Transom Drilling and Checking

[cpo1]

I've noticed some folks recommending a transom core drill to ensure that the transom is not rotted. Here are my questions. What size core drill is commonly used and what techniques are used to replace a good core? Epoxy resin? 1/4" or so Chamfer inside and out? Where are the common sites for test drilling transom core? Thanks for your replies.

 

[JASinIL2006]

The typical sites for drilling are low on the transom near the hull, around the keyhole (if an I/O), and below any thru-hull fittings (especially those below the waterline). A 1/4" or 5/16" bit works fine, and you only want to drill from the inside of the boat about 1.5" deep to avoid penetrating the hull.

If the shavings come out light-colored and dry, you can fill the hole with 3M 5200 Marine Adhesive Sealant or with MarineTex epoxy (or PC-11 epoxy, which is cheaper and sometimes easier to get). If the shaving are dark and/or wet, you have problems...

 

[Chris1956]

Do you have a reason to check the transom? Drilling holes in a waterproof member, that is working, invites rot, as it defeats the waterproofing.

 

[cpo1]

The typical sites for drilling are low on the transom near the hull, around the keyhole (if an I/O), and below any thru-hull fittings (especially those below the waterline). A 1/4" or 5/16" bit works fine, and you only want to drill from the inside of the boat about 1.5" deep to avoid penetrating the hull.

If the shavings come out light-colored and dry, you can fill the hole with 3M 5200 Marine Adhesive Sealant or with MarineTex epoxy (or PC-11 epoxy, which is cheaper and sometimes easier to get). If the shaving are dark and/or wet, you have problems...

Thanks for the information. Much appreciated. Are you saying, I don't need to drill with a hole saw bit so I can see the core? Just pay attention to the color and moisture content of the shavings? Thanks again for your reply.

 

[cpo1]

Do you have a reason to check the transom? Drilling holes in a waterproof member, that is working, invites rot, as it defeats the waterproofing.

Chris1956, I think I can detect some slight variations in transom sound when tapped with a hammer and I believe it warrants further inspection. Having gone this far, it just makes sense to replace the transom if it is indeed compromised. But I'm still curious. You say that core drilling invites rot. If the plugs come out strong, not needing to be replaced, the holes cannot be filled with a waterproof plug that will prevent rot around the plug? Thanks again for your comments.

 

[todhunter]

Correct - look at the color of the shavings. This is from mine. Top shavings are an example of good. Bottom are an example of bad. That dar or darker means it's been wet.

 

[Lectro88]

Todd, that is a great example for folks to actually be able to SEE the true difference.
However... IF I "think" If I were to have tried to drill my transom the shavings would have just been "Black Dust" as it was Mush/Gone.

Keep that photo handy for future posts.

**That Photo would make a good Stickey..**

 

[Lectro88]

You don't need to drill all the way through the hull. that way you Don't have to patch the exterior fiberglass.
Being an electrician and very used to hole saws... I have never heard of anyone using them. The larger core would certainly tell the tale.
The key would be removing or keeping the pilot bit from breaking through exterior fiberglass.
It would require a lot more material to patch around the core.
I would use epoxy or thickened epoxy to patch, if you don't have (3m 5200. $25 tube)
You could also use a wooden dowel with epoxy to plug hole.
If you leave the hole open,.. it will obviously allow water a freeway to insure rot later for sure.

Unless your transom is Absolutely Solid.
Going to the trouble to pull the cap, it would a shame not to replace transom while you're there. and have full access.
It "Should" be good then for at least 20yrs. if done correctly.
If you don't replace it now.. And you need to do all this again in 5/10yrs. for a transom, is food for thought.

 

[JASinIL2006]

Thanks for the information. Much appreciated. Are you saying, I don't need to drill with a hole saw bit so I can see the core? Just pay attention to the color and moisture content of the shavings? Thanks again for your reply.

No hole saw! Just a drill bit and inspect the shavings like todhunter‘s picture shows.

Also knocking on the boat will tell you virtually nothing. There may be some very experienced folks who can determine the condition by knocking, but for most everyone, it is probably about the most unreliable method you can use.

