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post #31 of 46 Old 09-29-2015
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Re: Thru Hull Fitting Questions

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Originally Posted by casey1999 View Post
Yes, I think I am going to do as you describe. Over the weekend I picked up a 1-1/2 inch thru hull fitting to compare the threads to the existing on the boat. Interesting thing is the threads seem to match (11 threads per inch) but the thru hull on the boat seems to have what is called (I think) a compound thread. That is a straight thread on the main body, but a taper thread at the very end. This would have been done so that one could take a standard ball valve (with taper threads) and screw it directly on the thru hull. Then one would have taper to taper threads. Still not a good install as the ball valve is sitting at the top of the thru hull fitting with very little support and a larger lever arm to stress the thru hull.

I even took the flanged lock nut from the new thru hull fitting and attempted to thread it on to the one on the boat- it would thread on until it hit the parallel threads and then stop.

In any case the threads are confused and I will pull out the old thru hulls and install new. Attempt to use your method to try to not damage the existing hole in the hull. I did basically use your method to remove the existing speed log thru hull fittings that were on the boat. I did grind off the lock nut and then used a sawzall as you described and was left with a perfect undamaged hole in the hull. I will grind it down 12:1 and glass patch it.

Thanks for all the feedback.
That's curious that the nut would stop, basically the combo thread is the same all the way down but tapered on top, it should be loose then fill in instead of stopping like that. I know you're past that point but it looks like you may have one of the non standard foreign threads. I've looked and cant find the "combination" threaded fittings where do you get them?
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Re: Thru Hull Fitting Questions

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That's curious that the nut would stop, basically the combo thread is the same all the way down but tapered on top, it should be loose then fill in instead of stopping like that. I know you're past that point but it looks like you may have one of the non standard foreign threads. I've looked and cant find the "combination" threaded fittings where do you get them?
Agree on the thread issue. The pitch and thread angle may be a little off. On the tapered end, there is enough "play" between the threads that the difference allows the lock nut to go on, but once it hits the parallel threads, that is now longer the case. I do not think the "combination thread" thru hulls are commercially available. They look to be original to my boat that was built in Australia in 1978. The fittings are commercial thru hulls, but I imagine the builder then machined a taper so that standard ball valves (with female taper pipe thread) could be fitted.

Here is some information on "Combination Threads" from Jamestown Marine:

Installing Thru-Hull Fittings and Valves - Groco

IN-LINE VALVE INSTALLATION
GROCO does not recommend the use of in-line valves as seacocks for these reasons:

An in-line valve has no means of attachment to the vessel hull or backing block, so the valve can turn or loosen from the thru-hull fitting with vibration or with normal use.
If the connected thru-hull fitting becomes damaged or broken, as might occur if the vessel struck a submerged or floating object, or if the fitting was inadvertently damaged or broken inside the hull, there would be no way to shut off the flow of water into the vessel.
In-line valves have NPT threads, which are not compatible with NPS threaded thru-hull fittings (unless the thru-hull fitting is machined with "Combination Thread". Installing an in-line valve onto a thru-hull fitting will create a mismatch of threads resulting in minimal thread engagement between valve and fitting, and an unsafe installation. Property damage, personal injury, or both could occur. If you choose to utilize an in-line valve as a seacock, the thru-hull fitting used must have "Combination Thread".
HowToWindow
FIGURE-2 shows a sample installation of an in-line valve used as a seacock.

STEP-1: Choose a location that is out of the way of foot traffic.

STEP-2: Cut a hole through the hull and backing block slightly larger than the thru-hull fitting OD.

STEP-3: Insert the thru-hull into the hole and tighten the lock nut.

STEP-4: Apply TFE thread tape to the thru-hull fitting and screw on the in-line valve securely. Use a thru-hull installation tool (GROCO THT-530) to hold the thru-hull during valve tightening. If the distance between the lock nut and the inline valve exceeds 1/2", remove the valve and thru-hull lock nut, and use a thicker backing block.

COMBINATION THREADS
Non-standard pipe threads on a thruhull fitting comprised of NPT threads at the lead end, blending smoothly into NPS threads for the remainder of the fitting to the flange end.

