Tabbing Bulkheads

[delmarrey]

Since my boat is no longer a racer I'm converting my forward sail loft into a full head and storage area. So I'll be putting in a full bulkhead with passage way about 4' forward of the main bulkhead.

I've gotten contradicting info on construction methods, so I thought I'd put it forward here for debate.
I know one should leave a little gap between the bulkhead and hull when tabbing in the joint and to put in a soft material between the two when tabbing. But I've also seen where some have used epoxy filler, West Systems #406, to fill the gap and fair in before tabbing.

Sooo, what is the proper procedure for a foam cored hull 1"+ thick?

[minaret]

Originally Posted by delmarrey

Since my boat is no longer a racer I'm converting my forward sail loft into a full head and storage area. So I'll be putting in a full bulkhead with passage way about 4' forward of the main bulkhead.

I've gotten contradicting info on construction methods, so I thought I'd put it forward here for debate.
I know one should leave a little gap between the bulkhead and hull when tabbing in the joint and to put in a soft material between the two when tabbing. But I've also seen where some have used epoxy filler, West Systems #406, to fill the gap and fair in before tabbing.

Sooo, what is the proper procedure for a foam cored hull 1"+ thick?

I am of the second school. In all of the cases I have seen where "something soft" was inserted between the bulkhead edge and hull, they procedeed to glass a regular tab over it, thereby defeating the purpose IMHO. Often when this is done they dont fillet the tabbing first, which results in an inferior tab. You won't have bulkhead print through on your cored hull either. I'd use temp. hot glue blocks to fix it in place on the aft side, fillet and tab the front, chisel off the glue blocks, and then fillet and tab the aft side. Easy!
I have some friends here at Shilshole who have a Choate 40' on the market. It's a nice one. Let me know if you know anyone who wants to emulate you!

[mitiempo]

Glassing a tab over the foam doesn't defeat the purpose.

The foam is there so there are no hard spots where the bulkhead touches the hull. The tabbing takes the load evenly.

It doesn't have to be foam. Morris uses spacers, tabs one side and then they are removed before tabbing the other side.

The foam can be cut in a trapezoidal fashion which gives you the approximate angle of a fillet to start with.

The foam has to be closed cell so it doesn't absorb epoxy and starve the tabbing of resin.

[roverhi]

The idea of tabbing is to keep the bulkhead off the hull and spread the loaded area so it doesn't cause a hardspot and print through on the hull. Any way that accomplishes this works.

I tried the foam thing and found it to be a super hassle working alone. It didn't really accomplish anything except to waste a lot of time. I just shaped the bulkheads and furniture leaving at least a 1/2 gap and then used some spacers, usually only took one or two, to keep the bulkhead off the hull while I glassed one side then removed the spacersand did the other side. The important thing in tabbing is to get a good bond to the plywood of the bulkhead. Some advocate through bolting after glassing, drilling holes and filling with Fiberglass cloth that you wet out with the first laminate, and putting grooves in the plywood to effect a better mechanical bond. I just glassed the bulkheads with at least 6" cloth overlap and there has been no problems in the nearly 40 years since we built the boat and probably more than 30,000 miles of ocean sailing by us and subsequent owners. If you are concerned about the bond of the tab, would use epoxy resin. Did do three layers of matt and cloth each side of the bulkheads and tabbed any furniture that got close to the hull.

Couldn't talk your wife into going cruising without a head I guess. Women, they are so irrational.

[mitiempo]

When I have glassed in bulkheads I cut the foam and hot glue it in place against the hull in a few spots before placing the bulkhead against it. Hot glue guns are a great invention - I work alone as well.

[delmarrey]

Originally Posted by mitiempo

Hot glue guns are a great invention

- I work alone as well.

I bought one just for this project. I need to build up some stick forms to get the inside dimension for laying out the bulkhead shape. So I guess it be handy for other stuff as well.

I also work alone unless I need some one to hold a wrench on the opposite side of a deck or hull. Then I let the wife help a little.

