Bulkhead Strengthening

[petecasey]

Hey All,

I have a 1972 Islander 36, and they’re known to have issues with the bulkhead tabbing. I’m thinking that the bulkheads that hold in the chainplates are too weak and I’d like to strengthen them by adding another layer of wood, then reattaching the chainplates.

I’ve seen plenty of discussions on replacing the bulkheads, but no real luck adding thickness to them. One of the bulkheads tabbing has let go, but the other one it is intact and fine.

I like working with my hands but wood and fiberglass aren’t my strong suit. To do this can I simply use epoxy and some bolts to attach another piece of wood (likely epoxied or encased in glass)? I’ll tab the new face into the hull and prep that area real well, but I am hoping to get away with just a quick sand instead of getting all the old paint off.

 

[PaulK]

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That will get you pointed in the right direction. Adding a layer of plywood to your bulkhead is not as easy as it first sounds. Getting the wood shaped so that it fits properly along the top, bottom, and side is not simple. Getting one piece of wood that large into position may not be possible -- you may have to build it in several sections. This is why using epoxy is an excellent idea. If you epoxy the new bulkhead to a painted surface the epoxy will stick to the paint, and it will be the paint that is holding the bulkhead together. That is probably not what you want. Remove the paint from whatever you are gluing together with epoxy. After the bulkhead has been "bulked up" you will need to tab it to the hull. Again, any paint needs to be removed to achieve a solid connection. Hopefully you will not have to actually remove the chainplates, but simply take out the bolts holding them in the bulkhead and put in longer ones to accommodate the thicker bulkhead. Good luck!

 

[Timm R Oday25]

As someone who has replaced their bulkheads ,here are my thoughts .
Our chainplates had elongated the holes that the bolts for the chainplates went through . There wasn't any rot ,even after 40 years
I thought I would go from 1/2" to 3/4" when doing the replacement . I spent some good coin , carefully traced the pattern from the original and spent several weeks varnishing and prepping the replacement .
When it came time to slip the new and improved version , It wouldn't fit in the channel ...Grrr ..bad words were mumbled .
I started over with the original thickness and made darn sure all the ends and the holes were liberally treated to epoxy to prevent future water ingress . I'd say I'm good for another 40 years. Your bulkheads don't look all that difficult to replace .

 

[dlochner]

The first question is the shape of the bolt holes? Are they still round? Is the wood solid or are there areas of rot or evidence of water damage?

If the plywood is in good shape, I wouldn't replace the bulkhead.

The tabbing looks pretty flimsy, maybe one layer of glass. Adding a couple of layers of glass on top of the existing tabbing might be a good idea. Sand it well and use epoxy.

Adding a backing plate for the chainplates will help distribute the load better than nuts and washers. This will also reduce any movement by the bolts in their holes, reducing the possibility of the holes becoming oval.

 

[Project_Mayhem]

The first question is the shape of the bolt holes? Are they still round? Is the wood solid or are there areas of rot or evidence of water damage?

If the plywood is in good shape, I wouldn't replace the bulkhead.

The tabbing looks pretty flimsy, maybe one layer of glass. Adding a couple of layers of glass on top of the existing tabbing might be a good idea. Sand it well and use epoxy.

Adding a backing plate for the chainplates will help distribute the load better than nuts and washers. This will also reduce any movement by the bolts in their holes, reducing the possibility of the holes becoming oval.

What about a tang as a backing plate and to spread the load further down?

 

[dlochner]

What about a tang as a backing plate and to spread the load further down?

The idea behind the backing plate is to spread the compression load from the bolts. This in turn helps to spread the tension load from the rigging. The larger surface area will increase friction put a little less tension on the bolts as they pass through the bulkhead.

A tang with holes matching the chainplates could serve as a backing plate. Using the tang to add an additional bolt would help a little, I don't think it would be as effective a proper backing plate.