Rick:
I am confident I can speak for other listers here to thank you for
taking the time to provide such pertinent and informative posts. It
takes time to do what you do and I for one appreciate it. Again, thank you.
Now regarding the cooler full of ice and beer on deck, I'd go sailing
with you any day. One wrong tack can negate any less weight aloft or on
the rail!
Rob Abbott
AZURA
C&C 32 - 84
Halifax, N.S.
On 2013/12/03 5:58 PM, Rick Brass wrote:
Mark;
You are probably close in your surmise that the rail meat is very
close to being directly over the center of mass of the boat when it
reaches 63 degrees of heel. However, there is still a righting moment,
though the moment arm is getting short.
As it heels, the boat rotates around the center of buoyancy, not the
center of mass. The center of buoyancy is above the center of mass
(the closer they are when the mast is vertical, the more tender the
boat. If the center of mass were above the center of buoyancy, the
boat would turn turtle at the slightest provocation.) and the center
of buoyancy moves to leeward as the boat heels because of the form
stability of the hull. In more modern hulls than ours, with relatively
flat bottoms and wide turn of the bilge carried from max beam to well
aft, generate a lot of form stability. Hence the center of buoyancy
moves quite a bit to leeward as the boat heels, while the center of
mass moves some amount to windward. It is the lateral offset between
centers of mass and buoyancy that provide resistance to heeling.
Paul;
I agree with your calculations, except that the length of the moment
arms for the rail meat and the weight aloft need to be adjusted
slightly to account for the leeward movement of the center of
buoyancy. Add a few inches to the righting arm of the rail meat, and
subtract the same number of inches from righting arm of the weight
aloft. So at 20 degrees of heel, the 10 pounds aloft might have the
same effect as 38 or 39 pounds on the rail.
Now I've not looked into purchasing any high tech halyards for my 38.
What I have (7/16 Cajun XLE) is large enough in diameter to have a
good hand and to not creep in the rope clutch. I have a Barient 27
halyard winch to preload luff of the main to 500 pounds or so and take
up the stretch in the line when the wind is strong, and I really don't
want to put much more load than that on the 3/16ths or ΒΌ inch Dacron
cord that reinforces the luff of the main. If I trim the vang and the
traveler right the load on the main from a gust of wind isn't going to
change by all that much to generate more than an inch or two of
additional, transitory stretch in the halyard.
But I have recently purchased floating, high tech spin sheets. They
needed to be about the same diameter as the old sheets in order to
have acceptable hand and work on the winch drums. My floating lines
are way stronger than they need to be, and consequently have no
stretch (which, unfortunately, you kind of want in spin sheets). What
I found is that the high tech, floating line was more than twice as
strong as the old sheets, but only about 4 pounds lighter for 100 feet
of line.
So the saving for my main halyard would be around 2 pounds. If I went
from 7/16ths XLE double braid to 3/8ths Spectra core the strength
doubles, the stretch goes from 12 " (@ 1300 pounds of load) to about
3", the halyard costs about $60 more, and the weight savings is about
3 pounds. The way I sail, I don't see that much value.
In my experience the racers who salivate over decreasing weight aloft
tend to be the same guys who have toothbrushes with the handle cut
short, and who leave the seat cushions, locker covers, power cord, and
all the beer and ice at the dock in order to save weight. Not that I
think they are wrong, it's just that we have a different perspective
than I do.
Maybe I should think about keeping a cooler full of ice and beer on
deck, so it can be moved to the high side of the boat to offset the
extra weight of halyards aloft. Now there's an idea that should make
the crew happy.
Rick Brass
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