Spritboom Sail Slab Reefing

By Peter Lord - Uppsala, Sweden

I sail an Apple 16 ( with a sprit-boomed mizzen sail of 5.4 sq m (= 58 sq ft) instead of the standard balanced lug sail. I had a tapered bendy fiberglass Zoom 8 dinghy mast, and decided to use a flat-topped sprit-boomed sail with it, because this sail is easily flattened for strong winds by tightening the snotter. I first had it sleeved, but the inability to easily raise and lower it while sailing or reef it led me to change to a track. I bought plastic track used to attach a shade awning to the side of a camping trailer and sewed short (25-40 mm = 1.75 in approx) lengths of the round plastic track to the luff. The track for the awning is a flexible plastic rod about 6 mm in diameter, and it has a woven fiberglass cover that forms a flange along the rod for sewing to the awning.


I sewed the longer bits (40mm) at the top and bottom and on either side of the plastic batten luff inserts for better support.

The reefing methods described for a sprit-boomed sail had disadvantages. The traditional method of using a line run from top to bottom through grommets behind the luff was unappealing because of the turbulence the bunched-up sail would create behind the mast. The method of using loops of rope or webbing at the clew and the leech reef point and shifting the aft end of the sprit up when reefing also was out because I did not want to be pulling down a flapping sail and then pulling inboard the clew and moving the snotter and then brailing up the redundant bottom part of the sail, while the boat was jumping around in the conditions that require reefing. Particularly as the clew of the mizzen is 5 feet behind the transom. So I used a slight modification of the standard method of slab reefing that I use on the mainsail, which I have not found described for a sprit-boomed sail. Slab reefing is fast, can be done without totally lowering the sail, and minimally disturbs the airflow as the bunched sail is parallel to it.

Reefing diagram. Click for larger pdf image.

The diagram (1.) above shows the way the luff and clew reefing lines are attached and run. I first measured a rectangle whose reference points for placement of grommets were: (1), where the reef grommet was to be placed on the leech about 3 feet above the boom to reduce the sail area to about 3 sq m, (2) on a vertical from (1), just above where the boom crossed the clew, (3), horizontal to (1) at the luff, (4), horizontal to (2) at the luff. The luff line is first fastened to the side of the mast through a small stainless saddle and a knot, above grommet (4) at the luff. It then runs down and through this grommet, up and through grommet (3) at the luff, and down to a cleat on the mast at a convenient height. When tightened, it pulls the bottom of the luff up and the top down, keeping the luff tight. The clew line is first hitched to the boom at the grommet (2), runs through it and up to grommet (1) at the leech, down and back and through a small block tied to a short line that is fastened to the end of the boom, and forward to a clamcleat on the boom.

Reefed mizzen

The photos show the luff (2.) and leech lines (3.) and the whole sail (3.) reefed. I use 4 or 5 mm Dyneema line for reefing and other small lines to trim the sails. The last photo (4.) shows the reefed sail in action, with a line through grommets in the middle of the sail and the reefing grommets to brail the loose folds together, which is not strictly necessary. I can easily reef the sail from the cockpit which is necessary because the mizzen sticks so far back over the transom.


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