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Old 16-05-2013, 06:42   #61
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Re: Marelon seacock failure

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Originally Posted by rwidman View Post
You are recommending not bonding underwater metals? The usual recommendation is to bond them. On my boat they are bonded.
I honestly don't know where the "usual recommendation" comes from.. There are many well respected industry experts in this field who don't necessarily believe in bonding and some who do. Hardly black & white or a "usual recommendation"..

I am a marine electrical systems specialist and do this stuff every day. I specialize in corrosion as just one of the many areas I work with. My own vessel is not bonded, except for lightning. Many of my customers boats are bonded because they have suspect wiring issues they don't want to spend the money to address. Even more bonding systems are so corroded they are really doing nothing and on many one can't even measure continuity.

I have some 40 year old boats I work on that are unbonded with perfectly operating 40 year old tapered cone seacocks. Not all builders bonded underwater fittings yet even at 40 years + these unbonded boat exhibit no issues..

That said this is not just a black and white answer and on many boats, with unknown wiring condition, wet bilges etc. bonding can be beneficial (certainly might buy you some time in an on-board DC leak).

On a boat that is perfectly wired I personally prefer unbonded as my own boat is done. I don't suggest everyone unbond however but organizations such as Practical Sailor the West Marine Advisor have and do...

Here's an excerpt from the West Advisor article originally written by Stan Honey and also published in Practical Sailor:

"Bonding and Electrolytic Corrosion Due to Hot Marinas

Do not bond any thru-hulls or other immersed metal that can be electrically isolated. Specifically, keep your metal keel/ballast, your metal rudder shaft, your engine/prop, and all thru-hulls electrically isolated, from each other, and from the engine.

It's worth understanding the reason. In an increasing number of marinas, there are substantial DC electric currents running through the water. If your bits of immersed metal are bonded, the electric current will take the lower resistance path offered by your boat in preference to the water near your boat, and the current will flow into one of your bits of metal, through your bonding wires, and then out another bit of metal. The anodic bit of metal or thru-hull that has the misfortune to be on the "out current" side of the current running through your bonding system will also become "out metal" and will disappear, sometimes rapidly.

Your zinc is only intended to protect against the modest galvanic potentials and therefore currents that are caused by the dissimilar metals that are immersed and electrically connected together on your own boat. Your zinc is incapable of supplying enough galvanic potential to protect against substantial DC currents that may be flowing in the water. These DC currents in the water will cause electrolytic corrosion to your bonded thru-hulls or metal parts."


Or Nigel Calder:


"Unbond & Isolate

The opposite approach to bonding and cathodic protection, which is more prevalent in Europe than in the USA, is to unbond all underwater fittings, isolate them electrically, and allow them to reach equilibrium at their own voltage....

We had an unbonded boat in the warm tropical and semitropical waters for 12 years and no signs of corrosion"


Are these the type of "usual recommendation" you were thinking of...


It is always interesting when folks try to paint or assume corrosion/bonding as a black & white issue. Would be nice if it was.....
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Old 16-05-2013, 06:59   #62
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Re: Marelon seacock failure

I like the Marelon over bronze. However, get the 93-series products and not those sold in chandleries. Forespar calls these "OEM" and sells them direct to manufacturers, but if you contact them, they will sell direct to you. The 93-series is bullet-proof and you don't need to worry about bonding or any other electrical issue. People complaining about Marelon probably have no experience with the 93-series products.

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Old 16-05-2013, 07:13   #63
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Re: Marelon seacock failure

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I like the Marelon over bronze. However, get the 93-series products and not those sold in chandleries. Forespar calls these "OEM" and sells them direct to manufacturers, but if you contact them, they will sell direct to you. The 93-series is bullet-proof and you don't need to worry about bonding or any other electrical issue. People complaining about Marelon probably have no experience with the 93-series products.

Mark
Just keep in mind that if you are converting from say a 3/4" bronze or other 3/4" fitting that the ID of the 93 series thru-hull is considerably SMALLER.

You don't want to starve your engine or have your macerator backing up all the time. You ideally need to go 1 size larger with the 93 series than with other bronze or standard Marelon fittings.

This is not something Forespar is very forthright about and perhaps why they are "OEM" fittings and not sold at retail very often.

If buying the OEM/93 series buy "one size up"...
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Old 16-05-2013, 07:23   #64
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Re: Marelon seacock failure

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Originally Posted by colemj View Post
I like the Marelon over bronze. However, get the 93-series products and not those sold in chandleries. Forespar calls these "OEM" and sells them direct to manufacturers, but if you contact them, they will sell direct to you. The 93-series is bullet-proof and you don't need to worry about bonding or any other electrical issue. People complaining about Marelon probably have no experience with the 93-series products.

Mark
I agree that the Marelon 93-series is the way to go. They are bullet proof.

My Catalina 380 had these for all the through hulls and we never had an issue with them.

