor to have in big breaking seas.



Swee****er (Swan 57) has a D/L of about 230. She certainly never gave us any
concerns on our circumnav and I would believe she is sufficiently seaworthy
for all "ordinary" purposes -- no Southern Ocean work, I think. A 230 D/L
does not mean "weak" as a simple glance around at the scantlings of a Swan
will show you.

Further point, heavily built is not necessarily stronger. Polyester resin is
brittle. In an early edition of his book on building the Westsail 32, Ferenc
Mate advocated using resin & newspaper to block in parts of the hull. This is
going to add zero strength. Lots of older boats with very thick hulls are
actually weaker due to the use of short strand mat, chopper guns, lots of voids,
cloth edges at odd points, etc etc.

All else being equal, heavier is usually stronger. But 'all else' never is quite
equal, and the strongest boats are the ones that are well engineered and
properly built with suitable materials. This doesn't happen by accident.

Fresh Breezes- Doug King