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.