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Old 22-05-2022, 07:30   #1
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Bulkhead replacement

Ahoy all, new to the forum here but have a question on some renovation plans Iíve got lined up,
I got myself a 35 fr 1972 Bristol that was about 95% eaten through by termites, full fiberglass hull, so that was fine, but we had to strip out that 95% of the internal wood, including all but 2 bulkheads,
Now, the issue Iíve hit with putting new ones back in, is that the originals were all one solid piece of ply that was installed before the top deck was put on the hull, and thereís no way I can get that size a board in through the companion way,
What Iíve come up with is the plan to build new bulkheads out of panels of plywood running horizontally, with support beams running vertically thru bolted to each plywood panel and then tabbing this entire structure to the hull and glassing over the seams between the panels.
I know this wonít be as strong as how itís supposed to be built, but accepting that we shouldnít ever put the old girl under full canvas after this rebuild, is this a horrible idea? Is there a better way I can rebuild bulkheads if I canít make it all one piece of plywood? Any advice would be appreciated, Iíve got the time and tools to try anything,
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Old 22-05-2022, 07:40   #2
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pirate Re: Bulkhead replacement

Dunno if the boat builders here will agree but.. I think it will work just fine if you epoxy the edges well before sitting the next panel wet on the first etc then glass the whole with 4oz fine glass and epoxy, plus a finishing coat.
Soak all cut/exposed edges well with epoxy.
Tab each panel to the hull as you go..
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Old 22-05-2022, 07:44   #3
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Re: Bulkhead replacement

Scarf the bulkheads horizontally. If you are careful the grain will match, if you intend to paint them the join will be invisible.
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Old 22-05-2022, 08:12   #4
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Re: Bulkhead replacement

You can rabbet the bulkheads together in the boat so you can get them inside. Horizontal or vertical, although horizontal will show less. Pick spots to do it that dont show like below the top of the cushion. Epoxy and screw or epoxy/bronze nail from the back side. For instance, on a main bulkhead, maybe screw from the head side below sink cabinet level etc.
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Old 22-05-2022, 08:15   #5
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Re: Bulkhead replacement

Sounds like a plan, and ditto on the above. The major issue will be the wood you choose. It would be a bit stiffer and weigh a bit less if you used 1x6 (actually 3/4) boards rather than 3/4 inch plywood, but then you can get pretty big sections of plywood through the hatch. I see no reason that you could not make her stronger than the original.

Good luck with it.
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Old 22-05-2022, 08:29   #6
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Re: Bulkhead replacement

That’s a good tip on it to be soaking the panels together as I go, I was originally planning to construct and then fiberglass coat, but coat while construction for sure makes better sense
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Old 22-05-2022, 08:35   #7
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Re: Bulkhead replacement

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Originally Posted by tkeithlu View Post
Sounds like a plan, and ditto on the above. The major issue will be the wood you choose. It would be a bit stiffer and weigh a bit less if you used 1x6 (actually 3/4) boards rather than 3/4 inch plywood, but then you can get pretty big sections of plywood through the hatch. I see no reason that you could not make her stronger than the original.

Good luck with it.
Id intended to work with 3/4 plywood and pressure treated 2x4 for the bolted on support beams, I’m suprised you say it may be stronger than the original, I had assumed having the glasses together panels would rob it enough that the supports would just be bringing it back to acceptable
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Old 22-05-2022, 10:07   #8
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Re: Bulkhead replacement

Another method I've used successfully in my 60+ year old plywood charter boat.

Make the panels out of plywood that is 1/2 the thickness of the original. For example, 3/8" panels for a 3/4" bulkhead. As you start, make the second panel half the width of the first so that the joint ends up in the the middle of the first panel. Now continue making panels of equal widths, and you will eventually end up with a full size bulkhead.

Laminate the front and back together using epoxy (thickened West works, but I find system 3 gel magic to be much more efficient). Before you glue, assemble the pieces dry and fasten with 3/4" (or whatever is appropriate for your final thickness) screws. If glassing or painting afterwards, you can leave them in, or pull them after the glue is dry. I usually just leave them in, but once the glue is dry, they do nothing for the strength of the bulkhead. Make sure that you use a tapered drill bit and that the hole is large enough on the side with the screw head that you get good clamping pressure.

If you have easy access to both sides, you can even put some screws from the back to ensure that you get even clamping pressure.

When you are done, you will have fabricated a new bulkhead that is the same thickness as original, the only difference being that you have one glue joint being epoxy instead of resorcinol or whatever it is that they use in marine plywood nowadays.

Either pull the screws and fill the holes with epoxy, or just fill the heads with epoxy and decide how to finish it.

If you are going for a natural wood look on the inside, you will have to put a veneer over the completed bulkhead. Laminate (formica) is another option, or simply paint it and call it good.
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Old 22-05-2022, 13:59   #9
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Re: Bulkhead replacement

CapnMichael:

Markusm is right. Do the bulkhead laminated from two layers the way he describes. I would use 1/2" material.

