Advice needed: Aluminum flat bottom transom replacement

mckinney004

Seaman Apprentice
Joined
Jan 26, 2016
Messages
46
First post here guys. Just wanted to say thanks for all the help you have been from the archives. This is one of the best forums I've seen. Everyone is helpful and the information is always relevant and to the point. Kudos to everyone who contributes here.

Now to the point.. I bought a 20'x6' aluminum flat bottom boat in desperate need of a transom repair. I've looked through the archives for transom repair posts, but most of what I find is related to fiberglass boats or boats with large motor capabilities. This boat is only rated for 55hp, and will likely never see a motor that size. That being said, I have two main questions/issues.

#1 Construction/treatment of the transom board itself. I plan to use 3 layers of 1/2" exterior plywood cut to full width and approximately 2/3 the depth of the boat. What do you all recommend as far as treatment of the board itself? In most of the posts I see, you all have been applying epoxy between layers and fiberglassing the outside. I surely do not need the extra strength of fiberglass in this case. Would a simple water sealant (such as a deck sealer) be sufficient to keep the wood from rotting? Or do I need to use some type of epoxy? Any other suggestions? I would like this to be as cheap and simple as possible, but I also don't want it to rot out in a couple years due to the amount of work required in the next question...

#2 Accessing the transom. Okay so here's the tough issue for me.

Option 1: I can cut the transom caps in the rear corners of the boat and either cut or bend the aluminum lip that comes over the top of the transom. This would allow the board to slide in and out easily, but requires some cutting and welding. I have a friend who's a welder with his own portable rig, but I'm not sure I like the idea.

Option 2: The other option is to drill out 22 rivets in the floor and rear side wall to remove all of the transom bracing. I've read where some people do this and then replace the rivets with stainless steel bolts with some sealant. This is nice because I don't have to rely on any favors and I don't have to stress about cutting some key components to the boat. However, the boat didn't leak a drop before starting this work and I don't want to change that. Most of the stainless bolt usage I've seen has been on leaking rivets throughout the boat. Would they still hold tight and leak-free under the stress of transom supports? What would you all do? I don't like the idea of cutting and welding on my boat, but I don't like the idea of drilling 22 holes in it either.

Working on getting some pictures posted. Thanks in advance to everyone for any input.
 

Tnstratofam

Commander
Joined
Aug 18, 2013
Messages
2,679
:welcome: Most people who replace their transom in an aluminum boat will seal the wood with either epoxy and then paint it or add a uv protectant, or they will seal it with spar varnish. Use a good water proof glue such as Tightbond III to glue the pieces of plywood to each other, and then seal the wood with 3 coats per side with a total of 6 on the edges.

If you go to the manufacturers forum page under Starcraft you will find many great examples of the work you are doing, plus you may find some great ideas along the way. I have a link to my transom repair in my sig line that may be of some help, although your boat will be slightly different you'll get the idea.

Good luck and post up some pics of your project so we can give better advice.
 

64osby

Admiral
Joined
Jul 28, 2009
Messages
6,799
You might look at using 3/4 ply. One sheet might be able to make the transom. Only have to glue once.

Sealing with epoxy, spar varnish, oil based paint or Woodonglass's Old Timers formula have all yielded good results.

Photobucket would help for you to post pictures of the transom.

Unless it is a welded hull, you should be able to pull the corner caps and a support or two and then the wood should be able to be removed.

Don't see many 20' flat bottom boats, love to see some pictures.
 

Woodonglass

Supreme Mariner
Joined
Dec 29, 2009
Messages
25,924
I totally understand not wanting to ask friends for help. Call a welder and inquire as to what they'd charge for the same project. Then ask your friend if you could pay him to do the same job. If he want's to discount the price then that's understandable and IMHO acceptable. I'm not a Tinner but If I were, and from What I've seen and learned here, I'd prolly cut it. Also, I'd prolly just use 2 layers of 3/4" ext grade plywood. NOT PRESSURE TREATED!!! Titebond III wood glue and Screww it together. Treat it with 1 part Boiled linseed oil, 2 parts Mineral Spirits, 1 part Polyurethane Soak the edges liberally till they won't absorb any more. Let dry for 3 days. Apply 3 full strength coats of Polyurethane and it'll last for decades. You'll have to knock out the drain tube to be able to remove the old transom. Lot's of people forget to do that.
 

mckinney004

Seaman Apprentice
Joined
Jan 26, 2016
Messages
46
Still having trouble getting pictures uploaded. You would think a 24 year old college student could handle that, right? I think my problem is the photo size is too large. I'm using my wife's Mac and don't know how to use all of her fancy programs to resize my pictures. Going to try to get the picture issue sorted out tomorrow. Can't be anything too hard.

