# Drilling Transom -- Best Way?



## NoMoSurf (Oct 2, 2007)

I'm about to uprade the motor on my little 16ft skiff. The old motor was a clamp on 40hp and the new one is a 55hp bolt on. What is the best route to go here? Should I just drill the 1/2 inch holes and cover the bolts in 5200 as I slide them through? Or should I over drill them and fill the holes with resin, then redrill to correct size? 

If over drilling is best route, how is the best way to keep the resin from running out of the hole before it cures? I am very familiar with working with various types of resins, but never tried filling a horizontal hole of such diameter. Maybe there is a trick?

Since I'm sure someone will ask.  The boat is a 1970 Kingfisher 154. It looks like a cross between a Carolina skiff and an old 70's Bomber bass boat. The transom is in very good condition. The boat was garage kept it's whole life until 2 years ago. It is gelcoat/fiberglass on the outside, I'm assuming plywood cored on the inside, and glass cloth on interior of boat.


----------



## markw4321 (Oct 4, 2007)

I am no expert but I have mounted a couple of motors. I slightly under drilled mine and coated the stainless bolts with 5200 and tapped them through. Then coated both sides with 5200 and used large diameter washers on both the head and nut side of the transom. Not sure why you would want to overdrill them maybe I'm missing the reasoning.


----------



## timeflies (Oct 3, 2007)

Mark pretty much said it. The large washers are really important. Spread that stress out over as large an area as you can.


----------



## NoMoSurf (Oct 2, 2007)

markw4321 said:


> Not sure why you would want to overdrill them maybe I'm missing the reasoning.


The idea is to overdrill the hole, then completely fill the hole with fiberglass resin that will soak into the wood and have a solid plug of resin through the transom. You then drill the correct sized hole through the resin. That way the bolt never touches wood and there is no exposed wood to allow moisture to intrude.




timeflies said:


> Mark pretty much said it. The large washers are really important. Spread that stress out over as large an area as you can.


Not a problem. I still have all of the hardware from the mounting on the last boat it was on. It was mounted using two 1/8" thick stainless plates as will as the afore mentioned washers. And I work at a fastener company that specializes in stainless fasteners.


----------



## markw4321 (Oct 4, 2007)

NoMoSurf said:


> The idea is to overdrill the hole, then completely fill the hole with fiberglass resin that will soak into the wood and have a solid plug of resin through the transom. You then drill the correct sized hole through the resin. That way the bolt never touches wood and there is no exposed wood to allow moisture to .


Gotcha. Sounds like that could work as well.


----------



## X-Shark (Oct 3, 2007)

> If over drilling is best route, how is the best way to keep the resin from running out of the hole before it cures?


The answer to that is mixing Cabisol into the resign...This thickens it. The more you add the thicker it gets.


----------



## Ocean Master (May 20, 2008)

X-Shark said:


> The answer to that is mixing Cabisol into the resign...This thickens it. The more you add the thicker it gets.


 You can mix it till it's like peanut butter..


----------



## NoMoSurf (Oct 2, 2007)

So which way is the right way to drill the transom. Correct sized hole with 5200 or oversized hole with "peanut butter"?


----------



## X-Shark (Oct 3, 2007)

I sleeve them.

It's mostly done in composites, but a wood core it works very well also.

You step drill the holes to keep them perfectly square. It's drilled oversize to the OD of 1/2in PVC The PVC sleeves are made just slightly short of the transom thickness.

The Sleeves are sanded with 80gt. They are then Epoxy glued in the holes. This creates a total watertight seal from the core....Plus you can't crush a piece of tubing stood on end....Not without a SERIOUS press.

The sleeves are set just under the surface of the inside and outside face of the transom and Epoxy/Cabisol mix that was used to glue them in is made even with the outside surface. After the mix is in a Green state, the excess can be carved cleanly out of the hole. Now you can seal the bolts easily with 4200 and never fear that water will wick into the core.


----------



## NoMoSurf (Oct 2, 2007)

Problem solved!!! 

I drilled the transom yesterday and found that the wood was soaked already! No need to have super seal! Looks like I get to have the adventure of a transom replacement this winter.


----------



## X-Shark (Oct 3, 2007)

I just happen to have a 4X8 X 1 1/2in piece of 26lb density Coosa Board for Sale. The would be the ultimate core material for your transom.


----------



## NoMoSurf (Oct 2, 2007)

X-Shark said:


> I just happen to have a 4X8 X 1 1/2in piece of 26lb density Coosa Board for Sale. The would be the ultimate core material for your transom.


That is pretty much what I was thinking of using. PM me with a price.

Also where did you get it. We are looking at getting another boat that is going to need a floor. We'll do the transom at the same time. And we were thinking of doing it in all coosa. The factory is about a hour or so north of here, so we were thinking of checking with them. They are much closer to me than Pensacola. But they may not sell to public...


----------



## X-Shark (Oct 3, 2007)

You have mail.


----------

