Balance is not just a matter of standing
on one leg!
I had a call last night from a customer who had not long
before launched a small gaff yawl to one of my designs. While
in comparison to the old deep keeled classics that one would
normally associate with that rig the boat was a light open
dinghy with underwater lines that allow the boat to plane
freely in the right conditions. A rig large enough to give
the boat a performance that would have been unthinkable, and
high form stability instead of a big slug of lead hung underneath
the boat did have an important characteristic in common with
the old gaffers.
On the modern cruising yawl the rig is well spread out, its
jib is way out the front on a bowsprit, and the mizzen mast
is about 3inches forward of the transom with the sail tagging
along behind the boat as she sails. In fact on a boat length
of 17 and a bit feet we have a total rig length of 23 feet!
But unlike the old cruiser with its full length keel the new
boat has just enough skeg under her to promote straight tracking,
and a centerboard that is about a foot and a half from the
leading to the trailing edge of the foil, and the rudder is
of course not hung on a skeg so there is very little lateral
plane aft or forward of the centerboard.
So we have a large and long rig blowing the boat sideways,
balanced on a short and concentrated lateral plane that provides
the resistance to that force. It is necessary to keep this
boat in balance and that can be an advantage if used with
skill, and cause all sorts of problems if not. There is an
opportunity for a savvy skipper to trim this kind of boat
to keep her balanced through a wide range of conditions, and
to do this much more effectively than many other and older
boats can.
My customers concern was that when he went sailing in really
rough weather for the first time his beautifully balanced
new boat had developed enough weather helm to make control
quite difficult. While the weather he was out in was bad enough
to keep anyone without a really compelling reason and a large
seaworthy boat snug ashore, and the area was notorious for
fast tidal flows and forcing through narrow channels against
the winds he did manage pretty well and by the sounds of it
he was not at risk in spite of a real lack of experience in
handling open boats in those conditions.
But how to handle that boat in those conditions?
First of all, what was happening there.
One, the boat was sailing with the jib rolled up leaving
the center of thrust from the sails a lot further aft than
optimum. Two, as a sailing boats speed increases the center
of effort of the sails needs to lead the center of lateral
plane ( the underwater point around which the boat will pivot
if pushed sideways) by more and more.
My mans problems came when the boat was getting close to
surfing, and with the jib furled and the centerboard right
down in its most forward position the sails effort was too
far aft, and the center of lateral plane too far forward relative
to the sails so the rudder was carrying a lot of weight and
the boat was relying on that rudder to stop the stern being
forced sideways. Its not designed to do that and under those
conditions is easily overpowered resulting in an uncontrolled
and often violent turn into the
wind. A "broach". Dangerous!
It's a matter of balance. To adjust the weight of the helm
or to correct a tendency to round up into the wind it helps
to visualize a seesaw with a moveable pivot. The speed of
the boat, the trim of the boat and the position of the centerboard
(as an adjustable keel, if fitted) can alter the position
of the pivot. To adjust the weight on the ends of the seesaw,
one must alter the center of the force that the sails are
generating in relation to the pivot point. Reefing from the
wrong end moves the center of the sails effort aft putting
more weight aft and overpowering the rudder causing excess
weather helm, moving the effective center of lateral plane
(the seesaws pivot) forward does the same thing and makes
the seesaw unbalanced. An effort needs to be made to move
the pivot aft, and the sails drive forward to get that balance
back.
In future that skipper will be shortening sail from the
other end, mizzen down first, then reef the main, and only
then furl the jib. Other ways of helping to restore balance
is to swing the centerboard aft by lifting the board a little,
to trim the boat stern down with crew weight and to ease or
trim sails to spill wind from the after part of the rig.
Remember that an increase in speed moves the ideal position
of the pivot aft, that the drive of sails can do the same
with an increase in wind strength and that the ideal balance
point of the rig will move forward as boat speed and wind
speed increase.
Adjust the sails and the boats trim to suit that change
and your boat will be a lot easier to steer.
Keep that seesaw balanced.
