Mirror dinghy modification

Hi all my first post. I own a 10ft mirror dinghy gaff and am looking to modify it and would like opinion or information on what I can achieve. I am looking to fibreglass the hull to make it more rugged for pulling on to beaches so was thinking strip back to bare plywood and glass with one maybe two layers one cloth and one Matt (opinions please) I am also re-jigging the floatation compartments to allow me to make this a nesting dinghy as well . I will glass two bulkheads with 3mm gap and fit 4 bolts with rubber washers ,then for my next trick cut it in two. I will then glass the whole boat. My only concern is we're to place the bulkheads. Also will this make the boat to heavy for sailing my biggest concern. I want to make this my sail. Row and motor boat. I would appreciate all feedback especially if you have done similar. The boat is 5mm marine plywood

 

You won't want to hear this but you are on course for ruining a perfectly adequate dinghy and doing an unbelievable amount of work in the process.Simply glassing the exterior is no trivial task and will require the removal of all existing paint if you are to achieve a good bond and in reality,adding glass above the chine will only provide protection for wear that isn't likely to happen.Until you have tried it you won't believe how much work it takes to get good finish over glass cloth and as for adding a layer of mat-well that just drinks resin and unless you seek out powder bound mat instead of the much more common emulsion bound mat,it won't wet out without using epoxy resin.Which means spending probably the value of the whole boat on epoxy resin....

As for nesting,well the geometry of nesting hulls is quite interesting and requires one part to fit within the other(s) and I don't think the buoyancy tanks in a Mirror will allow the bow to nest within the stern.It isn't hard to cut a boat in two but it is a bit challenging to do it neatly and to maintain the shape.Then there is the need to secure the bulkheads that you need at the joint interface without creating protruberances that make the joint something other than a good mating fit.Which pretty much dictates removing the tops of the newly split buoyancy tanks to bond inside them and then replacing them later.You would need to provide locating and locking arrangements to secure the two halves.

It might not be what you want to hear,but would you rather be standing next to a pile of plywood parts that won't go back together?I suggest you accept the boat as it is or sell it and buy or build something more suitable for your purposes.

 

Appreciate your advice but I'm up for a challenge.suppose only way I will learn. I have built a mobile home body in GRP for a pick up and turned out ok but that doesn't need to float or sail how much more weight do you think I'm adding. I may just sand and epoxy the desk side anti slip on deck side bottom of the boat. But really like to glass the hull for strengthening I will re-evaluate the nesting part.

 

As with all glassing,the amount of resin is related to the weight of glass that you add and there will be some wastage.You would really need to remove all the existing paint and apply a sealer coat.If you select a weight of cloth and calculate the area to be covered,I would begin with an estimate of 1.3 times that figure.A really good laminator would be able to achieve 1:1 resin/glass but not every body gets there in their early days.Then there is the miserable and tedious task of filling the weave and arriving at a good finish.You might try a small test piece to get an appreciation of the work involved.

 

Sabotage of a healthy classic dinghy!
Buy a used GRP boat to fulfill your ideas, both easier and probably cheaper.

 

Hi Joe, don't do it! The beauty of a mirror is that it is very light, can be carried on a car roof, is easy to rig and sail, and versatile. I have a similar boat by Jack Holt called a Heron, and in South Australia, Herons and Mirrors used to duel around race courses. Like a Mirror but with a pointy bow instead of a pram bow. I got my Heron and beefed it up to be 'indestructible', and now it is a slow slug handling more like a displacement hull, and doesn't plane anymore, unless surfing dangerously down a wave.
Maybe forget about adding glass all over, and just epoxy the bottom without glass, but with a wood binding additive in the resin, 'tprda' I think it's called, or something like that. Screw stainless or bronze wear strips down the keel both sides of the centre case slot, from stem to stern, and only glass the chines, and transom, with 3 inch wide glass tape, giving 1 1/2 inches of protection both sides of the angles. The keel and chines get the most wear, and the un-glassed resin bottom will be tough and glossy smooth with little effort. Just doing that will add several Kilos / pounds, and slow you down. There's plenty of work in just doing that. It will lighten your wallet plenty too. Also epoxy hates UV, so it will also need varnish or paint to protect it from the sun.
There are inflatable rollers that you can use to drag the hull up on even a shingle beach, with little or no damage, and a lot less work.
If you really want a nesting dinghy, buy one already made, or plans for one. If it has a centre case, you can put a Mirror rig on it, and it will be much less work, and more likely to succeed. If you really have to ruin the perfectly good boat you have, place the cut sternward of the back stays, and run a brace across the beam on the front section bulkhead gunnels to prevent the sides caving in on a broad reach. The bow section may then stack inside the stern section, but not 'nest' exactly.
I miss the speed that my boat was capable of, and there's no way I could car top it, without a ramp and winch, and a wide heavy car.
Don't be keen for un-necessary work, and you'll be sailing it sooner, and more often. And you won't have created a lemon with no re-sale value. Mine can not race anymore, and is virtually un-sellable now, unless I find another fool / fine fellow like me, into a tough heavy very small sailing dinghy. Look up on here: Jack Holt Heron re-imagined, for a saga of ruining a perfectly good boat. I hope it puts you off your idea.

