Can't get old thru-hulls loose from hull

[yesthatsue]

I'm trying to change our thru-hulls and seacocks, because one of them is an original 1976 gate valve that's gotten completely de-zinc'ed, and the control spigot broke off in my hand. I've ground through with an angle grinder all the way through the flange, down to the ring of adhesive, and they're absolutely not budging. There's a big mountain of adhesive all the way over the nuts and washers on the inside; I've tried cutting through that, but the old thru-hull assemblies still won't budge.

We're an old boat with a 32mm thick hull, so there's still a lot of sealant in contact with both the fitting and the hull inside the hole. I doublechecked to make sure that there wasn't still a spot where the inner core is still touching the flange, and it should be good to release at this point. But none of the three that I've ground so far have budged even a millimeter.

What do I do to get the crappy old thru-hulls to release? Launch is weekend-after-next, and we're now unlaunchable.

[Orion Jim]

Heat often helps to soften old sealant. If your replacements are slightly larger just use a hole saw to make a hole for the new throughhulls with the old ones still in place.

[lk240]

Check this out as an option

https://m.youtube.com/watch?v=lx_Zu9sW_Qk

[Bunji]

Bash a tapered wooden dowel in the hole (bung) and use hole saw size for trudesign fitting

[s/v Jedi]

I cut them out using my Fein Multimaster using a plunge cut straight into the fitting, cutting through it all the way through the hull. After that it easily comes out.

A hole saw works good too: cut a hole in a piece of scrap plywood, then position that exactly over the hole and use it to guide the hole saw into the hole.

I recommend to use the components and methods as described by Rod Collins on MarineHowTo blog for the new setup using Groco Flanged adapter etc.

[alaskanviking]

i Hve replaced all my thruhulls and seacocks. ive had a few stubborn ones, but never had them stuck that bad.

ground off the flanges with a grinder
then if i couldnt move/wiggle them out from the inside, i would take the heat gun and heat the bronze untill i could get them out. heat till the old sealant gets soft.

sometimes i took a hammer and hit the remaining center bronze of the thruhull from the outside to push it out enough to move it from the inside. have to be carefull and not hit the hull. use a metal chisel to get more force.

worst case you can get a sawzall and cut slits from the inside of the truhull out being carefull not to cut into the fiberglass. than use the chisel and hammer to punch the sections out. i didn't have any this bad

Sounds like they used the devils caulking - 5200. you can get a can of debond/debond it. thats supposed to loosen caulk.

[Wireless1]

I guess nobody knew about the thru hull step wrench.

[Jammer]

Good advice upthread.


My first choice on a metal fitting is always heat. Careful use of a heat gun is usually enough. Even more careful use of a propane torch will also work. Keep soaking wet rags close at hand in case you overdo it and start a fire, though they shouldn't be necessary if you're slow and careful. Wear gloves.



Any of the sealants will turn to drippy goo and break loose at around 300 degrees F. and then you can remove the fitting with little or no effort.

Originally Posted by Wireless1

I guess nobody knew about the thru hull step wrench.

It doesn't always help. Excessive force has its place but it will not overcome fittings properly bedded in modern adhesives.

[alaskanviking]

Originally Posted by Wireless1

I guess nobody knew about the thru hull step wrench.

I have one. Its more for putting them in than taking them out. You can only put so much force on those little ribs or on the aluminium of the step wrench before you have a bad day.

I made an oops on my last seacock, and had to pull it back apart. Heat from the heat gun followed by the step wrench with a 2ft cheater bar worked well.

Does not generally work well on 20-30+ year old 3m 5200 devils caulking.

More importantly it's not generally worth your time to pull them out properly when they're 20+ years old. I've found a lot of bronze that age was more on the brass spectrum and had turned pink or starting to turn as the zink was pulled out. If you have one like that it's a safe bet they all are. They are no good at that point so just grind off the flange really quick and be done with it. Slow and carefull will take you about 10 min or so per thru hull. Then pull the rest from the inside which makes it easier to pull apart the plumbing which may be saveable.

If you tried to use heat gun and a step wrench in the same scenario it's going to take around 10 min to heat it well enough and it could still fight you after. Bigger cheater bars help but the more torque your putting on it may damage the step wrench - all for a thruhull that's bad anyway.

Save your time and energy and replace with real bronze fittings.

I also recommend using the same company for the seacock and thruhull. That way your getting the same alloy for both reducing issues. May be microvolt electrodes between alloys but if you get red brass or high zink bronze instead of real bronze by accident than you can be replacing sooner than expected. That may be 10 years instead of 20 full disclosure but if your keeping the boat that is important.

