Is my Transom Repair OK ??

[Tinklespout]

Hi, I'm new here and wanted to run this by y'all before I cut into a nice piece of oak plywood. I'm planning three layers of 3/4 inch oak plywood under the motor; two layers outside and 1 inside. The 3/4 inch layer on the inside will cover most of the transom. I'm keeping it about 4 inches away from the sides and bottom. I thought this would make it stronger overall, there seems to be a lot of flex right now. I'm also making the center 18 inches (the four layer part) 1 3/4 inches taller because my engine shaft is too long. (right now the cavitation plate is 2 inches below the bottom of the boat).

Questions:
1) Would spar varnish be OK? I've read that epoxy paint is better but I can only find epoxy paint for metal appliances or concrete.
2) is 4 inches bare on the sides and bottom OK? I've seen pictures where it is run to the very edge and I've seen others where the transom is only about eight inches. My boat has real thin aluminum so It seems that I should try to add as much additional strength to the transom as I can.
3) is there any real benefit to the oak plywood? I've read that oak is very good for boats but am wondering if that applies to the plywood.
4) where should the cavitation plate be in relation to the bottom of the boat. I've seen recommendations that say at the water line (in line with the bottom of the boat, and others that say one to two inches below the bottom of the boat.

The internet seems to have so much conflicting information. I guess that's because there are so many different kinds of boats so I thought you guys would know best boats.

I really appreciate your help on this.

Thanks a lot!!
Kim

 

[Go Fish]

Kim-

Your repair plan is overkill. I've goy two layers of 3/4 inch ply holding up a 600 pound motor on my 22 foot offshore boat. One, or if you need it for personal comfort, two layers of ply will do just fine.

 

[Jdholmes]

I vote way overkill 2. I haven't heard of anyone going that far on a tin...most don't have wood on the outside and if they do it is one small piece...

In regards to some of your other questions...

Oak is a hardwood and is a good choice...in regards to benefits it depends on what you are comparing it to.

Spar Varnish....no. Varnish is not going to have the longevity as urethane.

In regards to the spacing I cannot answer that...what was the original design from the manufacturer?

 

[Tinklespout]

Thanks for the replies, I realized that I miss-stated the thickness. I corrected (edited) it.

I am copying what was on the boat but it may have been re-done and not what the manufacturer had originally. this is a good point, I'll try to find an original picture of the boat. The only thing I'm changing is the amount of coverage on the inside.

Thanks about the spar varnish. I'll use urethane instead.

I'll go with the oak.

Thoughts on the cavitation plate Height?

Thanks again, this is really helpful. I am pretty conservative.

Kim

 

[Ringo Steele]

When you get the urethane, make sure it's SPAR urethane, not regular polyurethane. Polyurethane will break down from the UV in sunlight, whereas the spar urethane will hold up much longer. I went one step further in the transom rebuild on mine and used epoxy to coat the plywood (exterior grade plywood). I used 2 sheets of 3/4" on the inside of mine, as that was the original transom thickness, and none on the outside. The outside piece you see on some boats is more for protecting the transom aluminum from the motor than for strength of the transom, and is usually 1/4" to 1/2" thick (some exceptions apply, as with most things!). Here's a picture of mine:

 

[Tinklespout]

Wow, that's nice. I appreciate the info. Why the metal plate on the center part? scuffing from stuff (gas tank,etc.) perhaps?

Kim

 

[Jdholmes]

A lot of boats have a thin piece of aluminum on top of the wood...mine was much smaller. I believe the purpose is to protect the transom surface, which you just protected with multiple coats of spar urethane, from being cut into by the motor brackets.

 

[fisherman58]

your oak ply is only a very thin vener of oak and is not exterior grade glued so it is not your best choice i use mdo plywood on all my boat work about 60$ asheet for 3/4 inch i put it in a friends boat 4 years ago he did not cover it with anything and it's still like new

 

[Jdholmes]

Ignore the last post. You will be fine with what you have, the important thing is that you do multiple coats of spar urethane...that is what protects it from the elements.

 

[fisherman58]

Ignore the last post. You will be fine with what you have, the important thing is that you do multiple coats of spar urethane...that is what protects it from the elements.

SORRY DUDE I DID NOT KNOW YOU WERE A #$%@^&* GENUIS

 

[Jdholmes]

No need to be nasty. The things I say with a sureness on here I say based on the brain trust of this forum alongside my personal experience. Many of the members of this forum have had great success with oak plywood, so there is no need to plant doubt in the mind of a person that already has lots of questions. The question has been well answered, so do take your nasty attitude and kindly move along.

 

[Tinklespout]

Thanks for all the info. I'm ready to go with it and will post a picture when I'm done.

 

[fisherman58]

No need to be nasty. The things I say with a sureness on here I say based on the brain trust of this forum alongside my personal experience. Many of the members of this forum have had great success with oak plywood, so there is no need to plant doubt in the mind of a person that already has lots of questions. The question has been well answered, so do take your nasty attitude and kindly move along.

my nasty attitude im not the one who said ignore the last post glad your a couple thousand miles from me

 

[Ringo Steele]

.

Wow, that's nice. I appreciate the info. Why the metal plate on the center part? scuffing from stuff (gas tank,etc.) perhaps?


It's to protect the wood and its finish from the metal cups on the motor mount screws. I made mine out of a door scuff plate (aluminum), and made it large enough to mount my gas motor and a transom mount trolling motor beside it

 

[Jim]

OK guys, lets move along here. Take it up via PM if you have issues. We have lots of readers that could be potential members and they will not join if they see this type of stuff.

 

[sixgun86]

My transom is the bestest. It was built with the fury of of Fishermans temper and the secret data files from Holmes laboratory, aka his mothers shed. FIBERGLASS! over Ply. Love thy stress cracks and De laminated sheets.

Ringo, your transom looks great!

Tinkle, What state was the picture taken? Nice setup!

 

[Ringo Steele]

Thanks Sixgun! I did find out from West Systems about their epoxy that I will need a top coat of some type...
"Our WEST SYSTEM® 207 Special Clear Hardener has a small amount of UV inhibitor added – but not enough to be a final finish. The UV inhibitor depresses the physical properties and our products are first and foremost structural adhesives, so we do not make just a final coating. We always recommend using an over coating – a clear urethane, varnish, or paint. Here is a link about Finish Coatings,
https://www.westsystem.com/ss/finish-coatings/"

I'll probably go with Spar Urethane for that.