Rudder design

It’s obvious that we use the rudder when we wish to change the direction of travel. However, the interplay between the centre of effort of the sails and the centre of lateral resistance of the hull give the boat a tendency to turn towards or away from the wind whether we wish it or not; therefore the rudder spends most of its time keeping a steady course and preventing the boat from turning.

F21 Seamew, showing the foot of the keel without a 3rd pintle

The centre of effort, or ‘CE’, of the sails (the focus of the wind’s effort on the sails) is designed to be in front of the centre of lateral resistance, or ‘CLR’, of the hull (the focus of the hull’s efforts not to be pushed sideways). As the boat heels in the wind, the shape of the hull on the lee side acts like a carving ski and tries to turn the boat towards the wind. This compensates for the action of the wind at the CE to turn the boat away from the wind. If these forces balance, the boat will steer itself in a straight line and is said to have ‘neutral helm’.



F24 Lady Christina, showing 3 pintles and a sacrificial anode on the lower strap

The desirability of neutral helm depends on your likelihood of falling overboard. If, when you don’t touch the tiller, the boat points up into the wind (called ‘weather helm’) then the un-manned boat will, in theory, round up into the wind and stop, allowing you (again in theory) to swim after it and climb back in. However, if the rudder needs to compensate for the imbalance of forces to overcome weather helm, then it is also acting as a brake and will slow the boat. The fastest boat is one which doesn’t require any rudder action in a straight line. (Lee helm, an imbalance that causes the boat to turn away from the wind, is always undesirable, as it will slow the boat when you steer to overcome it, and also cause the boat to run away from you if you should fall in.)






A boat will not have neutral helm in every sailing condition without corresponding sail adjustments. It may be beautifully balanced when close-hauled, but have too much sail behind the CLR on a run, causing the boat to want to turn back to where it came from. The worst consequence of having this form of excessive weather helm is that the boat turns itself across the wind and tips over, known as broaching. Depending on the type and design of the boat, this can result in a knock-down, and if the boom reaches into the the water then the boat will not be able to respond to leave this attitude. The solution to this is not to have a larger rudder but to remove the tendency by moving sail area forward.

F24 Martha IV showing strengthening straps added to overcome vertical split

The Finesse rudder is a hung by pintles and gudgeons off the transom and the aft end of the keel. IT is an unbalanced design (all the rudder surface is aft of the line of the pivots) and appears to have been made from a single, solid piece of wood. This can ultimately develop vertical splits. Although it is attractively shaped to accommodate the propeller, there is no dynamic tapering to the sides.

F24 Martha IV : Rudder maintenance at the top end, showing the cheeks between which the tiller will pass.

F21 Drifter with re-designed rudder and protection for the leading foot edge

The Finesse 21 often has two pintles, but the Finesse 24 has a more robust system of three.

By the time that sail 71 (Sea Pie) and sail 72 (Awel O Wynt)  were made, the F21 seems to have acquired a third pintle, placed on the keel (see picture below; thanks to Chris Brown for this information).

The design appears to have changed somewhat during the production of the boat, but all have cheeks added to the upper part which accommodate the tiller. It is often sufficient for the tiller to simply be tapped firmly into place with a wooden or rawhide mallet, as the tapering of the tiller end creates a positive engagement.

The lowest gudgeon is always submerged and should therefore be protected by a sacrificial anode.


Third pintle, on the keel of Sea Pie (later Finesse 21)

NB This article is not intended to be definitive (but is hopefully mostly correct!) If you have comments and / or corrections, please email me and I will act accordingly. -DM

This article was updated 3rd October 2020 – DM

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