Mirror Dinghy - a rotten story.

electrosys

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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.
 

ghostlymoron

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Thanks for an interesting posting. I acquired a Mirror a couple of years ago which had some damage which looked quite drastic but was easy to repair using ply, woven tape and resin. I no longer have it as i didn't have time to sail 2 boats but it is a brilliant design - thanks to Barry Bucknell the 60s DIY bodger.
Is you've got some photos you could send an article to PBO magazine and earn yourseflf £50.
 

fireball

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As you say - inspection hatches to remove the water from the tanks....

Dad modified our Mirror to put a drain tube in the stern - the majority of the water is then drained away whilst in storage - subsequently we put a self bailer in - that also helps.
 

sailorman

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As you say - inspection hatches to remove the water from the tanks....

Dad modified our Mirror to put a drain tube in the stern - the majority of the water is then drained away whilst in storage - subsequently we put a self bailer in - that also helps.

when i built mine i lined the forward tank with chop strand mat & resin ;)
 

G12

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I used to have a Bell Special. She was epoxy coated when new and therefore a little heavier than some but never stopped me from notching up a good few wins.
The best bailer to use is the Supersuck as it works at low speed too. The other designs only seemed to work if you were almost on the plane.
 

electrosys

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Is you've got some photos you could send an article to PBO magazine and earn yourseflf £50.
Good thinking - except I don't think my literary skills will stretch to that standard. Yes - photos - I have a few, so I've just knocked-up a 'quick-'n'-dirty' website: http://sae140.99k.org/

It ain't a pretty dinghy, but for zero cost, about £50 in materials, and 40 days most enjoyable work, it should provide some good fun during this coming year.
 

PaulJS

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Thanks. Excellent thread, I really ought to do proper repairs to my 1972 (?) plywood Mayfly dinghy.
I enjoyed looking at your photos and seeing how you'd tackled the various repairs, but I really liked your choice of workshop, a poly-tunnel - absolute genius - dry, warmer than outside, well lit..., and you can use it for plants once the boat is done!
 

EBoat126

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Did much the same (but not to such a high standard you achieved) last year with a £75 Miracle dinghy. 10 years in a leaky barn had had done no good for the floor.

1st sail after lots of jigsawing, fibreglassing and painting is very satisfying.
 

Claverock

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Excellent series of photos and explanation. It will make my task easier later this year when I have to rebuild a similar Mirror for my grandaughters in Australia. My son bought it sight unseen on e-bay, the saving grace being the trailer and outboard were in excellent nick. Thanks for an enjoyable article
 

electrosys

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Excellent series of photos and explanation. It will make my task easier later this year when I have to rebuild a similar Mirror for my grandaughters in Australia. My son bought it sight unseen on e-bay, the saving grace being the trailer and outboard were in excellent nick. Thanks for an enjoyable article

Many thanks to yourself and others who have commented kindly. My situation was similar to your own in that I bought a Mirror dinghy boat package via a Boats & Outboards advert (kudos to them) unseen, although I knew that there was a good Rapide Traiload trailer and a set of nearly new Jeckells sails included. These were the items which had set the price of £100 - the hull being included as a 'basket-case' more-or-less for free.

I think the worst part of the job for me was when I began to eat away at the rotten wood with an angle-grinder and coarse wire brush, instantly turning quite small holes into much bigger ones. But - it had to be done - after all there's no place on a boat for wood with the strength of Shredded Wheat !

The hull had thoroughly dried out over several years storage in a garage, and in many places small gaps had begun to open up along the glue lines as the wood had shrunk - particularly along the gunwhales and around the top of the dagger-board case. After some deliberation I decided to drip thin epoxy - from ABL Stevens (www.resin-supplies.co.uk - kudos to them, too) - into the gaps in order to 'tighten-up' the hull.
The alternative would have been to dismantle the hull completely to do a 'proper job', but there needed to be a trade-off between perfection, time, and also value, for no matter how much time and money is spent on this particular hull, the boat will never be worth more than around £200. So for me, it was an exercise in achieving a 'good enough' standard, rather than embarking upon a restoration to any level of perfection.

Incidently, before starting work on your hull, you may find it useful to visit http://mirror70407.com/mirror70407.aspx where a guy documents a Mirror dinghy build in detail - the pictures are particularly good for seeing what structures lie beneath the decking of the buoyancy tanks, just in case you need to know beforehand. There's also a copy of the original build instructions there: http://mirror70407.com/oldbuild.aspx.

Best of luck with your repairs.
 
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