# Transom replacement in Aluminum Boat



## Deepwaters

The transom was rotted out on my 1987 Sea Nymph Fishing Machine, so I decided to replace it myself because the boat repair shop was scheduling three weeks out. I have pulled the 40Hp motor and removed the old transom, and will use it for a template. When I got the old transom out, it was in much worse shape than I anticipated. I need to have a 1.5 inch thick transom, so I plan to use two pieces of 3/4 inch plywood sandwiched together. A guy at a boat repair shop that I talked to said that he uses 7-ply pressure treated wood, and simply screws them together with stainless screws, and drops it in the aluminum skin. I've read about problems with corrosion with PT plywood and aluminum. Does anyone have experiance with using PT plywood for aluminum boat transoms?

The alternative would be to use marine plywood and epoxy the outside to waterproof it before dropping it in. Using PT plywood sounds good because it is less prone to rot. Any advice would be appreciated.

DW


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## kumma

I did this last year on my 14' aluminum. I just used pressure treated plywood and used coated deck screws and epoxy resin. I ran a skim coat of epoxy over it as well simply because I had 2 gallons of epoxy resin left over from a nother project. No problems since its holding up fine. It was so simple I wouldnt even think of jobbing it out.


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## john warren

i put a new transome in my 21 foot lund. use exterior grade plywood, i has the same glue as marine grade so no worries there. then i encased it in fiberglass to protect it.


Deepwaters said:


> The transom was rotted out on my 1987 Sea Nymph Fishing Machine, so I decided to replace it myself because the boat repair shop was scheduling three weeks out. I have pulled the 40Hp motor and removed the old transom, and will use it for a template. When I got the old transom out, it was in much worse shape than I anticipated. I need to have a 1.5 inch thick transom, so I plan to use two pieces of 3/4 inch plywood sandwiched together. A guy at a boat repair shop that I talked to said that he uses 7-ply pressure treated wood, and simply screws them together with stainless screws, and drops it in the aluminum skin. I've read about problems with corrosion with PT plywood and aluminum. Does anyone have experiance with using PT plywood for aluminum boat transoms?
> 
> The alternative would be to use marine plywood and epoxy the outside to waterproof it before dropping it in. Using PT plywood sounds good because it is less prone to rot. Any advice would be appreciated.
> 
> DW


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## k8vol

P T wood is now not useing the old CCA the new style treatment will eat alumiam flashing on a home in about 2yrs. so I would not use the new treated wood . call around and get some 7ply 3/4 johnson work bench has it and they are all over the state so it's not hard to get . P.S. remember they changed all the screws to epoxy cover about two years ago to make up for the new treatment of wood becuse the zick covered one also got eaten by the pressure treatmeant of the new style wood.


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## double trouble

if you epoxy resin coat the wood then how would the treating process eat aluminum. it would be hermetically sealed.i still think that p.t. wood would be fine. whats the difference if it only lasts another 20 years. just remember that the edges are most important and often overlooked. seal them well and you will have a lifetime transom. instead of screwing it together i would use either gorilla glue or construction adhesive.clamp and set. they will never come apart. you could use a few screws just to lock the 2 halves together. much more permanint than screws.


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## The Whale




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## wild bill

unless you can find dry pt plywood i would just use exterior grade plywood when using epoxy. the more layers you can find the better.


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## wild bill

also i would just use the epoxy resin to glue the 2 layers together. coat both pieces and mate together. add weight to the top piece and let it set for a day. once cured i would put 2-3 coats of epoxy resin over the outside allowing each coat to cure inbetween coats. cheap foam rollers work great for this. also if you plan to drive any screws into the transom for a transducer or anything else plan ahead and drill your holes. once drilled you can drill them oversized and fill the holes with resin. when putting the screws in drill a pilot hole first in the resin plug. this will ensure no water can enter the plywood. west marine carries good epoxy resin but there pricey. the best price i have come accross is at http://www.boatbuildercentral.com/products.php?cat=41


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## snaggs

............I used 1/4 inch aluminum diamond plate and bolted it to the outside of my transom....this is on a 21 ft. Starcraft Mariner center console and it works just fine....did not have rot in the wood of the transom....but that is because the bottom 1/3 of the transom does not have wood...so do not get the ""wick"" effect....had a 115 Johnson on the boat and the weight of the motor plus the stress of the force when motoring caused the transom to flex somewhat...but with the added 1/4 inch diamond plate stiffens the transom right up...used galvanized bolts and Silicon II to seal up everything...keep it in the water at the cottage for 2-3 months of the year and in/out the rest of the fishing season...so far so good...now have a 75 h.p. Mariner which is a little lighter in weight and a real kick butt motor...and the boat runs...planes like new...knock on wood...


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## DangerDan

wild bill said:


> unless you can find dry pt plywood i would just use exterior grade plywood when using epoxy. the more layers you can find the better.


The wood will have to be dried before using it regardless. In this weather I think putting a salamander type heater infront of it in the a grarage would have it dried out in no time. I wouldn't try gluing or expoxy until all the moisture is out of the wood. 

I wouldn't ever use epoxy to seal screws unless you want to leave them there permanently. 4200 will seal screws just fine. 5200 works but sets up pretty hard so removing a faulty transducer could be tough.


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## Deepwaters

Thanks for all your comments and suggestions. In the end, I decided to buy the marine grade plywood, and encapsulate it well in West System Epoxy. After talking to the folks at the lumberyard, they were concerned about the warpage of the treated lumber. The marine plywood is pricey...$77 for a 3/4 inch thick 4'x8', but it should do OK once it is epoxied/sealed well. I should at least get another 20 years.

DW


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## jpollman

Sounds like you've made your decision. Personally though, I wouldn't have bothered with the marine grade. The only difference in exterior plywood and "marine grade" is that the marine grade has no voids in it. Marine grade is twice the price of exterior grade plywood. If I were doing it I think I would cut the pieces to a rough size. (a little bit larger than needed) Then laminate them together with a two part epoxy and then clamp and use some good stainless screws. Once it's set up you could lay your old transom on it and trace the template. Then get it to final size and fit. Then fill the screw head holes with some filler and use a good coat of epoxy over the entire outside surface and edges.

Just my .02

Good luck with the project!

John


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## wild bill

DangerDan said:


> I wouldn't ever use epoxy to seal screws unless you want to leave them there permanently. 4200 will seal screws just fine. 5200 works but sets up pretty hard so removing a faulty transducer could be tough.


actually if you use epoxy to seal the screws in a soldering iron will remove them quit easy by applying heat to the screw head.

what i was saying is when you put a screw into your transom you should create a plug in it. drill a hole larger than the screw that you plan to put in there and fill the hole with resin. when you put in your pilot hole and put the screw in it will be surrounded by the resin plug and water has no way of entering the wood.


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## Deepwaters

I thought I'd post (or try anyway) a pic of the new transom before it was installed. The camera angle is deceptive, as it makes it look larger than the old one, but it fit just fine. When I was removing the old transom, it actually cracked in half due to the wood rot.

I've only had a few hours here and there to work on it, so the project has taken a long time. The new transom has been epoxied with three coats of West Systems epoxy and installed in the boat. I've put most of it back together, and just need to mount the motor, and reconnect the fish finder. I'm eager to get back on the water!!


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