Your major problem will be getting the panels to fit TIGHTLY against the hull so that you can make your "tabbing in" of sufficient quality. Therefore: 1) Do you know how to "spile" a curve? 2) Do you know how to bevel an edge to a bevel that is constantly changing along its length?

In way of your mast, the finished, installed bulkhead, which in you boat forms the after bulkhead in your heads, has to withstand vertical compressive forces imparted by a deck stepped mast. I believe this load is taken to the keel by means of solid stock laminated to the inboard edge of the bulkhead so that these pieces of stock form a compression post. It is very important to get that right!

Best of luck with your project :-)!

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Old 23-05-2022, 09:14   #10
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Re: Bulkhead replacement

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Originally Posted by TrentePieds View Post
CapnMichael:

Markusm is right. Do the bulkhead laminated from two layers the way he describes. I would use 1/2" material.

Your major problem will be getting the panels to fit TIGHTLY against the hull so that you can make your "tabbing in" of sufficient quality. Therefore: 1) Do you know how to "spile" a curve? 2) Do you know how to bevel an edge to a bevel that is constantly changing along its length?

In way of your mast, the finished, installed bulkhead, which in you boat forms the after bulkhead in your heads, has to withstand vertical compressive forces imparted by a deck stepped mast. I believe this load is taken to the keel by means of solid stock laminated to the inboard edge of the bulkhead so that these pieces of stock form a compression post. It is very important to get that right!

Best of luck with your project :-)!

TrentePieds
I am unfamiliar with Ďspileí-ing Iíll have to do some research there and find out what I donít know,
as for the curves Iíve already replaced the floor beams and decking plywood with a combo of jigsaw and palm sander work to ensure Iím getting my angles right for contact to the hull contours, so I have confidence in getting a tight fit

Our compression post is still in place for most of the vertical force, thankfully it had minimal termite damage(no tunnels going in, just some divots) and could be left in place, surprisingly though the bulkhead had previously just been screwed to the compression post that is glassed in top and bottom, not even construction adhesive,

I will look up on splies and figure what I may need in my tool kit to do it right, thank you for the information!
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Old 23-05-2022, 09:32   #11
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Re: Bulkhead replacement

Do not put the bulkheads tight against the hull as has been suggested. This will end up with hard spots visible, to the trained eye, on the external hull. And the visible part is not even the main issue.
A far better way to do it is to leave a gap, 1/4 is nice but at least 1/8, between the bulkhead and hull. Tab one side. Fill the gap from the other side with a polyurethane adhesive. I would recommend the loctite marine sealant from home dopey for $12 a tube. Same stuff as 3m 5200 but reasonably priced.
After cure tab the other side.
Oh, and biaxail cloth is the stuff to use for tabbing. Available in various widths. If you use cloth half the weave adds no strength as it runs parallel to the joint.

There is literally a dozen ways to fit the bulkheads,you just have to choose which you want to do, and you should easily be able to return to or exceed original build strength.
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Old 23-05-2022, 14:57   #12
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Re: Bulkhead replacement

There is no reason to expect lesser strength than original, with some reasonable careful work you can equal or better the original.
In the above post by Allied39 he has pointed out some good stuff.
In high-end construction the bulkheads would be landed on tapered closed-cell foam strips so that the bonding/tabbing does not form a 90 degree "angle iron" of fiberglass between bulkhead and hull but rather an angled joint, but it's quite labor intensive.
Anyway, yes, a gap is better and worthwhile.
A couple of tabs to maintain position with some clamps/sticks inboard to support the bulkhead.
Then you just use squirt-foam to fill the gap, use some 40 grit to fair off the foam on each side and complete the glass taping of the joint.
Make sure all edges of wood are well sealed before installation.
You did not indicate if boat is afloat or on the hard.
If on the hard make all effort to ensure bulkheads are square and plumb with factory waterline.
If afloat things get more dicey.
Absolutely nothing so frustrating as trying to fit an interior to crooked/out of plane bulkheads.
If the grain of the wood runs horizontal, you will spend endless hours of labor to hide what can become an eyesore.
If covering with additional material then not so much concern.
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Old 23-05-2022, 17:36   #13
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Re: Bulkhead replacement

I had considered foam but if foam wears while the boat works , well it's gone. Polyurethane adhesive gives the advantage of movement and adhesion without the possibility of material loss.
Using small packing blocks to hold the bulkhead off the hull surface and then tabbing one side works well.
Tap out the blocks then shoot the gap full of sealant, just edge it with a finger and when dry tab over.
And few folks know of the loctite marine adhesive from home dopey, but it is polyurethane, and good for below water.....and $12 a tube.....which is what all the other sealants should be were it not for open blatant theft.
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