Transom replacement on my 12' Sears tinny

I am looking to replace the wood transom brace on my boat and would like some help. I have already had a discussion about what type of seal to use that you can see here if interested: http://forums.iboats.com/showthread.php?t=567885&page=2

So I have some pics below of my boat to give you an idea of what I am working with. As said, it is a 12' Sears V-hull made in 1970. I plan on using it for fishing with a buddy or two, or taking my wife and 2 small kids out to tool around. I have a 9.8 hp Merc and will never put anything bigger on it due to HP limits in the area (not to mention the boat).



So now that you have met, here is what I am looking at transom-wise: Previous owner had a 14" x14" home plate shaped brace on the exterior and a 14x3 brace inside. The wood has been removed and I did some cleaning with a wire brush last night. Before:



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Re: Transom replacement on my 12' Sears tinny

And after:



Took it out for a float test today on the advice of KFA in the previous thread and the bottom holes get some water through them with just me and the kids in it with no outboard. :facepalm: So we will be sealing those and obviously the wood will no longer go down that far. Good catch KFA! So now the question is, do I just keep my 14" wide piece and make it shorter, or do I extend the whole way across the inside of the boat. If you vote for the latter. How do I compensate for the small factory "bump outs" on either side of where the old transom was?

Re: Transom replacement on my 12' Sears tinny

I'd mimic what you took out: same size & same thickness plywood. Use an exterior grade A/C ply, douglas fir 5 layer ply if you can get it, marine plywood (non-pressure treated), MDO, Auraco (may be hard to find 1 of 2 production facilities had a serious fire), in a pinch underlayment plywood, among other choices. Depending on the maximum width your 9.8 Merc's transom clamps will fit over, plus some room to tighten the clamps & allow for the thickness of the hull, will make selecting which thickness ply you need fairly easy. If the absolute widest asjustment on the clampsprovides a 1.5" space, the maximum thickness ply you'll want to use is 5/8", 1/2" would probably be sufficient for both as well. At 5/8" they will be slightly thinner then 1 3/8" when doubled, add some for the hull thickness, the coats of sealer you've applied, and to be able to actually tighten the transom clamps. If you have any 'good', void free, waterproof glue plywood already in both 5/8" & 1/2" thicknesses, I'd probably use 5/8" on the exterior & 1/2" on the interior. Thru bolt them and call it good at @1.25" total installed thickness. This will give you a little more room to slide the motor on & off, and allow for some expansion of the plywood. You might also make a slightly larger plywood piece on the interior, then what was there, that would then follow the size of the pc on the exterior, perhaps just down until it's @ 1/4" above the start of the green interior paint.

Cut the pcs, sand & prep as necessary for the product you've chosen, as last I remember you were looking for Spar Varnish..

Clamp the plywood onto the transom 1 pc at a time & mark out the 6 mounting thru bolt holes. Drill the thru holes and start sealing the wood, multiple coats each side, and pay particular attention to the plywood's edges & thru holes. The edges & thru bolts are the likely start of water intrusion into your wood.

Let how & where you store this boat, and whether you store it w/ the OB installed or removed, dictate whether you thru bolt the OB to the boat (recommended for loss while under way & theft). That thru bolt will need to have it's hole drilled & well sealed. You can also use the 3M 4200/5200 to seal the bolts into the thru holes on installation of the bolts. Just dip them into 4200 & push them thru their bolt location while rotating the bolt (helps spread the sealant out inside the bolt hole. Clean the threads & surrounding surfaces before you tighten the nut & again after....

If you are going to prime & paint the rest of the boat, do that 1st, apply the plywood to the transom after.

On a boat this size w/ this size of motor, I wouldn't adhere the plywood to the inside or outside faces of the aluminum transom. Check the plywood regularly for cracking of your sealer along the grain of the ply, and on the ply edges. Touchup & re-seal as often as necessary to prevent water intrusion. Regularly check the tightness of the thru bolts for both the plywood & the motor.

Depending on the 'holes' and water leaking, there are a few ways to deal w/ that. I think you've got a handle on that from the original boat, w/ the torn out rivets & a damaged hull, that you flipped to get this 1.

Re: Transom replacement on my 12' Sears tinny

I see what you mean about the "in and outs" on your transom now Siggy, your transom has been "stamped" on a stamping press for added strength.

Re: Transom replacement on my 12' Sears tinny

Are you running in salt water or brackish water? Please be certain to get some zinc chromate primer on that newly cleaned aluminum. If you mount an outer transom board (highly recommended) and bolt it down you will create a space where corrosion will thrive! You might even consider a skim coating of 5200 as you mount that board.

We have seen many older aluminum boats with holes eaten through and now that the aluminum is scratched / cleaned it will be more susceptible.

For the 12' tin boats like that a nice 2 x 8 makes an excellant inside piece with a pice of plywood on the back varnished with 3 or 4 coats. That is plenty strong for a 10 hp motor.

Re: Transom replacement on my 12' Sears tinny

jbcurt00 said:

Let how & where you store this boat, and whether you store it w/ the OB installed or removed, dictate whether you thru bolt the OB to the boat (recommended for loss while under way & theft).

If you are going to prime & paint the rest of the boat, do that 1st, apply the plywood to the transom after.

Depending on the 'holes' and water leaking, there are a few ways to deal w/ that. I think you've got a handle on that from the original boat, w/ the torn out rivets & a damaged hull, that you flipped to get this 1.

Click to expand...

I bought some exterior grade 3/4" I will have to measure to make sure it is not too big. Did not think about that. I plan to store the boat beside my house outside, but for the winter figure I will have to bring in the motor, so I will probably take it off each time and bring it in.

I will likely paint the boat, but not for a year or two.

