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Kenneth K

Forespar MF850 Marelon Ball Valves

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I've replaced five Marelon ball valves on my '85 E32-3 since I bought the boat last year. It wasn't my explicit goal to change out so many valves, I only replaced the ones that stopped working. My E32 has 10 valves; three in the head, four in the galley, and three in the stern. All are either 3/4" (raw-water intakes for engine, galley, and head), or 1 1/4" (head pump-outs (2), galley sink drain, cockpit drains (3), and engine exhaust).

While Marelon valves take a lot of hits on this site, and I'm not happy about the nearly $500 I've spent replacing mine, I gotta say that some of these things are 32 years old and, despite a lot of neglect, are still working. I know they've seen neglect--at least 3 of mine hadn't been lubed or rotated in years because a PO built a (rather nice) multi-level plywood shelving unit in the lazarette--it blocked access to the 3 stern valves.

Looking at two of the original RC Marine Marelon valves I replaced this fall, I wondered, "can I rebuild them and keep them for spares." My attempt to re-build is the topic of another post, but I did get to learn the insides of the valves, and the differences between the old RC Marine valves and the improved Forespar MF850 series that replaced them.

As is commonly known, the weak link in the old RC valves was the connection between the handles and the rotating ball itself. Apparently, the ball expands slightly from absorbing a bit of water and, without regular lubrication and operation of the valve, becomes stuck to the point where the handle "strips" its connection to the ball stem, rendering the valve inoperable. The newer Forespar valves have been said to have fixed this problem. I wanted to see for myself.

The old RC valve handles had a "flattened hex" type socket that slid onto a like-fitting stem extending from the rotating ball. A screw through the handle held the two parts together. I don't know exactly why the hex fitting was flattened somewhat on two opposing sides, but the reason may have been that the flattened sides allowed just enough clearance to allow the ball to be popped in and out of the valve housing. It's a tight fit, but I was able to remove and re-install the ball-and-stem from the housing by pushing it out through the wider, bottom part of the valve.

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On the newer valves, the ball-to-handle connection is considerably thicker, and it's square rather than hex, thus, much less likely to strip or "round off" if the ball gets sticky. Further, the square fitting on the ball is attached to the ball with its own screw. A second screw through the handle holds the handle and the stem together. This is a substantive improvement, and results in a what appears to be a much sturdier valve. The handle stem is also shorter on the new valves, putting the handle closer to the valve body. This give maybe 1/2" extra clearance in tight spaces (are there any valves not located in tight spaces on a sailboat).

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Additionally, the old valve handles rotated only 90 degrees between open and closed. Two problems with this: One, when it came time to close a valve, there was no indication as to whether the closed position was to clockwise or counterclockwise of "open". On a smoothly operating valve, it's pretty easy to tell. On a sticky valve, you could break the handle by attempting to turn it in the wrong direction. Second, if the ball rotates only 90 degrees, you have to lubricate the ball from both the top and bottom of the valve to get both sides of the ball lubed--pretty hard to do unless you're both on-the-hard, and you've pulled some hoses. The new valves, however, rotate 180 degrees, so it doesn't matter which way you turn the handle to close it. And, you can lubricate both sides of the ball if you have access to only one side of the valve.

Finally, with the new valves, the handle can be re-installed "upside down," ie, the open position resulting in the handle pointing to the bottom, rather than the top of the valve. I did this on my exhaust valve replacement*, where the upper end of the valve is blocked by a bilge-pump hose. On the old valves, internal stops allowed the handle to be installed in only one orientation.

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So, in short: No, MF850s are not seacocks, and yes, Marelon ball valves still have their problems. I did consider replacing my old valves with bronze, but all my thru-hulls (also Marelon) and backing plates appear to be in good shape so I chose not to do all that extra work. But, yes, I think the new valves go a long way toward fixing the shortcomings of the old ones. With proper maintenance, I think they'll do fine for my boat.

*As for the exhaust valve shown--I didn't want to risk torquing a bronze valve onto that existing bronze exhaust elbow--that elbow is held in place by a Marelon thru-hull which I was afraid might crack under the forces required to mate bronze fittings.

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Updated 12-17-2017 at 11:53 AM by Kenneth K

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Maintenance and Mechanical


  1. bgary's Avatar
    Good info, thanks!

    With regard to the hex stud being flattened on two sides... my guess (!) is that it is that way so that you can't put the handle on at the wrong angle. Normal configuration is that handle in line with flow means valve is open, handle perpendicular to the flow means valve is closed. If the stud was a true hex, it would be possible to put the handle on 60- or 120-degrees off from that configuration.
  2. Kenneth K's Avatar
    May well be.
  3. hilco woudstra's Avatar
    When we bought Sketcher our E 35-3 in 1983 all the thru hulls were Fore spar.
    By 1986 I had with them. broken handles, inoperative functions. I did all the correct lubrications.

    All my thru hulls are bronze...not one problem.

    Hilco Woudstra
  4. Christian Williams's Avatar
    Excellent information.

    Many boat owners build shelves into lazarettes to neaten up storage. I ripped mine out. Immediate access to steering, valves, engine is critical in many emergency scenarios. An alternative to woodwork is a pennant system: gear lowered into the lazarette on a pennant and semi-suspended by a dedicated cleat.
  5. supersailor's Avatar
    These valves need to be opened and closed regularly. At the minimum, Forespar says every six months. I do mine once a month so I don't forget. Non-use = non-work.
  6. Christian Williams's Avatar
    The photo shows a bronze elbow and a Marelon product.

    Can you confirm that the thread forms are compatible?
  7. supersailor's Avatar
    Christian, The bronze Tee is a good thread fit. I used two of them but on the other end of the seacock. I changed the two 1 1/4" seacocks in the head during the recovery of Terra Nova. I put them on top of the Marlon Seacocks as I wanted no fittings between the ocean and the seacock. The reason for the bronze was the inability to find any Marlon Tees.This was due to my newly found allergy to water in the boat. The change did require a small cutout in the side of the sink basin. This winter, I am going to enlarge it and make a proper teak door for access. Maybe I will actually be able to get my hand in that compartment,
  8. Kenneth K's Avatar
    Quote Originally Posted by Christian Williams
    Can you confirm that the thread forms are compatible?
    "Is the thread compatible?" That depends on what the definition of "is" is..... Technically, no, as the bronze threads are NPT while Forespar threads are NPS.

    My shipwright won't put the two types together. He has to follow ABYC standards. When he replaced my raw water intake line, he pulled the existing brass fitting from the Marelon valve and replaced it with a Marelon fitting. Problem is, the ID of the 1/2" OD Marelon fitting was only about a quarter inch. I thought that was too small for a water intake, so I ripped the whole thing out 2 weeks after paying him to put it in. ABYC compliant, yes, but in my best interest? Hmmm.

    So, after some head scratching, I put my new Marelon valve back in exactly the way Ericson designed it 32 years ago-mismatched threads and all. A $100 valve and two hours labor and I was on to the next project. Not perfect, but if I'd replaced it with brass I'd have had to do the thru-hull, too. Maybe someday.
    Updated 12-29-2017 at 03:47 PM by Kenneth K
  9. Christian Williams's Avatar
    exactly the way Ericson designed it 32 years ago-mismatched threads and all.

    Yep. Mine that way too. And it failed the Jim Wallace survey. And I had to argue with the insurance company (eventually got a grudging win).

    When possible, or if starting over, thread forms should be compatible.