Filling bolt holes on transom

I’ve got a 16 footer with a 25hp that I purchased almost solely for trips to HP-restricted lakes in the boundary waters. We make 4-5 trips a year. Some lakes are 10hp limit and some are 25hp and I want to be able to swap motors at will. (Have a 9.9 as well). Last year we rented boats for the 10hp lakes and it definitely starts to add up, not to mention much less comfy and no modern electronics on board.

The 25hp has the thumb-screws to clamp it on to the transom, but it also has been bolted down. I’d like to remove the transom bolts so I can easily swap motors, but then I’m left with 2 holes in the transom. I can’t just replace the bolts and add fender washers with 5200 and seal them up, because the nut will interfere when hanging the motor back on the transom.

SO… looking for ideas/methods to properly fill and seal these two holes. Short of that, a recommendation for a good shop near the twin cities that would know how to handle this? It’s a wood transom so I don’t wanna mess around. I wish they’d never bolted that 25 down in the first place.

Double bubble gum from your kids Halloween stash for those boats value <$1500.

>$1500 gets juicy fruit.

This is pretty common, surprised you weren’t aware of this….

Gob them holes full of silicone. That way if you ever want to use them again just drill the silicone out without making new holes.

Deuces wrote:

Double bubble gum from your kids Halloween stash for those boats value <$1500.

>$1500 gets juicy fruit.

This is pretty common, surprised you weren’t aware of this….

That’s awesome, haha. Trick or treating was not very productive on our block this year, so I may have to go with option #2.

Dutchboy wrote:

Gob them holes full of silicone. That way if you ever want to use them again just drill the silicone out without making new holes.

Interesting. That’s it, eh? Something like this as opposed to 5200?

Thanks to ya both.

I would fill them with fiberglass auto body filler putty. This is NOT the same thing as the regular “Bondo”, it’s a fiberglass-reinforced putty that you add hardener to and then it cures within an hour. It’s thick enough that it will stay in the hole until it cures. If you ever wanted to use the holes again, the putty is easy to drill through.

I would put it back together with the bolts, nuts and washers that held the motor and appropriate sealant. If it didn’t leak with the 25 on it, it shouldn’t leak with nothing hanging on it and flexing.

In addition to the 5200, what about stainless elevator bolts?

HRG

Attachments:

1. 

   SS-Elevator-bolts.jpg
   

TheFamousGrouse wrote:

I would fill them with fiberglass auto body filler putty. This is NOT the same thing as the regular “Bondo”, it’s a fiberglass-reinforced putty that you add hardener to and then it cures within an hour. It’s thick enough that it will stay in the hole until it cures. If you ever wanted to use the holes again, the putty is easy to drill through.

Thanks for the reply. So the advantage to that over silicone is that it’s less runny/messy and more likely to stay in the hole and not drip down while setting? Looks like there is a product called “Bondo Glass” that would work.

SuperDave1959 wrote:

I would put it back together with the bolts, nuts and washers that held the motor and appropriate sealant. If it didn’t leak with the 25 on it, it shouldn’t leak with nothing hanging on it and flexing.

That was my original idea, and this is how I’ve filled transom holes on other boats. But in this case, if I want to hang the motor in the same spot, wouldn’t the nut on the exterior of the transom (or the head of the bolt if mounted from outside-in) be directly in the way, preventing the outboard bracket from laying flat against the transom?

Hot Runr Guy wrote:

In addition to the 5200, what about stainless elevator bolts?

HRG

Interesting, never seen those bolts. Those would work, in theory, if mounted with the flat side on the exterior and the nut on the splashwell side.

These are all great thoughts that are getting the gears spinning about my approach. Thanks everyone.

I recommend silicon, but would first seal up the wood in the hole with a sealer product that soaks into the wood. If you have any hobbies where you have bulk cyanocrylate (superglue), this works great to soak into wood and seal it up. Polyurethane or a slow curing epoxy thinned with a little alcohol will also work to wick it into the wood as added protection. If you prefer it to be more “clean”, cut bolts so you can insert them 3/4 of the way into the holes, and after sealing the wood, goop them with silicon and “plug” the holes. If done right, you should get many years of service without leaking.

Deuces wrote:

Double bubble gum from your kids Halloween stash for those boats value <$1500.

>$1500 gets juicy fruit.

This is pretty common, surprised you weren’t aware of this….

Don’t laugh,I fixed leaky rivets in an old Starcraft with melted bubble yum.Must have been those spider eggs in it?

The boat I have now came drilled out for a 50HP Suzuki.Used a 25HP Mercury on it for a year,and shoved some rubber plugs in the holes.I just then popped them out when I got a bigger motor.

what about using a carriage bolt smothered in silicone ? The head would be almost flush especially if tightened down hard then a dab of silicone on the nut and washer. If it wasn’t flush enough you could mount the motor off center an inch and never notice a difference especial y on a small boat

how about a piece of wood dowel with silicone? Cheap and fast.

I think the moral of this story is there are more than a few ways to skin this cat, ranging from redneck to elegant (that’s not a dig, redneck fixes are sometimes the best ones). Good to know I don’t need to overthink this too hard.

The plan is to use a combo of 3M marine grade sealant and those nifty elevator bolts.

Thanks again folks.

sorgy wrote:

how about a piece of wood dowel with silicone? Cheap and fast.

I saw a boat with this done and it looked to be working well.

sorgy wrote:

how about a piece of wood dowel with silicone? Cheap and fast.

This is the way I would do it just filling with silicone those are some pretty big holes. Find or make a dowel that fits really snug coat the dowel with sealer to keep from rotting and instead of silicone I would use epoxy and pound the dowel in, once dry coat the end with epoxy.

No need to overthink it. Gob some 100% silicone into the hole and reinsert the screw or bolt that came out. If you want to get really technical spread some silicone on the threads.

DONE

Been doing it this way for 25 years.

I would also use the original bolts. If the bolt heads are in the way for the other motor, I would glue a piece of starboard in there to even out the transom. (So the transom is even with the top of the old bolts.)

-J.