Instructables

Transom fabrication

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Typical small boats have transoms made of wood, as the years pass the wood will rot and become useless. This instructable will guide you in removing, fabricating and replacing the transom of that old boat you just bough againt your wife's wishes.

Materials

16 - 2" stainless steel carriage bolts
32 - Stainless Steel washers
16 - lock-washers
16 - Nylon threaded stainless steel nuts
2 - pieces of extruded aluminum "L" (optional)
1 - 6oz tube of 3M 5200 Marine Sealant
1 - 8' x 4' -½" Pressure Treated Plywood
1 - Can of fiberglass resin (Jelly)
1 - Bondo applicator
1 - 6oz tube of Gorilla Glue

Tools needed

Circular Saw
Palm Sander
Wood Clamps (you can use any type of weight if you don't have clamps)
Tape Measure
Straight Edge
Sharpie
Drill with stepped drill bit
Welding punch

Total cost: around $125
 
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Step 1: Removing the old Rivets

Picture of Removing the old Rivets
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The first thing to do is identify all rivets that run through the transom. In my case I had 16. After identifying the rivets to remove, mark the outside of the rivet head with a black dot with a sharpie. No use drilling out a good rivet.

After marking the rivets to be drilled out get your drill and get to work. Besides replacing the rivets with carriage bolts, this is probably the most difficult task of the process. Use a spring loaded punch to start a divot on the rivet head so your drill bit doesn't go all wild. Drill the rivet head as least as possible, once you see the head is about to be drilled through, stop immediately, no use making the hole in the hull any bigger than it needs to be. Repeat this task for all of the marked rivets. When you are done, the transom should be loose and with a little coercing, be ready to be removed.
weldor3 months ago

great 'ible! old boats should never be discarded because they are just, well, cool!

i used to work for a yacht building company and that is where i learned about the 5200. always were gloves because once it dries on you it is darn near impossible to remove. have to pluck it off in little bits. i know this from experience. you can use denatured alcohol (so-so), toluene or xylene to clean it off of surfaces (not your skin 'cuz it is toxic)

you will not ever find a better sealant/adhesive than that 5200. there used to be a 4800 that was considered semi-perm. the 5200 is rated for below the water line.it also comes in black, brown, and gray. it also will work on wood.

i mentioned this because years ago i helped a friend redo the transom on his grand-pa's old boat. I had a bunch of 1/4 thick alum which we made the transome out of. we cut it out with a circular saw (noisey and throws lots of hot chips -wear appropriate protection!)

we laminated the pieces together with the 5200 after drilling multiple holes in the metal. we then stacked them and inserted stainles steel 1/4-20 tpi bolts with washers on each side and tightened them down. we repeated the tightening several times over the next few days. we may have gone overboard on the amount of 5200 as it kept oozing out. is there really such a thing as over kill?

we then used the same process to install the new transom to the boat. it was about 1 1/4 inches thick when done.

there was also a leak in the seam at the keel. we used 5200 there as well. no more leaks.

the key to using 5200 effectively is make sure the surface is clean.

Great and helpful article. What size carriage bolts did you use? I was thinking I'd do like 3/8 inch and realize 1/4 might be just fine. I plan on putting a painted piece of red oak in as the transom but as I understand wood or paint against aluminum shouldn't be done. So I plan to clean rear inside and then use an etching aluminum primer like Rustoleum's and then spray on two top coats.

Now to find that fishing deck article mentioned..ready for that to happen next also!
lanakivee2 years ago
Help! I have an 8 foot inflatable West Marine dinghey that has a completely rotted transom and am trying to work on it in my shop. The old transom has been removed along with the plate for the outboard motor. I removed the transom and plate, and scraped the rotten wood pieces out of the grooves on each end of the area where the dinghey "locks" into place on each side, so it is clean of old wood and debris. My question is: My old transom is so rotted, if there anywhere I can purchase a new transsom for this OR any kind of "cutout" pattern that I can get so I can make the proper cuts into the new piece of marine grade wood that is to be the replacement. I would rather repair it using the wood I bought and use fiberglass to reseal, Does any one sell used or new transoms for dinghey boats and/or anyone have a cutout pattern that I can trace and make my cuts? I am pulling my hair out tryiing to fix this with the proper fitting on each end... Any help is appreciated.
gdhenson (author)  lanakivee2 years ago
Here is a good video of you boat and transom. You might be able to get a good idea from this video and a few measurements in your boat.

http://www.youtube.com/watch?v=Z0FSSffq5zM
Starcraft54 years ago
This is awesome just what I needed. I have a 16 aluminum starcraft with a 75 hp motor, the transom has rotted and it's time for a replacement. I have a few questions. I plan on doing this project right away, so I will not have time to let the plywood dry. Should i go with marine grade plywood instead or do you think exterior grade A/B plywood with the fiberglass resin would suffice?
Also, i was thinking about using 3m 4200 instead of 5200 because I read 5200 gives a permanent bond and would be very difficult to remove the bolts at a later date. What are your thoughts? Thx great job!
gdhenson (author)  Starcraft54 years ago
yeah you can use regular plywood, just be sure to seal it up good, be sure to coat your drilled blot holes especially.

