bulkhead tab

[PabloPicasso]

What is the proper method for attaching a plywood load bearing bulkhead to a GRP hull?
The bulkhead in question has the chain plate for the shrouds bolted through it.

 

[Deleted member 36384]

I was looking at this for my Rival 41C but for a different project. The drawings for my boat state that bulkheads are to be attached with angles formed from 3 x layers of 2 oz chopped strand mat On my own boat this is at the top where the bulkhead meets the underside of the deck and in 3 x places down the side, between the longitudinal stiffeners, on both sides of the bulkhead. The L shape is about 4" on the ply and at least double that on the hull, clearly tapered on both the ply and hull so there is no sharp edge, the vertical L length on the ply / hull is the length between the stiffeners, just short as I run cables through the gap. This is for a 20mm plywood bulkhead and was approved by Lloyds back in the mid 70's. Since then things will have improved as understanding has increased. Hope this helps.

 

[Tradewinds]

This is how C&N did it back in the 70/80s. HTH.

 

[Tranona]

The common method is as described by BoB. Usually the bulkhead would be slightly smaller than the hull so there was a space reducing the chance of hard spots. Some builders also chamfered the edges of the bulkhead before laminating as described to spread the loads. Using the bulkhead to take rigging loads was common with masthead rigs as the mast often sat on the main bulkhead and with in line main shrouds attached to the same bulkhead. This arrangement requires very good sealing where the chain plates go through the deck as any water getting in can cause rot or corrosion of the bolts. Diffucult to spot when as in some cases it all gets hidden under furniture or trim.

 

[TernVI]

On some boats the grp 'upright' (parallel to the bulkhead) is more than mere 'tabbing' for the bulkhead, it's more like a ring frame and the chain plates may be bolted through the top of it.

 

[Hacker]

Do a search on SailLife on YouTube. You will see Mads doing a lot of these. Depending on how visible the join is then you can either lay it over the ply, chamfer the ply (as above) using overlapping cloth or even do a glass-fibre butt joint. Remember to run a bead of filler, as a fillet, around the edge as fibreglass cloth doesn’t like 90 degree bends.

 

[dankilb]

This is how C&N did it back in the 70/80s. HTH.

View attachment 109536

Funny how so little changes... this is basically my method, but with 3 layers of 600gsm biax and epoxy. I know that some methods advocate something with more ‘give’ than epoxy where the bulkhead butts to the hull (to avoid hard spots), but Jeanneau appear to have used thickened polyester resin to bond ours originally so I just use thickened epoxy.

+1 for Mads’ method. Essentially what I use...