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Old 08-09-2020, 15:06   #46
Registered User

Join Date: Oct 2019
Location: Kennebunk ME
Boat: Owner built 60í Aluminum Expedition Yacht.
Posts: 275
Re: Seacock & thruhull replacement

Marelon. I am not the only person who has had problems with Forespar Marelon
sea cocks. A simple web search will do that. Frozen valves, handles that have snapped off. They even changed the design but continued to sell old stock.
Iím not an amateur builder. You can see my credentials in the about me section.
The Trudesign is not bolted to a backing plate. It is a supported valve, not a seacock. If the thruhull fails or loosens, it is very difficult or impossible to stop the flooding.
Iíve built both custom and production. Plastic valves are cheap and fast to install which saves money in production boats. Thatís a fact. Your boat, do what you wish. Iím only giving you the opinion of a professional. Till then...
Happy trails to you.
Captain Mark and his happy manatees
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Old 08-09-2020, 17:52   #47
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Join Date: Feb 2016
Location: Northport NY
Boat: Pearson 10M
Posts: 228
Re: Seacock & thruhull replacement

You absolutely can do this job yourself. The first year I have ever owned a boat I replaced every sea cock and mushroom myself. I needed a little help holding the mushroom while I screwed on the seacock, otherwise did it myself. As mentioned earlier, Go to Maine Sail's site and follow his directions. Really helpful.

The only tip I can share is removal of the old through hulls. I suggest that you get some soft wooden plugs. Hammer in the plug hard from outside, then cut it as flush as you can. Then use a hole saw slightly larger than the hole to cut the flange off. It takes less than 10 minutes and nothing can be damaged. The purpose of the plug is to center the hole saw. For backing plates you can buy 12x12 FRP plates from McMaster car. I tried to make nice pretty round plates with a hole saw but it was a bit difficult. I ended up cutting it in squares with a sawzall then rounding the edges on a grinder.

At least you'll know it'll be done right.
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Old 08-09-2020, 18:30   #48
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Join Date: May 2008
Posts: 2,672
Re: Seacock & thruhull replacement

Again - Forespar makes and sells two kinds of Marelon seacocks. They have for many years, They did not “change the design” or sell “old stock”.

The one to buy is the Series 93. I have never heard of a Series 93 failing, breaking a handle, or swelling. I’ve used them on three boats over 15 years and never had a problem. I’ve never lubricated one or needed to disassemble one.

If you had a problem with a “Marelon” seacock, please say if it was a Forespar Series 93 valve.

If you are going to switch from bronze to Forespar series 93 (which is what I did) be aware of a few things

A) You must use the thru hull that comes with it. The threads are different.

B) The thruhull is lightly larger than bronze. You will have to drill new holes or enlarge the ones that are there.

C) The size of the opening is slightly smaller so slightly less water comes through. This is only a concern with the smallest 3/4” valve. To be safe I always upsize 3/4” bronze to 1” Forespar Series 93

I have also heard good things about True Design but have no personal experience.

Here is Mainsail showing the Series 93 passing the ABYC side loading test. Many cheaper bronze seacocks fail this test.

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Old 09-09-2020, 08:03   #49
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Join Date: Oct 2019
Location: Kennebunk ME
Boat: Owner built 60í Aluminum Expedition Yacht.
Posts: 275
Re: Seacock & thruhull replacement

Hi. Iím referring to the Forespar MF 849 flanged seacock. On both this forum and SA , you can find the failure cases.
There is nothing about your credentials in your public profile.
Looks like you own a Shannon 55. Itís a beautiful boat. I worked in RI and knew a lot of Shannon people.
My boat is aluminum and we welded pre drilled and threaded 1/2 ď backing plates for each seacock. Iím not sure when we purchased them, but it was early on in the process. When I had a problem, Forespar walked away.
Would you ever deal with a company that tells you to eat it? Not me.
I really donít care what new products they have now.
As to the ABYC static test. If you were in the industry you would know the back story on lots of ABYC standards. Boatbuilders and repair people have very different standards than the FAA in building, training and maintenance schedule.
You are a boat owner, I have a record as a builder. Let people here see both
sides. I would not put a plastic valve in any boat I build . Period.
Enjoy you Shannon, good boat, very nice guys built it. Till then...
Happy trails to you.
Captain Mark and his TIG crazy, biscuit pooping manatee friends
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hull, men

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