Glenn Ashmore wrote
Matt/Meribeth Pedersen wrote:
In passagemaking, I don't see the moderate displacement boats
burning up the miles significantly faster than the heavy displacement ones.
I do think that you need to have adequate sail area to make a decent
passage, but when you're cruising, trying to keep the boat speed up over
about 1.2 sqrt WL is just too much trouble. As long as you are
powered up, then waterline length is going to govern.
Half a knot to a knot means a lot on a passage. That is 12 to 24 miles a
day which adds up pretty nicely on a 5 or 6 day run. Most of the time
you are not going to be driving at hull speed so a boat that can easily
be driven in light winds has a definite advantage. OTOH, the quicker
motion of the medium displacement boat can get a bit tiring.

I have spent the last three years cruising the Pacific in my 42 foot
medium displacement catamaran and I have observed the cruising fleet
closly. A speed to length ratio of 1.2 is very fast for passages
outside of the trades (eg. the islands to New Zealand). Most couples
sail and motor their boats to an S/L of about 0.8 over time, but many
are slower and few are much faster. Heavier boats are typically
motored more often and at higher speeds than lighter ones, so the
daily runs are similar. Some couples who don't like sailing as such
and aren't very advanced sailors love long term cruising and some very
good sailors don't. Most cruising is done at anchor anyway. It's
hard to know what kind of boat will meet your needs best before you
get into the life style, and, given all the boat modification that I
see in New Zealand, I'd guess that most folks don't guess exactly
right. I think a cruising boat should at the very least have a dry,
warm place to stand watch and the ability to make ground to weather in
20-25 knots of wind without beating the crew up very much. However,
given the right attitude and a bit of good luck, most any boat will
get you where you want to go.

BTW, motion in a seaway is largely a function of a small waterplane
area to displacment. Multihulls, with their narrow hulls, can make
comfortable sea boats even at light displacements.

Cheers,
-- Tom.

What is the 'speed to length ratio"? Are you referring to square root of the
waterline?

Paul
www.jcruiser.org
"Tom Webb" wrote in message
om...
Glenn Ashmore wrote
Matt/Meribeth Pedersen wrote:
In passagemaking, I don't see the moderate displacement boats
burning up the miles significantly faster than the heavy displacement
ones.
I do think that you need to have adequate sail area to make a decent
passage, but when you're cruising, trying to keep the boat speed up
over
about 1.2 sqrt WL is just too much trouble. As long as you are
powered up, then waterline length is going to govern.
Half a knot to a knot means a lot on a passage. That is 12 to 24 miles a
day which adds up pretty nicely on a 5 or 6 day run. Most of the time
you are not going to be driving at hull speed so a boat that can easily
be driven in light winds has a definite advantage. OTOH, the quicker
motion of the medium displacement boat can get a bit tiring.

I have spent the last three years cruising the Pacific in my 42 foot
medium displacement catamaran and I have observed the cruising fleet
closly. A speed to length ratio of 1.2 is very fast for passages
outside of the trades (eg. the islands to New Zealand). Most couples
sail and motor their boats to an S/L of about 0.8 over time, but many
are slower and few are much faster. Heavier boats are typically
motored more often and at higher speeds than lighter ones, so the
daily runs are similar. Some couples who don't like sailing as such
and aren't very advanced sailors love long term cruising and some very
good sailors don't. Most cruising is done at anchor anyway. It's
hard to know what kind of boat will meet your needs best before you
get into the life style, and, given all the boat modification that I
see in New Zealand, I'd guess that most folks don't guess exactly
right. I think a cruising boat should at the very least have a dry,
warm place to stand watch and the ability to make ground to weather in
20-25 knots of wind without beating the crew up very much. However,
given the right attitude and a bit of good luck, most any boat will
get you where you want to go.

BTW, motion in a seaway is largely a function of a small waterplane
area to displacment. Multihulls, with their narrow hulls, can make
comfortable sea boats even at light displacements.

Cheers,
-- Tom.

"Paul L" wrote in message ...
What is the 'speed to length ratio"? Are you referring to square root of the
waterline?

Paul


Yes, the speed to length ratio is the speed of the boat divided by the
square root of it's sailing length. The units are feet and knots.
The ratio gives a feel for how fast a boat is when corrected for
length. A speed to length ratio of 1.34 is the speed of the wave that
has a length equal to the sailing length of the boat and is called the
"hull speed". Hull speed is a topic that has been discussed to death
on this board in the past, but you could google it if you really want
to know. Anyway, the speed/length ratio comes out in weird units
(feet per radical knots) so it has been replaced by the Froude number
in most new work...

Cheers,

-- Tom