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Exterior Plywood for Bulkheads?

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Randall
Navigator

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123 Posts

Initially Posted - 10/08/2003 : 22:39:39

Kite's bulkheads are rotted and must be replaced. I'm not overly fond of the original darkly stained bulkheads, I think they make a small interior feel even smaller.

I'm considering using B-C grade 3/4" plywood for replacement bulkheads, and then covering them with a light colored Formica or fabric. Will Formica help keep the wood from warping or delaminating in high heat & humidity?

What if I seal the wood, then cover it with the interior fabric that the boat stores sell? Would it hold up as well as sheathing it in Formica? Might it also help reduce condensation, and perhaps improve accoustics for the stereo system?

Howsabout using A-B grade plywood and a lighter stain? I've been told that the only difference between "Marine Grade" and "Exterior Grade" is the surface layer of wood. True?

Randall
79 SK/TR "Kite"

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cch
Navigator

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202 Posts

Response Posted - 10/09/2003 : 07:42:40

Hi Randall,

I replied last night but it didn't go through so I will try again.

When you refer to A-B or B-C plywood it has to do with the quality of the outer veneer layer. If those layers will be exposed then you need to be concerned about that. I feel the most important issue is the glue used between the plys. I believe the main difference between marine plywood and exterior plywood is the glue used. My suppliers (I am in the contracting and cabinet business) tell me nearly all plywoods are manufactured with exyerior grade glue. Marine plywood may use a better glue but I don't know. At any rate investigate the glue and get the best you can get.

A plastic laminate like Formica could help reduce warpage but be sure to apply similar products or sealers to both sides of the plywood. If you were to use laminate on one side of the ply and fabric on the other the panel will absorb moisture differently and could cause warpage. Plywood is given to warpage anyway so be sure to treat both sides the same and seal all faces and edges.

Good luck, sounds like quite a project.

Chris Hunsicker
Panama City FL
Moonglade
80 C25 #2126 sr/sk
<img src="http://im1.shutterfly.com/procserv/47b3d636b3127cce8c9d4c83e7890000002010" border=0>

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ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 10/09/2003 : 10:15:36

Mahogany plywood might look really nice...

I like that formica idea though as a possible remedy for my two-tone (sunbleached) bulkheads.

Currently maintaining two holes in the water...'77 Venture 23 and new to the family,
'78 Catalina 25

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wmuchmore
1st Mate

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USA
56 Posts

Response Posted - 10/09/2003 : 14:02:08

Randall,

Having been in the crating business for 30 years and working with plywood, I would use nothing but marine grade plywood.

A-C, C-D, etc. refers to the appearance of the surface veneer. Non-marine ply with exterior glue will have voids in the core laminations, which marine ply will not have.

The important thing, as has been mentioned, is the glue. I have seen non-marine exterior glue ply delaminate after a few years in the weather.

You are going to a lot of work. Use marine ply.

Mike
"Calamity Jane" #2038 TR/FK

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John Mason
Admiral

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USA
687 Posts

Response Posted - 10/09/2003 : 14:33:21

Here's some info from the WestSystem website -
http://www.westsystem.com/webpages/epoxyworks/18/plywood.html

Use the tropical hardwood marine plywood and do the job once. The bulkheads are part of the structural integrity of the boat.

John Mason
<img src="http://www.users.qwest.net/~jamason/ali.jpg" border=0>
pronounced "Ali Paroosa"
1982 - FK/SR #3290

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lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Response Posted - 10/11/2003 : 12:02:25

Have you checked with the Catalina factory parts department to see if you can just buy the new bulkheads from them, already cut to the proper shape?

Larry Charlot
Catalina 25WK/TR Mk. IV #5857 "Quiet Time"
Folsom Lake, CA

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Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 10/11/2003 : 14:01:32

<BLOCKQUOTE id=quote><font size=1 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>
Have you checked with the Catalina factory parts department to see if you can just buy the new bulkheads from them, already cut to the proper shape?

Larry Charlot
Catalina 25WK/TR Mk. IV #5857 "Quiet Time"
Folsom Lake, CA
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

What he said.

<img src="http://members.cox.net/fhopper/Catalina25/sigbow.jpg" border=0>Frank and Martha in Wichita KS. Lake Cheney

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deastburn
Captain

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USA
334 Posts

Response Posted - 10/12/2003 : 22:22:19

Mike on "Calamity Jane" is right. You shoul use marine grade plywood, and make sure it is stamped "Marine grade"on the side of the sheet, and carries and inspection number (which you should save in case there are quality control problems you discover later.

A-B and B-C describe the quality of the fir veneer on exterior grade plywood, not the grade of the plywood itself. Most 3/4" ext plywood is five laminates thick. Most marine is seven, and uses harder, denser woods (fir is very soft and absorbent). Fir plywood will absorb moisure on a boat, will develop mold and mildew problems inside the layers of veneer, and will likely delaminate over time. Some older boats from the 70's used baltic fir plywood (usually seven layers, no voids, but soft and absorbent), and you will often see the surface of the plywood washboarded from delamination and constant changes in dimension.

