Drilling Transom for Auxiliary Motor Mount

K

Knipet

New member
I want to mount a Garelick style motor mount for a 6 hp kicker on my 22. I know it is highly suggested to enlarge the holes, fill with epoxy, and re-drill. Despite my extensive searching through the archives, I haven't found the specific technique on how to accomplish this task. From what I have surmised; the reason to do this is to prevent the balsa core sandwiched between the inner and outer fiberglass walls of the transom to "squish" or deform and to give a much more solid mount.

However, I haven't figured out the actual mechanics on how this is done, and what in the recommended enlargement for let's say 5/16" mounting bolts. I've read reference to using a Dremel tool, but not which bit or attachment to use. I've even read something about chucking an Allen key in a drill motor and auger out the balsa core between the fiberglass walls. Seems a little crude, and how much oversize to make the inner hole?

Also, when filling the enlarged holes, it baffles me on how to ensure proper filing of the horizontal holes even with thickened epoxy and to prevent air pockets in the upper cavity of the holes. Certainly one would tape up both sides the holes when curing, but what stops air pockets from forming?

I'm pretty handy, but am a little confused in the technique. Seems like an important process and I certainly don't want to screw it up. Thanks in advance for any suggestions.

- Steve
 
I just finished adding a Garelick tilting kicker mount to my Angler 19. I also pondered the questions you raised in your post. I decided on the following approach.

I first bought pvc type tubing that was a little larger than my 5/16 bolts. I then over driller the transom holes so the pvc would easily fit in the hole. I then filled the perimeter of the hole with 5200 and then inserted pvc tube sections the same length as the width of the transom and let everything dry. When dry, I smoothed around the pvc sections and filled edges with gel coat. When dry, I sanded smooth and installed my bracket.

I thought the pvc sleeves were the easiest way to insure the raw transom was well protected.

I’m sure there are better ways, but for me it looks clean and protects my stern!

Good luck?
 
Yakmandu":3gik04v7 said:
I just finished adding a Garelick tilting kicker mount to my Angler 19. I also pondered the questions you raised in your post. I decided on the following approach.

I first bought pvc type tubing that was a little larger than my 5/16 bolts. I then over driller the transom holes so the pvc would easily fit in the hole. I then filled the perimeter of the hole with 5200 and then inserted pvc tube sections the same length as the width of the transom and let everything dry. When dry, I smoothed around the pvc sections and filled edges with gel coat. When dry, I sanded smooth and installed my bracket.

I thought the pvc sleeves were the easiest way to insure the raw transom was well protected.

I’m sure there are better ways, but for me it looks clean and protects my stern!

Good luck?
Click to expand...

Going this route, I probably would have used PVC pipe cement. This dissolves the PVC and would let it bond with the balsa core.

C-Sharp":3gik04v7 said:
...
However, I haven't figured out the actual mechanics on how this is done, and what in the recommended enlargement for let's say 5/16" mounting bolts. I've read reference to using a Dremel tool, but not which bit or attachment to use. I've even read something about chucking an Allen key in a drill motor and auger out the balsa core between the fiberglass walls. Seems a little crude, and how much oversize to make the inner hole?

Also, when filling the enlarged holes, it baffles me on how to ensure proper filing of the horizontal holes even with thickened epoxy and to prevent air pockets in the upper cavity of the holes. Certainly one would tape up both sides the holes when curing, but what stops air pockets from forming?
...

- Steve
Click to expand...

In this method, pretty much bigger is better (IMO). An allen key in the chuck of a drill or motor tool is a good idea, a bent nail could be used as well and you could adjust the depth of the cut. To fill the hole, mask one side off with painter's tape and fill from the other side. West 610 comes in a tube that can be used in a caulking gun. If you are concerned about filling the hole completely, drill a 1/16" hole at the top of the cut out space as a vent and fill the main hole until epoxy comes out the vent. Cover the fill side of the hole with painter's tape til it cures.
 
Bob, You beat me to it! Thanks. I feel that the epoxy gives the best seal. I use the Dremel 115, 5/16" bit. There are other ways to do it--I prefer the smooth cut of the Dremel tool over the other techniques. But they all work. The core should be coated with "neat"--un-thickened epoxy, before you place the thick epoxy [about half cabosil (406 West) and half high density filler (404)]

The goal is both to seal the core--and give a compressive ring. Unfortunately virtually none of the builders do this. That is why boats end up with rot in the core or decks.

I used some of this today, making brackets for the 2nd Li ion battery. I mixed up the clear undiluted epoxy (I keep gallon container, plus quart of both fast and slow hardener in the shop.). I coated the areas first with clear epoxy. Then poured a small amount into another container-mixed up the Fillet material, did the Fillet, placed the glass cloth on top--then used the rest of the clear to saturate the glass cloth. (these steps are not part of the transom--but show quick use of the materials--there Is no reason to mix two batches of epoxy)

I work the epoxy into the hole, tamping it in with a 'popsicle' type of stick--split as a tool. Work the bubbles out. Fill all around the edges. The drill a small hole above, to the cut back area works well, especially if injected with a syringe. My material is a bit thick to inject however. When you redrill the hole for the bolt, you will see if the epoxy you put in has air bubbles or not...
 
Here is another good article with pictures about over drilling holes for bolts or screws through fiberglass/core sandwiches.

https://pbase.com/mainecruising/sealing_the_deck&page=1

I'm not sure what the core of your transom is. Mine (an '89 cruiser is not balsa but plywood). I seem to recall other years may have used other core materials. However, a Allen wrench or bent nail won't work very well if at all in plywood. A Dremel tool as described by Dr Bob is much better and in any core does a much neater job.
 
I was surprised when I drilled my 2004 transom for a ladder that the core material wasn't balsa but foam. Still, I sealed it up with penetrating epoxy before putting the bolts through (with butyl rubber for a belt and suspenders mounting).

One of the frustrations of a project like yours (assuming balsa) is that you first need a drill bit and a bent nail. No problem. But then you need four drops of penetrating epoxy, a teaspoon of West epoxy, and a tablespoon of cabosil. Unfortunately, you can usually only find this stuff in quart$ and half gallon$, which will sit on your garage shelf for years.

Maybe you'll be lucky like me and find other rot in the balsa core so that you can use up the materials.

Mark
 
Thank you everyone for clarifying the procedure to over-drill and fill with epoxy when drilling the transom. This has been very helpful and now I understand the process. Something as important as drilling holes in a vessel, I wanted to make sure I had it right! Thanks again.
 
For at least the 2005 models, structural foam was used in the transom. I found this when I replaced the Garelick motor mount on the transom.

As to putting PVC pipe over the attach bolts, the load would get transferred in one of 2 ways.

If the pipe lengths were (slightly) longer than the transom thickness, the motor loads (load and thrust) would get transferred to the transom through the the pipe and glue joint. If either broke down, the motor would push/pull until it hit the transom.

If the pipe was shorter then the transom, the attach bolts would bed directly on the transom and the loads would go directly to the transom. And, by the way, if the pipe was the transom's exact length, it would depend on Eulers modulus of both parts, i e, how much they would compress under the bolt load.

The epoxy insert would stiffen the transom in that area and the loads would transfer to the transom.

Boris
 
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