Drilling Holes in Transom

S

Saxe Point

New member
I'm not a C-Dory owner yet, but I hope to be someday! In the meantime, I was hoping I could tap into the collective wisdom of the group.

The kicker on the new (to me) boat that I just bought (18 foot Hourston) is a long shaft Yamaha 9.9 hp. It is mounted directly on the transom, which is clearly too low. Trolling in following seas results in the motor being swamped as waves will from time to time push over the transom into the splash well.

Out here on the West Coast of Vancouver Island, many fishermen avoid this problem by raising their kickers slightly with a plastic kicker plate that attaches to the transom and to which the kicker attaches. The picture of the set up on my old boat illustrates what I mean (the boat shop installed that one, not me).

I'm going to be putting a new plate on my new boat to raise the kicker. Because I was considering building a boat at one time, I've done a ton of research and know all about the importance of overdrilling holes in the transom (or, frankly, anywhere on a boat that's going to be exposed to water) and then filling the holes with epoxy. Then you're effectively drilling a smaller hole into epoxy, thus preventing moisture from getting into the core of your transom.

My question has to do specifically with whether it is necessary to seal the holes with 3M 4200 or some other similar sealant once you put the transom bolts through the holes. Using such a sealant makes sense, and I believe it is standard practice, where the holes are not overdrilled and filled with epoxy. In those cases, you need the sealant to prevent water permeating into the transom core. But if you've got nothing but epoxy surrounding the holes, wouldn't it simply be overkill to apply sealant? I'm all for the "belt and suspenders" approach if there is some real purpose to be achieved. But here, I am wondering if sealant is truly necessary at all.

I realize this is a pretty narrow inquiry. But I'd be grateful for any and all opinions and wisdom you can provide.

edit: I can't post a picture to show you what I am talking about.
 
It's a bit of a redundancy, but certainly not overkill.

For most items that are of any weight or that take a strain you will want the piece mounted to your transom in some kind of bedding compound. Choosing one that will also seal your screw holes is an easy decision. 3M 4200 is perfect.

For the record, you really only need to overdrill if you are screwing into cored fiberglass.
 
As you probably know, some people use a "Mini Jacker" to raise the kicker a few inches. Test-fitted one on my boat but wasn't happy with it and ordered a Garelick movable offshore bracket, which has arrived but hasn't been installed.

When mounting a swim step I overdrilled and filled the holes as you describe, but still used Life-Caulk sealant. It seems to stay flexible and is more of a sealant than 4200 (which is really an adhesive). Belt and suspenders.
 
I have used the up / down mounts, instead of a minijacker also. I use 4200.

One should always check the manufactures' web site about the specific sealant you are using. 3 M calls 4200 a "adhesive sealant". From your own reading you can determine if this is really an adhesive, you would trust your motor to alone? I consider the 3 M products an adequate sealant to trust that for all of the deck fittings of the Cal 46 we rebuilt for ocean crossings were sealed with 5200. After I put over 30,000 miles on the boat, the next owner cruised it for 14 more years, and many more thousands of miles with no failure of the sealant in over 20 years, and some of the most extreme conditions from Alaska to the Equator.

here is the technical site for 4200 fast cure
 
Weather is finally improving and I can get some stuff done. When overdrilling and filling the transom bolt holes, I was thinking of using System 3 Gel Magic or West System Six 10. They both appear similar in that they won't sag in the holes and are easy to use (no adding of thickeners).

Any advice as to whether this is the right way to go or not?

Much appreciated.
 
I used West with Cabosil for my balsa penetrations, including the transom. I first sealed with Smith penetrating epoxy, but that may be overkill. Cabosil putty will slowly creep out of a transom hole unless it is mixed really, really stiff. And when really stiff, it's difficult to make sure that you've completely filled the hole.

I went to the feed store and bought a couple of syringes used on livestock (w/o needles). Mix your slightly loose putty and put it in the syringe using a Popsicle stick. If you have a large hole (bigger than quarter inch), put a piece of duct tape over it and punch a little hole in the tape for the end of the syringe. Use the syringe to inject your putty until the tape bulges a little and keep squirting as you pull it out. Have a rag with acetone handy and another piece of tape to cover your little punctured hole. Keep it neat and the fill will be almost invisible. I've never felt the need to do further cosmetic work.

The syringe is a one time applicator, so you have to have everything staged if you have a few holes.

Mark
 
I have a series of pics in my album that will show you how to get your vertical transom holes filled properly. It's not very difficult.
 
Kushtaka
Thanks, that's cool. First time I've seen that way to fill the holes. I've always used thickened epoxy; a small putty knife; at times, a syringe and LOTS of fussing to back fill! I can see where a sharp chisel and green epoxy would make clean up quick. Next time I have holes to fill I'll try your way. Can also see where a variation of that method with the relief hole but no reservoir could work on horizontal surface. You're using unthickened epoxy? Do you heat it to thin it out before pouring?
 
I echo that. Thanks very much. That's a very helpful set of photographs that explains in detail the best way to go about it. Whatever kind of epoxy I use, now I know how to go about doing this project.
 
It is thickened with cabosil. I did paint the inside of the holes with unthickened epoxy first, but didn't take a pic.

I have only used this technique on horizontal fills where I've had to remove more core than would be necessary (usually because of some core issue or another), but with just a little extra core excavation to make a screw penetration it isn't really necessary.
 
I want to add one more point about using thickened epoxy for this:

Yes, it seems like the thick stuff won't flow, but it will. Be mindful of temperatures, and use the appropriate catalyst for the day. Mix up a bit more epoxy than you will use, maybe 3x or more. Keeping a larger volume of epoxy in your pot will keep it less viscous longer. Epoxy kicks more quickly when it has a high surface area to volume ratio, so even if you toss some (you will) you are keeping what you use in a workable condition longest. Absolutely stop and mix a new batch if you feel heat or notice any hard parts in your pot.

If you do your prep work before you mix, and have all of your tape down and well adhered, you should be able to simply pour the thickened epoxy into the reservoirs fairly quickly before the mix starts to set up. If you hedge anything, don't under thicken (IMO), make a bigger pot so your epoxy stays workable longer. If you do it all quickly it will flow just fine.
 
Okay, I got the holes overdrilled, filled with epoxy, drilled again. I got the poly board bolted in. I've even got the kicker mounted. It all looks great.

But, when I was bolting and sealing everything, I realized that I used 1/4 inch stainless bolts (4) to attach the board to the transom, but the kicker was previously mounted with 5/8 bolts (only 2 at the bottom, clamps up top).

Any issue about the strength of the 1/4 vs. 5/8 inch bolts or am I worrying for nothing?

How can I post a picture? I can show you what I've done.
 
Saxe Point":35t7ww48 said:
Okay, I got the holes overdrilled, filled with epoxy, drilled again. I got the poly board bolted in. I've even got the kicker mounted. It all looks great.

But, when I was bolting and sealing everything, I realized that I used 1/4 inch stainless bolts (4) to attach the board to the transom, but the kicker was previously mounted with 5/8 bolts (only 2 at the bottom, clamps up top).

Any issue about the strength of the 1/4 vs. 5/8 inch bolts or am I worrying for nothing?

How can I post a picture? I can show you what I've done.
Click to expand...

Sorry, they're not 5/8 inch bolts that were used to mount the kicker previously. They're either 3/8 or 5/16.
 
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