Rotten Bulkhead Repair

[Capt Ben]

Im seeking advice regarding structural integrity of the forward main bulkhead. Yes, this is the one that the chainplates attach to.

A design/construction problem 25 years ago, has manifested it's ugly head. Water, as it would come down the mast via halyards, etc., would be funneled to the forward side of this bulkhead where it would pool and slowly cause the rot that I've detailed in the included sketch and photos.

This bulkhead was glassed to the aft side of a main stringer.

My questions are the following:
1. Has the bulkhead integrity and hull stiffness been compromised?

2. Would new teak marine ply glassed back into the area with butt joints just above the bottom of the doorway passage be strong enough?

3. In conjunction w/Teak marine ply, would adding 1/4" alum plate as indicated on the drawing, that is scarfed over good solid existing bulkhead sufficiently re-enforce the bulkhead?

I'm thinking I'd drill 1/8" random holes and really scuff up the alum plate to enhance bonding. The alum plate would then be cosmetically covered with teak veneer to match existing. Total thickness would not exceed existing bulkhead thickness (about 3/4")

[roverhi]

You don't need or really want to use teak plywood. The teak is only a veneer with the rest of the plywood something else. AC exterior plywood would probably work just fine or marine ply if you don't care about the expense. Tabbing the new piece to the hull should be plenty strong enough.

[Capt Ben]

Thanks for the reply.
I happen to have some teak ply that's 1/2" and about 7 layers of plys. A different site responder to my questions suggested FRP which does sound like a good idea. No bonding or rot issues.


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[Capt Ben]

Still seeking a response to my fundamental question:
1. Has the bulkhead integrity and hull stiffness been compromised (if no repair is made)?

Obviously, I'm planning on repairing this. I've already removed all the rotten wood, etc. I just want to understand what, if any structural implications there are to this repair.


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[hellosailor]

Ben-
Have you tried contacting Farr yet?


I think that's
Farr Yacht Design
613 Third St. Suite 20
Annapolis MD 21403
+1 410-267-0780
info@farrdesign.com


They might know best about structural issues and recommended fixes.


FRP will weigh more than many plywoods, but it certainly eliminates any moisture issues. If honeycomb FRP is suitable, that gives you strength and gets weight off the boat. Either one can be surfaced with teak veneer if you want to keep the teak look.

[Capt Ben]

I guess I could call the Farr office. Though my boat was built in 1990 in Rio Dejanero, the design goes back to 1978 when Bruce Farr was in NZ.
My assumption is that even if they are willing to discuss this issue they will basically say 'yes it's structural' and that I should have a professional repair it. I can't imagine them saying much else due to liability issues. Then again...

[brantleychuck]

Not sure that you hull integrity question can be answered, my guess is that a fiberglass boat produced 25 years ago has plenty of strength even with the rotten bulkhead , but like you said , your going to fix it. I can't make out any fine detail from your pictures but I get the idea I think. With all the rotten wood removed and smoothed out I would simply lay pieces of fiberglass in and build area back up, use polyester or epoxy, I think polyester would be fine. I have done this on two different boat bulkhead repairs. Very quick and easy to do. With a boat like this I can't see weight being a consideration.


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[Capt Ben]

Great input from everyone THANK YOU.....
​So, after comparing densities of marine ply w/FRP I'm greatly leaning towards the much more expensive and heavier G10/FR4 that McMaster sells. I calculate that the Alum plate that I drew made of 6061 Alum 3/16" would weigh ± 2.2 pounds. The (2) 3/16" G10 doubled up would weigh about 3.2 pounds. The marine ply at 1/2" would be about 1/2 pound. I guess it's a good thing the weight change is minimal however I do race this boat.

As my original ply was likely 1/2" or maybe 5/8" thick, I'm considering using two thinner sheets of the FRP, 3/16" and applying one in place, and immediately inserting the second layer of 3/16" In this manner, I'm hoping that I'd be able to maneuver the thinner sheets down into the 2 1/2" to 3" cavity left from where the original wood went right down to the hull. And of course the second sheet would be well slathered in thickened epoxy to help fill any voids left.

