Marelon Seacocks

Tony · Post by **Tony** » Thu Oct 02, 2003 1:07 am

Howdy Y'all,

What is your opinion of Marelon as a material for seacocks and thru-halls? I used to work in the plastics industry, so I am semi-familiar with how many different plastics are out there, and I know there are many that are extremely strong and will withstand high temp, chem exposure, etc. Is this one of them? I haven't been able to find specs for the material anywhere. Would you feel safe using a Marelon seacock for a raw water intake in the engine room, exposted to normal engine room temperatures?

Thanks a bunch!

Post by **Tim** » Thu Oct 02, 2003 7:23 am

Forespar Marelon seacocks are designed to be used in any application where you might use bronze. I'm not aware of any limitations on their use. They are a glass-reinforced plastic that surely uses proprietary composition and construction.

Marelon valves and fittings are frequently found in engine rooms. I would feel comfortable in this installation. I actually purchased Marelon fittings for my boat originally, but decided to switch to bronze because the Marelon seacocks were overly bulky for the tight space beneath my cockpit, and I wanted consistency throughout the boat. The bronze valves were lower profile, so I went that route at each location.

Be sure to use only Marelon through hull fittings if choosing Marelon valves; likewise, use only bronze fittings with bronze valves.

Have you checked with Forespar itself for specs on the material? Since they're the only manufacturer, that would be the place to check. I didn't see any particularly useful info on their website, but there is contact information. www.forespar.com

Figment · Post by **Figment** » Thu Oct 02, 2003 8:47 am

I used Marelon fittings at my engine intake and head discharge. Just for fun, I took a sledgehammer to one of the leftover collar nuts (not used when threading thru-hull into seacock valve) to see what kind of beating it could take. a 5lb sledge on a monster anvil took 2 swings to fracture the nut. Trust me, I'm not a small guy, and I was "swinging for the fences".

To me, the greatest virtue of these fittings is that they completely duck the whole issue of bonding and galvanic corrosion.

I've heard it argued that Marelon shouldn't be used in an engine compartment because it can melt in event of fire. I figure that if I've got a fire on board hot enough to melt the seacock, I've got bigger problems than a melted seacock.

Curmudgeon · Post by **Curmudgeon** » Thu Oct 02, 2003 3:30 pm

I have both Marelon thru-hulls and seacocks, but was planning on replacing all the thru-hulls with bronze - the boat is 16 years old so it seems prudent to change them. Not having yet examined the thread compatibility between the two, is there some other constraint I need to be aware of Tim? (You warn against it in this post)

Figment · Post by **Figment** » Thu Oct 02, 2003 3:45 pm

Are you sure those fittings are as old as the boat? I didn't think that Marelon had been around for that long.

Post by **Tim** » Thu Oct 02, 2003 6:29 pm

I believe the idea behind using through hulls and valves of the same material is based around eliminating the possibility of differing rates of expansion and contraction between the two components, that sort of thing. I'm no engineer, nor do I wish to be, but why tempt fate? Stick with one material and play it safe.

Curmudgeon wrote:I have both Marelon thru-hulls and seacocks....the boat is 16 years old so it seems prudent to change them.

Do you have a reason other than mere age to be replacing these fittings? If they are truly Marelon, there should be no need to change fittings purely because of age. Just curious.

Curmudgeon · Post by **Curmudgeon** » Mon Oct 06, 2003 3:29 pm

Sorry, need to supply some pertinent info - this is a rebuild project. The boat is sitting in the backyard, and the interior has been stripped back to the hull, and liners. The plywood backing blocks for the thru-hulls are all delaminated, and the caulking is suspect. Additionally, I'm sure the holes in the hull weren't properly sealed off before the thru-hulls were installed. They have to come out anyway, so new ones make good sense (read: another "may-as-well").

I never would have given any thought to the different coefficients of expansion Tim - I suspect it would be minimal, except maybe when the boat is on-the-hard, but not worth taking a chance. Marelon it is!

Figment · Post by **Figment** » Fri Oct 17, 2003 9:22 am

Last night the wife brought home a boat magazine that I'd never seen before (how can that be??) called "DIY Boat Owner" http://www.diy-boat.com/. This particular issue had a brief article on the use of bronze thru-hull fittings in combination with marelon seacocks.

I don't remember it word for word, but the jist was that there's no compelling reason not to use the two in combination, as long as one is careful not to cross-thread during installation.

Is anyone here familiar with this publication? It's certainly no Practical Sailor. By appearances it bears a closer relationship to the Boat/US newsletter. The cynic in me wonders if it's a true maintenance journal, or if it's just another marine industry marketing device. If you can't get the article through the website, let me know and I'll transcribe it for you. It was only 500 words or so.

Ray Henry · Post by **Ray Henry** » Fri Oct 17, 2003 11:59 am

I have a subscription to DIY. It is a GREAT publication.

Just working on boats. Just projects. Just right.

Yeah, they have to bend to their advertisers just like everyone else, but EVERY issue is full of useful information.

R

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