I debated whether to follow up on my earlier comments. That was until I saw Jedi’s post about your test and your comment, “Will be interesting to see how sincere some posters are in their FACTS.” Please remember, TRUDESIGN has not provided either me or Mark with any FACTS about their material, so I used Dupont’s data on the material Forespar calls “MARELON.”
I’m surprised that the numbers (7 days and 60%) when used as part of a question would be construed by anyone as facts, even though both numbers are valid.
Instead of trying, via your “test,” to verify my “facts and sincerity”, I suggest that you request the following information from TRUDESIGN’s Ed Griffin, making sure you ask for the EMS-Givory data sheets
that provide the following: type of nylon resin, resin characteristics, % glass, % and type of fillers, type glass (long/short), and tensile strength, flexural modulus, elongation (bendability). The last three items in Dry as Molded, 50% relative humidity, 100% relative humidity, and saturation for starters. I tried 3 times in 2012 to get that information and like Mark, got next to nothing back. I intend to give it one more try.
However, here are the hard facts about 60%+ degradation numbers. Nonsense it’s not.
The data for Forespar’s Marelon, (AKA Dupont Zytel nylon 70G13L BK) is taken directly from Dupont’s data sheet: http://www.valueplastics.com/technic...nformation.pdf
Tensile strength (TS) Flexural modulus (FM) Elongation*
Dry as molded 17,500 psi 700,000 psi 3
50% Relative Humidity 12,000 psi 400,000 psi 8
% Change (DAM to 50%RH) 31.4% 42.9% 167%
100% Relative Humidity 7,500 psi 250,000 psi 11
% Change (DAM to 100%RH) 57.1% 64.3% 267%
These are the two strength characteristics (tensile strength and flexural modulus) that are used by ISO. The average of those values equals 60.7%, the 60%+ that Ed Griffin called "nonsense."
* As the elongation numbers increase, the materials “bendability” increases. At 100% humidity the TRUDESIGN thru-hull fitting will bend far more than the TRUDESIGN static load test picture show.
It should be noted that Shear Strength is also negatively impacted by moisture. You may not be concerned with impact, but not every boat
is as impact free as yours. The exposed threaded part of any thru-hull, like those found on the TRUDESIGN units, without any shielding and a bolted down flanged base, will bend under load, but will very likely to shear on impact.
I’m curious, as was another person on this thread, about your dual position regarding ISO and their thru-hulls and seacock standards. You stated, and I quote: “Beneteau' are very dodgy, they comply with a (ISO) standard that's dubious to say the least”. I agree and I also feel 9093-2 is a dubious non-metal standard, for example, why does ISO use a dry as molded standard for thru-hulls and seacocks that spend 100% of their time in water
? My question is, If you feel that the ISO metal seacock and thru-hull standard is dubious, why would you think the ISO 9093-2 non-metal standard is less dubious?
Regarding your test, the test was compromised well before you put the fitting in water. Jedi was correct when he said: “You ought to weigh it before the 7 day immersion and repeat weighing daily.” Saturation is measured as a % weight change from DAM (Dry as Molded). The issue is simple, the fitting you used has had a lot of time since it was molded to now to pick up ambient moisture. My guess is your part stabilized at around 75% saturation before immersion. Saturation in nylon is curvilinear as is the de-saturation curve. Different nylons change the curve slightly, but the trend is always significant acceleration then slowing. The curve starts out like a rabbit, then turns into a tortoise.
Several additional factors impact how quickly nylon absorbs moisture. Three factors clearly apply in your case, the actual material used, material thickness and temperature. The thicker the material the longer it takes to reach saturation and the warmer the temperature, the quicker it takes to reach absorption. If your fitting is a thru-hull, the time line will be far longer than 7 days or even 7 weeks. I looked at the temperatures and humidity levels on the Croatian coast, if the temperature is less than a steady 73 degrees the time line will be much longer again.
There is another factor, it has always seemed illogical to me, but I have read that, and I assume it’s true, but not necessarily with all nylons, is that the swelling seems to “grow” after full saturation as been reached. Again, the only numbers of value to you will be EMS’s.
There have been many past threads posted asking about the pros and cons of plastic and metal thru-hulls and seacocks on this and other boating forums
. And several individuals commenting on this thread have expressed real and valid concerns about the existing non-metal thru-hulls and seacocks. So I’ll be following up with another post directed to them.
I would love to see EMS’s data and would be pleased to know that there is a real, safe, reasonably priced non-metal seacock available for the marine
Again good luck and fair winds