 

[kcassells]

You need to reach out to the moderators and keep a single thread.

 

[Lectro88]

No hole saw! Just a drill bit and inspect the shavings like todhunter‘s picture shows.

Also knocking on the boat will tell you virtually nothing. There may be some very experienced folks who can determine the condition by knocking, but for most everyone, it is probably about the most unreliable method you can use.

I agree, it takes a very well trained ear to tell the difference by knocking.

And I wasn't sure of the hole saw idea either, I could have gone either way on the idea.

Follow the advise given,.No for the hole saw.

 

[cpo1]

You don't need to drill all the way through the hull. that way you Don't have to patch the exterior fiberglass.
Being an electrician and very used to hole saws... I have never heard of anyone using them. The larger core would certainly tell the tale.
The key would be removing or keeping the pilot bit from breaking through exterior fiberglass.
It would require a lot more material to patch around the core.
I would use epoxy or thickened epoxy to patch, if you don't have (3m 5200. $25 tube)
You could also use a wooden dowel with epoxy to plug hole.
If you leave the hole open,.. it will obviously allow water a freeway to insure rot later for sure.

Unless your transom is Absolutely Solid.
Going to the trouble to pull the cap, it would a shame not to replace transom while you're there. and have full access.
It "Should" be good then for at least 20yrs. if done correctly.
If you don't replace it now.. And you need to do all this again in 5/10yrs. for a transom, is food for thought.

Lectro88, Thanks for your help. This is great information and it brings to my mind the possibility of a new "library" on this forum. Type in a few key words: transom, rot, drill, test, etc., etc., and your picture shows up, along with the associated comments. Not a bad idea eh? I am almost certain that the transom is going to be replaced. I agree with you. Go this far and leave one of the most important structures on your boat still wanting makes no sense to me either. Thanks again.

 

[cpo1]

You need to reach out to the moderators and keep a single thread.

Thanks kcassells, how do I go about that? I'm understand the logic of it, but am wondering how you can reply to all the contributors in a single thread. Thanks and I'll look forward to more help or research about this.

 

[cpo1]

I agree, it takes a very well trained ear to tell the difference by knocking.

And I wasn't sure of the hole saw idea either, I could have gone either way on the idea.

Follow the advise given,.No for the hole saw.

Lectro88, you got me on this one. I'm on board with the negative hole saw. I just saw a photo of a plug on the forum somewhere, but didn't realize you can leave all the old glass intact as you add a new transom. Now I'm on to research the appropriate methods for transom replacement and type of structure to use these days. Thank you.

 

[cpo1]

No hole saw! Just a drill bit and inspect the shavings like todhunter‘s picture shows.

Also knocking on the boat will tell you virtually nothing. There may be some very experienced folks who can determine the condition by knocking, but for most everyone, it is probably about the most unreliable method you can use.

JASiniL2006:, Thank you. The light has come one for this one!

 

[Lectro88]

Lectro88, Thanks for your help. This is great information and it brings to my mind the possibility of a new "library" on this forum. Type in a few key words: transom, rot, drill, test, etc., etc., and your picture shows up, along with the associated comments. Not a bad idea eh? I am almost certain that the transom is going to be replaced. I agree with you. Go this far and leave one of the most important structures on your boat still wanting makes no sense to me either. Thanks again.

Man you are welcome, I'm just passing on what I learned. everyone on here helped me and continue to do so.

Everything Starts at the transom. thats the footer/foundation of the structure.

I did a way out in left field transom that was 3" thick. Basically a butcher block replica.. But it's Solid to say the least. and knee'd into the hull for added displacement of load.
welcome to have a look.
I started way simple and kept adding and seeing ways to improve in my eyes and it morphed out of control.
you should be able to find several transom rebuilds, if not ask we will put you on a few.

So far as materials that's a sky is the limit of what you want and how much your wallet is willing to part with.
There is several choices in wood, synthetic and finally ceramic pours or pour in a mold like concrete in a form.