boat repair

[sochr000]

I have a 14' Aluminum boat, alumacraft I think.  I'm getting a bit of a late start to the season, and was going to go out yesterday for a bit.  As I uncover the boat, bail out what little water snuck in, and get the motor ready to mount, I notice the wood mounts are in bad shape.  Figured I could get a day or two more out of them, but as I tightened the motor it might has well have been balled up tissue under the clamps.  And no, I can't just go buy a new boat.

So, my question is, what would you recommend I use to replace the mounts?  I am thinking I should use some 3M marine sealant under whatever wood I use, maybe get some new stainless bolts/nuts, but I've never done this before and don't want to spend money on something that isn't going to work.  Also, what kind of wood should I use for the inside and outside mounts?  I'm thinking either green-treat plywood or cedar, but since there's a little bit of curve to the back I don't want to split the cedar, although maybe if I use enough of the 3M sealer it doesn't matter if the wood cracks.  If I use cedar should I use any sort of varnish/sealer?

If any of you have suggestions I'd appreciate them.

[Woody]

A coworker had this issue a couple of years ago.  He used marine grade plywood-sandwiched to the desired thickness.  He used Gorilla glue to bond the sandwich together.  He's had no problems as of yet. 

I think it would only be to your advantage to seal the wood once it's complete.  I'd probably do it-cheap insurance.   

[sochr000]

And where would I get marine plywood?  I went to Home Depot and they'd never heard of it, and checked another area lumber yard and got the same look.

Edited to add:
As far as sealing the wood, what would you use?  I'm concerned that tightening the motor on would crack the varnish around them, and rot where it's most important.  I could just be over thinking things though.

[Fawkinnae]

I'm surprised that marine plywood would be hard to come by but I do remember it being expensive. When I replaced a boat floor I had intended to use a marine plywood but it was so expensive that I just used an exterior plywood and sealed it with a marine varnish. I would think the same combination would work for what you're doing.

[JoeFisherman]

A lot of the older boats used clear heart redwood.  Cedar is rather soft and really not all that weather resistant.  Oak would work well too.  The most important thing is to seal it well.  It's the wet/dry cycle with exposure to oxygen that rots wood.  Wood under water all the time or completely dry all the time won't rot.  Evidence of that can be found on wood fence posts and piers.  You'll notice they rot at or near the surface of the ground, or in the cast of piers at the water surface level.

[Bobby Bass]

If you are talking about the transom and are just looking at replacing the wood sandwich that acts as a motor mount buying a sheet of marine plywood would be overkill. Some 5/8 exterior glued plywood with a couple of coats of Varnish will last ya for years. Screw it together with some stainless steel screws and dap a little silicone on the screw heads to seal them. Been there done that. 

[Woody]

If you are talking about the transom and are just looking at replacing the wood sandwich that acts as a motor mount buying a sheet of marine plywood would be overkill. Some 5/8 exterior glued plywood with a couple of coats of Varnish will last ya for years. Screw it together with some stainless steel screws and dap a little silicone on the screw heads to seal them. Been there done that.

Overkill? Better safe than sorry!  While there is nothing wrong with using extrerior grade plywood-obviously there is a reason marine grade plywood exists.  While a sheet is expensive (approx. $45-50/sheet) I do not believe you'd need a whole sheet of it, nor did I say to buy a sheet of it.  Some places sell 1/2 & 1/4 sheets "handy panels".  Where I work, we go through a couple pallets of marine grade plywood a year.  They buy it from a wholesaler, so I'm not sure of a retailer that carries it.  Someone has to you'd think!

 
I'm surprised that marine plywood would be hard to come by but I do remember it being expensive. When I replaced a boat floor I had intended to use a marine plywood but it was so expensive that I just used an exterior plywood and sealed it with a marine varnish. I would think the same combination would work for what you're doing.

I second this recommendation since marine grade is hard to come by for ya. 

[Jdrummer]

I did this last year to my old alumacraft 14 footer. I used 3/4 Green treat plywood. Just replace the old screws or bolts with stainless or the cheaper grade that doesn't rust that bad. when you drill the holes in the wood put a helping of silicone in the hole and a little on the threads. I used my boat for over a year after replacing that wood and never had a problem! your lumber yard should have a 4x4 sheet of the wood .

If you run into any problems just take soem pics of your problem and we can help ya out on here! 

[Bobby Bass]

If you are talking about the transom and are just looking at replacing the wood sandwich that acts as a motor mount buying a sheet of marine plywood would be overkill. Some 5/8 exterior glued plywood with a couple of coats of Varnish will last ya for years. Screw it together with some stainless steel screws and dap a little silicone on the screw heads to seal them. Been there done that.

Overkill? Better safe than sorry!  While there is nothing wrong with using extrerior grade plywood-obviously there is a reason marine grade plywood exists.  While a sheet is expensive (approx. $45-50/sheet) I do not believe you'd need a whole sheet of it, nor did I say to buy a sheet of it.  Some places sell 1/2 & 1/4 sheets "handy panels".  Where I work, we go through a couple pallets of marine grade plywood a year.  They buy it from a wholesaler, so I'm not sure of a retailer that carries it.  Someone has to you'd think!

 
I'm surprised that marine plywood would be hard to come by but I do remember it being expensive. When I replaced a boat floor I had intended to use a marine plywood but it was so expensive that I just used an exterior plywood and sealed it with a marine varnish. I would think the same combination would work for what you're doing.

I second this recommendation since marine grade is hard to come by for ya. 

Menards here, marine  plywood is special order, mim 1 4x8 sheet. transom repair maybe 2' by 4' 10 bucks from the handi panel bin and you have it today.

[sochr000]

Cedar is rather soft and really not all that weather resistant.

Okay, I was just hoping it'd work because I have a fair bit of it in the garage already.

As far as the marine plywood, no idea why the local HD doesn't have it, I even broke down and asked someone who worked there if they knew where it was, nope.  Will probably just go ahead and use the green-treat on the outside at least, and seal it with marine varnish, and might have to use the oak that was suggested on the inside so it looks nicer.

Also, and yes, I know it'll cost a lot, but would oak work well for replacing the seats in the boat?  I've still got at least a year left before those give out, but figure if I start buying the stuff now I can afford to replace it next winter.  If oak wouldn't work well, what would you suggest I use for the seats?


Thanks for all the advice and input so far.

[Bobby Bass]

How about a couple of photos so we can see what you are talking about? Maybe someone here can come up with more ideas for your project. I have done a couple myself for resale.

[tom fellegy]

it is widely thought that the chemicals in the green treated plywood will react with the aluminum. it sounds like cost is a factor so marine grade plywood is overkill. the oak wood will work fine, but it is also costly. exterior grade plywood will work just fine for the transom replacement just seal it with some type of marine sealer. as far as replaceing the seats it depends on what type of supports are under the seats. 5/8 or 3/4 plywood will work for that also. just sand them good and put a good marine paint on them and it will last for years to come........tom fellegy