1970 NAUSET 16: Sealing Fastener Holes in Transom

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Inshan
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1970 NAUSET 16: Sealing Fastener Holes in Transom

Postby Inshan » Sun Apr 18, 2021 11:05 pm

There are old transducer mounting holes below the water line in the transom of my 1970 NAUSET 16. When I removed the screws from these holes, brown water dripped out. I left [the boat out of the water] to dry for a couple weeks. Then tried to fill the holes with 3M5200.
The 3M5200 never cured hard in the holes, and I was able to easily pull out a plug of cured 3M5200 that remained flexible.

I tried again with JB Weld Marineweld. This time the upper holes seemed to cure hard, but the lower holes--still wet--are still soft.
I just want to seal up these holes to ensure no water can enter the hull through them.

Give me suggestions on how to fill and seal the old fastener holes below the water line in the transom.

ASIDE: I intend to use a [product called a] sternsaver to mount the SONAR transducer.

I recorded a presentation to show the holes that still have the soft JB Marineweld in them. The end of the presentation shows me squeezing the 5200 plug I pulled out of the hole.

https://www.youtube.com/watch?v=HMKI3kbICj4

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Phil T
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Re: Seal screw holes in transom

Postby Phil T » Mon Apr 19, 2021 9:23 am

I would suggest the material you inserted into the holes did not cure due to the presence of moisture.

Okay, gently put down the tube of 5200 on the ground and slowly step away.

3M5200 and its brother, 3M4200 are adhesives with a sealant element. Unless you are constructing something where you need a product similar to "Liquid Nails" there is no reason to ever use this product on a Boston Whaler.

If the hole is still damp after weeks, you may have a larger problem.

Two options:

If you have a wet material, consider using Gorilla Glue. It is an expanding epoxy that chemically kicks off in moisture.

Dry the hole with a hair dryer for a few hours then use Marine Tex, Locktite Marine Epoxy or JB Weld.

Aside: The creator of the Sternsaver used continuousWave members in his prototype testing back in the day.
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jimh
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Re: 1970 NAUSET 16: Sealing Fastener Holes in Transom

Postby jimh » Mon Apr 19, 2021 9:39 am

I believe I can comprehend your situation without needing to see an audio and video presentation.

To fill and seal old holes from fasteners that were below the water line on the transom, the holes should be dry. If water continually seeps out from an old fastener hole, that is a sign water has been allowed ingress to the embedded wood in the transom. If after a reasonable amount of time, say a week or two, water continues to seep from an old fastener hole, you may have to begin the repair with a somewhat wet hole.

I would use a heat-gun or a hair dryer to blow hot air into a wet fastener hole to evaporate as much water as possible immediately before initiating the final assembly of the repair. Do not use a hot air gun on high temperature setting. Too much heat is worse than not enough heat. You just want to warm the area to promote drying, not get it so hot that foam and laminates start to melt.

In the past I have used small-diameter tapered wooden plugs made from soft pine dowel to fill old fastener holes that are less than 0.1875-inch as from a #8 screw that was used for mounting a SONAR transducer or used for holding a cable in place. I would not use a dowel for a larger hole. FOr larger holes the grain orientation of the dowel is wrong, and the plug should be cut from plywood with a plug cutter with transverse grain orientation.

Since the existing old fastener hole was more or less a tapered hole, I used a tapered plug. If you wish, you could enlarge the existing hole with a drill to make the hole uniform in diameter, and then a non-tapered plug could be used

In the case of a wet old fastener hole, I would use a heat-gun or a hair dryer to blow hot air into the hole to evaporate as much water as possible immediately before inserting the plug and its adhesive sealant. Again, use only moderate heat.

In the past I have used WEST System epoxy as an adhesive and sealant to adhere the plug into the old fastener hole. The epoxy will cure in about 30-minutes. I don't have experience with how well WEST System epoxy will bond to wet wood. I recommend you research that topic.

For the purpose of keeping the wood plug in the hole, another adhesive could be used, perhaps something water soluble. The wetting of the wood might not impede the adhesion as much.

In the past the plugs I have used have a length that when inserted into the hole leaves the plug top below the surface of the transom. That depression is then filled with tinted WEST System epoxy resin mixed with a low-density soft filler.

To hasten the cure time of the epoxy, the area can be heated with an hot air gun or hair dryer. But, again, just get the area warmer than ambient.

Since the repaired old fastener holes on the transom are below the water line, the essential goal is to make them watertight. Epoxy is a water-tight repair substance. As for cosmetic appearance, if the epoxy is mixed with a white powder filler, it results in a reasonably good match to the hull color. Because these holes are below the waterline, they will only be seen when the boat is on the trailer, so making them indistinguishable from the rest of the transom can only be a secondary consideration.

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Re: 1970 NAUSET 16: Sealing Fastener Holes in Transom

Postby jimh » Mon Apr 19, 2021 9:44 am

Re the cure time for 3M5200: that product takes about a week to completely cure in air. To cure underwater takes even longer.

ConB
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Re: 1970 NAUSET 16: Sealing Fastener Holes in Transom

Postby ConB » Mon Apr 19, 2021 11:18 am

I would use West System G/Flex epoxy if the wood was damp.

https://www.westsystem.com/specialty-epoxies/gflex-650-toughened-epoxy/

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Inshan
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Re: 1970 NAUSET 16: Sealing Fastener Holes in Transom

Postby Inshan » Mon Apr 19, 2021 8:57 pm

Thank you all for the detailed responses. I think I will go with the wood plug method sealed in with epoxy. I will update when I do it.

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Don McIntyre - MI
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Re: 1970 NAUSET 16: Sealing Fastener Holes in Transom

Postby Don McIntyre - MI » Tue Apr 20, 2021 8:05 pm

In addition to what Jim posted. For filler, be sure to use a low density filler. Using a high density filler will make the sanding and leveling more time consuming.

Regards - Don

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Re: 1970 NAUSET 16: Sealing Fastener Holes in Transom

Postby jimh » Sun Apr 25, 2021 2:34 pm

Don McIntyre - MI wrote:In addition to what Jim posted. For filler, be sure to use a low density filler...
My earlier comment mentioned using a low-density filler.