Thursday, August 7, 2014

Freshwater Tank -- Are Bugs Swimming the Back Stroke in There?

One of the things that Drew at Sail Delmarva does is to design venting systems for large industrial tanks. When he talks about tank vents for boats, we should all listen:
According to the plumbing code and AYBC, there should be a screen on the freshwater tank vent to exclude mosquitoes, other bugs and reduce dust. But many builders, including PDQ, leave these off.  On the PDQ 32 the vent line simply goes up and then down through a mushroom fitting under the bridge deck. Yup, I've seen bugs in there, so while I was up-grading my water system, I decide to fix this too.

Clean, huh? Though a strainer won't stop bacteria, it will reduce convective airflow.

The solution was to splice in a simple strainer. The code calls for 16 mesh, but no-see-ums are known to crawl through that, and 50 mesh is common anyway. This strainer is large enough to manage any air venting flow and serve as an over-flow too, though when filling fast, water will back out the fill even without the strainer in place.

Shurflo 255-323. Be warned, PDQ used 1/2" hose on 5/8" barbs. I stayed with the 1/2" hose (cleaned out the gook with a 1/4" rope, soaped up and fished back-and-forth a few dozen times--tie knots in the ends while you're scrubbing) and used a little K-Y to get it back on the 5/8" barb after cutting a fresh end. Great stuff for working with hose.

The PDQ is a catamaran and the pressure water system is located on the bridge deck, between the hulls. Thus, the tank vent actually discharges down, through the floor, about 20 inches above the water line.

A 15 minute fix. No more bugs. Fewer bacteria and mold spores. Mostly self cleaning, every time I over fill the tank, but also easy to clean and easily accessed. I suppose I should clean the tank one last time, but the new filter is doing great.

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