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  Topic Review (Newest First)
09-03-2010 02:10 PM
tommays House Plywood does NOT stay stable

NOW its better the Pressure treated Plywood

BUT NOT near as stable as Marine Plywood
09-03-2010 01:38 PM
Originally Posted by Sabreman View Post
In the case of an interior bulkhead, there should be no moisture at all! I certainly don't want the cushion next to it to have any moisture on it, so why should I be concerned that the would will delaminate if it's submerged? If it's submerged, I have way more problems than concern over delamination!
Bulkheads are often submerged without the boat sinking. Leaky windows, leaky this that or the other thing, any time water gets in the boat from anywhere the base of that bulkhead is going to get wet. If the chainplates (or maybe other nearby hardware or windows) leak, water's going to come in. There's just sooooo many ways for water to get in and ruin your day. That's why you choose materials & prep them for a worst-case scenario ("Water got in somehow yet again.") versus best case ("I sealed the boat so now it's not and never will be an issue again").

These are big annoying projects, so you're better off doing it right the first time rather than skimping and having to redo it all later.
09-03-2010 11:16 AM
mitiempo Good exterior plywood uses waterproof glues but as posted above there are voids that do not exist in a good marine ply like Joubert, Aquatek or Hydrotek ply. The marine ply has more plies for a given thickness as well. The 3/4" Hydrotek I used is 11 plies and the 3/8" I used is 7 plies - all void free. Occume or Meranti that is used in marine ply is a more stable wood than fir and nothing in domestic exterior grade really compares. All plywood will eventually rot if it gets wet and stays that way. So you're getting more strength, probably better quality glues, no voids whatsoever, and more stability with marine ply. It finishes better if you are painting it as well. The Hydrotek I used is best I have had the pleasure of using in decades.
My local supplier in Victoria, Westwind Hardwood, has domestic fir marine ply listed in their catalog but it has not been available in good quality for a long time so they do not stock it.
09-03-2010 10:32 AM
TintedChrome QuickMick - My original order didn't ship - i think they realized that $6+ shipping for the book was a problem.. Found another copy for ~15, and I got shipping confirmation on Tuesday! Should be here today or Tuesday (Monday's a holiday for us north of the border [Edit: looks like it is for you too! My bad..]). I'll definitely let you know what I think!

LookingForCruiser - I was exploring the g-10 as a full-blown wood alternative, but after realizing that ply can do the job and should last as long as I maintain the boat I've dropped it from my radar.. I'm doing a bunch of research right now on exterior vs marine grade ply. It seems a major difference is the tolerances for voids between the layers. I.e. marine has none, exterior allows for some which concerns me a little bit seeing as chainplates are bolted onto it. For lake sailing it would be a no brainer, I'd go with the exterior ply. However there's some offshore in this boat's future and the higher loads that it entails. That said, I see that Sabreman's chainplates are bolted to his. Aaaahh... decisions, decisions!

I have plenty of time to work this out.. the 'heads aren't getting done until mid October when the boat gets moved (much) closer to home.
09-03-2010 10:00 AM
As for exterior plywood, I don't see how you'll get a decent finish with it
I generally agree, because fir is hard to finish, but if properly sealed prior to final coating an acceptable finish can be achieved. But for my interior, I prefer some sort of veneer. I used teak veneer over the ply for one bulkhead and formica for the other. I bond the veneer with Tightbond II or III. Sabre used 1/2" teak veneer marine ply with 5 laminates. I used exterior ply with 7 laminates and did my own veneer. The result is the same thickness. The result is at least as strong as the original construction.

Veneering is not that difficult, relatively inexpensive, and does not necessarily require specialized equipment. For small panels, clamps can be used. Larger panels require a vacuum bag or can be bonded with contact adhesive. The later requires an extra step to seal the veneer prior to finishing, but if done properly, will not delaminate and the bond will strengthen over time. Contact Adhesives don't like solvent finishes, but if the veneer is sealed with dewaxed shellac prior to finishing, there will be no delam. Just a few time-honored tips.... don't mean to hijack the thread.
09-03-2010 09:17 AM
QuickMick tinted chrome, did your book come in? when it does i like your thoughts on it, i think it is full of great projects w/good illustratons... just curious
09-03-2010 09:14 AM
Originally Posted by TintedChrome View Post
like when I build my cockpit lockers..
That makes sense since it will be exposed to the elements. No question; we're in total agreement.

In the case of an interior bulkhead, there should be no moisture at all! I certainly don't want the cushion next to it to have any moisture on it, so why should I be concerned that the would will delaminate if it's submerged? If it's submerged, I have way more problems than concern over delamination!
09-03-2010 09:11 AM
LookingForCruiser From wanting Garolite G-10 to exterior plywood is quite a transition in quality...

Anyhow, about G-10 - I just cut some backing plates out of it. It's a nightmare to work, it's basically like cutting solid glass. I wouldn't want to do big projects with it unless there was no other way. I was going to replace some weathered stand-offs for my hatch hinges & chocks with it, but after cutting the backing plates I've decided to just epoxy-coat wood instead. Much easier to deal with.

As for exterior plywood, I don't see how you'll get a decent finish with it, and it's not as structurally sound as marine plywood (but maybe that's balogna - I'm not an expert). You might be harming the boat, since you'll probably need to use the same thickness as the marine plywood you're replacing. It will definitely delaminate easier than marine plywood, the glue job doesn't compare.

I'd try to find a source for marine plywood if I were you.

I'd also just grab the multi-tool and chop things out wherever there isn't liner, and then see if you can remove the stuff that's between the liners. Maybe you'll get lucky. Wouldn't cut the liner as a first action, but only as a last resort. It looks like you have pretty good access to the bulkhead in your pictures.
09-03-2010 08:24 AM
TintedChrome Sabreman - That's a good point.. isn't it great when someone that's relatively detached from a situation offers an alternative to the "this is how it HAS to be done" tunnel vision that sets in?

Given the abuse and rougher weather this boat will likely encounter, my biggest concern is strength and rigidity. If the ply (outdoor or marine) is coated in epoxy to seal it anyways, holes for chainplates drilled oversize-filled-re-drilled, all things being equal it should be watertight and I'd make the assumption a high-quality outdoor ply is a lot more cost effective with all the same attributes as marine.

Like you say though, in a more exposed environment I'd go for the marine ply in a heartbeat.. like when I build my cockpit lockers..
09-03-2010 07:52 AM
Sabreman One small comment regarding the type of plywood.....

When I started repairing our bulkheads, I went in search of marine ply. Since I live about 70 miles from the marina, it is very difficult to acquire marine ply in our home area. I really didn't want to make a special purchase through a local mill yard due to the extreme cost. I used my wife as a sounding board and she asked why it had to be waterproof. I replaied that it was for the boat, etc. When she pointed out that this was for an interior use and should NEVER be wet, the logic was hard to dispute.

I know that this is sacrilegious, but I went with a high grade, multi-ply (7 layers) exterior plywood. I feel that for interior applications that will not come in contact with water, exterior ply is adequate. Indeed, Sabre used marine ply and due to leaky chainplates, it rotted. So it seemed to me that if I keep the chainplates sealed properly, I had nothing to worry about. So far, there is no issue with either bulkhead and I expect that there will be none in the future.

On the other hand, if I was building a plywood boat, marine ply is the only way to go. It's just that marine ply didn't do us much good in the original application so I didn't feel a need to get too twisted about using "Marine" ply - exterior ply was sufficient for an interior application.
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