I learned a long time ago that when doing the work myself, buy the best quality materials and tools you can get. You're already saving on the labor. I built my house, and the difference in cost between using cheap materials and the best available was about 30%. Wherever I fell prey to the temptation to cut corners is where I now have to go back and replace or repair. Take my humbly offered advice: do it once and do it right.

Dave on "Wood Duck" (#2616 - SR, FK)

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CatalinaGuy
1st Mate

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USA
55 Posts

Response Posted - 10/13/2003 : 15:35:52

I recently refinished my entire boat inside and out. Took about 9 months of steady part time work. I learned a ton in the process. Here's my thoughts on your bulkhead questions:

a) If possible purchase pre-fabricated bulkhead panels from CD. The fit must be precise as there is very little room to manouver these panels into place, they have to be exact. The factory panels have numerous angles and thicknesses where they meet with the fiberglass interior sections, which will be difficult to reproduce from bare plywood.

b) These panels are structural and take most of the deck load and some of the mast loads. They must be high quality marine grade ply of the correct thickness, and they must fit correctly. The large aft port panel is the most critical.

c) I agree with you regarding the dark teak making the cabin look small, cramped and dark. I coated mine with west system epoxy to seal and fill the grain, then (after sanding smooth) used Pettit Easypoxy white undercoater (2 coats) and finished with Pettit Easypoxy semi-gloss white (2 Coats) they look awesome, and completely change the inside of the boat. I love how they look.

I'm just finishing off some electrical wiring now and will take the after photos from my refit. I'll post the before and after pictures ASAP.

Doug Hibberd, 'Shiraz'
C25 SK/SR 1983
Austin, TX

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Randall
Navigator

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123 Posts

Response Posted - 10/14/2003 : 21:41:57

Ummmm, no, I actually hadn't thought about checking my CD catalog, but I will. I will probably wind up going with homemade bulkheads, however, since I plan to make a lot of changes to the interior layout and want everything to match.

Thanks all for the info on marine vs. exterior grade plywood. I have been told in the past by authoritative-sounding lumberyard guys that the only diff between the two was the outer ply. Guess they didn't know, or didn't want to mess with a special order for two lousy sheets of plywood.

My old bulkhead has rot at the bottom edge, but is intact enough to use as a precise template for tracing a new one, so I'm not overly concerned about matching the shape to the hull. What I am pondering is: what do I use for the padding material that goes around the edges to cushion it and prevent squeaks?

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deastburn
Captain

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USA
334 Posts

Response Posted - 10/15/2003 : 09:46:09

My guess is you can get the padding material from Catalina Parts or something very similar from an RV parts catalog.

Dave on "Wood Duck" (#2616 - SR, FK)

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Mark Loyacano
Navigator

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USA
247 Posts

Response Posted - 10/15/2003 : 10:43:53

If I were going to fabricate and install new bulkheads, I would consider "tabbibg" instead of "padding" (like the original). Most refit guides explain the technique and the reasons for... such as added structural integrity.

The bulkheads, as they are now, don't offer all that much strength. I've sailed all year with the forward bulkhead removed (more forepeak and bunk room that way). There is no evidence, yet, that it was doing anything while screwed in. However, we don't have waves or sea motion to factor in here (on our lake).

Mark L.
Cat 25 SR/SK #549

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frog0911
Master Marine Consultant

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USA
1349 Posts

Response Posted - 10/16/2003 : 00:05:25

I was going to replace my bulkheads also, but never got the chance since I sold it first. I was going to use 3/4 inch fiberglass trailer panels to make them. This stuff is 7 ply with the outer ply on both sides made of 1/16 white fiberglass. I put this on the roof of my boathouse, did not seal the edge, and it took 10 years for it to split from water intrusion. This stuff polishes up like the gel coat on your boat. I did make shelves out of it for Penny and the General love them.
You can probable get some from a container repair facility in your area pretty cheap since it is not used anymore and most are willing to have someone take it off their hands and there cost.
If you would like to see some pictures EM me and I will fire them off to you.

Frog and The General
<img src="http://im1.shutterfly.com/procserv/47b3ce35b3127cce804c28b809cc0000001010" border=0>
04 Wing #743
Pretty Penny II

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Randall
Navigator

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123 Posts

Response Posted - 10/28/2003 : 20:41:54

A-l-l-l-l-righty then! I removed the portside bulkheads this weekend and realized that the dark & dreary stain I complained of was actually the handiwork of the previous owner. The factory stain was only half as dark as the brooding, Victorian-look the PO had imparted with his interior "upgrade". Still, I plan on going with a brightly painted, Formica'd or carpeted replacement.

I have 3 sheets of marine grade plywood on order. Thanks all for your input-- I don't want to cut corners on this project, and I had no idea that there were so many differences between marine & exterior plywood.

I was surprised to find that the bulkheads are only 1/2", not 3/4", which made me wonder just how structural they really are. After all, they are only held in place with a dozen screws, & not tabbed in, as Mark suggested would be better. I also like the idea of leaving out the forward bulkhead to open up the v-berth area.

Randall

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