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Technical Manual

Fitting Out An OK

The first thing to do when fitting out your new hull or refurbishing the old one is precisely nothing at all. Well at least nothing as far as the boat is concerned. Start by planning the work. What are the most important jobs? What fittings to use, and where to screw them? How will the controls work? All these questions should be answered before you drill the first hole. It always helps at this stage to have a look at other boats. A visit to an open meeting with your camera and tape measure could provide hints.

As a priority it is vital to consider the basic safety and integrity of the boat. Mast step and rudder failures, and kicking strap breakage are the three most common causes of racing retirements in the OK Class. Therefore it makes sense to look at these three essentials before more cosmetic considerations.


The mast bearings. should be of alloy or tufnol plate to minimise wear and ensure high strength. Most boats use an easily adjustable deck level bearing. whereby the plate is set into the deck and can be moved fore and aft by T-shaped chocks placed in front or behind. The bearing plate should be through bolted to backing plates under the deck beams which stop it lifting. but allow fore and aft movement. The chocks are then held in simply by shockcord, and can be quickly moved to adjust rake.

This easy and flexible adjustment at deck level should give all the fine tuning of mast rake you will ever need. This means that the highly stressed bottom bearing can be fixed in one place and hence made much stronger. This fixing must be absolutely fail-safe, as there is nothing more depressing than seeing the effects of the bottom bearing coming loose. The mast usually takes the deck with it, as it neatly punches a hole in the chine! Similarly the key and peg arrangement (required by the rules) to keep the mast secure in the bearing must be foolproof. You may add a bar across the mast ring. as illustrated in 'So you think your mast won't fall out'. Recommended locations for both the deck and bottom steps are considered in 'Building the OK Hull'.


The same principle applies to kicking straps. Choose a system that gives the best compromise between strength and adjustability. The choice will depend on the rig you use and the manner in which you sail the boat. The simplest would be a single fixed wire between mast and boom, but it would totally unsuitable for a bendy mast. To achieve adjustability there is a problem caused by the narrow clearance between boom and deck, but many methods have been used to overcome this. A stiff mast which requires little kicker adjustment and high ratios are difficult to achieve. For kicking strap adjustment on a close reach a ratio of at least 20 to 1 is needed. Most owners would go for a higher ratio than that. This necessitates the use of an axle winch possibly with a compression strut. However, it is more difficult to make such a system fail safe and care must be taken to eliminate potential weak points.


The shape of the rudder and the way an OK is sailed put a lot of stress on the tiller, pintles and rudder blade.. The tiller extension universal joint is a common weak point and often the only solution to any problems is a new fitting. The tiller need not protrude into the cockpit space at all and should be in a fixed position relative to the stock.

The rudder needs to be strong, but as light as possible. Plywoods are strong, but much too heavy. Lighter woods are vulnerable to splitting as a result of the twisting forces, and have to be sheathed in GRP or cheeks added to strengthen the stock. Only have a lifting rudder if it is necessary for local conditions as it can never be as strong or as light as a fixed blade. In order to counteract the forces on the pintles bolt them through the transom as far apart vertically as possible. A watertight hatch in the stern allows regular inspection. Similarly bolt the rudder fittings through the stock.

Now we can consider the other fittings:-


The ability to adjust the control lines easily in any conditions will mean a more versatile control of the rig, which must be worthwhile. In the days of all wooden masts, most boats had overdeck controls which, although unsightly, were perfectly functional. However, the advent of metal masts allowed these control lines to go below deck through the top bearing ring and then through a sheave box to cleats on the bulkhead or side deck. Underdeck control lines must be led through tubes in boats measured since March 1984; recommendations as to how this is achieved appears in 'Do You Think You Need Underdeck Controls?' Control lines must pass through bulkhead with 35cm of centreline.


This is to hold the boom out when you are heeling the boat to windward during off wind sailing. The shockcord is taken from a hook halfway along the boom, through a block attached to the towing eye and then back to the boom. If the hooks are attached near the top of the boom the shockcord should clear the plate handle when tacking. It needs to be tensioned tightly enough to hold the boom in place when out in the running position.


In almost universal use is a three part mainsheet system. The sheet is taken from the boom, through a block on the mainsheet traveller and back to a block on the boom behind the first part. The final lead is best taken through a ratchet block on the cockpit floor behind the plate case, with the cleats on the inside of the side deck level with the traveller.

The traveller bar, preferably curved, is commonly six inches behind the bulkhead and should be firmly attached to the side decks and plate case. The take off points on the boom should be as close together as possible and placed directly above the traveller when it is furthest from the centreline. This will ensure the purchase stays efficient even when the boom is right down on the aft deck.


Many people use an endless system which allows the board to be adjusted even when sitting out. The rope is taken from the handle of the centre- board to a block behind the mast, back to one gunwale level with the front of the cockpit, across to the opposite gunwale, back to the centreline behind the centreboard slot then forward to the handle again.

Also finding favour is a simple system consisting merely of a single line led from the handle back to a cleat immediately behind the slot. This system requires one to lean in to adjust but it need cause little disadvantage with practice. Simpler still, would be the use of a friction rubber on the centreboard rubbing on the inside of the plate case.


Bolt the towing eye through a very strong backing plate. I am always wary about using this in practice and much prefer to tie my towing rope around the mast on those occasions when you are being towed fast. The mast gate after all is designed to take very large forces.


One compass mounted centrally with clearly visible scale is adequate, but if. you are affluent one each side is better.


These are worth fitting to help right that stubborn capsize. A rope is attached to the underside of each side deck and then led back to cleats on the stern.


Metal masts allow an internal halyard with the lock fitted at the bottom of the mast. This clearly reduces windage and allows easy derigging when afloat. However, many owners prefer not to drill holes in their masts and external halyards are still to be recommended for that reason


The relative position of the toestraps to the sidedeck in crucial to be able to race properly. Since it is difficult to decide on their position before sailing the boat, an adjustable rack for the mountings on each bulkhead allows the position to be decided later. The attachment to the bulkheads should be with bolts through to large backing plates mounted low down near the floor. This will ensure that the considerable forces do not dislodge the bulkheads.


I prefer one very large bailer and one small. The small bailer can be left open during those rough weather races and it will cope with all the water shipped aboard, whereas both will be needed in the 'rare' event of a capsize.


If you have just spent a week repairing the hull you will not need me to tell you this is an essential. Anyone who is prepared to put the work described in 'The Perfect Bottom' will certainly not begrudge the expense!


References to 'So You Think Your Mast Won't Fall Out', 'Building the OK Hull', and 'The Perfect Bottom' are to other articles in the British ''Newsletters' and 'Manuals'.
The winch and strut vang rarely finds favour these days. The simple lever is preferred.
Underdeck controls, very popular in Britain in the 1980's, are no longer in vogue.