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  #11  
Old 05-03-2013
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Re: Through-Hulls

Quote:
Originally Posted by sailordave View Post

My little boat only has a couple of thru-hulls... but I think I am going to look into those Grocos when I replace them
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  #12  
Old 05-06-2013
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Re: Through-Hulls

Katsailor,

Just a few thoughts for you to consider regarding Forespar's Marelon 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.

Many people have used Forespar’s Marelon Comparison table to show its strength as compared to bronze. This table has been on Forespar’s website for some 8 to 10 years, and in all that time it’s been in error, or so they claim.

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 us 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 of the Marelon.

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.

Main Sail 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. They thru-hulls are non-standard in ID and OD. On most of the units the OD is too big and the OD is too small.
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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  #13  
Old 05-07-2013
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Re: Through-Hulls

Watercolor

Yikes, scary stuff you linked too.

Thanks for the information. Once again it proves that you get what you pay for; I guess I will be going with bronze.

After reading a lot of information on another thread about composting toilets I am very tempted to remove my MSD system and associated through hull fitting. Then I will only have four holes in my boat to worry about. Both my sinks drain below the water line and are equipped with sea cocks and through hull fittings plus my raw water and salt water/MSD supply through hull fittings.

I suppose I could eliminate the MSD supply through hull too. Do I need a saltwater wash down system? My sinks are not plumbed for salt water and I kind of like to keep the salt water outside the hull.

Is it good practice to use one larger fitting for saltwater and engine cooling or should they be separate?
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Last edited by katsailor; 05-07-2013 at 08:38 AM.
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  #14  
Old 05-07-2013
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Re: Through-Hulls

One school of thought says, the fewer thru hulls, the better. Another says, if you have a failure, you lose everything, if they're combined.

Fielders choice. We have literally almost 30 thru hulls. I know, its crazy. OEM design.
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  #15  
Old 05-07-2013
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Re: Through-Hulls

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Originally Posted by VentureCat15 View Post
Hello everyone,
I recently purchased my first keelboat, a Pearson 30, hull 225, and I've been having fun tracing out systems, exercising sea-cocks, replacing hoses, etc. I replaced the head suction hose with 3/4" heater hose from the auto shop. I found four seacocks, none of which have been moved in many years, I'm afraid. One raw water to head, one is raw water to sink, one is engine cooling water, and the fourth was the old head overboard which has been closed and sealed off in the hose.
I tried to exercise the three working ones, and was partially successful. The engine cooling water is a 1/4 turn ball valve and works fine. The head suction moved after some persuasion, but the sink water seacock handle broke off in the channel lock jaws. I then backed out the tapered plug and went to the local shop to get a replacement. The shop told me that a replacement plug was probably not available, and that I should just remove the entire seacock and replace it with a 1/4 turn ball valve. They said to be careful that the through hull does not turn - have an assistant hold it on the outside of the hull (two nubs on the ID - jam in a flat handle and hold it with an adjustable wrench?). They said the threads may be straight, not tapered, and the new valve would be tapered threads.
What do you guys recommend? Should I replace the through hull as well? Can I find a replacement tapered plug and save myself some hassle?
Tapered cones are a factory matched fit and are not replaceable about 98% of the time. When you have a frozen tapered cone valve you loosen the nuts and then use a light tap with a lead or brass mallet to drive the cone out. Trying to move them with the handle usually results in expensive mistakes..

Spartan still makes and sells tapered cone seacocks but they are pricey so you are likely looking at a complete replacement with a ball valve style..

If you still have some cone valves that are not broken:

Servicing Tapered Cone Seacocks
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  #16  
Old 01-03-2014
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Re: Through-Hulls

I read through the material here and on MainSail's blog on thru-hull fittings. I have a question. Is the Sikaflex 291 used to bed the mushroom on the hull (not shown in pictures) and on the materials inside the hull (as shown in pictures)? Also, how are the screw heads sealed on the outside of the hull?
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Old 01-04-2014
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Re: Through-Hulls

GREETINGS EARTHLINGS; I do not see or hear tell of you having any soft wooden bungs in case of emergancy thease should be tied around the hose with plenty of cord so to enable the fitting incase of failure (I Sail offshore) tha saying on my boat is "safty first me second"
AS ALWAYS GO SAFE.
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Old 01-04-2014
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Re: Through-Hulls

Quote:
Originally Posted by captflood View Post
GREETINGS EARTHLINGS; I do not see or hear tell of you having any soft wooden bungs in case of emergancy thease should be tied around the hose with plenty of cord so to enable the fitting incase of failure (I Sail offshore) tha saying on my boat is "safty first me second"
AS ALWAYS GO SAFE.
No reason not to, but plugs are a limited use and you need an accessible hammer too. The hole must be fairly round to work well. I suppose, if the hose let go and the handle wouldn't move, they would be good, or if the thru hull just happened to cleanly depart the hull.

I think it's more likely that it is broken by impact or partially departs. I like the idea of Stay Afloat, which can be jammed into any opening.

stayafloatmarine.com

p.s. I seem to collect leak mitigation. Plugs, goops, cones, all of 'em.
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Old 01-04-2014
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Re: Through-Hulls

gbgreen59 - Can't speak directly for Maine Sail re. the use of Sikaflex for bedding the thru-hull (mushroom), but that is what I've always done, Either Sikaflex or 4200.

Regarding the bolt issue, I believe he thru-bolts all his seacocks. However, he does provide an alternative to thru-bolting that i prefer, Seacock Backing Plates / Alternate Method / No Through Bolts Photo Gallery by Compass Marine at pbase.com

I'd love to get a sense as to what purpose thru-bolts serve?
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Re: Through-Hulls

Heater hose from the auto shop really has no place on a boat, and particularly not on a through-hull that's subject to suction. You should use the re-inforced Trident cooling hose, at least. Also use good quality marine clamps at both ends, preferably doubled up if there is space. (don't if there isn't, can do more harm than good)
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