I hate to drill the transom for a swim platform but…

[pcrussell50]

It seems like the best swim platform solutions involve drilling into the transom. Which I hate to do. I even 4200’d plywood pads onto the bottom of the transom for transducer and speed paddle.

Anyway, is it really ok just to drill it and fill the hole and surrounding area with some sealer like 4200 or Life Caulk? Or something else that you guys like?

Now, this is not a boat that stays in the water. It’s a trailer boat, kept in a desert climate. Never spends the night on water. Just day trips.

-Peter

[David - WI]

I would try to design one that used the 4 motor mount bolts and the two corner hold-downs. Probably need a diagonal brace from near the lower motor mounting bolt to the outer corner of the platform?

[takuma]

It seems like the best swim platform solutions involve drilling into the transom. Which I hate to do. I even 4200’d plywood pads onto the bottom of the transom for transducer and speed paddle.

Anyway, is it really ok just to drill it and fill the hole and surrounding area with some sealer like 4200 or Life Caulk? Or something else that you guys like?

Now, this is not a boat that stays in the water. It’s a trailer boat, kept in a desert climate. Never spends the night on water. Just day trips.
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-Peter

Drilling into the transom for a swim platform can indeed feel daunting, especially when considering the integrity of your boat. Using sealers like 4200 or Life Caulk to fill the holes can be effective, but it's crucial to ensure a proper sealing process. Since your boat primarily stays on a trailer in a dry climate, the exposure to water is limited, reducing the risks associated with drilling. However, meticulous sealing and regular inspections are vital to prevent any potential water intrusion. Exploring alternative swim platform solutions that minimize or eliminate drilling might also be worth considering to maintain the integrity of your transom without compromising functionality.

[MattGreen]

It seems like the best swim platform solutions involve drilling into the transom. Which I hate to do. I even 4200’d plywood pads onto the bottom of the transom for transducer and speed paddle.

Anyway, is it really ok just to drill it and fill the hole and surrounding area with some sealer like 4200 or Life Caulk? Or something else that you guys like?

Now, this is not a boat that stays in the water. It’s a trailer boat, kept in a desert climate. Never spends the night on water. Just day trips.

-Peter

Yes it is OK to drill through the transom and that will likely be your strongest approach as opposed to cantilevered brackets. A few hints:

1) Once you have a pilot hole established where you wants the bolts to go, drill a fairly deep countersink so that the full diameter of the final hole size bit bites only into glass (not the gel), and will still be covered by the exterior washers and bracket. The goal here with the countersink (aside from preventing chipping the gel while drilling, and subsequent stress-cracks), is to create a recess for a nice bead of sealant to sit once it's all bolted together. Basically, you'll make a custom o-ring right around the bolt. You can do this on the inside of the transom as well, and that's a good idea on at least the lower bolts so bilge water doesn't get in from the inside.

2) Use only fresh polyurethane sealants like Sika-291 or 3M 4200 (i.e. don't use silicones - it will eventually fail). You don't need 5200, it works well but is murder to get off. De-wax the surfaces you are sealing to (Prep-Sol that auto painters use works well and won't hurt the gel).

3) Drill the transom holes about 3/32" oversize, and inject (or brush) un-thickened liquid epoxy into the plywood throughout the hole. Do a couple coats - it will suck into the wood a fair bit initially, come back say 10 min later with more. You might need a Slow hardener depending upon the ambient temperature. Once it cures, re-drill to the size you need, giving enough clearance around your bolt to still have some sealant (i.e. not so tight that it all squeezes out). Ideally you have "sleeved" the bolt hole in epoxy. Depending upon the viscosity of the epoxy you used, you might want to thicken the second coat a bit with cab-o-sil.

You now have 2-3 layers of protection from water ingress into your transom: the sealant O-ring is #1, the sealant on the bolt shank is #2 (or an extension of #1 depending upon your viewpoint), and the epoxy-protected wood is #2/#3. It will be fine for decades at that point

Matt