Maine Sail makes an important point If buying the Marelon OEM/93 series buy "one size up"...
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Old 16-05-2013, 08:02   #65
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Re: Marelon seacock failure

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I got confused by this thread: let me explain: I need to replace the seacocks and thruhulls on my Beneteau Oceanis and my impression was that the Marelon ones would be the absolutely best for the job. Even better than bronze (for me at least) as I would prefer to forget about electrolysis (and grounding/isolation) and the Marelon would seem to offer just that.

Here is a link to the Forespar site regarding Marelon: About Marelon Marine Boat Plumbing

I do realize that Forespar needs to make money just like any other business and thus they would not like to highlight any issues with Marelon.
But the bad things said here about Marelon, are they just opinions (they are like ***, everyone has one, etc etc.) or should I really stay away from Marelon? If I decide to chooce Marelon will I regret it (not going for the bronze) or are the differences so small at the end of the day that they are insignificant?
Marelon is ideal for everything but hot water. Over time the constant heating and cooling will send the plastic brittle. On most boats this just means the outlet beneath the sink but maybe on some the engine salt water out.

My Marelon seacocks were fitted in 2004 and every one still works just fine.
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Old 16-05-2013, 08:25   #66
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Re: Marelon seacock failure

I don't know about the hot water thing. Our engine outlets are Marelon and they show no signs of problem at 15 years. A sink drain outlet will have standing sea water in it, so the thruhull will not be experiencing hot temperatures.

Our 15 yr old Marelon sink drain thruhulls are above water (see hot drain water all the time with no sea cooling) and also show no problems.

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Old 17-05-2013, 07:51   #67
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Re: Marelon seacock failure

Here are a few points to consider regarding Marelon. For those of you who’ve “never had a problem with Marelon” please note that what I’m presenting here is not my opinion, but facts provided by Forespar, Dupont, and Forespar seacock users who have had serious problems with Forespar’s 93 series seacocks.

First, Forespar calls Marelon a “polymer composite” and a 21st century material. The fact is Marelon is simply a Forespar trade name for Dupont Zytel 70G13L – BK 13% glass-filled carbon blacked 6/6 nylon (that’s not carbon fiber). The nylon 6/6 resin used in Marelon has been around for over 70 years. And the 70G13L – BK can be purchased by anyone. It’s an off the shelf material, nothing exotic.

It has a tensile strength (TS) of 17,000psi and a flexural modulus (FM) of 750,000psi. Both these values are measured “Dry as Molded” (DAM). The DAM measurement is important to remember, especially with nylon. Nylon is great in rode because in water it looses strength and elongates. The material Forespar refers to as Marelon will 7.1% by weight water adsorption level at saturation. This is a significant saturation level.

Second, several forum members have quoted Forespar’s comparison table to make the case about Marelon and bronze. This table has been on Forespar’s website for some 8 to 10 years. This table is seriously flawed.

Look at the following Forespar sites:

http://www.forespar.com/pdf/930136-m...-standards.pdf
http://www.forespar.com/pdf/930136-m...comparison.pdf

Besides the obvious mPa “error”, it should be psi, Forespar has provided you with two different values for Marelon. There’s a significant difference in values. Why? Dupont Zytel 70 series comes in several flavors, the 70G13L (13% glass) has a TS of 17,000psi and a FM of 750,000psi (DAM). The 70G33L (33% glass) has a TS of 27,000psi and a FM of 1,300,000psi. The 33% glass material makes a better comparison to bronze than the 13% glass don’t you think.

Third, “Marelon doesn't corrode.” This is an absolutely correct and totally useless statement by Forespar or anyone else. Metals corrode, PLASTICS DEGRADE, sadly we simply give Marelon a pass on corrosion and ignore degradation. Put your boat in the water with a properly installed bronze seacock and a Marelon seacock for 6 months what will happen, a 60% overall loss in TS and FM values.

In six months in the water, the bronze seacock will still have a TS of 35,000psi and a FM of 15,000,000psi. The Marelon seacock and thru-hull will have a TS of 7,500psi and a TS of 250,000psi. This is a average 60% loss of strength. These figures are directly from the Dupont data tables. These Dupont/Marelon values are lower than good grade PVC. Good quality PVC has a TS of 7,500psi and a FM of 400,000psi. The PVC will loose virtually no strength in water.

Mainsail has done an excellent job testing these seacocks and putting some substance to this long running discussion. Even he will admit that his testing is less than perfect, however, they are a good representation of the facts. I wish Mainsail would explain about why he decided to do his tests, it’s all about impact.
The ABYC in H-27 and corresponding UL 1121 Seacocks and thru-hulls standards have a static load test but no test for impact. Yet impact is the issue of concern of all the marine experts, as Mainsail will attest.

I’ve done some impact testing on marine fittings and Forespar does not fair well at all. A 15 lb alternator or a 150 lb person hitting a thru-hull can do many more times the damage than a 500 lb hanging weight.

