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Old 08-09-2008
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Yet another seacock thread

So, I'm explaining to the guy who's about to install our generator why I want to use the Groco flange adaptor on the through hull for the raw water intake for the genset. Among other things, I mention the difference between NPS and NPT threads. He comes back with: but how does it seal if the threads between the through hull and the seacock aren't tapered? I really didn't have an answer for him. My thinking was that you use sealant on the threads, but he had an interesting point that the valve being NPT causes a seal between the through hull and the valve, which you wouldn't have with a traditional seacock or the flange adaptor. He also showed me that he could thread the NPT valve on the throughull with about 5 turns or so, leaving only about two or three turns left.

That doesn't address the other reaons to use bona fide seacocks (flange, etc.), and I'm still swapping out the valves over the winter, but thought I'd raise the issue here to see what others have to say.

Thoughts?
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Old 08-09-2008
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Check this link;

Boat Projects Gallery Photo Gallery by Maine Sailing at pbase.com

I can't remember if I found it via this board or not, but its definitely the way I'm going to go.

The Incredible Hull
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Old 08-10-2008
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Sorry this is so long and I wish I had taken a photo.

Before I did mine I had several different boat yards say the same thing. "I have been doing this for 40 years......bla,bla,bla. After I took my old ones off and found only two turns of threads connecting them. I feel so much safer now. I did the right thing.

But you do need a sealant around the mushroom flange. Even doing it the wrong way as your yard guy wants to, it has to be sealed under the flange. The mixed threads will seal, but you will get no strength at the connection. What if you bump a log or something, I think the weak connection would just pop the flange off.

Some will say I did mine wrong, but this is how I was told from a guy who only installs the flange a lot.

Remove the old flange by cutting it off with a sawsall. Don’t spend all day trying to be nice to it, just cut it off. I cut off the seacock then stuck the saw blade into to hole of the thru hull and cut it in several places around the flange. (Care full don’t cut to deep or you will cut the boat hull)
Cut a backing plate to size. Glass the backing plate and let dry.
Now put backing plate over hull hole and drill hole to match from the outside in.
Now take a thru hull and insert through the backing board to the flange adapter. Now drill holes for the flange adapter and bolt it to the backing board. Now remove the thru hull.
Now the flange adapter is connected to the backing board, I installed the sea **** valve at this time.
I then took a cheap plastic cutting board and cut the same size hole into it as the thru hull. I had a 6 inch piece of thru hull with no mushroom flange on it. (I used a long thru hull that was damaged and cut the mushroom off) I waxed the threads and inserted it thru the backing board into the adapter plate. I taped the threads with masking tape to make the threads smooth to the depth of the hull and waxed the tape

So now I have the adapter plate bolted onto the backing board with the sea **** installed and have a threaded pipe sticking out the hole.
I then sanded and cleaned the hull around the hole. I mixed a much thickened epoxy and really put a nice thick layer on the backing board and around the pipe at the base.
Now from the inside of the boat I stick the pipe into the hull thru hole. Position the flange and put something heave on it. I used my tool box. Now I go out side to find the pipe sticking out the hole. I put the cutting board with hole over the pipe and then put the thru hull nut ring onto the threaded pipe and tightened the whole thing up. Recheck the inside for proper placement and removed excess epoxy to make it look nice. I then went home. When I came back the next day everything was set and hard.
I removed the thru hull nut that I placed on the outside of the boat and took off the plastic cutting board. I used that because epoxy won’t stick to it. I then took a pair of channel locks and unscrewed the pipe, this came off very easy as I had taped the threads to make it smooth to cover the threads and had waxed it to keep it from sticking to the tape.

Now I have the flange adapter bolted to the backing plate and the plate epoxyed to the hull. I also glassed around the edges to the hull
I then measure and cut a new thru hull to length, just start the threads to hold it in place and seal around the thru hull and under the flange and tighten it home and clean up the mess. Let it cure fore a few days, hook up the hose and launch the boat. This worked well for me and was a pretty easy one man job. I can also replace the seacock valve very easily if needed. It is very hard for one person to remove a seacock valve without destroying the thru hull seal. But install with a flange adapter it is easy.

Disclaimer
Please seek professional advice first. But I think your man is wrong. imoho
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Old 08-10-2008
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You are right the NPS on the thru hull piece and the base of the flange does not seal like a tapered thread. There for you have to use 5200 sealent on teh thru hull between the mushroom and the hull of the boat. This seals water out of the boat. The thru hull needs to be NPS because you have to cut it to length because the thickness of the hull .
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Old 08-10-2008
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It seals because...

It seals because the head of a thru-hull fitting is concave or has a groove to capture sealant and also sealant is applied under the flange between it and the backing plate.

Sealant gets trapped in the concave part:

Sealant gets applied here too and trapped in the bevel near the threads:

Like This:



If this guy working on your boat is asking questions like this perhaps he should not be working on your boat? Especially if he feels NPS & NPT are a safe match because he got "five" threads... Really makes you wonder why we pay so much for these "experts" to work on our five, six and seven figure toys...
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Thumbs up Halekai36, thanks for a great website on this subject and others...

I linked to it above but could not remember where I found it. Outstanding stuff.
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Old 08-10-2008
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Quote:
Originally Posted by halekai36 View Post
If this guy working on your boat is asking questions like this perhaps he should not be working on your boat? Especially if he feels NPS & NPT are a safe match because he got "five" threads... Really makes you wonder why we pay so much for these "experts" to work on our five, six and seven figure toys...
Yeah, you're preaching to the choir on that one. The guy's a good guy, and he's a generator guy who's installing our genset, so he's adding a through hull. In fairness to him, this is the way he's always seen it, this is the way he's always done it, he's never had a problem or even heard of a problem. Plus, he's not a fibreglass guy or plumber. It's sort of like asking your plumber why he makes the electrical connections on the water pump in an odd way. It's something he does, but it's not his area of expertise.

