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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #51  
Old 01-08-2014
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Re: Through-Hulls

Quote:
Originally Posted by Watercolor View Post
BubbleheadMd –

Also, Gary states that, “Marelon is the only plastic that meets the rigorous ABYC standards.”

This is simply not true. There are at least 24 plus plastics that I know of that meet and exceed the ABYC standard.

jed
As far as I know ABYC does not test materials - ie plastics - but finished products. If that is true ABYC would only test seacocks that were made of any particular material and presented to them for testing. I have only heard of one other seacock made of synthetic materials and they come from New Zealand if I recall. And even if the material was satisfactory that doesn't necessarily mean that the finished product is going to meet their standards. It is conceivable that a good material can be used to make an inferior product that doesn't measure up.

I work at a marine store that sells both bronze seacocks and through hulls - Groco mainly but other brands also - as well as the Forespar Marelon seacocks. I personally would not buy a Marelon through hull or seacock.
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  #52  
Old 01-08-2014
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Re: Through-Hulls

Mitiempo - You're correct, what materials standards ABYC had (tensile strength and flexural modulus) have been removed. What's left for material standards is in UL 1121? And you're right the NZ company Trudesign makes a fairly standard designed nylon based ball valve and thru-hull. The material is about 30% glass filled low water absorption nylon. The ball valve design is far superior to the Forespar one as is the material. But unless TruDesign wants to go the Forespar route and create super thick thru-hulls, they're smaller sizes won't handle the hanging weight test.

I believe the new Forespar 93 was designed to try and accommodate a poorly chosen material.

Again. if you want a plastic ball valve or thru-hull
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Old 01-09-2014
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Re: Through-Hulls

Jed,

I've installed my Marelon components over a year ago, so too late for that.
I already have the DuPont tables for Zytel, so no need to send them.

For what it's worth, the water absorption that occurs, is not cumulative, and is totally reversible in less time that your average, winter haul-out. DuPont's table says 125 days, and the properties of Zytel return to normal. So, when you relaunch after the winter, you start off at full strength.

I did step up a size when I replaced my failed, bronze through-hull and ball valve. The old installation also incorporated a 90 degree elbow, which further impedes flow. The new installation is larger, and straight. My engine is getting plenty of water.

FWIW, I have a friend who has done two, complete, double-handed circumnavigations who uses Marelon seacocks for every hull penetration. He does agree with some of your concerns, but doesn't seem to feel that Marelon should be avoided "at all costs". He feels that for someone with my level of attention to maintenance, I am safe enough.

Between my installation, and the handle redesign, I am satisfied that my lone, Marelon fitting is safe enough until my next, major refit.
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Old 01-15-2014
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Re: Through-Hulls

For what it’s worth. I’m not really addressing this for just BubbleheadMD’s consideration, but for those boaters simply looking for some additional information.

I admire anyone who’s made circumnavigated, and twice is even more impressive. Bermuda is the farthest my wife and I have sailed. However, FWIW, his sailing skills and anecdotal evidence of no problems, no matter how extensive, really aren’t applicable here.

Regarding your statement about water absorption and desorption in Marelon , you are correct in part.

1. Dupont Zytel nylon 70G13L and Zytel nylon 8018 both absorbs and desorbs moisture at specific rates depending on the material composition, temperature, etc.

2. You use the term, “totally reversible”, in describing the absorption and desorption process, in theory you’re correct, from a practical perspective your boat’s Marelon fittings, in an Annapolis boatyard setting, will never, at the start of a new season, be anywhere near “full strength.” The “DRY AS MOLDED” (DAM) value, what you term “full strength,” is used by the ABYC, but it is a manufactured value, it doesn’t exist in nature. The DAM value is used in the molding process, some materials can be molded with a significant amount of moisture, other materials require almost no moisture. And in a marine environment, the only real useful value 100% relative humidity.

