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- Matilda 16
- Matilda 20
- Matilda 23
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Weather Helm (& How To
Looking back through the forum posts I see a lot of posts on this topic, and
some confusion as to what the different factors are that can cause or cure it.
My two cents worth:
The balance of a
sailboat is mainly dependent on the relationship between CE (Centre of
Effort) which is the centre of the sail area and the CLP (Centre of Lateral
Plane) which is the centre of the underwater area of the hull when viewed
from the side.
If CE is too far
ahead of CLP, you will experience “lee helm” – a dangerous condition
that will allow the boat to sail away from you if you fall overboard, and
can also make the boat more difficult to bring about.
Too far back and you
get excessive “weather helm”.
Although it might
seem that static CE should be directly above CLP to produce a balanced helm,
Ted Brewer, author of the leading yacht design primer “Understanding Boat
Design” (and, coincidentally, the designer of the Matilda 23), explains
that CE should be slightly forward of CLP. This is because as the angle of
heel increases in strong winds, the CE moves to leeward while the CLP stays
approximately the same. This creates a luffing force that turns the boat to
windward, and this is reduced by having CE slightly ahead of CLP.
Apparent weather helm
also increases on most sailboats when the wind increases because all of the
control forces (sail sheeting pressures, helm weight, etc) are greater. In
many cases, the effectiveness of the rudder decreases as the boat heels,
both because the rudder blade area in the water may reduce and it has less
direct steering effect when operating at 40 degrees to the water rather
than, say, 20 degrees. Reducing sail to limit the angle of heel will
minimize this effect, as well as making sailing in heavy weather more
comfortable, greatly reducing the loads on the boat and equipment and
increasing the safety margin to cope with stronger gusts.
Moving the CE forward
to reduce weather helm can be achieved by raking the mast forward when
setting up the rig, using a larger foresail, reefing the main early if it is
windy, or, more drastic, moving the mast forward and/or fitting a bowsprit.
Moving the CLP aft
would also reduce weather helm, but involves major structural changes such
as repositioning the keel! In one post, someone enquired whether the Matilda
20 design originally had a keel that rose vertically rather than with the 10
degree rake. I don’t believe it did, and based on the CLP/CE factors
above, this would have the effect of moving the CLP forward thus INCREASING
Finally, as far as
the Matilda 20 is concerned, there have been some posts about the need to
have a mechanism to hold down the rudder blade, and this is essential.
Without this, the centre of effort of the rudder moves way back from the
pivot point. When hanging straight down, the centre of effort is probably
about 9 inches behind the pivot, and if you hold the tiller 2ft 3in (27
inches) forward of the pivot point, you are getting 3:1 leverage. If the
rudder swings up so that it trails at 45 degrees, I wouldn’t be surprised
if the centre of effort moves back nearly to the 27 inch point so that close
to 1:1 and no leverage would result (right when the effort needed is at its
greatest). No wonder it feels so heavy! The effectiveness of the rudder has
also been reduced since the blade area actually in the water is
significantly smaller AND it is lifted into the turbulent wake instead of
remaining in the cleaner water further below the surface.
Enough of the theory! If
you are suffering weather helm my recommendations would be:
Experiment with raking the mast
forward a little from where you normally have it, but don’t go too extreme with this, since forward rake reduces
windward pointing ability, and aft rake improves it.
If your boat has more
than one mast mounting position (and not all Matilda 20s do) use the forward
most mounting position - Chris Holderness
reports good results with his mast in the most forward slot and with about 4" aft rake at
Use, say, a 130%
genoa rather than a 100% jib, but NOT where this will make the amount of
sail too great for the prevailing conditions!
Reduce sail early in strong winds - although this FEELS less exciting, you probably
won’t go much/any slower, especially as a rudder used to counteract
weather helm tends to act like a brake. This advice applies to just about
any sailboat, not specifically to Matilda 20s.
Make sure the rudder
blade is held down in the position the designer intended - again, Chris
reports that on the same day, same sail trim, same heading, he has observed
that the difference in tiller pressure at 6 kts with/without downhaul is from a few ounces to well over 20 pounds!
Last updated 26 February, 2007 - © Matilda Owners Association.