When it comes to the fact that some people have never had a problem with Marelon seacocks and thru-hulls is nice anecdotal information, but it’s not something you want to base your decision on. And Forespar seacocks have had a lot of problems that relate both to design and materials. Most people know about the problems with the Forespar 849 seacocks and the stem/handle breaking off. Forespar relegates that to a maintenance problem, that might be part of the issue, the real issue, I believe is a material and design problem. As for the 93 series they have two basic issues.

1. The 93 thru-hulls are non-standard in ID and OD. Forespar in their infinite wisdom created only three (3) 93 thru-hull sizes for all six 93 seacocks. On most of the units the OD is too big and the OD is too small. It appears that Forespar has come to the conclusion that their standard 849 series seacock thru-hull was not quite as robust as it should be. So they redesigned the 93 series thru-hulls in a very unique manner. The ½” and ¾” units have on OD of 1.10” and an ID of .62”. What this means is that the 1/2” unit has acceptable flow capacity, but requires an oversized hole. The ¾” unit has a ¾” flow rate with a slightly oversized hole requirement. The same is true for the 1” and 1 ¼” units and the 1 ½” and 2’ units.


2. The redesign creates a serious hazard. I’ll just say read the following:

CRITICAL UPGRADES - DO THESE OR ELSE!!!
Catastrophic seacock failure! - Page 3 - Catalina 36 International Association Forums

There’s a lot more to be said. But I’ll stop here for now.
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Old 17-05-2013, 08:18   #68
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Re: Marelon seacock failure

Regarding hot water and Dupont Zytel nylon (AKA Marelon), nylon does well in higher temperatures, like commercial hot water which would be the highest you'd see coming of an engine.

I can't say that the constant heating and cooling of nylon doesn't have an impact. Nylon is hydroscopic and adsorbs moisture at a high by weight level. In a saturated state you're heating both the nylon resin and the water. I have no good sense as to what effect the added water expansion has on the nylon resin plates and add to that the fact that the salt crystals can become imbedded in the nylon.

The salt I believe is why nylon rode gets "brittle" stiff over time. The salt in the salt water gets imbedded in the nylon resin.
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Old 17-05-2013, 08:24   #69
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Re: Marelon seacock failure

Hmm, I seem to get the idea that the Forespar Marelon seacocks are not as good I thought? If I went for the bronze ones I should expect far less (at least) horror stories like this?
What I would really prefer is to have a complete peace of mind about my seacocks...
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Old 17-05-2013, 09:06   #70
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Re: Marelon seacock failure

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Here are a few points to consider regarding Marelon. For those of you who’ve “never had a problem with Marelon” please note that what I’m presenting here is not my opinion,...............
Apparently, you are not a fan?

They are ABYC and USCG approved though, right?
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Old 17-05-2013, 12:35   #71
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Re: Marelon seacock failure

rwidman - To your first question, "Apparently, you are not a fan?" I'll say simply that my comment was based on facts about Forespar's seacock design and materials. The only thing I feel is my opinion is on the issue of impact.

I am a fan of well designed plastic seacocks. I personally feel there are plastics materials that are potentially even better than bronze.

Your question "They are ABYC and USCG approved though, right?" has three valid answers, yes, no and maybe. My first response would be, How many people here have throughly read ABYC H-27 and it parent UL 11221?

Let me ask you or anyone else on this thread a question.

The ABYC non-metals standard is Tensile strength (TS) 10,900psi and flexural modulus (FM) of 500,000psi. Good quality PVC has a TS of about 7,200psi and a FM of 384,000psi when saturated in water. ABYC, USCG, and most professionals will tell you not to use PVC. Marelon saturated in water has a TS of 7,500psi and an FM of 250,000psi. I know that this is a leading question, but bear with me. If PVC can't meet the H-27 criteria for TS and FM how is it that Marelon does meet the criterion?
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Old 17-05-2013, 12:49   #72
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Re: Marelon seacock failure

Sorry, should have been criteria not criterion
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Old 17-05-2013, 13:44   #73
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Re: Marelon seacock failure

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Let me ask you or anyone else on this thread a question.

The ABYC non-metals standard is Tensile strength (TS) 10,900psi and flexural modulus (FM) of 500,000psi. Good quality PVC has a TS of about 7,200psi and a FM of 384,000psi when saturated in water. ABYC, USCG, and most professionals will tell you not to use PVC. Marelon saturated in water has a TS of 7,500psi and an FM of 250,000psi. I know that this is a leading question, but bear with me. If PVC can't meet the H-27 criteria for TS and FM how is it that Marelon does meet the criterion?
It's pointless to ask that question on a web forum. If you want an answer, you should address your question to the ABYC.
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Old 17-05-2013, 17:13   #74
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Re: Marelon seacock failure

Ron,
+-*
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Old 17-05-2013, 17:19   #75
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Re: Marelon seacock failure

Ron,

The +-* wasn't a comment on your prior statement. Something dropped on the keyboard just after I typed in your name. And then I somehow hit the reply button.

I'll try again.

Sorryabout that

jed
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