Remember this end of season blog? Specifically the bit at the end about replacing the wheelhouse bulkhead with something other than plywood? Well – forget all that, things turned out a little different!
It turns out that the uPVC panels I had in mind are no longer made with the reasonably dense foam core, but instead use polystyrene as the core material, which of course has little or no compressive strength. Added to which the additional thickness of 28mm was going to cause complications with the door fitting. So – 18mm marine plywood was ultimately the material of choice.
Lifting the Lid
Firstly it was necessary to raise the wheelhouse by a couple of inches or so. Having removed the fastening screws, I used a series of wooden wedges to carefully lift the wheelhouse by approximately 6cm. This is tricky only in so far as the headlining is tucked under the join and is covered in glue and care is needed to separate this without tearing it.
As for the bulkheads, there is really not that much retaining them in position, other than the few wooden cleats screwed to the exterior. Most of the strength is the black adhesive mastic, used to seal the bulkhead to the GRP cockpit moulding. Once this is cut through with a sharp knife, it is relatively easy to remove the bulkheads – having firstly removed the doors and door frame. Here’s the result:
That space is great! It would be nice to keep for sunny days 🙂 The rot in the starboard bulkhead extends even further than the photo suggests.
A History of Repairs
All that time watching TV forensic dramas has not been wasted: using my acquired sleuthing abilities it was easy to see a history of repairs to the bulkhead over the years! The starboard bulkhead is original. I already knew that a 3mm sheet of ply had been added to the inside, but it is clear that a 3mm section was also added to the exterior – just the bit exposed in the cockpit (i.e. the white bit in the righthand photo). That meant the total thickness of the starboard bulkhead was approximately 23mm, which required the previous owner to modify the window frame and has left me with a few gaps to fill!
The port bulkhead had been replaced at some stage with a sandwich of 15mm ply and 3mm ply – this thin ply being teak-faced.
How to keep the water out
As you will have gathered from my previous post, I was determined that my new bulkhead should be more rot-proof than the old one. That meant doing a really good paint job on the new one before it was fitted – added to which it is so much easier to paint surfaces when they are horizontal, not vertical. The exterior side had an International Perfection two-part epoxy treatment: three primers, three undercoats, and three top coats, being careful all the time to seal the end grain of the ply. The interior side had one coat of woodstain plus six coats of satin varnish.
I had often wondered why the old bulkhead was so rotten. I think most of the water had leaked past the hardwood cleats on the exterior, but I also think some had reached the back of the bulkhead through the sandwich construction of the cockpit moulding. You may remember my previous post about the extent of rot in the balsa core here. Well interestingly, the core is exposed where the cockpit moulding is cut to accept the bulkhead, and it is only a short distance from the forward most coaming locker:
The bottom few cm’s were soft and wet – I think this is a perfect conduit to deliver any water that gets into the core from the coaming hatches directly to the rear of the bulkhead, hidden from view. I replicated my earlier treatment of the coaming locker edges by raking out the loose balsa, applying liberal amounts of wet-rot/wood hardener and then sealing with Sikaflex 291i:
Fitting the new bulkhead
With the wheelhouse roof raised, this was actually fairly easy. My starboard bulkhead fitted exactly (hooray!) although the port bulkhead needed sanding by just a few mm here and there – possibly because this was a copy of a previous copy of the original. Anyway – here’s the progress:
It was not necessary to remove the longitudinal panel and lockers outboard of the interior helm position: the new bulkhead slid between this and the cockpit moulding.
I widened the channel in the old door frame sections with a router, by just a couple of mm as all that paint meant the ply no longer fitted!
Refastening the wheelhouse
The original hard rubber seal between wheelhouse and coachroof was brittle and missing in places and I had long suspected that it no longer provided a waterproof seal. The old glue was hard, dirty and no longer doing anything useful. I removed all of the old stuff and cleaned up the mating surfaces.
To ensure a good seal I adopted a slightly experimental solution: 15mm x 3mm butyl rubber tape immediately outboard of the screws and a substantial bead of Sikaflex 291i inside of that, along all of the screw holes. Butyl tape is really useful stuff, but it is difficult to move an object after initial positioning – you have to bring the surfaces together in just the right way:
On the positive side, it is easy to trim off the excess immediately after fitting using a sharp knife (definitely sharp), which leaves a very neat finish, almost impossible to see at first glance:
(You can just see that I also used plastic sealing washers under the screw heads)
The task is not quite finished – I need to finish replacing the wooden cleats to secure and seal the bulkhead in position, and complete the section below the companionway steps, but with the glorious weather we have enjoyed over the last two weeks, I have been preoccupied with varnishing (and varnishing and more varnishing):
Next: Tidying up the exterior 🙂