Repairing a hard to reach bulkhead

venntim

venntim

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Yesterday I unearthed a sorry sight in my boat – the bulkhead behind the pilot berth of my Avance 36 has rotted because there has been deck leak unchecked for years. To make matters worse, it is a complex mess of a headliner, bulkhead and a storage locker behind it. Accessibility is poor at best.

For pictures, see: http://balticsailing.blogspot.fi/2012/10/rotten-bulkhead-bad-bad-bad.html

I've been thinking of cutting away the rotten bulkhead in as big piece as possible in order to get a template for the replacement. Probably I will have to epoxy the new bulkhead in pieces and maybe reconstruct the locker. And of course I'll have to find the leak, but first the bulkhead must go (I guess I'll need some bracing to prevent any further damage).

Any ideas, hints or advice? Thanks!
 
I don't fully understand - is the piece you have removed the bulkhead in question?

If not, and you can get to both sides, why not use the rotten one as a former for laminating a grp b/h on each surface? After drying and cleaning obviously.
 
Ouch, no. Maybe I was a bit vague. The piece that I took off was just a decoration which is easy to replicate and repair. The horror is shown in the first pic. It's a bit hard to get from the outside, only a minor part of the bulkhead can be accessed from the locker. Maybe I'll have to cut out the locker as well.

Do you suggest that I'd laminate over the rotten bulkhead? I wouldn't like to do that as then I would have a partially unsealed, rotten and molded piece in the boat. But maybe I misunderstood – English is not my mother tongue ;)
 
OK, I understand.

Yes, I am suggesting exactly that. If you can get it grease free and thoroughly dry it won't be far from similar strength characteristics of some of the foams used in foam cored bulkheads and stringers. Drying would need the use of a dehumidifier and moisture gauge checks.

You do need to do both sides though, and I don't know if that is possible.
 
You can cut it out and manufacture a new bulkhead that will fit in a bit at a time. To make it strong, you could make it in various sized pieces and double it or triple layer it with the joins in different places. The smaller pieces can be put together like a jigsaw. Epoxy with screws to clamp it all together as it sets.

It would help to cure the leak while you are at it!

What is access like from the back end? I wouldn't want to leave rotten wood in place in the boat either.
 
You really have to get the rotten section out as it will very difficult to ensure that it is completely dry and free of mould spores.

Repairing the bulkhead in sections will produce a final bulkhead that is at least as strong, or even stronger than the original one.

Measure out the cut lines on the old bulkhead and try and establish appropriate sections that are easy to remove and replace using straight lines and right angles. The only curved bits being against the hull. Before you remove the old bulkhead, make good any joints to the hull that are sound and will be left in place.

I would be inclined to use lap joints with epoxy glue rather than just butt joints to join the sections together. The main advantage of the lap joint is that it is more tolerant of misalignment.

I would start by shaping the sections that fit to the hull and concentrate on getting a good fit and shape. One side curved to fit the hull, the other side vertical or paprallel to the cut line on the old bulkhead that is being left in place. Then I would epoxy glue the hull sections into place making sure that they were aligned on the same plane as the remainder of the bulkhead.

Once the hull sections of the new bulkhead are in place, offer up thin ply between the gaps and draw templates. The thin ply allows it to be bent in to fit small places such that it springs back to shape when placed against the gap that has to be filled with new bulkhead sections. This will allow you to establish if smaller panel sizes are needed to fit through any tight gaps and adjust the final number of panels.

I would advise that you now glue on butt joint flanges on the back side of the bulkhead panel / sections that are in place. Then cut your new bulkhead sections according to the templates and fit onto the lap joint flanges. If all is okay mix up the Epoxy glue with a structural filler and glue the sections into place.

A Multitool such as a Feign where the cutting head can be rotated at right angles my allow you to get neat cuts in enclosed spaces.

