Dear Boat Doctor,

I am planning to replace the freshwater hoses on my boat this spring. The lines are currently a combination of hose and soft copper tubing. The tubing I can see is pretty black, and I have to assume this is impacting my water quality. I’d like to replace it all, but I am not sure what to use.

Neal Evans

Sarasota, Florida

Dear Neal,

Water lines do get cruddy over time, and I assuming since your boat is partially plumbed in copper, those lines could be 30 to 40 years old. These days you have essentially two options: reinforced PVC tubing or PEX tubing, cross-linked polyethylene. Reinforced PVC is the traditional clear hose with the little threads running through it for reinforcement. It is attached with hose barbs and stainless hose clamps. Its biggest benefits are that the tubing is pretty flexible and can be removed with the hose barbs should you need to open a line.

PEX is an opaque semi-rigid plastic tubing that comes in a range of colors. The tubing is terminated to the fittings in a variety of ways. Its benefits are easy-to-make watertight fittings, but you generally can’t remove them once made. The tubing costs far less than PVC, and the fittings are priced equivalently. 

Unless ultimate tubing flexibility is important, I’d recommend PEX tubing over PVC. In either case I would choose tubing with a half-inch inside diameter.

There are a few ways to terminate PEX: stainless crimp ring, copper swage fitting, quick-release mechanical or a tubing expansion method.

The stainless crimp rings are the most economical in terms of fittings and tools, but they are reported to not be 100% reliable. The copper rings are very reliable, but not quite as easy to make up, and the tools are a little pricey too.

My favorite PEX termination system is from Wirsbo-Uponor (www.uponor-usa.com/residential-plumbing.aspx). This technique uses the thermal expansion memory of the tubing, you expand the end of the tubing, slip it on the fitting, and the tubing recovers its original dimension to make the seal. The system does requires PEX-A tubing, which is a little more expensive than normal PEX. A benefit of the system is that the fittings are a little larger for a given diameter so the flow restriction is a little less.

A tool is required to expand the end of the tubing. It consists of an “expanding cone” which is placed in the end of the tubing. The tool costs about $150, but it works well and can be used to stretch standard tubing onto traditional hose barbs as well.