THRU-HULL FITTING
A flanged NPS-threaded fitting of sufficient length to penetrate hulls of various thickness, and to accept a seacock having NPS threads. The flange is usually grooved to accept caulking material, and is drawn tight against the outside of the hull by the fastening of the seacock inside the hull. A thru-hull fitting is for above or below waterline use, and may be machined with "Combination Thread".

Here is a clearer PDF:
http://www.defender.com/pdf/groco_install_guide.pdf

Here is one way to get a taper thread on a straight thread thru hull:
http://forum.woodenboat.com/showthre...for-ball-valve

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Last edited by casey1999; 09-29-2015 at 03:08 PM.
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Re: Thru Hull Fitting Questions

I actually found a company that sells the "combination" thread thru hulls (down load the catalog and read the description).
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post #34 of 46 Old 10-19-2015 Thread Starter
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Re: Thru Hull Fitting Questions

I removed one thru hull, one more to go. Job not too bad. Used 4 inch angle grinder to grind away just the head of the flush head thru hull on the outside of the boat. Then inside the hull ground away the glass that covered the nut of the thru hull and cut the nut in half so I could remove it. Then put a pipe wrench on the thru hull and screwed in into the hull. left with a near perfect hole to install the new thru hull. The old thru hull looked like the day it was installed 37 years ago. Only surface patina and solid bronze.
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post #35 of 46 Old 10-19-2015
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Re: Thru Hull Fitting Questions

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I actually found a company that sells the "combination" thread thru hulls (down load the catalog and read the description).
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Good find, all the through hulls on my Boat are (should be anyway) combination threads. Wont know until I take one off. They all look good but I will change all soon weather they need it or not.
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Re: Thru Hull Fitting Questions

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Good find, all the through hulls on my Boat are (should be anyway) combination threads. Wont know until I take one off. They all look good but I will change all soon weather they need it or not.
I think it is a good idea to just remove the combo thread thru hull. Although available, seems to be really poor practice to use them- cause nothing but trouble and cannot allow for proper seacock install. I like the Grocco adapters:
GROCO MARINE PRODUCTS
Makes for nice easy install using inexpensive (relative to seacocks) bronze ball valves that can be changed our easily. Incidentally, I looked at many seacocks, and the ball is still stainless, so probably not much better than using a ball valve with Grocco adapter. An all bronze seacock is available from places like Spartan, but at a very high cost- that valve should last 100 years.

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Re: Thru Hull Fitting Questions

Almost done on the new thru hulls and valves. Still need to bed the thru hull and adapter plate with caulk, and drill and tap for the three bronze bolts to hold down the Grocco adapter plate.

I did need to trim the base plates to clear some boat structure bulk head tabbed to the hull right at the thru hull area. Only a small slice off the circle, should not effect anything as far as strength. I did install two pieces of 1/4 inch G10 as a base plate foundation epoxied together and then to the hull, then on top of that the Grocco base plate. The added height allowed for clearance of the bulk head. Will drill and tap the g10 to except the bolts going into the Grocco base plate.
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post #38 of 46 Old 12-22-2015
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Re: Thru Hull Fitting Questions

I saw a write up on tapping the G-10 I think its all you need. The triangle base does two things strengthens the assembly and keeps it from turning if you need to replace the Valve. I'm going to use that base on some of mine this spring.
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Re: Thru Hull Fitting Questions

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I saw a write up on tapping the G-10 I think its all you need. The triangle base does two things strengthens the assembly and keeps it from turning if you need to replace the Valve. I'm going to use that base on some of mine this spring.
How about bronze lag bolts down into the G10 base and/or partially into the hull? Dip them in epoxy before setting them in.

I've asked this question elsewhere, but never got an answer. Through bolting the flange right through the hull sounds extraordinary, but it seems like a bit of overkill. Hope I don't live to eat those words.


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Re: Thru Hull Fitting Questions

It's in Maine Sail's tutorials. To me, it seems like 3 more places for a leak to happen. With modern epoxies and sealants, it seems overkill, but I'm not the expert.

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