In any event, I'm going to invest a number of hours correcting the situation on the through hulls on our boat over the winter, and I'm going to use the flange adaptor, which I learned about from you (thanks so much). I'm actually going to try to do it by keeping the existing through hulls, and add the backing plates and cut the through hulls to length while they're installed. That last part will be the trick to determine whether I can do this without ripping out the actual through hulls, which would make the project substantially more difficult and time consuming.

On another note, I saw on your website one install that I would think twice about. It's the one where you need to make the 90 degree turn right off the through hull, and you attached the elbow right to the flange adaptor, and then the valve after that in the line. To me, that's questionable because you don't have the valve right on the fitting on the hull. So, if the elbow breaks or leaks or whatever, you have no way to shut the water. One disadvantage of the flange adaptor is that you have a fitting between the valve and the through hull (i.e., the flange adaptor itself). To me that's a reasonable compromise under the circumstances. But, adding in the elbow before the valve probably isn't. If it were me (which, as you say on your site, consider how much you're paying for this opinion), I would use a traditional flanged seacock on this one through hull, and fit the elbow to the seacock. That will get you the clearance you need, and still keep the valve right on the through hull.

And FWIW, I wholeheardely concur with others about your website. Very nicely done, and remarkably informative and clear. Thanks.
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Quote:
Originally Posted by danielgoldberg View Post
Yeah, you're preaching to the choir on that one. The guy's a good guy, and he's a generator guy who's installing our genset, so he's adding a through hull. In fairness to him, this is the way he's always seen it, this is the way he's always done it, he's never had a problem or even heard of a problem. Plus, he's not a fibreglass guy or plumber. It's sort of like asking your plumber why he makes the electrical connections on the water pump in an odd way. It's something he does, but it's not his area of expertise.
Simple enough and that's a good reason why he did not understand.

Quote:
Originally Posted by danielgoldberg View Post
In any event, I'm going to invest a number of hours correcting the situation on the through hulls on our boat over the winter, and I'm going to use the flange adaptor, which I learned about from you (thanks so much). I'm actually going to try to do it by keeping the existing through hulls, and add the backing plates and cut the through hulls to length while they're installed. That last part will be the trick to determine whether I can do this without ripping out the actual through hulls, which would make the project substantially more difficult and time consuming.
I would not do it that way for a number of reasons but it's up to you. It takes me all of about five minutes per thru-hull to get them out with a pipe wrench. New thru-hulls are cheap even if you destroy the old ones..

Quote:
Originally Posted by danielgoldberg View Post
On another note, I saw on your website one install that I would think twice about. It's the one where you need to make the 90 degree turn right off the through hull, and you attached the elbow right to the flange adaptor, and then the valve after that in the line. To me, that's questionable because you don't have the valve right on the fitting on the hull. So, if the elbow breaks or leaks or whatever, you have no way to shut the water. One disadvantage of the flange adaptor is that you have a fitting between the valve and the through hull (i.e., the flange adaptor itself). To me that's a reasonable compromise under the circumstances. But, adding in the elbow before the valve probably isn't. If it were me (which, as you say on your site, consider how much you're paying for this opinion), I would use a traditional flanged seacock on this one through hull, and fit the elbow to the seacock. That will get you the clearance you need, and still keep the valve right on the through hull.
It's not always possible on an older boat to do things to ABYC standards even if you try. While not ideal, that installation is in it's own separate access space/locker where nothing could possibly bang into it. The elbow is a heavy duty bronze one and the threads were made up very tightly prior to install in a large bench vise. I have no worries about it as the original was just mismatched threads on a thru-hull with no backing plate. Again not ideal but when that is what you have to work with and there is NO room for any other option, believe me I looked, you do the best you can.

Quote:
Originally Posted by danielgoldberg View Post
And FWIW, I wholeheardely concur with others about your website. Very nicely done, and remarkably informative and clear. Thanks.
Thanks!!
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Old 08-10-2008
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I'd go with new bronze through-hulls, since you're pulling the boat. Then you'll know they're bedded, backed and installed properly. I'd also add that it often takes more time to fix what someone else did wrong than to do it right from the beginning.
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Old 08-11-2008
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Quote:
Originally Posted by halekai36 View Post

I would not do it that way for a number of reasons but it's up to you. It takes me all of about five minutes per thru-hull to get them out with a pipe wrench. New thru-hulls are cheap even if you destroy the old ones..
Curious, what are the reasons?

The reason I'd like to do it the way I'm planning is that the through hulls are installed with 5200, so getting them out will not be without heartache. Plus, if I pull the through hulls I'm sure I'll be doing something that will have an impact on the warranty, or at least the builder certainly will claim that in the future if there is a problem, whereas merely adding flanged adaptors cannot possibly give rise to such an argument. (And Dawg, because I'm doing this over the winter, I will have sailed the boat a bit by then, and believe me I'll be checking the through hulls, so if they were not bedded properly in the first place presumably I'll learn that this season. In any event, as noted, if they're not bedded properly now, I have recourse; if I pull them and then have a problem . . . ) Plus, I actually don't plan to through bolt the flange to the hull. I know, I know, but I just don't like the idea of increasing the number of below-the-waterline holes in the hull by a factor of three. I'm planning to 5200 the backing plate to the hull, then 5200 the flange to the backing plate, and screw the flange to the backing plate (with screws deep enough to get bite, but not deep enough to go through the backing plate to the hull). Assuming I can cut the through hulls to size with them already installed, this should not present a problem, unless I'm missing something.
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