Correct way to Tab bulkheads

[Tsalta]

Hi,

When tabbing fibreglass at a right angle is the correct method to lay the largest mat first and work to the smallest, or smallest first finishing with the largest, or does it not matter?

Thanks
Jeff

[coopec43]

Originally Posted by Tsalta

Hi,

When tabbing fibreglass at a right angle is the correct method to lay the largest mat first and work to the smallest, or smallest first finishing with the largest, or does it not matter?

Thanks
Jeff

I don't think it matters which way you lay up..

I used an Airex "Buffer" to spread the load. I primed the timber with a thinned down acetone/polyester resin (10% acetone) before laying the glass.

I cut 2in. holes about every 8in. around the perimeter of the bulkhead. I then fiber-glassed from each side so that the tabbing on both sides joined through the holes. Probably an over-kill but that is what Bruce Roberts recommended in his designer jottings. You can see the "holes" in the bulkhead in the following photo

[Benz]

Your tabbing will be tidier looking if the widest strip goes on last, so all the edges of the inner ones aren't visible. Lately I've been in the habit of finishing every lamination with a layer of 10-oz woven cloth, very carefully put on so it looks good when dry.
That saves a lot of cosmetic sanding later.

[coopec43]

Originally Posted by Benz

Your tabbing will be tidier looking if the widest strip goes on last, so all the edges of the inner ones aren't visible. Lately I've been in the habit of finishing every lamination with a layer of 10-oz woven cloth, very carefully put on so it looks good when dry.
That saves a lot of cosmetic sanding later.

Good idea if the tabbing will be visible but all mine is hidden behind beds, cupboards, headlining etc.

[Tsalta]

Ok, great.

Thanks

[Allied39]

Depends whether you are looking for "looks good" or is structurally sound.

Largest first gives the largest adhesion area. Anybody who does fiberglass repairs knows this. Small to largest demonstrates somebody does not know what they are doing.

I do not use foam, foam degrades with movement, obviously. Tab one side with a gap, 3/16 to 1/4. Fill the gap between bulkhead and hull with a polyurethane sealant. If you are in the US (lucky you) the Loctite marine sealant sold at home dopey is about the best priced polyurethane sealant available. Think 3M 5200 without the silly price.

You want polyurethane over polysulphide, preferably.

Then tab the other side after the sealant has cured. Good job done properly which will last.

Do as you please.

[wyb2]

Originally Posted by Allied39

Depends whether you are looking for "looks good" or is structurally sound.

Largest first gives the largest adhesion area. Anybody who does fiberglass repairs knows this. Small to largest demonstrates somebody does not know what they are doing.

…..

This seems to be one of those things that the internet is very adamant about, but pros seem to be less worried about.

The logic that it gives the largest adhesion area doesn’t really make sense. Every layer is put on with resin, the final surface area that sees resin is the same regardless of order.

In reality it likely doesn’t matter, the difference between the two methods should be negligible compared to the safety margin the joint should have. If the joint fails, it will be because not enough glass was used, not enough surface area was used, or there was some problem with the bond (like poor prep) - not because of the order the layers were applied.

[Chotu]

I agree with all of the above posts. But like was mentioned, make sure you float those bulkheads. Otherwise you end up with awful looking lumps on the outside of the boat.

I’m also having a little bit of difficulty picturing why you need so many layers of glass.

All of my bulkheads are glassed in fully (not just tabs) using a single layer of 12” wide 12oz (I think) biax. The glass goes all the way around the bulkhead on both sides. In a complete circle if it’s a full bulkhead.

And boy did those get put to the test yesterday in Tampa Bay. I was doing 7 kn into the chop. Pounding the crap out of the hull. Just out of curiosity anyway. Just to see that it can take it. I hit HARD off some of that chop. All is well

[s/v Jedi]

The nice thing using foam is that it keeps everything in place and provide the radius for the fiberglass to lay correctly in the corner.

Once the epoxy has cured, the foam prevents the hard spots and stress noise while underway.