 

If it's what you want to do, then do it. Yes - get all the paint off the plywood before glassing. Since the idea is to be able to beach it, coat the hull with neat laminating epoxy and completely fill and fair the plywood before putting a glass skin on the hull. You want to be able to peel the glass off later if need be. Overlap the glass on the keel line and chine, and add a strip of dynel or more glass to the keel. Do this after you have parted the hull into pieces, and glass the faying pieces as well. If you want to put a kicker on it, I'd use a 6 oz weave, and add a decent glass pad for the motor bracket - say a patch of 1708 biax for a 3hp OB.

I camp-cruised a 14' Mac Dingy that was based on the Mirror for many years. It was built in the fifties in England and died in Georgia in '89. It was converted to a centerboard and kick-up rudder, the rig was switched to Marconi, we had full kicking straps, and the glass tape seams were all replaced a couple times, but it never got a full glass job.

 

So decided after reflection not to nest this boat. But will glass and paint the keel and chines taping these. Question bottom of the hull where weight from I guess feet from inside has caused a couple of fractures on the plywood not right through and not large areas, two in fact. So will stripping to plywood and filling covering with epoxy just those areas be right way to repair, and only using tape where needed I will finish with primer and top coat. Advice please

 

Your new plan sounds much better Joe. Yes take back to bare wood for the epoxy areas; if most of the hull is in good condition leave the good bits except for light sanding for fresh paint. The original ply has probably lasted decades already, and the epoxy alone will make it stronger and tougher. Just make sure the cracked areas are thoroughly dry to get the best results, and maybe some glass tape over the cracked areas on the inside, so the outside remains smooth to water flow. Don't use bog to fill any gaps or cracks. They often had removable floor board panels of slats both sides to keep feet off the bottom, so the hull keeps it shape. Maybe someone has removed them, common if they get too much damage; replacing them will protect the bottom shape greatly, because your weight is spread over the tops of the bottom frames, not the actual bottom; and you don't get wet feet.
Mix your epoxy in exact proportions part A and B, and additives, using fine scales, or correctly proportioned dispensers, and follow instructions to the letter because it is fussy stuff, and may never set if mixed badly; not fun scraping off unset goo. Lay your tapes first, then fair the edges and sand when hard, then second epoxy coat to seal the faired glass and fill the tape's dimples. Be sure to use a good face mask when sanding paint, glass, and epoxy, it's all toxic to lungs. You should be back on the water in weeks; or days in a warm shed.

 

Fiberglass does not take hard corners, so any hard edges need relieving and typically for amateur, this is 3/8” radius. For a thin ply bottom this is not possible. If your radiuses are sharper; you can apply a woven tape to edges and then apply peelply over it and plastic with masking tape for a tighter radius. It is fussy business, though.

After you remove all the finishes; you’ll keed to precoat the bottom with mixed epoxy and say a 10cm roller. Use a rate of 2oz epoxy per yard. Old wood is thirsty wood and it will suck the resins from your woven and leave ruined glass behind.

The boat needs to be flipped for the work. Forget glassing upside down.

 

On to it fallguy, good reminder. On my dinghy I laboriously pre-folded a length wise crease down the middle of the glass tape, rolled it up tightly for a day or two, and it worked out OK, with only a couple of lifts, which I held down with cling wrap and gaffer tape, not ideal but it worked. Yes I forgot about the pre-coating bare wood, that also helped to hold the glass down, which I applied while the first resin is still sticky, before wetting out with fresh resin. It needed a lot of preparation and organisation and good timing to do it, one side at a time, then the transom, with the hull upside down, at an angle. Mixing small batches while addressing runs and lifts. Tapes pulled tight and held down by cling wrap patches with bits of brick on top of ply wood offcuts, and sticky tape. The chine / transom corners needed some trimming afterward. The front end of the chines tape was cut in an arrow shape > to avoid an abrupt square start. Cheap 1 inch wide paint brushes (not too cheap or they fall apart), and used tooth brushes for wetting out. I did it all alone, but a good assistant would have been a help. Think it all through with a dummy run first, going through the motions, preparing for Murphy's Law, and have everything possibly needed ready to use, close by.

 

Bottom splits are very common. These were barely 1/8 ply if I remember. You can add small longitudinal stringers to help distribute loads. The plywood gets softer quite fast if you leave it in the water for a few consecutive days. I added two mahogany stringers that were about 3/4 inch wide and crowned and maybe 1/8 at the edges and 1/4 in the middle as part of the center board conversion. Check to see the trailer bunks land on the seat transom-hull joint. If the bunks are short - like a foot long - double up on the seat transom tabbing in that area. Mine trailered thousands of miles and that's usually where the tabbing started to give up first.