Designing a boomed staysail

When a boat is made of wood, it is that much easier to make modifications. You may be inspired or you may be misguided, but you can set about it with a drill in ways that would be reckless in glass fibre. Having committed to installing a gaff rig on Lady Christina, I somehow got it into my head that a self-tacking staysail would be just the thing. I saw a picture of an example on the 78ft sailing ketch ‘Vigilance’. It looked promising. I put the drill on charge.

Classic Marine made up a 1/2” diameter stainless steel horse to span the cabin roof in front of the mast. This was straight, with welded stops, and with threaded ends to pass down through the deck. John Leather recommends that a horse should be carried outboard as far as possible, but I bottled out- I didn’t fancy drilling through the structural beams around the cabin edge. So, for better or worse, this horse is quite short and it passes through the ply decking (and plywood pads to spread the load). I used a snatch block, rather than a plain shackle, to act as a traveller.

The self-tacking method is only an option when the sail(s) ahead of the mast are considerably smaller than the mainsail and do not overlap the mast- usual in a gaff or sprit rig. There are pretty exacting dimensions for the staysail, particularly for the foot and leech, so that the clew is positioned correctly near the horse. The clew attachment to the traveller needs to assume the correct angle to tension both the foot and the leech. In addition, if the horse does not span the whole deck, the fuller the sail is made (on a reach or run) the longer the clew attachment needs to be; the sail can then lift and lose its shape.

But the clew does not have to be attached directly to the traveller and horse. It can be attached to a staysail boom. There are three types of boom: a ‘club’, which is laced to the aft end of the sail foot, and which offers a choice of sheet attachment positions (and hence sheet angles); a boom pivoting on the forestay just above the stem and reaching the full length of the foot; and a shorter boom, pivoting at a point aft of the stem. This latter design is discussed briefly by Tom Cunliffe in his book ‘Hand, Reef and Steer’. I decided to give this one a try, and pivoted a shorter boom (fashioned from a piece of cedar, with gooseneck and mastband hardware from Classic Marine) from a drop-nosed pin passing through a couple of eye-bolts secured through the Samson post.

In this arrangement, the further the boom is sheeted out, the fuller the sail becomes. There is just one sheet, of course, and it is routed back to the cockpit by whatever ingenious route provides the least tripping hazard on the deck. Currently, ours starts its journey at the mastband on the end of the boom, passes down to the traveller, through a single block and back up to another single block just forward of the mastband. Then is runs forward the full length of the boom (so that its length is not affected by the boom angle). Turning for home, it runs along the length of the cabin roof, through bullseye fairleads, in parallel with the jib furling line.

Our sail itself was picked from Jeckell’s ‘Sails in Stock’ ( Richie Dugdale sold me a 63 sq ft white sail listed as ‘barely used’. It should have been priced at £433 new. It was new, but they had cut it already and on their hands; they finished it to my specs for £192. The Jeckells list is always worth a look for the less well-heeled or experimentally minded!

The angle of the clew attachment to the boom is dependent on the height of the tack along the forestay, since this changes the fore-aft position of the sail.

In action, the boomed staysail tacks very efficiently and does not leave the boat in irons. One added bonus is that, on a run, the staysail will goose-wing itself when it finds itself in the lee of the mainsail. This unexpected behaviour is not only useful, but it is also a handy warning of the danger of a gybe.

3rd November 2020- I finally found a picture of the sail set (see the comments section).

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