[SkiprJohn]

I used the foam (hard surfboard foam) and it worked easily enough. It stayed in place by pressure from the bulkhead against the hull either by gravity or fit. It makes an easy 45 degree transition instead of 90 and helps bend mat and cloth to conform. On one bulkhead I cut slots so that the mat and cloth could be threaded but I thought that was a bit overkill so just roughed up the rest of them. I use epoxy. The prior owner/builder didn't use epoxy and didn't use much tabbing. Some of his bulkheads broke free and provided a space for dirt, grime and dry rot to hide.
Good luck in whichever way you choose.
kind regards,

[cat man do]

Originally Posted by roverhi

Some advocate through bolting after glassing, drilling holes and filling with Fiberglass cloth that you wet out with the first laminate, and putting grooves in the plywood to effect a better mechanical bond.

I and thousand of others have just put in bulkhead, hot melt glue to hold it and then pulled a medium density cove (I use a 40mm scraper with a rounded end)
Do it neat , let it kick/green and glass, no need to sand.
When that has kicked/green mix a mayonnaise consistency/runny bog and wipe in.
I actually do this and smooth with my hand (rubber gloves)


A joggle stick is a great device for getting bulkheads measured and fitting accurately
joggle stick

On my primary/main bulkheads I added an additional 300mm wide glass tape onto hull, same as hull laminate (600gsm for me) first for the bulkhead to sit in the belief that this would help spreading loads.

I only use epoxy

[SkiprJohn]

Cat Man Do,
Doesn't that create a hard spot on the hull kind of like mitiempo's left hand drawing on the glass mix is where the ply meets the hull?
Just a question. I'd like to understand your system because it does sound simpler.
kind regards,

[cat man do]

Originally Posted by SkiprJohn

Cat Man Do,
Doesn't that create a hard spot on the hull kind of like mitiempo's left hand drawing on the glass mix is where the ply meets the hull?
Just a question. I'd like to understand your system because it does sound simpler.
kind regards,

By the time the cove is done it has made it approx 2 inches wide where it hit the hull, similar to the right side of pic
The simple fact that that countless thousands of boats have been done in this fashion as recommended by designers would suggest that it is fine.

[sabray]

No one has mentioned how the plywood is addressed. I prefer you taper the edge exposing multiple laminates. Deep groove in a x pattern through out the tabbed area and then bore through several 3/8 holes. when you tab put fiberglass cord through the holes and glass these both sides of the bulkhead then lay your tabbing along the roughed out edge of the bulkhead.

[Celestialsailor]

I have a method that worked well for me and will share it here at the expense of CMD belly laughing at me...
...I tab (on one side) the bulkhead slightly off the hull. Then I layer a X-mat with a generous radius. Next I take spray foam (low expansion) and lay a bead in the gap. After it is dry, I shape a radius on the foam and glass over that. then sand smooth the whole affair.

[mitiempo]

Originally Posted by Celestialsailor

I have a method that worked well for me and will share it here at the expense of CMD belly laughing at me...
...I tab (on one side) the bulkhead slightly off the hull. Then I layer a X-mat with a generous radius. Next I take spray foam (low expansion) and lay a bead in the gap. After it is dry, I shape a radius on the foam and glass over that. then sand smooth the whole affair.

That sounds like a good way to do it.

The goal of the foam (or whatever is used) is to let the tabbing take the loading evenly.

[cat man do]

Originally Posted by sabray

No one has mentioned how the plywood is addressed. I prefer you taper the edge exposing multiple laminates. Deep groove in a x pattern through out the tabbed area and then bore through several 3/8 holes. when you tab put fiberglass cord through the holes and glass these both sides of the bulkhead then lay your tabbing along the roughed out edge of the bulkhead.

Have you ever tried to bust out bulkheads that have been put in with a simple cove and a single layer of 400gsm db?
Think diamond blades, heaps of cutting swearing and sledgehammers.

My last cat had the majority of the structural furniture simply coved in with high density, no glass.
A 40 ft cat I know of was sailed and raced hard for over a decade with structural furniture held in with low density coves no glass which finally failed but only after after a collision in the side.
The hull itself never lost water-tight integrity.

I think people seriously underestimate the strength of modern composites and overbuild not only overcomplicating the build as your example shows but adding unnecessary weight robbing performance and also adding additional cost.

I suggest some of the posters here try some destructive tests to allay their fears.

[sabray]

A lot of tabbing in many boats was done with polyester. This bonded poorly with the wood. If the bulkhead is non structrual and the hull has little flex it really wont matter. If your tabbing structural bulkheads the method I described is belts and suspenders. something else may work but this is really good form. Epoxy is my preferred resin choice