Deckhead repair

[Tim Stewart]

Over the years the plywood in the sandwich construction of my deck, which is supporting my deck stepped mast, has turned to mush. This has allowed the mast to form an indent in the deck at the base of the mast, due to years of tightening up the rigging screws a bit at a time.
I would be most grateful if anyone could suggest a repair that I may carry out. I have a idea how I am going to do the job, but I won't mention it just yet, because I don't want to influence any forth coming suggestion.
Thanks in advance.
Tim Stewart

[Brian Duff]

You haven't really told us even what your boat is made out of, so I will assume it is fiberglass and the plywood is a core sandwiched during construction ?
If so you need to remove the spar, open up to sandwhich from oneside or the other (I preferr top) and replace the wet crushed core with solid fiberglass, or new core, taper everthing to spread the load and increase bond area.re glass over exposed side of core. restep spar and keep new step well bedded.

That would do it.

[Tim Stewart]

Thanks Brian for your quick response.
Sorry for not mentioning what type of boat I had. I was in a bit of a rush when I was writing. It is an Achilles 24, built locally in South Wales, UK. in the 70s. It is fibreglass, plywood, fibreglass sandwich construction. I was going to attack the job from underneath so as not to disturb the visable topside finish. The underneath is rough finished fibreglass covered by the deckhead lining, so it can be covered up again when I've finished.
The mast has already been removed.
I was planning to cut out the bottom layer of fibreglass very carefully with an disc cutter. Then pick out the 'mush' plywood. I was then going to place a fresh piece of marine ply or a solid piece of plastic sheeting in position,jacked up in place, and glassed over.
Do you think this will do the job.
Could you please let me know why you prefer attacking a job like this from the top. As I would find it harder to make the top look as good as it was prior to the start of the job.
Thanks again.
Tim Stewart.

[osteoderm]

Tim,

Have you ever 'glassed overhead? Trust me, you'll find re-finishing the top of the deck pleasureable by comparison. The upper surface will have to be "raised up" to the surrounding deck level for a proper job in any event.

Yuri

[Tim Stewart]

Thanks Yuri for your reply.
The reason I was not going to attack the job from the top is because, although I know how to glass in matting and mold to match the shape of the deck, I don't know how to finish off the top layer 'gel coat' finish, and I don't know how to blend and bond the finished deck with the original deck to make it look as one.
I will now be approaching the job from the top, but can you or anyone else reading this please advise me.
Tim

[Ian McColgin]

Start with a smallish hole right under the step so you can evaluate whether you simply have crushed wood or whether, as it unfortunatly likely, you have water intrusion and the attendent rot. If you want some insight before you do too much tearing up, you may require a surveyor to take moisture content reads traveling out from the step to determine how far the problem may have spread.

In any event, once you get going, you'll need to rip out anything that's got a tinge of rot. You might get lucky and find a damp perimeter of damp but not yet rotten ply where you can stop, buy you'll want to get it well dried before going much further.

I recommend sealing the edges of the existing wood you leave in with CPES or a similar penetrating epoxy sealer. This may be hard to find in UK but you could check in at the WoodenBoat magazine forum (www.woodenboat.com and then click to forum and ask under repair) where you'll likely find a neighbor - it's a big community - and get a bit of umbridge for having a frozen snot boat but your question is about wood and epoxy.

The exact sequence of the repair depends on how much deck ply you rip out, but you should certainly make the bit right under the step dimensional wood. You may even want to make a beam gunnel to gunnel.

Glass/plywood'glass decks usually involve structural plywood whereas glass/balsa/glass uses the core as a seperating structure, if you see what I mean here. In the former case, any new ply or dimensional wood you put down should have 8:1 beveled edges and land on an identical bevel to give a nice long glue joint that will support people romping about on deck.

You're going to have a major refinishing job no matter what. For the repair, use epoxy to lay your new deck glass to a thickness equal to the original deck - again with the bevel though in this case you'll end up with a bump at the perimeter that will require grinding.

Consider either a creative color scheme that allows finish coating just the repair area, or plan on refinishing the whole deck. There's a huge variety of finishes suitable for this. Seek local advice.

G'luck

Ian

[osteoderm]

Tim,

Carefully colour-matched gelcoat can be sprayed in small batches, and the feather edge wet-sanded with finesse to leave virtually no trace of a repair, but this is (i lament to say) often best left to a professional.
As Ian wisely advises, it will be best to elimanate all traces of compromised wood. If the resulting area doesn't actually extend too far from the mast step, i'd be tempted to fill the gap with a high-strength filler such as West 404 instead of using a wood patch. In any event, the surrounding wood ought to be well-sealed with a penetrating/thinned epoxy.
A lovely tapered scarf might prove problematic; instead, a step-scarf is straight-forward to achieve with several router passes. A scarf is a good idea whether filling with either epoxy or wood.
In addition to Ian's suggestions, the transition from a smooth area to a non-skid area is a good way to camoflage a repaired area.

Yuri

[Tim Stewart]

Thanks very much to everyone who replied to my question. It has given me a few things to think about, and has helped me plan for the way forward.
Cheers everyone.

[Brion Toss]

Hello,
Many of our clients face similar problems, especially with older boats. In addition to the above suggestions, you might want to check out a recent issue of "Professional Boatbuilder", which deals with this subject in novel ways. Then contact the WEST System people, for free info on these repairs.
I think it's best to have something more crushproof than plywood under a mast, like solid "glass" or epoxy. If the mush is really extensive, transition to core further out, lest you make the boat too top heavy. And check around any conceivable water entry points for similar damage; the birdbath around you mast might just be a canary in the coal mine, if you'll pardon the mixed metaphor.
Fair leads,
Brion Toss