Bulkhead repair, tight fit or bedding?

[McFrancis]

I've got a rotten piece of bulkhead caused by a long term leak that has now been repaired.
I've cut out the offending piece and the fibreglass tabs joining it to the hull. The boat is a Westerly Seahawk.
I'm in a quandary, I've seen conflicting advice, some say that the bulkhead should be hard against the hull, others that it should sit on a bed of silaflex, to avoid hard spots.
I've made the replace piece of bulkhead tight to the hull, but not fitted it yet. It would be easy to take a couple of millimeters off the hull side of the new piece of bulkhead if bedding is the way to go.
Any advice welcome. Should it be tight or bedded in?

 

[ridgy]

I did a similar repair a couple of years ago but under the deck where chainplates had leaked and left it 3 or 4mm short and filled the gap with thickened epoxy before tabbing. I can't imagine sikaflex being suitable in this application since the new tabbing won't stick to it(?). With epoxy you can make a nice bevel so the tabbing curves rather than trying to make a 90 degree angle.

 

[ducked]

As above, (except I might not use epoxy). Fitting the (ply) edge tight to the hull seems an undesirable stress concentration and might "print through"/distort, though if its only a portion of the bulkhead perimeter the rest of it might provide sufficient support.

I would want something sufficiently incompressible to spread the load. I would expect Sikaflex to squish.

I'd think the default course would be to copy what was done originally and is still in place on the rest of the bulkhead perimeter, assuming you think its been OK

 

[Hacker]

Personally I would fit tight (snug but not too tight that it is pushing the hull) then run a radiased bead of thickened epoxy before tabbing. The tabbing helps spread the pressure.

 

[Moodysailor]

My understanding is that the advice is based on the point loading. Provided the load can be spread over a large enough area to avoid a stress point, then tight fit is OK. The advice to bed in would work when it's a non-structural bulkhead and the tabbing can't be done over a wide enough area.

I am not an expert, so this advice may benefit from additional insights.

 

[Stemar]

Watching RAN Sailing building their new boat, their bulkheads are a reasonably snug fit, glued in and filleted with thickened epoxy, then tabbed with glass cloth and epoxy to spread the load.

 

[Refueler]

The answer lies in the bulkhead that was removed ... how was that ?

Bulkheads in boats can serve two purposes ... 1 - to separate spaces ... 2 - structural ...

If to separate spaces and not expected to bear loads - then they do not need to be tight fit .. a little 'give' can be good.

If structural - then they need to be load bearing - means a good fit but not too tight .. bedded and faired in to spread the load.

OP says that water damage occurred to original .. repairs made. It may be an idea to have a small relief 'hole' to alllow any condensation / water collection to drain ?

 

[Tradewinds]

This is the way Camper & Nicholson specced it on my Nic39.

 

[Poignard]

The answer lies in the bulkhead that was removed ... how was that ?

(...)

^^^^^^