High Performance/Low Cost Sails for
Small Sailboats
JIB and
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Jibs and
genoas are two types of headsails set before the main that have dual functions.
First, these sails can help the boat turn quickly; and second they can funnel
the wind over the main sail to help improve its performance. Both sails are
usually set with the luff on a forestay of stainless cable or non-stretch line
attached to the mast and to the bow or an extension over the bow called a
bowsprit. Today, these headsails are often wound up electronically on a tube
over the forestay, or roller reefed. The jib is the smaller of these two
triangular sails and is distinguished from the genoa by its smaller size,
higher clew, and by having most of its leech before the mast. The genoa, on the
other hand, often was a “deck sweeper” with its foot near or on the deck and
with most of its leech extending well past the main mast.
One of the
problems all headsails have is called luff sag, which results from the way the
sail is mounted on the forestay. These cables or lines, even when highly
tensioned, often have some sag toward the middle that tends to push the draft
of the sail aft. The problem is compounded with heavier winds and fuller cut
sails such as genoas or reachers. So as wind increased, for example, smaller
headsails with shorter luffs and higher clews were often hoisted until finally
the very small, but stout, storm sail was put up.
In years past nearly all headsails
were cut with an S curve in the luff to help compensate for the sag of the
forestay. The following measurements relate to a fairly large dinghy jib. Near
the head, an 18' luff was hollowed by up to 3/4" for the top 1/3 of the
luff. The bottom 2/3's was rounded by up to 1 1/2" with the greatest
rounding at the point where a line drawn bisecting the clew would intersect the
luff. These figures assume a highly tensioned luff wire. The rounding in the
bottom 2/3's of the luff should be decreased for stronger winds. For headsails
used primarily in heavy winds, sometimes the entire luff was hollowed.
The 10' foot of this sail had about 6" of rounding 1/3 of the way back
from the tack. The 18' leech had about 6" of hollow half way up the leech.
Again, as the wind increased, more hollow was needed. Sometimes, battens were
included in the leech, even with leech hollow, so that there would be a flatter
runoff at the aft edge of the sail. It was important that the sheet bisected
the angle of the clew and that the leech had no curl when beating. Often a leech
line was included so that the tension in the leech could be released or
adjusted depending upon whether the sail was set for beating or reaching and
running. Curl in the leech when beating was dangerous because it indicated the
draft had moved aft, increased the heeling moment, and sometimes unexpectedly
backwinding the main.
The jib can be rigged in various ways. The most common rigging on racing
dinghies is to have two lines called fairleads attached to the clew with no
boom on the foot. The fairleads are fed to opposite sides of the mast where the
crew controls the active line and the second line is cleated with plenty of
slack. As the boat tacks, the cleated line is released and becomes the active
line while the other line is cleated. It is important that the fairleads are
angled down to blocks on the deck so that they follow a line bisecting the clew
angle. A jib can also be made self-tacking by attaching a boom to the foot then
running a strong bungee cord to the deck and to a point on the boom about 3/4’s
back from the forward end. Sometimes the deck can also have a track that allows
the deck end of the cord to move from side to side across the deck.
When making
a jib from polytarp, use a 5.5 oz. or heavier material and reinforce the clew
heavily. It’s a good idea to use a #3 or larger spurred grommet with a rolled
rim at the corners of this sail since a jib is subject to extreme stresses
particularly when tacking. Novice crew members are sometimes surprised to have
the fairlead ripped from their hands when the boat tacks in a stiff breeze.
It’s a good idea to wear gloves if you are handling the jib or genoa fairleads
in strong winds.
Lay out the
sail on a tarp and shape it as shown in the diagram above. If you will be
attaching this sail to a low stretch line, you may need to increase the hollow
and rounding in the luff. Add about 1” to the dimensions of the luff and leech
and about ½” to the foot to compensate for the foreshortening that occurs when
you tape and sew up your sail. Once you have your sail laid out on the tarp,
follow the generic instructions
to complete your jib. Below are a couple of different ways to tape, reinforce,
and accent the corners of your jib.
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PolySail International
Email polysail@polysail.com or call Dave Gray at 317
385-3444
PolySails–Sold on the Web since
1996. Customers in all 50 states and around the globe.
This page
updated on 1/11/2010
Copyright
1/11/2010