In an Annapolis boatyard, you’d be lucky to find a Marelon fitting at less than 65% relative humidity (RH). In fact, today (1/15/14) the humidity in Annapolis is 100% and the January average is around 65%. My guess is that your boat’s internal January average humidity will be closer to 75%. Also, remember the lowest humidity usually occurs on the coldest days and adsorption and desorption is slowest in cold weather and highest in warm weather. In fact, at below freezing temperatures, it almost stops.

Let’s see how your boat’s Marelon fittings will fare.

Zytel 70G13L (AKA Marelon) Flexural Modulus DAM = 700,000 psi.
50%RH = 400,000 psi
100%RH = 250,000 psi

Please note, the Dupont Zytel 8018 used in the 93 thru-hull fittings has a much lower DAM flexural modulus and tensile strength than the 70G material.

So at the start of the season you can expect to have a Flexural Modulus value of about +/- 350,000 psi. That’s a starting value of some 72% of the total loss potential. That’s a far from a “full strength” start for the season. And remember, high quality PVC can have a flexural modulus of around 350,000 to 400,000 psi and has very little impact from humidity, like 5% max vs. 60% for Marelon. I’ve worked with a plastic that has exceptional impact strength (about 10 times that of Marelon) that in a 28 day moisture test lost no more than 6% of its strength. And that loss occurred within the first 6 days of testing and there it stabilized.

There’s a lot more to be said, the effect of residual salt left in the nylon, the effect high levels of water in the nylon at freezing temperatures. I know of a ski rack manufacturer who learned the hard way about that problem.

If you or anyone else, for what ever reason, choose to replace the Marelon 93 flanged valves, you will have an over sized and odd sized hole that will need re-glassing and drilled before putting in a more standard thru-hull. The ID and OD of the Forespar 93 are totally non-standard.

When I refer to impact, I’m not talking about only internal impact, but also external impact. The longer a boat with Marelon thru-hull fittings (849 or 93) the greater the potential for impact related problems. External impact is probably more disastrous than an internal one.

Here’s a simple example, this happened to me in the Elizabeth River on the Chesapeake We sailed from Sandy Hook, NY to Norfolk, VA and about a ľ mile shy of the Hospital Point anchorage (it was blowing about 10 kts and sunny) we were motoring at about 6 kts and hit a submerged something quite hard. When I dove on the hull I found a 4 ft long, ľ” deep gouge about 6 inches below the 2 galley thru-hulls. From the motion of the boat, the sound of the hit and the gouge I’d say the object was not small and had some heft to it. If those thru-hulls were Marelon and the object had hit 6” higher at least one, if not both, thru-hulls would have been destroyed. I know what the effect of such an impact would do to a Marelon fitting, especially at full saturation or 50% saturation for that matter. It wouldn’t matter if it were my boat, your boat or an experienced circumnavigator’s boat. In a flood, the stuff coming down the Chesapeake or the Hudson for that matter is a disaster waiting to happen.

I’ve taken apart both an older and current Forespar 93 seacock, and I can say that there was no handle redesign. There were several problems with the 93 that I’ve been aware of and they all dealt with the nylon threads that the SS handle lag (?) bolts screw into. The only changes I noticed were (a) the “ball section of the ball/attachment unit” has been improved and (b) they replaced the screw used to hold the handle to the ball unit. It’s now slightly smaller with a sheet metal type thread. A handle redesign is somewhat a stretch.

My biggest problem with Forespar is that this isn’t the first time they’ve had serious know problems with their products. The reason they built the 93 series was to try an solve 2 major problems with the 849. Yet, they never told the public about the problems on the 849 and continued to sell it as if it had no problems. In fact, even today, many marine “experts” still think the 849 unit is ABYC approved. They’ve never told anyone, recalled the products, or offered a fix.

There is a lot more on the Forespar topic than I’ve presented here. I hope to have a blog up and running in February discussing this and other marine issues. I’m trying to write an article or series of articles on this topic. Thru-hulls and seacocks are to me a most important boating topic.

I’d love to get comments or questions, preferably by private post.
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