bulkheads with foam or no?

cyrano138

New member
24
3
Venice, FL
Replacing all bulkheads on my Cal 20. The original build seems to be half inch or 3/8 plywood tabbed directly to the hull. I don't see any spaces or foam. I don't see any hard spots on the hull either though. Is there a way to do a decent job of it without using foam? If not, what foam do I use? I have done a fair amount of searching and YouTube watching and it seems like most people just set the new bulkheads into a thickened epoxy mixture and then tab them in.

 

Santanasailor

Charter Member. Scow Mafia
1,357
707
North Louisiana
A decade ago, I replaced the Santana’s bulkheads with factory fiberglass/plywood bulkheads that did not fit.  Used thickened epoxy to fill in the blanks.  Messy/lousy job that I have hated ever since. Looks really bad.  The only thing I can say, it is a very strong.   If I was to do it again, I would have fabricated my own, out of that most nasty of stuff, treated plywood, Fitted it closely too the hull, tabbed it in and called it done.  The stuff does take paint, and the finished project, with paint would be one hell of a lot better looking.  

So, while I am not familiar with the Cal 20’s hull/cabin, my suggestion is to fit them as closely as possible, tab them in and use the bare minimum thickened epoxy.   

 

SloopJonB

Super Anarchist
68,782
12,403
Great Wet North
I tried that but it wouldn't fit through the hatch.

Pantograph_550x300px.jpg


Seriously, the joggle stick is stone axe simple, can be made quickly for a specific situation and, as I said, creates a flawless cut line provided enough points are taken.

And it's very quick - fitting and plumbing the tick board it the only setup required.

 

cyrano138

New member
24
3
Venice, FL
A decade ago, I replaced the Santana’s bulkheads with factory fiberglass/plywood bulkheads that did not fit.  Used thickened epoxy to fill in the blanks.  Messy/lousy job that I have hated ever since. Looks really bad.  The only thing I can say, it is a very strong.   If I was to do it again, I would have fabricated my own, out of that most nasty of stuff, treated plywood, Fitted it closely too the hull, tabbed it in and called it done.  The stuff does take paint, and the finished project, with paint would be one hell of a lot better looking.  

So, while I am not familiar with the Cal 20’s hull/cabin, my suggestion is to fit them as closely as possible, tab them in and use the bare minimum thickened epoxy.   
I think the idea is that there needs to space (or something soft like foam) between the hull and the wood to avoid deforming the hull under stress. The only thing people seem to agree on more unanimously than that you should build it that way is that no one actually bothers to build it that way.

I don't even know what kind of foam to use. Polystyrene foam seems to throw out a ton of gas when epoxy is laid up over it (regardless of thickness or exothermic intensity), making it a royal pain to work with, and I don't know if you can buy something more like polyurethane foam (which might not be compatible with epoxy anyway) in sheets or strips.

I tried that but it wouldn't fit through the hatch.



Seriously, the joggle stick is stone axe simple, can be made quickly for a specific situation and, as I said, creates a flawless cut line provided enough points are taken.

And it's very quick - fitting and plumbing the tick board it the only setup required.
I'm actually super pumped to try the ticking/joggle stick method. I was legitimately worried about having to get the old bulkheads out in one piece to use as a template until I learned that I don't have to. There is very little room to work in the back half of the cal 20.

 

SloopJonB

Super Anarchist
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Great Wet North
Read a few of the entries on the web before you start - there are a lot of variations in the details. The link I posted was just an example.

The saw tooth joggle stick is better and easier - less prone to error than the old tick stick method.

Edit: number the "valleys" on the stick and record those numbers on the traced outline on the tick board - makes alignment on the workpiece much quicker and more certain.

 
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cyrano138

New member
24
3
Venice, FL
Read a few of the entries on the web before you start - there are a lot of variations in the details. The link I posted was just an example.

The saw tooth joggle stick is better and easier - less prone to error than the old tick stick method.

Edit: number the "valleys" on the stick and record those numbers on the traced outline on the tick board - makes alignment on the workpiece much quicker and more certain.
Oh I thought they were the same thing. I think I'm thinking of the joggle stick. I planned on using a longer one with two or three saw tooths. Numbering is a great idea! I will do that for sure.