I've decided to remove the transom caps to access the wood. I talked to my welder friend today and he agreed to help me with any of the welding work I need. I just couldn't bear the thought of 22 potential leaks in a 100% leak free boat. My transom caps are welded on, but I'll get them cut off and start prepping my wood tomorrow.

tnstratofam- I looked over your entire thread. Looks like you did a great job. Hoping mine is about 10% the amount of work yours was (easy access). I thought our Missouri lakes were pretty, but that pic of the TN lake was neat with the mountains.

64osby- I'll add some pics of the boat once I figure out how to add the transom pics. We don't get many 20 footers around here. I have a 14' and always wanted a big, deep 16-17 footer. Bought a 16' and about a week later this 20' came up on craigslist and I had to have it. Wife thinks I'm crazy after buying 4 boats this year! (We bought a pontoon in the spring). The 16' will be sold soon though. I don't need two big flat bottoms. I'll get pics posted soon, but to give you an idea it is 20' long with a 4.5' floor up to 6' wide at the top rail. Bench seat in the back and one bench seat in the middle. Small platform up front. Always wanted a completely open floor plan, but with that size boat I still have plenty of room even with the seat.

woodonglass- Thanks for the recipe. I haven't decided how I'm going to seal it yet, but that sounds like a good formula
 

mckinney004

Seaman Apprentice
Joined
Jan 26, 2016
Messages
46
Okay it looks like I finally got photobucket to work for me. Here are some pictures to show you all what I'm working with. I'll post some pics of the entire boat tomorrow. The transom was one solid piece of plywood. It was so swollen/decomposed I'm not sure how thick it was. I've measured the gap between supports and the hull and its right about 1.5". I'll get some better measurements before I purchase the lumber.









 

Tnstratofam

Commander
Joined
Aug 18, 2013
Messages
2,679
I may be wrong but I'm thinking instead of removing the transom cap and corner pieces you could possibly remove the braces on corners that connect to the inside of the transom and the sides, then remove the knee braces, and the other support in the middle and pull the transom out by pulling the bottom towards you and then down from the top.



The corner pieces and knee braces look like they are riveted to the hull from the pics, and then simply screwed to the transom wood. If they are welded or if the rivets aren't accessible for replacement then my idea would probably be harder than removing the transom cap and corner braces and lifting it straight up and out.

It's hard to tell from the pics, but the transom cap looks like it's either part of the outer transom skin folded over, or is welded in place along the back of the transom.
 
Last edited:

64osby

Admiral
Joined
Jul 28, 2009
Messages
6,799
IMO the cap(s) should not be cut.

Remove the knee supports and at least one side of the side to transom bracket. Bend up the inside of the top cap enough to slide or pull the wood forward and out. One corner will come out and move downward the further it is away from transom.

If able try and keep the wood in one piece to act as a template for cutting the new transom wood.

When you reinstall the brackets they will have to be fastened with new solid rivets or stainless hardware.

My .02.

Have fun. :D
 
Last edited:

Woodonglass

Supreme Mariner
Joined
Dec 29, 2009
Messages
25,924
Totally agree. Again, NOT a Tinner but...based on what I see, removal of the knee braces etc and removing the wood my sliding it down and out appears to be the practical way to do this replacement. These members are giving Good Sage advice. Your transom is1.5" and the new one should be made to that specification. Take some careful measurements in order to duplicate it as closely as possible.
 

mckinney004

Seaman Apprentice
Joined
Jan 26, 2016
Messages
46
Remeasured the gap today. Looks like it's only 1" thick for the transom. I was working on my 14' boat today to remove the transom I put in a few weeks ago. I never knew about this new treated lumber/aluminum reaction until I researched for this bigger boat. There is quite a bit of pitting. Looks like someone had pressure treated wood in there before I did. There was actually one small pinhole that ate all the way through. I was going to start a new thread, but figures it's relevant to anyone else rebuilding an aluminum transom. What's the best treatment for the pitting on that boat? Also, I was looking into gluvit for another project. Is there any smaller size than the 2lb container for $50? Seems to be the smallest I can find.

Last question. I was brainstorming earlier about building an all aluminum transom. Why do we (and boat manufacturers) even put wood in there? A few rows of 1" square tubing and a 12x12 1/4 inch plate attached where your motor bolts on and you have a perfect transom forever. Just an idea.
 

jbcurt00

Moderator
Staff member
Joined
Oct 25, 2011
Messages
24,829
Wood works, is cheap and distributes loads across the entire transom area.

Manufacturers dont need (or want) a forever transom when they build and sell a boat.

Start a topic about the boat project w the PT pitting, post some pix.
 

