Wanderer Dinghy – Mast Step Repair – Part 1

The Wanderer dinghy – mine at least – has marine plywood cunningly concealed at the lowest point of the boat. The plywood runs from the front buoyancy tank, under the mast step, and to the centreboard case. Sitting at the lowest point of the boat, the wood is often sitting in water. My boat is now 40 years old and poking around in the front buoyancy the wood appeared a bit softer than I’d like. Well – the wood at the top could be pulled apart with my fingers.

The view from inside the buoyancy tank

In addition, my boat has a free-standing mast without shrouds. This is both a good and bad thing. The shrouds help to keep the mast upright, but they mostly try to pull the mast through the bottom of the boat. The wood is obviously designed to resist this downwards pull. However, the free-standing mast has huge sideways forces at the foot and if that foot isn’t really attached to anything strong then this would be a disaster – both for the boat and anyone sitting near the mast.

So it was time to have a look. I took my trusty Aldi multitool and removed the GRP around the mast foot.

Removing the mast step GRP

I made the cut lines below the floorboard level as far as possible, so that it should be possible to put it all back together without showing too much. What was inside?

Plywood attached to underside of GRP

There was some plywood glued to the underside of the GRP. As you can see from the photo this wasn’t in good shape. I assume water had got in through the mast step, foot straps and tabernacle screw holes. No structural integrity whatsoever.

Main plywood

The main bit of ply is in better shape, although absolutely saturated with water. With the top off the box it will have a chance to dry out. I did attack it with a chisel to see how soft it was and whether I could remove it easily. It isn’t in new condition and not as good as I’d like, but it is still pretty solid and would provide a decent (if not ideal) mast support.

I intend to reinforce the mast step with ribs across the width of the floor. This will probably be ply covered in epoxy and taped to the boat. All will be under the floor so won’t be visible in normal use.

The ribs need to be attached to the main ply in the centre. To make this possible I needed to cut down the GRP on each side. This also allowed me to check out the main ply some more.

Some more cutting

Cutting the GRP with the Aldi multitool was easy. Cutting the ply was very hard!

Note that my tabernacle is epoxied into place. On most boats this will fall out when you take the bolts out which will make access much easier.

So – conclusions so far:

  • The plywood attached to the GRP has completely disintegrated. This would be a big problem for a conventional stayed mast as it wouldn’t take the vertical load. It isn’t quite as serious with an unstayed mast but isn’t great.
  • The main plywood is just about ok. There is some damage at the front of the section I cut out but it appears to be localised. There may be more damage at the front and at the bottom where there is more water exposure but it is hard to know at the moment. It must be very high quality plywood to have survived in these conditions for this length of time!
  • The fibreglass on each side of the ply (tabbing) isn’t really attached to the plywood any more. This is a known problem with polyester resin and wood – it doesn’t bond well enough, although it does a great job of holding the water against the ply!

What next?

I’d like to remove the existing polyester GRP tabbing and replace it with epoxy GRP. The main issue is access – the GRP and ply will need to be clean, dry and abraded to take the new GRP and it isn’t easy to get in there! I will probably need to remove more of the existing GRP. On the plus side I don’t think the existing GRP is particularly structural.

I would also like to get a better look at the main plywood – particularly at the bottom of the boat. With the old tabbing removed it should be possible to see what is going on.

Putting it back together

I have a few ideas for how it will go back togther.

As discussed above there are lots of horizontal forces at this mast step due to the unstayed mast. I intend to add a couple of cross-members under the floor to transfer these loads into the bottom of the boat and the sides where the side buoyancy tanks are attached. The cross members will be epoxied and taped to the hull. They will attach directly to the main ply in the centre. I will also put in a large area under the mast step to secure the mast rack to.

I really want to isolate the plywood from the front buoyancy tank. At the moment any water getting in there (and there is some – even without the boat in the water) drains to the area around the plywood. It is hard to get the water out of this area. Yes – I need to make sure that buoyancy tank is properly sealed but one job at a time!

The original GRP from under the mast step should go back in ok. This will be the only bit visible once the floors are in place so it will all look fairly original.

I will be replacing the original mast step rack with something rather stronger (70mm wide, 3mm thick stainless steel) and a much bigger (10mm diameter) pin.

Update: further installments:

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