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Boats fitted without a skeg have been known to lose their rudders. One solution is to drill a locating hole through the top of the rudder post to take a bolt - this will positively secure the rudder and prevent it dropping downwards. Another solution is to fit a skeg with a pintle and pin fitted at the lower end - see pictures below.
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Images
Footloose is a junk-rigged Corribee fitted with an inboard BMW engine. The skeg may have been fitted at a later stage as it doesn't look like the standard Corribee shape.
The skeg and rudder on Clareen, a 1984 mk3 Corribee. This is a standard factory-fitted skeg shape. Note the identically shaped rudder in both pictures.
The following has been kindly provided by Peter Willson, who owns Blue Moon, a Mk II bilge keel Corribee manufactured in 1978.
The rudder on Blue Moon was showing a number of problems. There was osmotic blistering especially on one side of the rudder; there were rust stains at the base of the rudder; the rudder was not in alignment in two planes - the stock being bent as might have resulted from hitting an underwater obstruction while the rudder was inclined 20 degrees to starboard; there was also evidence of corrosion of the (phosphor bronze?) stock where it entered the top of the rudder; the head-stock had at some time had a through bolt fitted (good idea to prevent lost rudders) but was drilled out of alignment so the tiller was out of line with the rudder blade.
I had also read of problems with tang failure so decided to open up the rudder and check it out. I had no information on how the rudder was built so used a stud detector to try and find out what was inside. This reveals a stock that goes about 50% of the way down into the rudder with just two tangs running at right angles to the stock and in the top half of the blade only. I opened the rudder by disc cutting and sawing around the edge and finally splitting the rudder with the aid of wedges, trying to preserve the G.R.P. outer shells as much as possible. This was a fairly brutal business, on account of the method of construction the rudder doesn’t just split apart like splitting slate. It shows that the rudder was constructed of the stock and tangs, encased in a G.R.P. shell, with the void being entirely filled with a dense filler of some sort. Although I could now straighten the stock the corrosion at the point where the stock entered the rudder reduced the effective 1” diameter by some 15%, a reduction in cross sectional area of some 38%, also the tangs – two pieces of ¼” mild steel round bar were very rusted and wasted away where they were joined into the stock – no wonder some have reported tang failure.
I decided to replace the stock with 1” 316 grade stainless steel, to lengthen it to reach ¾ of the way down the blade and to fit three 8mm round bar tangs (an interference fit into the stock protruding slightly from the ahead side) also of 316 stainless in order to prevent any problems with galvanic corrosion caused with dissimilar metals being in contact in a saline environment. The shells were then cleaned up - a long job with the angle grinder - (most of the gelcoat and anti foul removed from the outer and all traces of filler from the inside) and the two halves re-enforced with chopped strand matt on the inside before being joined together enclosing the stock with woven roving tape. A 25mm hole was made in the one of the shells so the filler could be introduced. All was then carefully aligned before filling the void. After some research and advice from CFS resin supplies I decided to use a mixture of polyester resin mixed with talc. This was mixed resin plus 1% catalyst first to ensure thorough mixing then the talc added to an equal amount by volume. The resulting mix was added through the hole in 500mg amounts and allowed to go off before introducing the next amount. (how was this done in the factory – does anyone know?) This was all to keep the temperature from rising too high as can occur with large castings. Finally the hole was closed. It was now time to grind out the osmotic blisters some of which were very deep and smelled of the characteristic vinegar when opened. These were filled with a polyester/talc mix. The surface was then covered with G.R.P. flow coat. Sanding this off to provide a smooth surface is another long job as flow coat doesn’t self level like paint. Finally, and after advice from International Paints the surface was finished with Intercoat epoxy primer and Trilux hard anti-foul as Blue Moon is dry sailed.
The head stock was refitted with a through bolt but I also added a stainless steel collar just below the head stock which has a set screw into the stock to ad an extra degree of security to guard against rudder loss (Blue Moon has no skeg). Blue Moon sails well with her renewed rudder and should now be set for another 30 years.
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