Repairing bulkheads...have I dropped a clanger?

[Iain C]

The main bulkhead in my boat was starting to come adrift of the hull. The hull is in great condition but I think she may have been a "home finish" job and the bulkheads were very badly bonded in with very dry CSM.

I could almost rip out all the dodgy fibreglassing with my hands, and spent the day glassing the bulkhead back in with epoxy. Very chuffed with a hard days work done, I nearly cried when I looked in a book in the bar and it said that the large gap between bulkhead and hull which I had carefully filled, should be left! Aargh!

However a quick iPhone trawl of the web has suggested that if any voids are filled with epoxy/colloidal mix, and given a very generously radiused fillet before glassing over, this is in fact perfectly acceptable. I do hope so, because this is exactly what I have done. The large radius fillet should avoid and real point loadings/hard spots.


As the chain plates are bolted to this bulkhead, I want it to be properly bonded to the hull, not coming apart as before. Can someone reassure me that I have not dropped a clanger with my carefull filleting and glassing? I understand the need to avoid hard spots, but surely a carefully bonded and filleted bulkhead that carries rig loads is a good thing? Boat is a 70s cruiser that is (apart from the home finished bits) built like a brick outhouse hull wise...

Thanks (fingers crossed...)

 

[Iain C]

This is the pic I found which is what I have done...

 

[Wansworth]

In my limited experience whilst working building those types of boat your work will be ok.The amout of bodgeing involved in glassfibre boat building has little relation with the books.The hull on a sabre 27 will be thick enough to bend round a bulkhead.Bonding in bulkheads was always a prob to get the glass to stick well.Some designers had hloes cut in the plywood so the glass could grip to itself around the bkhd.

 

[oldsaltoz]

I would have filled and classed as you have done, I used a fish paste jar to form the fillet, it was made of epoxy resin mixed with Micro fibres.

Good luck.

 

[ghostlymoron]

I would have filled and classed as you have done, I used a fish paste jar to form the fillet, it was made of epoxy resin mixed with Micro fibres.

Good luck.

What brand of fish paste - I have never come across jars made of epoxy resin and micro fibres, all of mine are made of glass.

 

[nimbusgb]

As you have already realized bulkheads are traditionally not made to fit closely to the hull and a variety of point-load relieving techniques are used. I have seen a foam filler used at the interface point.

My comment would be that even what you found to be a poorly laid up original bonding structure lasted 40 odd years even with the rig loads imposed on it. The hull of your boat is probably overspeced. I wouldn't worry about it in the least. Mark one job off the list and move on to the next one.

 

[Iain C]

OK cheers for setting my mid at ease chaps. Asking some professionals at my club the general consensus was that an older boat like the Sabre will be fine, and having the rig loads being transferred to the hull by as strong a joint as possible is a good thing.

I just had this horrible sinking feeling that I'd wasted a day and about £30 of materials! But it's now very nice to see good strong fillets and the tape/biaxail on top of that, where there used to be grotty dry CSM coming away from everything!

 

[Yacht Yogi]

Bulkhead to hull skin joint

The problem that you are trying to avoid here is the sudden change in stiffness where the flexible hull skin laminate crosses a rigid support at a bulkhead. The sudden change in stiffness results in local out-of-plane bending of the skin that can cause cracking of the skin when it is subjected to pressure from water, fenders or bumping against something. On a metal hull this results in the classic "hungry horse" look but in a GRP hull it shows up as vertical cracking in the exteral gel-coat and hull laminate either side of the bulkheads.

Your generous blend radius and tapering out of the glassfibre fillets over a couple of inches beyond the corner ought to be enough to prevent any problems. If still worried then keep an eye on the external surface of the hull in the region of the bulkhead. If gel-coat cracking begins to appear then add some more but wider internal fillet GRP to spread the blend over a greater distance either side of the bulkhead.