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Weather Helm (& How To Cure It)

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 weather helm

  • 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 the top. 

  • 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!

Keith Denham

Last updated  26 February, 2007 - © Matilda Owners Association.