Blackmagick Sails
Stiffening the Rig
Right, so I have this new super light weight racing spar for my one metre, but it
wants to act like the snake! What can I do with it to make it stand up and not bend
all over the place when I put my sails on?
This is a question I've been asked more than once of late, the answer is very
simple, PRE-BEND. This is a must if you have a flexable mast and want good tension
on your forestay to prevent the jib from becoming to full in a breeze, and to stop the
mast from bending back to far and turning your mainsail inside out. In other words
to much bend for the built-in sail shape of your mainsail. Pre-bend is not so hard to
do, and only if you are very rough with your mast will you do it any harm in
attempting to pre-bend it. However the amount of bend you attempt to put in your
mast mostly will depend on if you have a very flat or very full maisail to begin with.
Generally with a full main you can get away with a little more aft bend in your
mast, indeed some people like quite a lot of aft curve in the mast as this helps set
up an elliptical shape in the rig. Theory would have it that an ellipical shape is more
efficient moving through the air and water, most aircraft wings are semi-elliptical.
Unfortunatly unless you have a swing rig like some marbleheads have, to much
curve in your mast can lead to other problems when you go to ease the sails out for
a reach or run!
How do I do Pre-Bend?
It might sound a little gruesome if you have just
payed out a lot of money for a piece of lightweight
alloy tube, if I suggest to you pick it up and bend it
over your knee! But that is basically what you will
have to do to pre-bent it. It really will have to be
trial and error with you if this is the first time you
have done this, as I cannot really tell you how much
effort to put into this bending of the mast over the
internet! Best under do it I think to start with.
What you are attempting to do here is to put a
permanent bend in your mast in a forward direction,
so you must be sure you have the fore and aft line
correct on your mast before you start this
operation.  You will not want much bend down low,
maybe none, start about halfway up and bend it just
ever so slightly from mid point right to the very top
first time around. If you have got it right you will
have maybe two or three inches of forward bend in
it and it will look cazy but this is what you will need.
The more you bend it forward the more tension you
will be placing on the rig when you pull it straight
with the backstay later. It is a case of balancing the
tension you want without over doing it, as I said
before, maybe you still want a little aft bend when
the mast is on the boat, ok so don't put so much
pre-bend in the mast. Trial and error is the only
way, you may have to ajust the bend down low a
little more to suit the sail, maybe more bend up
high, or less, it will take a little time to get it right
but it is so important to have the rig or mast match
the sail, it is worth the time! As you get a little
better and more confident you can do a little
tweaking of the mast bend while it is on the boat,
but be careful of the sail and what you might be
doing to the hull! Let everything go slack on the
boat if you are going to try it to attempt this. More
on prebend next page.......
This 'Viper' Marblehead shows an elliptical
rig taken to the extreme, you need a swing
rig to make this much mast curve work for