Info here on preparing joints: http://www.westsystem.com/ss/use-guides/

In particular 002-970 Wooden Boat Restoration & Repair from the link has information on repairing wooden sections which may be relevant, including repairing rotten ply and methods of joining.

Good luck.
 
If, and it is an important if, the rotten ply is dry - as I proposed, it will be fab as a substrate for a laminated bulkhead. In the early 1980s we used the equivalent of long cardboard toilet roll tubes as stringer formers in 60 foot sidewall hovercraft designed to run at 25kts. That was hollow and just acted as a former.

I'd use dry rotten ply as a main bulkead core, but might make some link holes to keep it all parallel.
 
Thank you for all the comments. This is really a great resource with knowledgeable contributors!

boguing: I suspect that I can't use the old bulkhead as a form as it is very wet and access from the other side is limited. Without removing it, it will be next to impossible to find and fix the leak as well. But as a concept, I think I would be valid in some other places. Of course, it would have to be 100 % sealed in order to prevent mold etc.

BlowingOldBoots: Sounds like a good idea to use lap joints – I had thought that butt joints would be satisfactory, but lapping makes perfect sense. Thank you for the West System link. I didn't realise that they had such material available.

"Before you remove the old bulkhead, make good any joints to the hull that are sound and will be left in place."

Do you mean that I would leave parts of the old bulkhead joints in place if it's not rotten? I was planning on cutting the whole bulkhead away as closely as possible with Bosch's equivalent to Fein. Then I could use that as an template to get pretty accurate curved form. Or is there a flaw in my thinking?

john_morris_uk: The back end is probably as bad as the front end. You can partly see it in the last pic on my blog post. Most likely I will have to cut away the locker as well as construct it anew from the scratch. I agree that I shouldn't leave any rotten stuff there.

One thing to consider is bracing. This is a pretty narrow boat and I think that removing the bulkhead shouldn't cause any deformation. But maybe I should brace it somehow to be on the safe side?

I'll have to check how far the cradle pads are from the bulkhead. The hull is solid GRP.

This is project that will take a bit time – it's minus 5 degrees Celsius outside and our club regulations won't allow me to leave the boat unattended with a heater on.
 
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I sympathise with you - I had a to do a similar job when I bought my Moody 33 a few years back. The access was a lot easier, the babystay chainplate had been leaking for years which the survey picked up. The bulkhead did have reasonably easy access though but had laminate/Formica on both sides which fortunately peeled off easily. I had to cut out the rotten bulkhead and epoxy in a new piece, suitably reinforced with stainless plates. Where I had to cut the laminate I covered the cut with a strip of teak and the stainless plate I left as a feature. You do have to look carefully to see the repair.
 
Andy – I suspect that most of the water has come throught the genoa track bolts but the anti-siphon valve is a good choice as well. I wonder why they placed it there in the locker as the access would have been far better on the other side – does it matter on which side of the engine the valve is? Mine has been on stb and the engine is the old and rusty MD7.

PetiteFleur – thanks for sympathy, I need it! I guess this is one of the inevitable joys of owning an ageing boat. The main difficulty in these repairs is the fact that the boat is in a windy and cold marina and the bigger tools such as band saw are somewhere else. It takes quite a lot of time to reach a point where you can actually start laminating the stuff back together.
 
venntim said:
... does it matter on which side of the engine the valve is?
Click to expand...

Not as far as I am aware, as long as it is in the correct place in the pipework, and above the (heeled?) waterline - I think there is a recommended minimum distance above - 12" springs to mind??

In case you're not aware: the workings inside of those anti-syphon valves get dirty / scaled up and stop sealing, resulting in a permanent stream of water out of the vent when the engine is running. An option is to remove the innards completely and just pipe the vent tube overboard.

Andy
 
Thanks, I didn't know that. It could explaing some things... I'll have to check the valve next time when I visit the boat. Regarding the valve position – if I placed it on port side, I wouldn't have to do those silly through bulkhead cuts.
 
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