installing a bulkhead, how tight should it fit before fiberglassing?

[alexlago]

I'm on the way of installing a bulkhead in my boat.
three stages : copy the shape of the hull on cardboard, cut plywood according to the shape, filleting and fiberglassing the foot of the bulkhead.

It's been quite a hassle to accurately copy the shape of the bulkhead on cardboard before cutting the plywood. So the new bulkhead is more or less well adjusted to the shape of the hull (they are some gaps left between the plywood and the hull)...

So I wonder how tight the bulkhead should fit on the hull before filleting and fiberglassing? is there a recommended way to fill up the gaps left at the foot of the bulkhead, with resin? wedges? resin over wedges? something else? (or there shouldn't be "any" gap and there is a better way to copy the inner shape of the hull...)

 

[RupertW]

The whole thing will flex and twist with the hull once it's in motion so the answers would be different depending on whether it's a true structural bulkhead, intended to be waterproof and able to hold back a flooded compartment, or simply a partition.

In my boat none of the bulkheads are intended to structural or watertight and seem to slot tightly into roof and floor fittings with gaps pretty much all round.

 

[TQA]

It should not be a tight fit. There should be a small gap about 3mm which you can fill with foam before tabbing.

With a tight fit you create 'hard spots' on the hull which will create problems.

 

[Plum]

I'm on the way of installing a bulkhead in my boat.
three stages : copy the shape of the hull on cardboard, cut plywood according to the shape, filleting and fiberglassing the foot of the bulkhead.

It's been quite a hassle to accurately copy the shape of the bulkhead on cardboard before cutting the plywood. So the new bulkhead is more or less well adjusted to the shape of the hull (they are some gaps left between the plywood and the hull)...

So I wonder how tight the bulkhead should fit on the hull before filleting and fiberglassing? is there a recommended way to fill up the gaps left at the foot of the bulkhead, with resin? wedges? resin over wedges? something else? (or there shouldn't be "any" gap and there is a better way to copy the inner shape of the hull...)

There should be a gap all the way round, say 6mm. You can wedge strips of rigid foam in the gaps to maintain the gaps, then apply radiussed resin fillets then glass/resin to bond the bulkhead to the hull on boyh sides of the bulkhead. All this will ensure loads are transferred smoothly over a larger area of your hull without any stress-raisers.

Www.solocoastalsailing.co.uk

 

[alexlago]

The whole thing will flex and twist with the hull once it's in motion so the answers would be different depending on whether it's a true structural bulkhead, intended to be waterproof and able to hold back a flooded compartment, or simply a partition.

I think it's structural as it is on the port side, though it's only 10" wide, and as on the starboard side, there is a cockpit locker, but no bulkhead.

 

[alexlago]

@TQA and Plum
What kind of "foam" do you use to fill up the gaps?

 

[chuzzlewit]

Plum and TQA are right.

 

[Plum]

@TQA and Plum
What kind of "foam" do you use to fill up the gaps?

I would use something like this as long as it is closed cell and firm enough to supportport the bulkhead before bonding http://www.decoratingdirect.co.uk/v...Fq9HL3VhDGnkG9_RGLP28FvCvBJO5wmEaAsrNEALw_wcB

Www.solocoastalsailing.co.uk

 

[PCUK]

Wedge it in place with thin ply. Add some mat/resin tabs and once cured take out the ply and complete glassing of the rest.

 

[William_H]

I think the answer in practice will be whatever gap appears when you have cut the ply. I think it undesirable to have a large gap simply from difficulty of filling the gap to hold up the grp over the fillet. Use a resin (epoxy is best with filler like micro balloons or talk to get a consistency that will make a nice fillet. Like I imagine 1cm radius or 1cm onto ply and 1cm onto hull. You then need to lay glass over this fillet. The way to do that is to cut the glass at 45 degrees to the weave. ie get a large square sheet of fibreglass and cut from one corner to the other. Then cut your strips from that cut line. The 45 degrees from the weave allows the glass to bend and follow the fillet. Give it a few layers of fibre glass.
Regarding it becoming a structural bulkhead or not depends on a lot of factors my guess is that if this is a problem it will start to crack around the join bulkhead to hull. In which case repair might be necessary. I don't imagine it will cause a hard spot on hull flexing but then some boats flex more than others. I can't see it practical to fit a flexible bulkhead. ol'will

 

[DownWest]

It's been quite a hassle to accurately copy the shape of the bulkhead on cardboard before cutting the plywood. So the new bulkhead is more or less well adjusted to the shape of the hull (they are some gaps left between the plywood and the hull)...

Re cutting a pattern: Cut a rough one that misses all the way round. Then use a 'tick stick' This has a point at the end, which you touch the hull at multiple points. Each time, you run a pencil tound the back of the stick on the pattern. Laying it on your new ply, you can mark each point from the pattern and stick. Then join the dots with a springy bit of plastic conduit to get the curve. Give it the 6mm clearance and fillet up.