Tests have shown no measurable difference between tabbing layup schedule biggest piece first or last. Importance should be on using epoxy, mixing it correctly, and using an aluminium thin roller to work the air pockets out.

For a neat finish, apply peel ply last.

[Chotu]

One more thing to add about the foam. You can definitely use foam. It’s preferable. Just like Jedi says.

And interestingly enough? You can use nothing. Seriously. If you put a little 1 cm piece of foam in a few spots and float the thing in the air, that’s just fine. The bulkhead does not rest on the hull to transfer the load. It’s transferred through the fillet cove joint that you make and the glass and you are talking about doing.

If the foam is deforming because the bulkhead is moving, you have some really serious problems. That means your boat is falling apart and is going to basically fail at sea. Lol so that’s not going to happen if you properly glass the bulkheads in. They won’t ever move again. Whatever you put in there to space the bulkhead, chewing gum? Ha ha It doesn’t matter.

[Bowdrie]

Originally Posted by wyb2

This seems to be one of those things that the internet is very adamant about, but pros seem to be less worried about.
The logic that it gives the largest adhesion area doesn’t really make sense. Every layer is put on with resin, the final surface area that sees resin is the same regardless of order.

^ This.
As stated previously, largest last invariably produces smoothest most visually pleasing results with less work involved.
That 2nd pic, showing the bulkhead spaced off of the hull is the "pro" way to go.
Eliminates hard spots/stress risers and "print thru", particularly in thinner hulls.
Also, common procedure for Pro application is grinding on the top layer of veneer on the plywood back from the edge a bit so the first-on narrow layer(s) are not so prone to produce bumps/lumps on the surface.
An angle grinder with a VERY course disc, (like 36 grit,) make that go fast and produces a surface that has better bonding characteristics for the initial layer(s).

[s/v Jedi]

Originally Posted by Chotu

One more thing to add about the foam. You can definitely use foam. It’s preferable. Just like Jedi says.

And interestingly enough? You can use nothing. Seriously. If you put a little 1 cm piece of foam in a few spots and float the thing in the air, that’s just fine. The bulkhead does not rest on the hull to transfer the load. It’s transferred through the fillet cove joint that you make and the glass and you are talking about doing.

If the foam is deforming because the bulkhead is moving, you have some really serious problems. That means your boat is falling apart and is going to basically fail at sea. Lol so that’s not going to happen if you properly glass the bulkheads in. They won’t ever move again. Whatever you put in there to space the bulkhead, chewing gum? Ha ha It doesn’t matter.

Indeed, the foam doesn’t provide any additional strength and an air gap would be okay, but to lay properly radius corders with the tabbing, having something to work against is required or you get voids in the laminate.

The bulkheads don’t move, but they flex as does the tabbing. The whole hull flexes. Plywood is very stiff and will make noise when the edge touches the hull. Not just from flexing, but also changes in temperature and moisture.

[HeywoodJ]

Originally Posted by coopec43

Good idea if the tabbing will be visible but all mine is hidden behind beds, cupboards, headlining etc.

All the more reason to do it very neatly. Exposed stuff is easy to work around, but there is nothing like reaching into a hidden hole because you have to work on something way out of the way, and stabbing yourself on some strand of fiberglass sticking out from the tabbing (or anything else)

I'd prefer a perfectly smooth finish in all the place I can't see than all the places I can.

[JBP]

A time saving tip is to cut all your glass to the same width and shift it when installing.
E.g. cut glass to 6 inches wide, first layer is 2 inches one side vs 4 inches on the other, second layer shifted the opposite, and third layer is even 3 inches on each side.

[UserError]

The surveyor who advised on my keel stubs rebuild stated a preference for smallest first, that in the event of any laminate separation, each new layer edge represented a new barrier to the separating forces, whereas once the 'big layer on first' starts delaminating, there's nothing to stop it. I buy that reasoning behind smallest first. Vaitses shows small layer first and Staton-Bevan shows largest first - you pays yer money. As has been said, if it's done properly, its probably a moot point.