Tnstratofam

Commander
Joined
Aug 18, 2013
Messages
2,679
Good catch on the pressure treated wood. For the pitting you should clean the area and sand lightly. Then you can use jb weld to skim over the pitted areas including the pin holes. Make sure you put light even smooth coats as the jb weld will be extra tough to sand smooth. Then you should primer all the spots, or the transom skin completely with a good aluminum self etching primer. Then paint and reinstall your new transom wood. I bought the primer for my rebuild from Lowes. I used Rustoleum Aluminum primer in the spray can along with some spray paint that matched my hull's color.

I have no idea on the gluvit as I've not bought any myself. If you only have a small area to seal you could possibly use 3M 5200. It is a good sealant that stays flexible and seals seems and or cracks really well. It is messy, but works well.

On the idea of an all aluminum transom. I 've seen flat bottom river boats people around where I live have them. Usually on the better quality higher end boats. Most manufacturers, and backyard boat builders use wood because it's cheap, and easier to work with. No welding skills required. That being said it can be done.
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,585
mckinney004, here is my $0.01 1/2 cents worth.

Go with quality exterior 3/4" plywood and double up on it for your new transom. Yes there are lots of other materials you could use and even a total aluminum setup. But why? Think how old your boat presently is? If you replace the transom the correct way, you can figure that it will be there way after you're tired of the boat. So don't over think this like every other boater does when thinking about making it better then ever.

We all went through your same thought processes and arrived at the conclusion that good quality exterior grade plywood, properly sealed and glued together, is still the best thing going. And believe me, that isn't compromising on anything either. Once you finish this transom build, you will agree as well.

I also think removing the braces and side brackets IS the best way to remove the old transom and install the new one. Leave the top aluminum parts on each side alone. JMHO!
 

Woodonglass

Supreme Mariner
Joined
Dec 29, 2009
Messages
25,924
A 1" transom on that size boat seems a bit small IMHO. I'd recommend more inspection and measurements at multiple points prior to making a final decision. 1.5" IS the standard dimension.

Coat-It is the same product as Gluvit just different MFG. You can purchase it @ Academy Sports. 2lb kit for $20 bucks

http://www.academy.com/shop/pdp/amaz...at-it-2-lb-kit
 

jbcurt00

Moderator
Staff member
Joined
Oct 25, 2011
Messages
24,829
Depending on who built the boat, a 1in inner transom board might be correct because there was an exterior transom board too.

A 55hp on a 1in transom seems like a lot, so, I suspect it had an exterior board too.

Crestliners oftwn have inner and outer transoms.
 

Woodonglass

Supreme Mariner
Joined
Dec 29, 2009
Messages
25,924
Ahhhh, Now that's a distinct possibility.

Based on this pic, there doesn't appear to be evidence of that outer wood transom, i.e. outline pattern or bolt holes where it might have been attached. But....:noidea:

That's why I'm just and Old Dumb Okie any You're a Tinner Guru!!!!!!
 
Last edited:

mckinney004

Seaman Apprentice
Joined
Jan 26, 2016
Messages
46
For those who wanted to see the whole boat


Another reason I'm considering having my friend come out and weld the caps is these cracks on each side. It looks like the previous owner went this route when replacing the transom with this wood.




He could fix these cracks when he welds the cap back on. Or would rewelding this just further weaken the area?

And for those who inquired about the thickness of the transom I took these pics. I can almost squeeze 1.5 inches in the middle of the boat by flexing the skin out, but I can only get 1 inch close to the sidewalls where there will be much less flex.


On the knee above and the side bracket below

 

Woodonglass

Supreme Mariner
Joined
Dec 29, 2009
Messages
25,924
OK, I totally agree now. I" is what you need. 2-1/2" pieces laminated together.
 

jbcurt00

Moderator
Staff member
Joined
Oct 25, 2011
Messages
24,829
Yep ^^^

And enlarging the transom pix you posted, it doesnt look like there was ever an exterior transom board.

Heavy guage and welded construction mean 1in is probably enough. I bet that 20ftr weights a lot.
 

mckinney004

Seaman Apprentice
Joined
Jan 26, 2016
Messages
46
I drove to St. Louis to buy the boat. Guy told me they used these boats to guide barges on the Missouri and Mississippi. Not sure if that's true or not but I looked up some pics and have seen several similar boats with gvt tags on them. And no it's not light. Wish I knew the actual weight. The other thing that is deceiving is the color you see is actually paint, not bare aluminum. That makes me wonder if there was an exterior board before this transom was put in and then painted. This paint was definitely put on after this transom because the bolts holding it in were all covered. Could have covered up any traces of an exterior board. However, it is a pretty thick skin, so maybe not. The ones I saw online didn't have one. I'll be picking up plywood tomorrow to get started.
 
Top