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Technical Manual

Overdeck Controls

by Don Andrews

Only the British OK fleet has developed underdeck control systems to the virtual exclusion on recent boats of overdeck controls. Both the North Europeans and the Antipodeans have retained, and imaginatively developed, overdeck systems. Both approaches have something to be said for them. Apart from the neat and tidy deckline, underdeck controls, if the lines are led through the mast ring or through a semi-circular slot in the deck step, permit the mast and boom to rotate freely, to the 90 degree position and beyond.

Advocates of the overdeck approach point to the greater simplicity of hull construction, as no tubes are required through the station 2 and station 3 bulkheads. They point to the ease of diagnosing and correcting problems, and to the reduction in friction, since it is possible to reduce the number of angles through which the lines need to turn. They make no claim for a 'clean' deck, and prefer the functional appearance of a dinghy which has all the working parts on show.
Overdeck controls, though, do have to be well planned and well executed if they are all going to operate smoothly. The major problem is getting them all to work when the boom is out to the 90 degree position, or when the boom is hardened down on the beat. The latest continental systems, and no doubt others, achieve this.

The boat illustrated was built by Kurt Hein of Hamburg and is owned by one of the Danish OK fleet. There are four sail controls, inhaul, outhaul, kicker, and cunningham. The inhaul and cunningham are single purchase, with the lines crossed over from one side to the other, presumably to reduce the chance of lines and blocks snagging each other.

The 'kicker is the now common 'McIntyre' lever with multiple blocks and a wire strop around the front of the mast. The outhaul block can be seen emerging from the underside of the boom, and will probably end up with the standard 4:1 purchase.

There is no attempt whatever to keep the lines in, or along, the boom. Only the inhaul has a turning block on the mast. The rest go direct to their blocks all mounted on individual short wire strops attached to the deck just forward of the mast, and then directly to deck mounted cleats above the station 1 bulkhead.

All blocks are substantial ball bearing blocks, with no attempt to use mini or micro versions. Clearly, the bigger the bearing surface on the sheave that a line under tension can run on, the less likely is a build up of friction between the line and the side of the block. The lines are of 6mm diameter. This means that they are confortable to the hand, and give the high quality ball bearing cleats something substantial to grip on. If the hull is down to weight, there is no advantage in using light lines or light chandlery, as both can be included in the hull weight.

So, for a successful overdeck system, the basic rules are:

  1. turning blocks well forward of the mast
  2. substantial blocks, cleats, and lines
  3. blocks mounted on strops so that they can move easily
  4. a minimum of angles for the lines to turn through


Additional Illustrations

Don Andrews supplied some pictures of his OK GBR2064 to better illustrate some of the control systems :