It seems more sensible to me that a light, strongly built
boat with a fast hull, would carry loads much better than a
boxy hull that was heavier to begin with.



Wayne.B wrote:
It really boils down to what is the impact of your cruising gear on a
light displacement boat vs heavy displacement.

Agreed. But I think it's easy to overgeneralize in a way
that reinforces one's prejudices.

... Let's for the sake of
argument say that you've got 4,000 lbs of cruising "stuff", e.g.,
extra water, extra fuel, larger batteries, extra anchors, chain,
windlass, solar panels, cruising canvas, food, refrigeration, tools,
spares, dinghy, motor, etc, etc.

On a 10,000 lb boat, that is a 40% increase, a considerable amount
which will no doubt adversely affect performance.



Same gear on a 20,000 lb boat is only a 20% increase.


Except that it doesn't quite work that way. What you need to
know is how the load will affect the center of gravity and
the wetted surface area, mostly... lighter weight boats
generally have higher ballast displacement ratios and more
reserve stability, and have so much less wetted surface than
a crab-crusher that the increase from loading is negligible.

A useful figure would be the pounds-per-inch-immersion for
each hull. Just a percent of gross displacement isn't going
to say anything that can be generalized about how the two
boats sail, comparatively.


Assuming both were the same speed to begin with, the lighter boat will
be more severely impacted.


Well, show me two boats of the same LWL with the same PHRF
rating, one at 10k and the other at 20k!

Another factor is that the heavier hull will have a lot more
volume and tend to be more heavily loaded. And the faster
boat will have more sail area, so the SA/D ratio isn't going
to take such a hit (given equal increases in disp).

Of course, my prejudices tend towards performance boats and
so I work towards justifying that.... but there is a good
bit of logic along with some real world experience in the
justification also.

Fresh Breezes- Doug King

On Mon, 26 Jun 2006 13:06:28 -0400, DSK wrote:

Of course, my prejudices tend towards performance boats and
so I work towards justifying that.... but there is a good
bit of logic along with some real world experience in the
justification also.


I did two Newport-Bermuda races on a nice fast Frers 41 displacing
about 10,000 lbs give or take. No extreme conditions encountered,
just typical offshore 15 to 20 kts, fast reaching through 6 to 8
footers. The boat was extremely uncomfortable with a fast squirrelly
motion that defies explanation, but in my view totally unsuited to
extended cruising in those conditions.

On two other N-Bs with a custom Ron Holland 50 displacing over 40,000
lbs, and in far worse conditions, we had a very comfortable ride. Not
exactly an apples to apples comparison because of the length
difference, but two very valid data points nevertheless.

It's one thing to go out for a couple of days on a light weight boat
and bash around a race course, but an entirely different proposition
to take off for 6 months or more of serious liveaboard cruising.

Wayne.B wrote:
I did two Newport-Bermuda races on a nice fast Frers 41 displacing
about 10,000 lbs give or take. No extreme conditions encountered,
just typical offshore 15 to 20 kts, fast reaching through 6 to 8
footers. The boat was extremely uncomfortable with a fast squirrelly
motion that defies explanation, but in my view totally unsuited to
extended cruising in those conditions.


understood... and to a large extent agreed... a boat can be
relatively light and not be bouncy though. It's a
combination of straight D/L ratio, PPI, reserve bouyancy,
CG, and weight distribution.

It may be that this very same bouncy uncomfortable boat
would change it's motion noticably if about 2 tons of
cruising were added, and the weight distributed to dampen
the bounciness.


On two other N-Bs with a custom Ron Holland 50 displacing over 40,000
lbs, and in far worse conditions, we had a very comfortable ride. Not
exactly an apples to apples comparison because of the length
difference, but two very valid data points nevertheless.


It's possible that the D/L ratios of the two boats were not
that different. Size alone makes a big difference...
aircraft carriers give an extremely smooth ride.


It's one thing to go out for a couple of days on a light weight boat
and bash around a race course, but an entirely different proposition
to take off for 6 months or more of serious liveaboard cruising.


As you pointed out, it wouldn't be a light weight boat then

Fresh Breezes- Doug King