DSK wrote:
Merry Christmas to all!
wrote:
SailCare.com says they replace the "resin" that is on new sails and
they restitch whatever needs it. I want to know how to evaluate the
shape of a sail so I can decide the most effective way to restitch to
renew the shape.
2 ways sails are shaped, luff round & broadseaming. Luff round is the
easiest to change, this is just a big curve built into the front of the
sail so that when it is hoisted on a (relatively) straight mast, there
is extra material in the middle. Broadseaming is cutting the horizontal
edges of the panels in a curve so that the sail will form a 3-D curve
when the edges are sewn (or glued) together.
.... I agree, older material is probably not as strong as
newer but many sails arre very lightly used.
Well, between flogging & UV even a "lightly used" sail can be shot.
.... Quite frankly, I simply
do not believe what sailmakers say about sails aging just by sitting on
a shelf.
Well, I'm not a sailmaker, and I told you (or tried to). Believe what
you want, it happens to be true.
... I also think that a considerable part of the stretch of an
older sail is in the stitching and not in th ematerial itself.
Certainly the stitching can loosen and give the sail a baggier shape,
but the stitches will not stretch. It's strictly a one-way process!
... Even
sail material that has stretched probably has not gone beyond the yield
point of the material so unless it is actually worn or degraded by UV,
I think that most of any loss of strength is in the stitching.
So, how does one evaluate the shape of a sail?
A couple of ways. One is to lay the sail out in a loft or yard, and
fasten the tack, foot, & clew at about waist height with a line on each
that can be tightened. Tension the luff first, then lightly haul the
foot up. Another is to watch very carefully what the sail looks like
when sailing. Looking up from the midpoint of the foot, you should see a
nice classic airfoil shape, and you should be able to see definite &
consistent change when the "sail shape adjustments" are pulled.
A blown-out sail will have one or more-
-max draft too far aft (IMHO 55%+ is shot)
-draft too deep even when sail is adjusted for max flatness
-Lack of response to shape adjustment
-Lack or elasticity, ie sail does not return to shape consistently when
shape adjustment eased
-hard spots in camber, particularly at inner batten ends (I have seen
many sails that were described by the owner as "old but still got a lot
of life" with upper sections forming a V)
By reducing luff round, camber can be reduced but it also shifts aft. If
a sail is going to be restitched, the broadseams can be adjusted but
most sailmakers dislike doing this. BTW it's not just the stitching, the
cloth thru which the stitches are sewn also lose strength. I have
personally used sails that have been restitched 4 times, when I took
them in for the 5th time the sailmaker said "Y'know Doug, there's not
enough cloth here left to sew" and showed me the close network of holes
from old stitching.
Blown-out sails will affect the boat badly-
-inconsistent helm, and excessive weather helm
-excessive heeling
-little or no acceleration in gusts
-poor windward performance, especially pointing
-slower
Old sails with weakened cloth & stitching are also at much higher risk
of shredding under load. I've had this happen a number of times, too.
It's a bummer.
K. Smith wrote:
The modern sail cloth is pretty strong & it will last years & years,
Actually, if you expose it to UV all day every day, and put it under
strain 24/7 it will last surprisingly short time.
.... It's just the boy racers imagining they'll go lots faster with
new ones
Spoken like a "sailor" who as 1- never won a race and never will, and 2-
has never sailed a tuned-up boat with good sails.
As to the shape this is not usually a problem
Wrong
If you want to check it just lay it flat on a floor
wrong
How the heck are you going to examine a 3 dimensional shape laying it
flat on a floor? Oh wait, you don't think shape is ever a problem...
Proving once again that usenet is a great source of horribly wrong info.
Fresh Breezes- Doug King
Sorry Doug like most "customers" you have bought the sail maker BS,
most sails of the type we're talking about here, are cut lying staked
"flat" on the loft floor. (save the super new high tech materials &
laminates but they effectively mould the shape into them over a jig)
It's easy enough to confirm?? just lay the sail flat on a floor; or
measure the panels you'll find most "normal" sails have parallel panels.
The shape is induced when a curved edge (the luff or combination of
luff & foot) are stretched to varying degrees, in an essentially
straight line. (often along a forestay, mast, boom etc.)
K