Forespar still uses the RC logo/brand on their cheaper valves and seacocks like the one @Maine Sail pulls above, which would explain your question. Personally, I don't think these should still be sold, and I'd get rid of any on my boat.
Mark
Marelon Ball Valve VS Marelon Sea Cocks
- Thread starter Project_Mayhem
- Start date
Mark
I think I'm most nervous about overtightening these plastic threads. The resistance increases very linearly. Most other threaded pipe has a sharp increase in resistance. I'm guessing that's due to the tapered threads.
They will be replaced. There's a long list of items that need to be addressed. The boat is still on the hard
Interesting. Thanks for the info! Do you prefer sealant, tape or both for the threads?
Ahh that makes sense!
It's on the list of projects to tackle before launch!
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jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,496
We owners are a penny pinching lot. For various reasons between 1994 and 2024 the boat challenged the owner. “Hey there! I’m wetting myself. My valve is leaking! Fix me!”
Looking at the replace parts options the owner found a discount bin with a valve in it. Having just spent the money he’d been saving for his wife birthday present on the new battery powered VHF radio system, he snatched up the old questionable valve. Problem solved. Now what to get for the birthday maybe the pretty iron I saw at the Goodwill store. It looked new.
Plausible?
It's totally possible. I was leaning more towards that older valve is what Catalina found in the back of their warehouse. The history on the RC buyout seems to be a bit murky
It looks like some are still being sold with the RC Marine name on them
https://defender.com/en_us/forespar-mf-849-marelon-seacock
https://defender.com/en_us/forespar-mf-849-marelon-seacock
Sea cocks and thru hulls use straight threads not tapered which is why they are hard to seal. With tapered threads, the gap gets smaller as you tighten. It stays the same with straight. On the oringinal thru hull and ball valve, the threads are NPS straight. On the new 93 series, they are straight Butress thread so the two are not compatible. The buttress thread is very strong but has a larger gap between the male and female threads which makes sealing it more difficult. I only had one out of four successfuly seal with using Tefon tape only. I then redid them with a generous smearing of pipe sealant and covered that with two wraps of Teflon and no further problems.
Are buttress threads unique to Marelon sea cocks? Bronze sea cocks do not use them. Well, Grocco seacocks use NPT and NPS.
dj
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The Buttress thread is not unique to Marelon but as far as I am aware, they are the only company that uses it in thru hulls. The tread is easy to recognize. A normal NPT or NPS has a 60º bevel in each direction. The buttress is 90º and 45º, so the mating threads have 0º slope between them.
Buttress thread - Wikipedia
I know what buttress threads are. But they are typically not used where the threads are meant to seal. I find their use in this application a bit unusual.
dj
I agree, typically they are not used which is why I stated that to the best of my knowledge, only Forespar Marelon uses them. I also agree that they are more difucult to get to seal due to the greater anular clearance of the mating threads which is why I needed to use both paste pipe dope and Teflon tape.
I suspect that they found that the greater strength enabled them to exceed the ABYC load requirement which was the limiting state of the design. If you look back in the archives, you will find a long post from me blasting Forespar for their installation instructions which still to this day recommend only Teflon tape to seal the threads. In my case, that lead to a 75% failure rate due to leakage between the thru hull and flange of the seacock.
I am still a big fan of the 93 series seacocks but recommend using belts and suspenders to seal the flange. One other commenter recommended using 4200 to seal the threads and that would also work but might make it rather difficult to remove if needed.
4200 isn't bad to get undone. I've done it numerous times quite easily. Now, 5200, that's a different story...
dj
dj
I mentioned earlier that I use sealant on the threads, but didn't mention which type. coincidently, it is 4200. Once installed, I've never had a reason to remove one for many, many years, and when I have, I just cut off the mushroom head of the thruhull and pull the assembly out and remove the stem out of the valve with channel locks. I've done this even with 5200, and it still unscrews.
The reason for cutting off the mushroom head is because you are going to break that hull bond anyway twisting the valve off, and new 1.5" thruhulls are only $12 through Forespar direct. So I find taking two people to remove a valve, and picking out all the old sealant from the thruhull threads, to be more time and effort than just paying Forespar $12 for a new one.
Personally, I dislike the design, but Forespar has the only configurations we need for certain applications. Trudesign uses a nut on the thruhull, so it stays tight and sealed to the hull no matter how much you twist the valve around getting it on/off (Forespar requires two people in/out of the boat and a special tool just to install them). Trudesign uses BSPP threads, which seal well with teflon tape, but compared to Forespar they say to use sealant and not teflon tape.
Mark
The reason for cutting off the mushroom head is because you are going to break that hull bond anyway twisting the valve off, and new 1.5" thruhulls are only $12 through Forespar direct. So I find taking two people to remove a valve, and picking out all the old sealant from the thruhull threads, to be more time and effort than just paying Forespar $12 for a new one.
Personally, I dislike the design, but Forespar has the only configurations we need for certain applications. Trudesign uses a nut on the thruhull, so it stays tight and sealed to the hull no matter how much you twist the valve around getting it on/off (Forespar requires two people in/out of the boat and a special tool just to install them). Trudesign uses BSPP threads, which seal well with teflon tape, but compared to Forespar they say to use sealant and not teflon tape.
Mark
When I replaced my thru hulls and ball valves with seacocks, I wanted to use the TruDesign but could not get them in the time I had available so ended up with the Marelon which were available locally, delivered to my marina the next day.