Boat floor and lower unit questions.

I am preparing to redo the floor of my 79 16ft sylvan. I have read posts going back a while about not using treated wood. Has anyone who has used treated wood in their boat had any issues? I know that the copper/arsenic preservatives in contact with the aluminum can cause corrosion, but has anyone actually had a problem with this? Its going to cost me 100-150$ to ship marine ply to ND plus 150-200$ for the wood itself. I was thinking of using treated wood (30$). If I hear that people are having actual problems with treated wood I will cover all the aluminum contact points with roll on bedliner(20$). I could potentially save 250$ which is a big deal for me. I’m going to cover it with deco-dot vinyl.

Secondly and more importantly, when I winterized my boat I drained the gear lube and there was about 1-2 cups of water in my lower unit. I have a 1985 mercury 75hp outboard. Do I need new lower unit seals, or could it be something else?
Thanks for the input.
Sam

I replaced my floor of a 1987 Lund with 9/16″ green treated plywood 4 years ago. It seems to be holing up fine. I carpeted it so I’m not sure what is going on underneath the wood. I think the marine plywood is slightly more rigid than the cca plywood which flexes just slightly more. But for the difference of $120 per sheet, I can put up with that.

As for the water in the lower unit, I would take it directly to a marine repair shop and have it re-sealed and tank inspected. This is one area that can cause enormous problems and is very tough to diagnose for the average Joe.

My $0.02

Good luck.

regular exterior grade plywood would be fine. wood is treated to fend off mold and insects like termites.

I rebuilt my ’79 16 foot Sylvan way back in the 80’s and used exterior grade plywood (not marine) and not the green treated stuff. I used that boat for 10 years afterwards and had absolutely no issues. The floor was solid as new when I sold it. I looked for marine plywood back then and it was hard to find as well..but my alternative turned out just fine.

A buddy (Doug) and I gutted a 16ft Sylvan down to the hull and started rebuilding it using pressure treated wood. One day while carpooling with a carpenter friend of mine he was telling me that I should pull up the floor and take a look at it because of the possibility of corrosion; so I did. After a week’s time there was pitting in the aluminum . My carpenter friend suggested that I use ProtectoWrap tape between all aluminum/wood contacts so Doug and I went to work doing just that. You can see it in the photos. A lot of extra work led to a lot of peace of mind. I think bed-liner sealer would work just as well.

Good luck and have fun!

You can use AB grade untreated plywood after cutting to size, then seal it with epoxy before installing it. Don`t use fiberglass resin as it allows moisture in. The AB is more rigid and has fewer voids in it, that is where rot starts as the voids trap moiture in the wood. Marine grade plywood has no voids.

Good Luck and have fun

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then seal it with epoxy before installing it.

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Tom, what brand of epoxy? Is it a paint or just some kind of coating? What about deck sealer? I have used marine varnish before and got by without problems, but thought some kind of epoxy would be better but did not know what to use.

I took an old Evenrude to the dealer with those same kinds of problems. $$$$ later, it was worse than when I started. Never did know what the real problem was. They seemed reluctant to work on it in the first place.

Not sure about aluminum, but from deck building and basement remodeling, I know the new green treat to eat the galvanizing off desk screws, so folks now buy 3X galvanized or simply use stainless screws when building decks. The same would apply to the boat, that you would want to use stainless fasteners if working with the latest green treat.

In the basement, one drills a hole through the green treat and into the concrete with a masonry bit & hammer drill, then inserts a piece of copper wire and pounds a stainless nail into the concrete to hold the walls to the floor for the same reason… the green treat eats away the galvanizing from the nails…

So, if using green treat, my advice is to not only pay attention to the aluminum surfaces, but also what kind of fasteners you would be using to secure the wood.

That’s a good point Weldon.

We used stainless for all of the fasteners on our project as well.

Did you mean like the epoxy you put on garage floors? I also was looking around and found rubberized pool paint to seal swimming pools. 44$ for a gallon and its enough to do 250 square feet with 2 coats. If I were to use this I would do it on the underside of the floor to prevent rotting from below.
I have decided against treated wood, I will just use regular plywood, and just seal it above and below. what other types of products would be good to seal it?Rubberized pool paint.

Sam, what they’re talking about is epoxy like you’d build a boat with. Something like web page or west systems or something similar. Actually, to waterproof wood really, really well you put woven fiberglass cloth and a coat or two of epoxy on it on every side. The epoxy will crack without the cloth. Predrill the holes and epoxy the inside of them also. It isn’t the cheap way to go, it’s the deluxe way.

You could also just paint the plywood really well on all sides. Your real goal is just to keep it from soaking up water. Lower units have a few seals. Even a bad seal around the fill screws can let water in or the classic fishing line wrapped around the shaft under the prop. A shop will fix, pressure test, etc. You gotta keep oil in there or it’s toast.

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then seal it with epoxy before installing it.

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Tom, what brand of epoxy? Is it a paint or just some kind of coating? What about deck sealer? I have used marine varnish before and got by without problems, but thought some kind of epoxy would be better but did not know what to use.

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What was recomended to me when replacing my transom is called The Rot Doctor ie. ( Restore Not Replace ) http://www.rotdoctor.com. It is a 2 part and no fiberglass cloth needed it contracts and expands with the wood. Not cheap but so far totally pleased with the performance. It also comes in different formulas for cold, warm or hot temperatures for curing time. Ease of use and quality of product I give it a big

Home Depot sells marine plywood, it has to be ordered special, $72 for 3/4inch 4 X 8 sheets. You order it at the contractors desk. They will make two cuts on each sheet for you but will not guarentee exact cuts. That was last year, two years ago I redid my decks and last year built and changed some compartments, price was still the same.

I’ll second the Home-Depot option. I just purchased 6 sheets of 5/8″ Marine ply to redo the floor in a crestliner boat. Total bill was 310$ for the wood. Picked up 10yds of vinyl, and a gallon of felt backed vinyl adhesive and have so far (still in progress) yet to see any issues. From what I understood after asking the guys at the lumber yard, the marine plywood has, no voids, waterproof glue and most knots should have been checked or sealed. CCX or CDX types of plywood (from what I was told) have a different glue and the potential for more voids.

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Home Depot sells marine plywood, it has to be ordered special, $72 for 3/4inch 4 X 8 sheets. You order it at the contractors desk. They will make two cuts on each sheet for you but will not guarentee exact cuts. That was last year, two years ago I redid my decks and last year built and changed some compartments, price was still the same.

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At which Home Depot are yoiu reffering to?? Selling “Marine Plywood” Exactly what are you reffering to as marine ply?

Thanks,
Denny O

First Post – and let me clarify I’m not an expert. I am replacing my fiberglass cracking no longer encapsulated rotted plywood floor. Here’s what I’m doing: I bought marine plywood $88 sheet 3/4″ – I’m using 100% solids epoxy coating then covering with Durabak coating. I have 2 seams that I’m connecting with stainless steel pockets screws and using a splice plate with spare plywood for strength.
Plywood wasn’t cheap nor was the Durabak coating ($100+ gallon). After both side are sealed and coated I’m going to glue to top of remaining fiberglass flooring with 3M 5200 adhesive. – I hope this works. It was nice reading through this thread.