Bulkhead repair suggestions Gemini 105M

[Fore and Aft]

Tharch any chance you could rebate one side of the bulkhead 6mm by 75mm so that way your two half pieces are not just relying on a butt join to stay located in the bulkhead. I don't see why laminating two 6mm pieces of plywood with epoxy glue will be any weaker than one solid 12mm section. Then I would cover both sides of the bulkhead repair with 450gm double bias cloth in epoxy resin. With a layer of peel ply so you should not need to grind it afterwards. Then it's just a matter of making it look like there was never a repair there.
Cheers

[tharch]

Originally Posted by Fore and Aft

Tharch any chance you could rebate one side of the bulkhead 6mm by 75mm so that way your two half pieces are not just relying on a butt join to stay located in the bulkhead. I don't see why laminating two 6mm pieces of plywood with epoxy glue will be any weaker than one solid 12mm section. Then I would cover both sides of the bulkhead repair with 450gm double bias cloth in epoxy resin. With a layer of peel ply so you should not need to grind it afterwards. Then it's just a matter of making it look like there was never a repair there.
Cheers

You mean like a 12 to 1 scarf between the new replacement and the existing bulkhead wood?

Makes sense.
Thanks for the idea

[Cheechako]

Originally Posted by tharch

Any further suggestions? Especially, my plan of making a replacement in 2 halves?

Thanks

I dont see a problem with it. Can you put a doubler on the back side also a bit wider/taller than the inserted new piece and glue it all together? What's back there?

[tharch]

Originally Posted by Cheechako

I dont see a problem with it. Can you put a doubler on the back side also a bit wider/taller than the inserted new piece and glue it all together? What's back there?

Hi Cheechako

I can access the other side. It is just under the liner in the master bed room and the bathroom

So, no issue hiding the doubler there. In fact i can put the doubler in the front too and hide it behind a hanging locker as well

[s/v Jedi]

I recommend to put the doubler in the back, then do a neat repair in full sight in the front. Don’t hide it.

Use a good quality marine plywood from exotic hardwood and a router template to create the inlay with perfect fit. With the doubler in the back you could inlay the full thickness of the bulkhead but I would use one size thinner to create room for epoxy. Route the cavity deeper for epoxy and use spacers like toothpicks glued in with superglue to get the front 100% flush.

I would even use plywood with contrasting color face veneer to highlight the repair

[tharch]

Hi Jedi

Route the cavity deeper - do you mean make the inlay just a tad smaller so the epoxy fills the space between the edge of the inlay and the old bulkhead?

Original bulkhead is cherry laminate. Is it better to use cherry wood or a meranti type marine ply? Won't the strain of plywood edge being pulled against the edge of hardwood lead to separation of plies?

Thanks

[Sailorman Ed]

Tharch, this is not an uncommon problem. One of the worst cases is detailed here: https://geminicatamarans.groups.io/g...C40%2C95635348


Jim did a fabulous repair job ( I went to see it in person) and it very knowledgable now. But he had to replace the complete bulkhead. Yours doesn't sound as bad. I only had to replace the outer sections myself. If you have this much rot, you MUST check the lower chainplates...they are only mild steel. Keep in mind, to access the 3 lower bolts, you have to remove the master cabin headboard. Not difficult, just messy, just took a couple pics to show you.


Just notice you have an M not Mc but I think are done the same. Join the Gemini Groups forum, lots of good information there from helpful Gem owners.
Ed

[tharch]

Originally Posted by Sailorman Ed

Tharch, this is not an uncommon problem. One of the worst cases is detailed here: https://geminicatamarans.groups.io/g...C40%2C95635348


Jim did a fabulous repair job ( I went to see it in person) and it very knowledgable now. But he had to replace the complete bulkhead. Yours doesn't sound as bad. I only had to replace the outer sections myself. If you have this much rot, you MUST check the lower chainplates...they are only mild steel. Keep in mind, to access the 3 lower bolts, you have to remove the master cabin headboard. Not difficult, just messy, just took a couple pics to show you.


Just notice you have an M not Mc but I think are done the same. Join the Gemini Groups forum, lots of good information there from helpful Gem owners.
Ed

Hi sailorman

Considering this is my first real boat, if i have to replace the entire bulkhead, i will probably have a nervous breakdown 😬

It does not look too bad. Looks like some water seepage was not caught in time and it did it's magic over time. I think i only need to replace a small area thankfully.

Thanks fir the link
I did join the group and read over there too

[s/v Jedi]

Originally Posted by tharch

Hi Jedi

Route the cavity deeper - do you mean make the inlay just a tad smaller so the epoxy fills the space between the edge of the inlay and the old bulkhead?

Original bulkhead is cherry laminate. Is it better to use cherry wood or a meranti type marine ply? Won't the strain of plywood edge being pulled against the edge of hardwood lead to separation of plies?

Thanks

You need room for the epoxy glue. Take a couple of toothpicks and superglue them to the repair piece to be glued into the cavity. The thickness of the repair piece incl. The toothpick should be the depth of the cavity. Now you can use a notched spreader to apply epoxy glue to the cavity and press the repair piece in firmly. The toothpicks will act as spacers to make it completely flush while still leaving ample space for the epoxy. You need to add filler to the epoxy: first microfibers to syrup consistency, then add colloidal silica to peanut butter consistency. The nothes in the spreader twice as high as the toothpick diameter, but try it on the scrap piece… pull the repair piece off again and see if there was enough epoxy. Now you know how much to put in the cavity.

There should be a tiny bit of epoxy visible around the perimeter of the repair piece. 1/64” is plenty. It will become a dark line when finished.

I would use meranti plywood. I think you have jatoba, which is sometimes called exotic cherry. It’s darker than domestic cherry and like domestic it will darken with Uv exposure. You will never get it to match so make it contrasting instead. This works much better than hiding it.

[Bowdrie]

Originally Posted by s/v Jedi

You will never get it to match so make it contrasting instead. This works much better than hiding it.

^
Yes, then it looks like an installed "part", instead of a "patch".

[NYSail]

Not familiar with the boat, however a load bearing bulkhead, I would replace a significant amount. It holds up our mast.

Good luck!

Greg

[coopec43]

Originally Posted by NYSail

Not familiar with the boat, however a load bearing bulkhead, I would replace a significant amount. It holds up our mast.

Good luck!

Greg

I couldn't agree more.

Imagine the strains on the chain-plate in a sloppy sea?

I am alarmed that some seem to think that cosmetics are more important than structural integrity

[NYSail]

Originally Posted by coopec43

I couldn't agree more.

Imagine the strains on the chain-plate in a sloppy sea?

I am alarmed that some seem to think that cosmetics are more important than structural integrity

I would never want to be double thinking a repair in 30+ kts winds after a pretty repair to my bulkhead. Functional beauty.

[coopec43]

Originally Posted by NYSail

I would never want to be double thinking a repair in 30+ kts winds after a pretty repair to my bulkhead. Functional beauty.

Yes. There is a lot of rubbish being posted here.

Maybe theArch should be looking at posts on other forums? There's several youTube videos on the matter but I don't know how good they are./

https://www.google.com.au/search?q=c...client=gws-wiz

[tharch]

Hi Greg, coopec43 and NYsail

I am ok with the repair showing as a repair. I agree, I want the repair to hold in a harsh condition more than it's appearance. I can put a small locker or some other contrivance to make it look better. I am going to replace all the rotten part and around 6 inches around. Then I can put doubler plates and epoxy / glass the whole thing. Apparently, gemini bulkheads are designed to be not very rigid.

Thanks