Mirror 69667 - Bold Forester was damaged (T-Boned) by Restronguet Pirates in July 2024
As you can see, there was quite a bit of damage, mainly a long split just above side deck level as well as the outer gunwale broken in a couple of places and a split extending across the inner gunwale.
Boat builder, Ian Ridge, did this when he restored Mirror 152 (a Mk 1). See the boat article for 152 for details.
This video shows the side deck batten problem. It's pretty common on wooden Mirrors, and normally occurs at the forward end of the side deck where the crew sits. With no load on the deck, the panel pin head is level with the top of the deck, but if load is applied to the deck (such as the crew sitting on it), the head of the pin disappears, leaving a hole. Take off the load, and the head of the panel pin reappears. Needless to say, water can then get into the hole, lifting the surronding varnish and discolouring the ply around the hole.
As background, you need to look at page 14 of the original building instructions and plate 43 (plate 43 shows the foredeck beams, but the side deck beams are fitting in a similar manner - i.e. just glued and pinned to the underside of the deck, not notched or joined into any other beams inside the tank).
Click to expand
The sketches above explain why this problem occurs. I understand that, when the boat was being designed, there was a need to keep things simple so that the average man or woman in the street could build the boat.
From an engineering viewpoint, this method (i.e. just glued and pinned to the underside of the deck) of supporting the sidedeck (and foredeck) is less than ideal.
_Building_Instructions/mirror_canadian_building_instructions_page_49_photo_6.jpg "Photo from page 49 of the Mirror Sailing Developments (CAN) Building Instructions")
A better way is to cut the batten up and run it athwartships, across the buoyancy tank, and notched into the stringers (part 21 in original Bell instructions) and the carlins ( part 22 in original Bell instructions) which support the side decks. This has long been the practice in Canada (see the MSD building instructions, page 30 and photo from page 49 shown above), and with top UK professional builders, such as Duffin Marine.
My preference is to cut the side deck batten in half lengthways to create more beams (about 12) with a smaller cross section. I use a cross lap joint to join the end of each beam to the stringer and carlin. The result is a side deck that feels rock solid. This will also solve any adjacent joint cracking problems with the deck.
Sadly to do this you have to take the side decks off, which can be quite tricky. With the decks off, you could also fit a side tank bulkhead to stiffen the daggerboard case.
If you can't face taking the decks off, a possible shorter term solution would be to taper the end of the side tank batten as shown in the sketch above (actually shown in plate 43 but not mentioned in the text). This should (in theory anyway) distibute the tension over a larger area which might be sufficient to delay or even stop the initial breakdown of the glued joint. This approach is similar to the shaping of the ends of floating braces on a acoustic guitar top.
The Mirror dinghy is designed with a lot of built in buoyancy, but owners need to check the tanks are airtight, otherwise they could prove ineffective when the boat capsizes. An annual buoyancy test or inspection is a Class rule for those who race.
To check the tanks out, you need about 1m of tube, say garden hose, which needs to be a snug (i.e. airtight) fit in the bung hole. Then, with any hatches in place, blow one good breath (individual side or aft tank) or two good breaths (bow tank or combined aft & side tanks) into the tank. Hold your finger over the end of tube, wait 20 seconds, remove your finger. The tank should "blow back" strongly . If it does not, then the tank is leaking. You need to find the leak(s) and fix them and re-test until the tank "blows back" strongly. If you want a less subjective method, you can always make up a buoyancy tank pressure gauge such as a Class Measurer would use.
If a tank has more than one leak, the worse one will show up first and will need to be fixed before it's possible to detect the next worse one.
For those with tanks without bung holes (mostly GRP boats), you will need to buy a hatch cover, and modify it by drilling a hole and gluing in a bung hole fitting. It's a Class rule that each tank has to have either a bung hole, or a hatch.
It's best to test in a garage etc. with the doors closed so you can hear the hiss of the air as it escapes (if you have a hole). Washing up liquid plus a bit of water brushed on can help find the leak. Most likely places for leaks are around fittings (like the bung hole fittings), badly taped joints, hatches (check the "O" ring is present and in good condition) and where the beam fixed to the topsides, which supports the decks, passes through (oversize) holes in the stowage and aft bulkhead. Another possible souce is between the top of the forward bulkhead and the underside of the foredeck.
You can get leaks from some wierd locations. For example on a wooden boat, if the two panels of the foredeck don't meet perfectly under the foredeck butt strap, you can get a 'tube' formed by these 3 parts and the top of the mast web. This tube can go from the front tank and leak air into one of the cuddies and the leak could be 150mm or more from the forward bulkhead. You can get something similar on the aft transom if there is a gap between the solid wood doubler and the plywood aft transom panel. In this case the leak could let air escape along the top edge of the transom, or around a transom scupper.
One Bell/Ferranti GRP boat I tested had the aft tank connected to the front tank.
Once the tanks are airtight, you should find that they remain airtight year after year.
Mirror 68440 - Doc is a wooden boat built in 1987 and in June 2014 was damaged during a training session at Restronguet SC. Collision was with the bow rubbing strake on 15563 - Blyskawica.
First step was to cut away the damaged glass fibre tape & resin and most of the damaged ply with a sharp chisel. Then remove varnish around the hole using coarse sandpaper (80 grit used dry). Then I marked out the area where the patch would go with a very short ruler and marking knife across the grain and ideally a scratch awl (if you have one, or something similar) along the grain (don't cut too deep). In this case the damage was just above deck level, so I used the surface of the deck to define the bottom edges of the patches. Because the damage runs over a join, the patch in the topsides has to be longer than the visible hole on the inside, and run all the way to the outside face of the bow transom, so I didn't draw around a cardboard template as I would with a floating patch in one panel.
Made up patches and glued them in. Very awkward place to get clamps into, could only get one of my deep throated clamps on each patch because of the bow shapes. Once patches are glued in, clean up with sandpaper etc. prior to adding glass fibre tape and resin. I use 40mm wide open weave tape (it's easier to wet out and get to go nearly transparent) and after the resin is dry, rub down and apply a second coat of resin. This is just cosmetic, but it makes a smoother surface to varnish.
With tape and resin dry, rub down with fairly fine wet & dry (I used 240 grit) used dry so the varnish will bond. Using International two-pack, first coat was thinned with International Thinners no. 9. After that I was able to put on two coats per day to build up the coating thickness (weather was warm which helps) and rubbed down every two or three coats. I applied filler (epoxy resin & filler addititve) to the outside and rubbed down prior to adding more paint.
After the final coat of varnish and paint, the repair is complete.
