What sealant do you guys use to seal mounting bolts for main motors, kicker bracket, screws for transducers, or anything that goes through your transom and is under water when you are afloat? I have been using 4200 but wonder if sikaflex 291 is better or is there yet another sealant that works better?
Assume the best way to apply these sealants for mounting bolts(eg. Kicker bracket or main motor mounting bolts) is to apply sealant to hole and area where bolt shaft would be near hole and then tighten nuts to leave 1/4" - 1/8" from whatever you are mounting to the transom. Let sealant fully cure and then tighten up until its snug and there is no gap. This should prevent the sealant from oozing all out if you tightened the bolts up all at once. Is this the correct method of applying sealant?
Oh maybe a more specific answer would have been useful for you also: if it goes through your transom, it depends on what your transom is made of.
If it's something like coosa board with glass on either side, or solid glass because you have an inboard or something, 291 is great for that and your method will work well, although personally I would probably let it skin for a bit and then start slowly cranking it in so you can have it formed nicely to shape before it sets completely.
No point using 5200 on those; you're not really using it in a way that maximizes the properties it was engineered to have. It's a pretty good sealant but it's not like it's the best sealant ever made or anything, it's just a good sealant and a powerful adhesive of certain materials. For that application, I'd way rather have 291...just easier to deal with, and at least as good a sealant.
One thing to watch...most of these products have multiple formulations. 291LOT is the slow-cure stuff, Long Open Time, and it has slightly different properties than other formulations of 291.
The same is true with 5200. The 5200 Fast Cure is nowhere near as strong as the original in any testing I have ever seen. Granted in this case you don't need adhesive strength, so a weak adhesive isn't really an issue. But it's worth knowing if you ever want to use 5200 to bond anything: the original bonds fibreglass really well, and other substrates if prepped right. But the FC stuff...pretty weak, considering it's supposed to be 5200.
If you have plywood in your transom, totally different deal and I would not use any of the caulks or sealants - and if you want to know about that, well, I know a lot about what you have to do to make plywood a good boat building material I will happily tell you how to put fasteners in it for the long haul (short version: drill bigger than you need by at least 1/8" all around, fill hole with epoxy/cabosil/wood flour, drill new hole inside that). But if you have a composite transom, 291LOT is my favourite for what you're doing.