By laminating this repair up I figure that I can not only get the material built up in these difficult locations, but that the end product would be even stronger. This build up method would also make it easier to scarf the joint into the vertical sections of the good existing bulkhead on either side of the passage door (only about 2" in width. Essentially replacing on my drawing the aluminum plate with the 2 laminated up to 1/2", (2) 3/16" FRP panels.

[minaret]

Originally Posted by Capt Ben

Great input from everyone THANK YOU.....
​So, after comparing densities of marine ply w/FRP I'm greatly leaning towards the much more expensive and heavier G10/FR4 that McMaster sells. I calculate that the Alum plate that I drew made of 6061 Alum 3/16" would weigh ± 2.2 pounds. The (2) 3/16" G10 doubled up would weigh about 3.2 pounds. The marine ply at 1/2" would be about 1/2 pound. I guess it's a good thing the weight change is minimal however I do race this boat.

As my original ply was likely 1/2" or maybe 5/8" thick, I'm considering using two thinner sheets of the FRP, 3/16" and applying one in place, and immediately inserting the second layer of 3/16" In this manner, I'm hoping that I'd be able to maneuver the thinner sheets down into the 2 1/2" to 3" cavity left from where the original wood went right down to the hull. And of course the second sheet would be well slathered in thickened epoxy to help fill any voids left.

By laminating this repair up I figure that I can not only get the material built up in these difficult locations, but that the end product would be even stronger. This build up method would also make it easier to scarf the joint into the vertical sections of the good existing bulkhead on either side of the passage door (only about 2" in width. Essentially replacing on my drawing the aluminum plate with the 2 laminated up to 1/2", (2) 3/16" FRP panels.

Use Coosa board. Go with BW26 for a main bulkhead.


Consider a Scarffer attachment. Makes scarfing in place much easier.

[Capt Ben]

The Coosa board BW26 looks prey cool. From checking out their distributor's web sites, it looks near impossible to get small amounts. The thinest seems to be the 1/4". If this stuff is as stiff as I think it is, I still think I need to laminate the repair up with (2) layers.

As I haven't worked with this product or the G10, can anyone advise how much flex say a 10" x 24" wide strip might have if it is 1/2" thick? I need to flex it a bit on the narrow dimension such that I can insert it into place.

[minaret]

Originally Posted by Capt Ben

The Coosa board BW26 looks prey cool. From checking out their distributor's web sites, it looks near impossible to get small amounts. The thinest seems to be the 1/4". If this stuff is as stiff as I think it is, I still think I need to laminate the repair up with (2) layers.

As I haven't worked with this product or the G10, can anyone advise how much flex say a 10" x 24" wide strip might have if it is 1/2" thick? I need to flex it a bit on the narrow dimension such that I can insert it into place.

Coosa is a direct replacement for marine grade ply, and is designed to have similar properties in all areas but rot resistance. If you can bend a 10"x24" strip of 1/2" ply enough, you can very likely bend the Coosa enough. Maybe even more, as the ply would probably fail sooner. You should be able to source half sheets, ie 4'x4'.

[minaret]

If you can't find it locally, call these guys.



Marine & Boat Supplies Since 1928 | Fisheries Supply

[CarlF]

G10 is really hard to bend. But since you are going to laminate two pieces, just cut each piece in half with the cuts offset. The thickened epoxy plus some screws driven through both layers will make it as strong as a single unit.

Use thickened epoxy to fill any gaps where your piece meets the old fiberglass and then tab it with several layers of fiberglass tape (as you planned). Get the old fiberglass really clean (sanding and acetone) so that the tab adheres well.

[MarkSF]

I am slightly concerned by the discoloration of the veneer, under the doorway, after removal of the rotten part. I saw similar discoloration on a bulkhead that was hiding rotten ply. The problem is that the teak veneer can be solid, but the underlying ply can be rotten. Are you sure you've removed all the rot?

[Capt Ben]

Originally Posted by MarkSF

I am slightly concerned by the discoloration of the veneer, under the doorway, after removal of the rotten part. I saw similar discoloration on a bulkhead that was hiding rotten ply. The problem is that the teak veneer can be solid, but the underlying ply can be rotten. Are you sure you've removed all the rot?

You are absolutely correct about the underside of the doorway and partly up the starboard side. In this more detailed view from aft looking forward you can see the forward sole support moulding (no bulkhead remaining). I do plan on removing more as I go up each side for the scarfing in of the repair material.