Thru-Hulls

[markpj23]

Surveyor says my prospective new (old) boat has nylon thru-hulls below the waterline. Who woulda thought in 1992 Endeavour yachts would do such a thing!! (I suspect the owner).
Anyway, when I put the new bronze units in, what type/brand of bedding compound should I go for? What 'gotchas' or tricks should I know about?

[captaineddie]

I've always hada good luck with bronze fittings bedded with Lifeline Caulk.

Ed J

[ssullivan]

You'd be surprised... my 1987 has them as well. I will replace next season (they have already lasted about 19 yrs, so.... they probably won't sink me in 1 season)

[delmarrey]

Are you sure they are nylon. If they have threads and a flush head, chances are they are Marelon which is a proven material for below the waterline. If they are mushroom head, it is possible, but boat manufactures are suppose to know the differance.

The differance by eye, is the nylon is usually more transparent to light. And Marelon has a bit of a ceramic look to it when new.

I like 3M - 101 for bedding thruhulls. It's real sticky and it's EZ to get the thruhull back out. It seals just fine.

Over & standing by........................._/)

[markpj23]

Valid questions... Survey report says " should be marelon or bronze..." so I assume the guy knew how to tell the difference.

If I go the marelon route, any change to the installation / backing plate arrangement? Is marelon easy to gorilla-wrench off... similar to schedule 80 PVC fittings? I've seen lots of people wrench those off...

[delmarrey]

Personally, I use SS backing plates, But if the hull (inside) is nice and smooth you may not need one.

For flush head, there maybe a differance in the size of the head. That goes for bronze as well. The newer series seems to be smaller in diameter. It could be just a manufacturer differance.

As for getting them out? Everone is differant. If they will not screw out then I grind them with a rotory file (burr) from the inside untill I hit the threads, then chip out the rest. Don't pound them out, unless they move easily. It could cause damage to the hull. (don't know what boat your dealing with) Try a couple hits with wood and a hammer, then quit if no movement.

When installing them, you don't need to torque them hard. Just good and snug. The sealant should be doing the seal not the Marelon/Bronze.

While your in there make sure the the core of the hull is sealed. If it's wet you'll have more work to do!!!!!

Over & standing by.........................._/)

[markpj23]

Upon closer inspection I am concerned about how I would remove a plastic or marelon thru-hull insert that is screwed into a marelon seacock.

The beat-it-with-a-bigger-hammer scenarios wouldn't seem to work. I'm concerned about:

- the sealant / bedding around the insert would make it impossible to unscrew it
- cutting the insert would probably also damage the female threads in the seacock
- digging out the insert could damage the hull

How have others done this?

[Alan Wheeler]

How have others done this?? by the ways you suggest and usually with the results you predicted. Not always the case though. But yes, if it has been sealed in wth a sealant, then you are in for trouble and it may have to be a new Seacock.

ssullivan once whispered in the wind:
You'd be surprised... my 1987 has them as well. I will replace next season (they have already lasted about 19 yrs, so.... they probably won't sink me in 1 season)

Sean, I have a horror story about that. Bottom line is be extremely careful while cleaning the bottom, or warn anyone you might hire to do that job. A friend of mine almost lost his trimaran when the diver broke the thruhull out while scrubbing the bottom.The owner was asleep on board at the time, and it was a 1.5" thruhull, so it was only luck that they were able to save the boat.

[delmarrey]

I've remove many a thru-hull. And the best way I have found is just grind it with a rotary file, or sometimes called a carbide burr. Welders use then all the time for grinding out welds and such.

I've banged my head against the wall trying to save a thru-hulls and have finally given up that idea.

I have an over sized dramal sp? type electrical grinder I use. An air grinder with a 1/4" collet is what they are designed for, but air is not alway available so I hord my electrical motor.

Anyway, from the bottom I start grinding away the inside until I start to see threads. Then I'll go inside, if I can reach, and grind or cut the fitting off fairly flush with the inside deck. Then with the burr grind out the inside of the thru-hull some more until I see threads again.

Then I start at it with a pick tool and hammer and start chiseling out what is left. The threads will usually peel right out. It works both on bronze and Marelon.

Bronze is a little nasty. The metal chips like to stick in the skin, so gloves and a long sleeve shirt are in order along with safety glasses for both.

The spiral single fine cut burrs are the best. The double cut don't cut very fast and the course tooth grab and spin around in the hole.