My plan for the two holes is to use stainless bolts with nylon washers inside and out. No other leaking rivets.

jigngrub said:

I see what you mean about the "in and outs" on your transom now Siggy, your transom has been "stamped" on a stamping press for added strength.

Click to expand...

Yes! Stamped, thanks!

I will be running in only freshwater. I wondered about how to prep the aluminum now that I have shined it up. I like the look of the aluminum (not necessarily shined but the same color as the rest of the boat). I'd rather not paint it. I had read about a vinegar and water mix, will that do to prep it before mounting the transom, or do I need to seal it with something else? Good catch on that Bob. Also, should I use the drill to remove those stickers, or is there a better way?

Re: Transom replacement on my 12' Sears tinny

Want to shine to aluminum......... you polish it. Google polishing aluminum

Then you want to use a preservative such as "shark hide" google that too!

To remove stickers????? Razor blade, chemicals such as a stripper, and you can try a pin stripe eraser wheel sold at most auto stores.

Re: Transom replacement on my 12' Sears tinny

I don't really want to polish it. I just want it to match the rest of the boat. If I put shark hide on it now, will it be shinier than the rest? Does that mean I need to brush the rest of the back?

Re: Transom replacement on my 12' Sears tinny

I just returned from Ace Hardware where I purchased some spar varnish, stainless steel screws, nuts, and washers as well as some self etching primer. Turns out shark hide costs almost more than I spent on my boat. Speaking of price though stainless steel hardware is about 30% cheaper at Ace than West Marine and they had a better selection, just FYI. So what I decided to do with the two holes that are at the water line is to put a small bolt through them with nylon washers on either side. Thoughts? Now off to cut my wood transom pieces!

Re: Transom replacement on my 12' Sears tinny

here is what i did : http://forums.iboats.com/showthread.php?t=548413

WHITE oak for inside transom, 5 coats of spar varnish.......... outside i made a 1 inch aluminum plate and bolted her on............ came out sweet.........

3M 5200 to seal everything and SS nuts, bolts and washers all around

oh, and P.S.

do not use pressure treated wood at all, period

Re: Transom replacement on my 12' Sears tinny

s freud said:

I don't really want to polish it. I just want it to match the rest of the boat. If I put shark hide on it now, will it be shinier than the rest? Does that mean I need to brush the rest of the back?

Click to expand...

i cleaned the entire boat, then shark hided it all around........ i can now shave in the reflection

i am fresh water as well, and mounted magnesium anodes instead of zinc, works awesome in fresh water

brackish water= aluminum anodes???

salt water=zinc anodes

Re: Transom replacement on my 12' Sears tinny

jbcurt00 said:

On a boat this size w/ this size of motor, I wouldn't adhere the plywood to the inside or outside faces of the aluminum transom. :

Click to expand...

Why not?

Re: Transom replacement on my 12' Sears tinny

You'll be fine to do anything you want with your transom wood as long as you put a primer coat of paint on the aluminum first and seal your wood well with multiple coats of varnish.

The primer paint will prevent galvanic corrosion and the sealer will preserve your wood. You'll be good to go for years and years.

Re: Transom replacement on my 12' Sears tinny

+1 Jig's got it

Re: Transom replacement on my 12' Sears tinny

Thanks guys. Do I need to put anything over my rustoleum self etching primer, or will that be enough?

Edit: On the boat that is, I am applying at least 3 coats of spar varnish (6 for the edges and holes) to the wood.

Re: Transom replacement on my 12' Sears tinny

In addition to the above question, will I break my nylon washers if I overtighten them? If so, how do I know when to stop?

Re: Transom replacement on my 12' Sears tinny

Nylon washers ??? Just use SS washers and 3m 5200 on the bolts enough will get on the washer. I tightened my transom boats on my 14' wood tansom until the washer was flush wit the wood.

Where are you using that primer?

Re: Transom replacement on my 12' Sears tinny

You can just use the primer or put a top coat on too, you just mainly need a barrier between the aluminum and the wood.

The nylon washers are less than desireable... all you need is a bolt, a nyloc nut, and a good sealant like 3M 5200 or Loc-tite marine epoxy.

Something else that's good to have when you own a tinny is a rivet setting tool and an assortment of closed end blind rivets, a CEB rivet of the correct diameter in those holes will work as well or better than all of the above... they come in handy for doing other stuff on your boat too.

Re: Transom replacement on my 12' Sears tinny

s freud said:

Thanks guys. Do I need to put anything over my rustoleum self etching primer, or will that be enough?

Edit: On the boat that is, I am applying at least 3 coats of spar varnish (6 for the edges and holes) to the wood.

Click to expand...

s freud said:

In addition to the above question, will I break my nylon washers if I overtighten them? If so, how do I know when to stop?

Click to expand...

SE Primer is primer, and only needs to be a light coat:






It will look spotty, that is good coverage, like above.

When you install those bolts, washers & nuts, you should use some 3M 4200/5200 to absolutely seal those hull holes up. 5200 is best described as permanent, may even be on the label. It is available here at HD or Lowes, I can't remember which. I think it is avail in both a smaller squeeze tube & a 'regular' sized caulk gun tube.

Watch your washers as you tighten them, they will start to distort as you go from well tightened to too tight. It's a touch/feel I can't describe any better then that.

Re: Transom replacement on my 12' Sears tinny

Ug. What would I do without you guys. I got the nylon washers for the two lowest holes where there will be no wood. I thought the seal would be better than with the SS washers. I guess I will exchange them, or buy a couple small SS ones. I have 5200 that I plan to use liberally as you all have described above, cleaning out the threads after insertion and the like. Thanks too for the pics those are very helpful. I am sure I would have seen it looking "spotty" and been sure I had done something wrong. You all are the best!