electrosys
New member
Good play on words, eh ?
Last year I decided to source a small boat which could be chucked on the roof-rack or trailered to the coast for the afternoon 'on a whim', whenever the weather was kind, and for little money - so the summer found me repairing a Mirror Dinghy, and here are my findings regarding the rot for which the design has become somewhat infamous.
One obvious cause of rot is the poor choice of plywood - thin outer veneers with a wide inner core which is prone to 'wicking'. Apparently this quality of plywood is still being supplied (no comment ...) for class-compliant panel repairs. Liberal amounts of epoxy applied to the end grain of the plywood, plus an application of epoxy to exposed surfaces is all I can recommend here.
The next cause of rot I discovered is due to the buoyancy tank drainage bung fittings, which sit some 1/4" or so proud of the lower surface, thus any water entering the chamber cannot fully drain away - there will always be a small puddle left around the drainage bung fitting to maintain a high humidity within the chamber, thus encouraging rot spores to develop. The obvious solution here is to fit inspection hatches to each chamber - as many have already done - and use a sponge to mop-up any residual water.
The Mirror Dinghy cockpit floor is notorious for failure, and I found the principal cause of this to lie with the method of fixing battens to the floor - in my case half a dozen screws were used per batten, with a half-hearted dab of glue applied every so often. Over the years, muck had lodged in the gaps under the battens thus trapping moisture there, resulting in 'lines' of rot developing which eventually 'ate' their way through the cockpit floor. In my own case I 'double-floored' the hull as a plywood/glass/plywood sandwich and then glued new battens in place along their full length, finally sealing them with epoxy to fill any remaining gaps.
It also occurs to me that there is no provision for the draining of water from the cockpit when the boat is stored, and covering the hull with a PVC cover will only serve to then create a humid environment under the cover. Ideally, some form of drainage (perhaps through the transom chamber ?) might be the answer here.
Well that's it: all-in-all a great little dinghy, and an inspired design. Having given attention to the above points, I'm rather hoping mine will now live to see it's 50th birthday.
Last year I decided to source a small boat which could be chucked on the roof-rack or trailered to the coast for the afternoon 'on a whim', whenever the weather was kind, and for little money - so the summer found me repairing a Mirror Dinghy, and here are my findings regarding the rot for which the design has become somewhat infamous.
One obvious cause of rot is the poor choice of plywood - thin outer veneers with a wide inner core which is prone to 'wicking'. Apparently this quality of plywood is still being supplied (no comment ...) for class-compliant panel repairs. Liberal amounts of epoxy applied to the end grain of the plywood, plus an application of epoxy to exposed surfaces is all I can recommend here.
The next cause of rot I discovered is due to the buoyancy tank drainage bung fittings, which sit some 1/4" or so proud of the lower surface, thus any water entering the chamber cannot fully drain away - there will always be a small puddle left around the drainage bung fitting to maintain a high humidity within the chamber, thus encouraging rot spores to develop. The obvious solution here is to fit inspection hatches to each chamber - as many have already done - and use a sponge to mop-up any residual water.
The Mirror Dinghy cockpit floor is notorious for failure, and I found the principal cause of this to lie with the method of fixing battens to the floor - in my case half a dozen screws were used per batten, with a half-hearted dab of glue applied every so often. Over the years, muck had lodged in the gaps under the battens thus trapping moisture there, resulting in 'lines' of rot developing which eventually 'ate' their way through the cockpit floor. In my own case I 'double-floored' the hull as a plywood/glass/plywood sandwich and then glued new battens in place along their full length, finally sealing them with epoxy to fill any remaining gaps.
It also occurs to me that there is no provision for the draining of water from the cockpit when the boat is stored, and covering the hull with a PVC cover will only serve to then create a humid environment under the cover. Ideally, some form of drainage (perhaps through the transom chamber ?) might be the answer here.
Well that's it: all-in-all a great little dinghy, and an inspired design. Having given attention to the above points, I'm rather hoping mine will now live to see it's 50th birthday.