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!
Last edited:
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,353
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
Last edited:
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