The marine grade plywood in my area is about $85 for a 4x8 1/2" sheet. It's ultra expensive compared to PT or regular plywood. If you seal it up good, the regular should last ages.

I've never used the 4200 before, but everyone I talk to swears by the 5200.
Just wanted to send you some Kudos. I followed your advice and it came out perfect. The hardest part, was removing the old 30 year old rotted wood. I've used the boat now for 2 summers and have had no problems. I would highly recommend this for anyone trying to rebuild their own transom. Thx for your help.
robandjen4 years ago
NEVER NEVER put pressure treated plywoom against aluminum!!!! It will eal away the metal where they meet!! This is a well proven FACT! Research it a little and you will see the horror
gdhenson (author)  robandjen4 years ago
Thanks for the comment Rob. If you read step 5, you'll see all the plywood is coated with fiberglass resin. So no worries.
I read that, And it just confused me more. Why use pressure treated wood if it was just going to be covered with glass anyhow? There no strength difference between treated and non treated wood. All I see the treated wood does is add weight and adds a risk if failure of bolts do to corosion with the treated material. I know it seems I am harping about  nothing but I am a boat builder by trade and have seen the bad effects of aluminum and pt wood contact, Also PT wood to desinged to air dry over time and leach out the extra weather treatment. Hence thay say to let PT wood stand for 30+ days before sealing it like decking and such. If you cover the PT wood with glass before the wood drys completely it will never be able to and it will eventually mold and become weak. Seems like a small thing but can lead to big problems. There's such things as marine grade wood for just such  reasons. 
gdhenson (author)  robandjen4 years ago
Hey Rob -

Once again thanks for the comment. Constructive criticism is always welcome. The reason I used PT is because I had 3 or 4 sheets laying around from a project earlier in the year, no use buying more if you already had some laying around. They had been against a wall in my garage for 3 or 4 months, so they were plenty dry. All holes drilled thru we coated with 3M 5200 sealant and I used stainless steel carriage bolts.

I am currently redecking a 19' boat and I bought untreated plywood for this since it's cheaper. I priced marine grade plywood and it's close to $100 for a 4x8 sheet. I have some old time boat guys in my family (uncle and grandfather) and both agree that a regular sheet coated with an epoxy resin would be equally as good if not better than the marine grade.

I appreciate the tips. While I am not a boat builder by trade, I tend to over research things before starting a project, I probably spent 10 times the time it took to build transom reading and researching the best way to do it.

When I'm done with my larger boat this summer, I'll post some pictures of the progress.

Greg
I've been building boats for years. And there's a product PL premium Construction adhesive. It's in the same class as 3m 5200 (which is great sealent) But it comes in a calk tube and is under 5 bucks! Lowes-Home depot. It's even good enough to make fillets with.I have used it for years on hundreds of things. I agree that regular untreated pylwood coated with epoxy is just as good! But epoxy and hardner is $146 a gallon. So really it's a cost/labour thing. And if it's something like decking the first time you drive a nail or screw thru it you just made a breach in the cured epoxy so it needs to be done again after the piece is installed. But I have done it this way. I put a new floor in my 46ft. Bertrum last may and using marine grade would have put me in the poor house! I used 23/32 exterior grade ply from Lowes and it was toung and groove! It made instalation easy and so far is holding up well! I used MAS epoxy and completely coated it with a roller both sides before I installed it and then re rolled this top side with a slightly thickened Q cell mix before painting and carpeting it.

 I see in step 6 you mentioned it's hard to clean 5200 off your hands, Try WD-40 it works pretty good to get it off.
allen_idaho5 years ago
Another option would be to make a new transom from aluminum and weld it in if that boat is aluminum and not fiberglass. Aluminum transoms are normally only 3/16" or 1/4" thick and plenty durable. If you've got access to an ac/dc mig welder and some basic shop tools, it would probably take about an hour to fabricate and install. However, you would also need to make yourself an outboard mounting bracket to fit your motor into place.
Ghost Wolf5 years ago
That's cool dude so you restored a old boat or you had it laying around?
gdhenson (author)  Ghost Wolf5 years ago
It was actually an old boat someone else had laying around.
What type is the boat? I want to know because I want to get a boat like that in the future
agdollison6 years ago
to set the time and date on my camera either leave the batteries out for a day and it will ask you to set the date or go to menu and find time stamp setup
gdhenson (author)  agdollison6 years ago
okay. I'll try that tonight. Thanks for the tip!