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Old 04-25-2012
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Proper way to tab bulkheads on a fiberglass boat

Hunters and other production boats seem to use a piece of roving, with no epoxy filler under it, to tab in bulkheads. I read somewhere that the lack of filler is to prevent "hard spots" in the hull.

What are "hard spots"? Are these more of a problem on coastal boats with thin hulls than on quality boats with thicker layups?

Better quality boats, such as C&C's, seem to use several layers of regular glass instead of a single piece of roving. Being opaque, I can't tell whether there is glue/filler at the actual joint and under the glass.

Can anyone help me, what is the best way to glass in a bulkhead?

If I wanted to add a bulkhead to my boat, should I do it "stitch and glue" style, with a bead of epoxy and filler covered by a few layers of glass cloth, or will that create "hard spots"? Roving would be easier to use, but it is considered inferior to several layers of say 10 oz glass by Don Casey. Is there a significant difference in strength and quality of the joint?
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Old 04-25-2012
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Re: Proper way to tab bulkheads on a fiberglass boat

I installed my new bulkheads with a strip of closed cell foam between the bulkhead and the hull or deck. This is to prevent the hard spots. The hard spots develop when the bulkhead is in actual contact with the hull or deck. Keeping a space with either foam or an epoxy filet is how you prevent this.

I then used a couple layers of biaxial cloth and epoxy to tab it to the hull.
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Re: Proper way to tab bulkheads on a fiberglass boat

Evidence of a 'hard spot' is when you can actually 'see' the location of a bulkhead from outside the boat.. most common with single skin hulls as opposed to cored, and most noticeable with a shiny hull surface.
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Re: Proper way to tab bulkheads on a fiberglass boat

I am not sure... but we will hear from the experts before long probably...but I will say that I think a small fillet along the tabbed areas with a few layers of glass over it would be needed to reduce any bulkhead movement and seal joints to reduce moisture migration ...sealing the butt ends of the ply with epoxy is critical so it doesnt wick up moisture. Then consider leaving a small expansion-type gap at where the bulkhead, etc. panels meet the hull/coachroof that can be sealed as part of the epoxy fillet...and then tab over with light/heavy glass layers...the epoxy filled into expansion gap you left purposefully should move a bit with temperature changes/hullor deck pressure if you follow...allowing the panels to have some flexibilty under loads without encouraging any warp tendencies...I am not an expert but I have heard this is a good way to approach tabbing..please correct me in the gallery if I am mistaken...I don't want to give false info on boat construction yet..I'll wait till I know a bit more before I do that...
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Re: Proper way to tab bulkheads on a fiberglass boat

Actually, Beersmith said what I said and probably said it better... in about a third of the amount of wordage I used...bravo Beersmith!
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Re: Proper way to tab bulkheads on a fiberglass boat

If you have failed tabbing on an otherwise sound bulkhead, assuming you have access, you can improve the situation by cutting slots in the bulkhead above the original tabbing edge, and lay in biaxial glass or epoxy as shown below.. this creates a much more powerful bond with the hull and 'locks' the bulkhead in place without relying solely on the "sheer resistance" of the normal parallel tabbing layup.... FWIW...

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Re: Proper way to tab bulkheads on a fiberglass boat

I have a couple of additions to the good advice listed so far.

First, coat the surfaces of the ply, where the glass will go, with epoxy, BEFORE you start the installation - not just the end grain of the edge of the bulkhead. The wood will absorb some resin and if it's not precoated, it will have to pull this out of the first layer of glass, weakening this most critical bond a bit.

Next, an easier method than Faster's slot method for anchoring the tabbing is to simply drill through the tabbing and bulkhead, after the glass has cured and been finished, and install appropriately sized machine screws. This bolts the tabbing and bulkhead together, preventing any movement which could cause delamination. The attached (poor) picture shows one of them beside the starboard chainplate. I installed eight of them like that, equally spaced on each bulkhead.

Last, a very tidy and craftsman-like installation can be done one of two ways - install a slightly thinner than normal bulkhead and then epoxy laminate thin facing panels over each side of the bulkhead and tabbing strips so the total is the correct thickness for the bulkhead.

Or;

Rout a rabbet the width and thickness of the tabbing into the edge of the bulkhead before glassing.

Either of these methods will keep the tabbing from sticking up above the finished bulkhead surface. Makes a very nice installation on bulkheads that show. Not worth the effort on hidden ones.
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