[sjrider]

I changed out are 30 year old thruhulls and seacocks a few weeks ago. I ended up using a grinder with a cut off wheel. I cut the seacock off of the thruhull. Next I used a step bit to drill out as much of the outer thruhull as possible. I then had to use a heat gun to soften the remaining adhesive that was used. A few good hits with a punch and a hammer from the inside, and they came out.

It was a huge pain, and there must be a special place in hell for who ever thought that a gate valve was a proper seacock, and that thruhulls should be permenatly bonded to the hull.

It was a major pain but worth it.

[Wireless1]

Originally Posted by alaskanviking

I have one. Its more for putting them in than taking them out. You can only put so much force on those little ribs or on the aluminium of the step wrench before you have a bad day.

I made an oops on my last seacock, and had to pull it back apart. Heat from the heat gun followed by the step wrench with a 2ft cheater bar worked well.

Does not generally work well on 20-30+ year old 3m 5200 devils caulking.

More importantly it's not generally worth your time to pull them out properly when they're 20+ years old. I've found a lot of bronze that age was more on the brass spectrum and had turned pink or starting to turn as the zink was pulled out. If you have one like that it's a safe bet they all are. They are no good at that point so just grind off the flange really quick and be done with it. Slow and carefull will take you about 10 min or so per thru hull. Then pull the rest from the inside which makes it easier to pull apart the plumbing which may be saveable.

If you tried to use heat gun and a step wrench in the same scenario it's going to take around 10 min to heat it well enough and it could still fight you after. Bigger cheater bars help but the more torque your putting on it may damage the step wrench - all for a thruhull that's bad anyway.

Save your time and energy and replace with real bronze fittings.

I also recommend using the same company for the seacock and thruhull. That way your getting the same alloy for both reducing issues. May be microvolt electrodes between alloys but if you get red brass or high zink bronze instead of real bronze by accident than you can be replacing sooner than expected. That may be 10 years instead of 20 full disclosure but if your keeping the boat that is important.

Thanks for posting. All very good points for everyone doing this job.

Not sure who makes your step wrench. I forget the name of mine but it's a cast steel one that is plated and weighs in at nearly 2 Lbs. It does 1/2" - 1 1/2" sizes

I'm getting rid of my dreaded mismatched threaded t-hulls in my Beneteau 473. There is one in the engine intake that once the boat is out and blocked I'm going to hit with a hammer. I'll bet it snaps right off. I will be replacing all t-hulls with Groco seacocks using their glassed in backing block method with the threaded bronze inserts. All my parts are Groco. That should do it.

I have a Multimaster tool for flush cutting the t-hull lips. It's been years since I'v done t-hulls and believe me I'm not looking forward to it mostly because , as you say, the devil caulk. And at the age of 72 it's hard to stay curled up for long in tight spaces! Ha!
Oh, and I forgot to mention; dealing with the hull liner too!

[s/v Jedi]

FYI: I have an ongoing long term test comparing three systems:

1. Forespar Marelon plastic seacock (with flange, fastened to the hull)
2. Groco bronze seacock, the real deal.
3. Groco flanged adapter with their full flow ball valve

I am still waiting for #1 to fail but it doesn’t. It’s been in there for 17 years and works as well as day 1. Yes, I feel the handle bending when I operate it... just like it always did.

#2 is rock solid. My gut feeling says #3 is best because it’s easy to replace the valve but #2 is so solid that this simply doesn’t happen. That said, if it does start leaking, it is easy to fix #3 as you can even screw a cap on if you don’t have a replacement valve, while for #2 you need a plug hammered in, probably from outside the hull.

In practice all work well but #1 fails the side loading tests as demonstrated by Rod Collins.

[bobnlesley]

Originally Posted by alaskanviking

...ground off the flanges with a grinder...took a hammer and hit the remaining center bronze of the thruhull from the outside to push it out enough to move it from the inside. have to be carefull and not hit the hull...

That's worked every time for me, if you leave the seacock fitted and preferably closed, you can stick a piece of timber inside the remains of the through hull to get a decent transmission of the hammer blows; most often it's been the inner nut/collar that wouldn't come free anyway.

[Hank Giffin]

Wireless 1, can you pls provide the make/model of your steel through hull tool?
if possible, pls email me at hankgiffin@cox.net.
thanks, Hank

[Hank Giffin]

Wireless1, can you please provide the make/model of your steel through hull tool? if possible, please send to hankgiffin@cox.net.
next week I start replacing a 1.25inch leaking Groco with a soft bed plate in my Crealock 37. thanks, Hank