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Technical Manual

Outhaul Control

by John Derbyshire

Now that sails have gone round from the old full foot and flat headed, open leeched type to the current flat footed, full headed, hooked leeched type of today, it is increasingly apparent that the 'lash it to the boom and forget it' technique for the clew is just not on anymore and that yet another 'tweak it and see' string must be added to the cats cradle that wends its way to the Americas Cup type of control consul that our station 2 bulkhead has become.

The secret of an outhaul control, as will all other controls, is that it should be positive in action, easy to operate under load, but without having too many yards of rope to pull.

First, if your sail does not have one, fit a nylon slug (HA 158, or similar) at the end of your bolt rope. This slides much more freely in the track and prevents the rope end coming off the sail. Next use ball bearing blocks wherever possible to reduce friction further. The shock cord is important to pull the wire back, overcoming any friction still left in the system. Also useful is more shock cord at the inhaul attachment point (at the tack).'

Now, before fitting the gear, make sure that the end of your boom is not sticking out more than 80mm beyond the INNER edge of your black band, otherwise the measurer may make you saw it all off!!

Right, look at the sketch. A thin wire is secured to one side of the boom end, passes through a block shackled to the cringle of the sail and then through a block on the other side of the boom. The original 'Needle' block is removed and replaced by a new (ball bearing) one on the side instead of the centre of the boom. This needs a retaining loop over the end to prevent the slack wire coming off the sheave. The wire then runs inside the boom, emerging in front of the mainsheet take-off points through a double sheaved fairlead which is suitably modified.

Fixed to the wire at a point such that it will not foul the fairlead, is a length of shock cord which is anchored at the bottom back edge of the boom. The tension in this is made such that the wire is pulled back on release of the rope from the cleat. A hard eye in the end of the wire prevents it from going back up the boom when not tied to the rope which runs forward to the mast and divides by way of a final block to the port and starboard control cleats. This gives a 4 - 1 purchase (two at the clew x two at the final block), enough to give the control we need.



John Derbyshire is now, 1998, the British Olympic sailing coach. He won the British OK National Championship and the German Open Championship, in spite of being relatively light in weight for competitive OK sailing.
His comment about the length of the boom being limited to 80mm beyond the band no longer applies. Many owners use one of the modern fabrics based cords rather than wire these days as it combines strength and minimum stretch with flexibility. But to guard against breakage through chafe, a safety line is often fitted in addition to the control line.