 

Zonker

Super Anarchist
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5,686
Canada
Foam strip is a good idea to soften the joint on lightly built foam core race boats. It probably does prevent telegraphing the bulkhead through thin solid laminates. But 95% of boats of that era were not built that way. If you did it, you would use a boatbuilding foam like Corecell, Divinycell etc. Something with a high density of 5 lb/ft3 (80 kg/m3) or so. Not polyurethane or polystyrene (shudder)

On a Cal20 I would not bother. Just thickened epoxy in the gaps, a nice fillet and tab it in.

 

cyrano138

New member
24
3
Venice, FL
Foam strip is a good idea to soften the joint on lightly built foam core race boats. It probably does prevent telegraphing the bulkhead through thin solid laminates. But 95% of boats of that era were not built that way. If you did it, you would use a boatbuilding foam like Corecell, Divinycell etc. Something with a high density of 5 lb/ft3 (80 kg/m3) or so. Not polyurethane or polystyrene (shudder)

On a Cal20 I would not bother. Just thickened epoxy in the gaps, a nice fillet and tab it in.
My background is more from surfboard building, hence my only really knowing those two kinds of foams. I appreciate the suggestions because I never would have known where to start.

I also appreciate your recommendation specific to my boat. I am happy to hear that it's probably not necessary for the cal 20. Anything I can do to simplify the project is helpful as there's a tremendous amount still ahead.

 

DRDNA

Anarchist
573
13
Ventucky
Hey Cyrano 138, I've used polyurethane foam (5 lb density) quite a bit with epoxy resins- it's actually pretty good.  PVC foams like core cell, divinicell, etc. is even better at not absorbing water.  Lots of boats made in Santa Cruz just left a small gap between hull and bulkheads to avoid hard spots- I'm not good enough to leave a gap.

 

SloopJonB

Super Anarchist
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Great Wet North
Oh I thought they were the same thing. I think I'm thinking of the joggle stick. I planned on using a longer one with two or three saw tooths. Numbering is a great idea! I will do that for sure.
This is the style I used.

I made one long one and one short one.

The inner edge of the tick board needs to match the inner edge of the bulkhead you are marking out. You align it to the edge of the bulkhead material so after marking the curve and cutting it you are finished.

mf029tx.jpg


 

CaptainAhab

Anarchist
849
230
South Australia
Oh I thought they were the same thing. I think I'm thinking of the joggle stick. I planned on using a longer one with two or three saw tooths. Numbering is a great idea! I will do that for sure.
You don't need the teeth. Simply take a stick of wood, cut a 45 or more degree angle on one end. Leave the other end square. Push the pointy end into the thing you are scribing. Run your pencil down the straight side. Run your pencil across the end. You will now have a L shaped line on your template. Easy to index off of when you go to cut your part. 

It also gives you the option to easily make your part smaller(like fitting foam??????). If you want it smaller than an exact fit, shorten the stick by exactly the about you prefer when you transfer your ticks. This only works if the tick lines are more or less tangent to the shape you are templating. Other is gets a bit off.

You can also easily make more matching spiling sticks. You've got one inside the boat spiling one template, your conscript is cutting a part using a matching spiling stick because it's simply a defined dimensional stick. 

The teeth are a waste of time.

 
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Steve

Anarchist
563
77
duluth, mn
You don't need the teeth. Simply take a stick of wood, cut a 45 or more degree angle on one end. Leave the other end square. Push the pointy end into the thing you are scribing. Run your pencil down the straight side. Run your pencil across the end. You will now have a L shaped line on your template. Easy to index off of when you go to cut your part. 

It also gives you the option to easily make your part smaller(like fitting foam??????). If you want it smaller than an exact fit, shorten the stick by exactly the about you prefer when you transfer your ticks. This only works if the tick lines are more or less tangent to the shape you are templating. Other is gets a bit off.

You can also easily make more matching spiling sticks. You've got one inside the boat spiling one template, your conscript is cutting a part using a matching spiling stick because it's simply a defined dimensional stick. 

The teeth are a waste of time.
I agree, there is no need for all the fancy notches and shapes. I use a much longer angle on the pointy end than 45 deg though and just cut a notch on the end, almost anything works fine as long as its asymmetrical.  I used to do a lot of work with the joggle stick method 40-50 years ago before hot glue guns became available and i got wooed away by a "better" method. That was a mistake. Just this winter i showed my son the joggle stick method to replace all the bulkheads in an old one tonner and remembered  what a good system it still is. 

 




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