Semi Automatic Leeboards  
By John Tompkins - Leicestershire, UK

Canoe sailors often deride sails like the Lateen or the Chinese Junk for having one tack less efficient than the other but they are quite happy to sail with the leeboard on one side only – creating far greater efficiency losses.

The Niblett Semi-Automatic Leeboard system is designed to make tacking easier and reduce leeway when compared to the throw-over type, while retaining the efficiency of always having the leeboard on the lee side rather than bolted permanently to one side of the boat. Although this was designed with a canoe in mind it would work just as well on a Dory or Dinghy etc. and the shape of the foil does not affect its operation.

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Figure 1 -

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The Origins of the Niblett Semi-Automatic Leeboard System

Named after John Niblett who gave us the original idea and his son Roy Niblett who built the original prototypes for his sailing canoes Zahir and Elfwyn. Roy used two stainless steel hinges per side which, when we made my version, we decided was over specified and I have used one hinge per side which has proven to work just as well.

The originals were all mounted on thwarts, which has an advantage - if you don’t want to modify your boat you can lash or clamp it on - but my next move was to remove the thwart and bolt directly to the gunwales. This lightened the system, making it look prettier and also facilitated sleeping aboard (the fewer thwarts you have across the sleeping area the better).

How the Semi Automatic System Works

For the purposes of easier representation I will describe the version with the thwart (its easier to draw a thwart than a canoe). Looking at Fig 1 (not to scale) you will see that there are two leeboards, one each side (obviously). These are attached – by pivot bolts - to cheeks which are hinged off the thwart and connected together by the interlock. The interlock is a doubled length of 8mm pre-stretched rope. We did considered using a length of wood or tube, but then it would be impossible to lift both boards at the same time for running or landing in shallow water.

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On the water; sailing with both boards on deck and the wind anywhere on the beam, swing the leeside board out until it is at right angles to the hull. The weight of the board will cause it to drop until the tip is in the water and the boat will make leeway approximately the length of the board. As it does this the board will go deeper and come to rest when it reaches the limit of the interlock. If the interlock length is set correctly the board will be about 4 degrees out from touching the hull. (As shown in Fig 1).

To tack: Before you get to the turn swing the windward board out at right angles to the hull, leave the leeward board where it is. Make the tack and as the wind comes onto the other side of the sail you will notice the board - that is now on the lee side – drop into the water and as before come to rest against the limit of the interlock. With the lee side board down the interlock lifts the board on the windward side and because the boards are on pivot bolts the windward board can then be pivoted forward onto the deck (see fig 2).

This system doesn’t save the effort of manipulating the boards but it saves you having to do it when you are occupied with tacking.

How to Make Them


  • 2 – Stainless steel hinges
  • 1 – Thwart the same width or wider than the hinges (if you are using a thwart)
  • 2 – Cheeks the same width or wider than the hinges
  • 2 – Leeboards
  • 1 – length of 8mm (or greater) pre-stretched rope – measurement dependent on boat width
  • 2 – Pivot bolts (coach bolts) stainless
  • 2 – deck eyes
  • 16 – c/s bolts stainless

Cheek, thwart and hinge

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First you need to decide where you are going to fit the leeboards. If you haven't yet positioned your mast then the best place for the leeboards on a canoe are halfway along the length (or at the widest point) – the mast (or masts) are then fitted to suit the leeboards rather than the other way round. The reason for this is to reduce drag caused by water trapped between hull and leeboard and the steering effect of the leeboard following the line of the hull. On a dinghy or a canoe with mast already in position fit the leeboards in relation to the centre of effort of the sail.

Make a thwart to sit on top of the gunwales, the length should be the maximum width of the hull (including outwales). Attach a stainless steel hinge to each end – so that it can stand at right angles to the thwart or fold back inboard as shown (see fig 4)

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The thwart can be either bolted (fig 4), clamped (fig 5) or lashed to your canoe. My first one was bolted through the centre thwart. By simply drilling two holes through the leeboard thwart and two corresponding holes through the centre thwart – two 10mm bolts were then pushed through and wing nuts tightened. (If you choose not to use a thwart – as I now have – make sure your hull is strong enough to stand the strain of the loading.)

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The cheeks should be made of 20mm plywood, be the same width as the thwart and approximately 20cm tall, the cheek hinge holes and the thwart hinge holes must be counter-bored deep enough so that the nuts sit below the surface on the opposite side of the cheek and thwart from the hinge.(fig 6). Use the Countersunk bolts to attach the cheeks and the thwart to the hinges

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Using coach bolt with head on the inside attach leeboard to cheek. Tighten wing nut on the outside to increase friction on the board.

Repeat at other side and attach deck eyes above the pivot bolts.

Tie the doubled length of pre-stretched rope between the deck eyes and set it so that when one board is up the length of the rope tops the other board about 4 degrees before it would be upright.

Attach to boat using your chosen method and you are ready to sail

click to enlarge cheeks with interlock line fitted
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Leeboards fitted with one in reet position

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