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How To Install A Freshwater Washdown

Photography by Capt. Vincent Daniello

Water Water Anywhere

Adding a freshwater shower or washdown outlet is easy.

Wouldn’t it be nice to have a freshwater hose handy to rinse off beach sand, marina grime, or salt before it’s tracked throughout the boat? How about a cool shower on the bridge while sunbathing, or a hose to wash the tender and flush its engine? With quick-connect fittings for cross-linked polyethylene tubing used on most boats, adding any of these is easy.

A Freshwater Washdown on Your Boat

The hardest part of the job might be determining what size freshwater tubing you’ve got aboard. PEX tubing is used in houses, so it’s made to work well with standard copper pipe, but copper pipe sizes are taken from their inside diameter, not outside dimensions. Half-inch “Copper Tube Size” PEX common on boats is ⅝-inch outside diameter and about 15/32-inch inside diameter, while ⅜-inch CTS PEX measures ½-inch outside diameter.

Add in, too, that metric 15mm outside-diameter tubing was the standard for all boats until the late 1990s and is still used on about half the boats built in the U.S. today. It’s only 0.9mm smaller than ⅝-inch outside diameter PEX, so metric tubing seems to lock into imperial-size fittings, but joints leak. 

Larger boats often use ¾-inch CTS or 22mm PEX, which is also nearly—but not quite—identical in outside diameter. Often ¾-inch PEX main feeds are reduced to ½-inch runs to individual fixtures.

This article originally appeared in the October 2012 issue of Power & Motoryacht magazine.