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