Above the waterline thru-hulls

[AJ_n_Audrey]

Thanks to all for answers and links to resources. The only other reason to look at bronze for the thru-hull deck fitting is that I suspect the reason at least one of the scupper thru-hulls cracked is that something was dropped on it - it's a little exposed. So SS or bronze eliminates that possibility. And yes, I do hope to live another 40 years.....;-)

[alaskanviking]

I don't recommend using plastic thru hulls on the sides at all. Maybe on deck as a deck drain, or into a motor well, but even then uv weakens plastic too much. Marlon is a different story, that meets strength standards. Stainless is ok but can get hidden crevice corrosion. Bronze is preferred, permanent repair, doesn't corrode, as strong as stainless or close to it depending on the alloy. If you need shiny, then get chrome plated bronze. Not that expensive I seen 3/4" for $10. $30 or $40 for 1" if I remember right.

Don't use gaskets, use sikaflex 291 or 3m 4200 UV.

If the thruhull is within 6-10" of the waterline when heeled over, than use a seacock or Groco flanged adapter with valve. Think getting knocked over

It's not worth sinking your boat by saving a few bucks using plastic thruhulls. At least use marelon if you must use plastic.

[Manateeman]

I’ve built a lot of boats in 50 years and the worse mistake I made was using Forespar Marelon seacocks. I’m pulling them all out and going Groco flanged adaptors that let you change ball valves.
Forespar didn’t stand behind their product and in a builder!
I like Apollo bronze seacocks but I have an aluminum hull.
Anything but plastic no matter who produces it.
Happy trails to you.
Mark and his professional boatbuilder manatees

[stormalong]

Originally Posted by Manateeman

I’ve built a lot of boats in 50 years and the worse mistake I made was using Forespar Marelon seacocks. I’m pulling them all out and going Groco flanged adaptors that let you change ball valves.
Forespar didn’t stand behind their product and in a builder!
I like Apollo bronze seacocks but I have an aluminum hull.
Anything but plastic no matter who produces it.
Happy trails to you.
Mark and his professional boatbuilder manatees

So you had a problem 30 years ago with a Forespar seacock and will never do business with them again. So someone today looking for a thru-hull shouldn't use Forespar Marelon? I have removed 30 rear old Marelon thru-hull fittings and found them to be as tough as new so I will disagree.

[AJ_n_Audrey]

Again, thanks to all for your input, particularly on sealants. I'm going to go with bronze on the side deck drains because it's a permanent fix and it can't be cracked by something heavy falling on it. I'm still thinking about the cockpit drains, but I'll probably go with bronze there as well.