Lagoon4us - I asked my question in all sincerity. If you knew that within a week of putting your thru-hull/seacocks on your boat they would loose over 60% of their tensile strength and flexural modulus, would you buy them.

I have, by the way, emailed TruDesign and asked about their thru-hull/ball valves, twice - type of resin and % and type (long/short) glass. All they were willing to tell me is that they were glass reinforced/ nylon resin. Nylon resins are pretty straightforward, the most common are Nylon 6 or Nylon 6/6. They are virtually the same for marinepurposes. It's most likely TruDesign uses Dupont Zytel glass filled nylon, or at least the nylon resin and has a local compounder make the molding pellets.


My goal was simply engage you in a conversation by asking the question: "Would you be willing to accept a thru-hull and ball valve if you knew it would lose 60% or more of its strength within 7 days of installation on your boat?" And then providing you with the following information for you to use as you saw fit.

You mentioned that the fittings met ISO 9093-2. I'm well versed in ISO 9093-2:2002E and have raised a few questions regarding the wording of the standard, which no one at ISO seems capable of answering.

In ISO 9093-2 there is the following:

4.5 Mechanical properties
Materials for fittings shall meet the following minimum physical properties at room temperature in dry condition:
? tensile strength: 60 MPa (ISO 527); 8,700 psi
? flexural modulus: 2700 MPa (ISO 178); 391,600 psi
? impact strength: 9 kJ/m2 (ISO 180/A).
NOTE The mechanical properties relate to the materials in the non-stabilized condition.

My questions were:

1. Why would you use a "dry as molded" (at this point there is virtually no moisture in the part) for a standard when the part will spend its life saturated in water?

2. Why would you want to test the parts in a "non-stabilized condition?" Especially when nylon becomes stabilized with moisture.

They weren't able to provide an answer.

The ABYC has a similar statement in their H-27 standard.

The fact is some plastics degrade in water, and some degrade in water in a serious way. Nylon is one of those plastics. Nylon is great as rode, it absorbs moisture and elongated (stretches) and swells. There are a lot of excellent plastics out there that would give bronze and SS a run for their money, nylon is not one of them, I've worked with nylon and just don't feel it the plastic for that purpose.

The fact is nylon is hydroscopic, it absorbs tremendous amounts of water. It softens and swells. Forespar's Marelon, (AKA Dupont Zytel 13% glass filed nylon 6/6) will lose 57% of its tensile strength and 64% of its flexural modulus within a week of being put in the water. Nylon 6 is nylon 6. I can tell you with 98% certainty the TruDesign fittings will do the same.

Nylon's a wonderful product, just a plastic I'd use for a thru-hull or seacock on a boat.

I'll stop there for now.

Good luck and fair winds