No aspect of boat maintenance is more crucial to vessel safety than proper maintenance of the plumbing systems. Since they often manifest themselves as one of the sailor's more unpleasant tasks, plumbing systems are also one of the most neglected. So without further ado, here are some thoughts to get you started in the right direction for inspecting the plumbing systems on board your boat:
When the boat is hauled, especially for a spring re-fit, or before relaunching in the spring, the thru-hulls and seacocks are the most critical areas to check. These items can only be serviced or replaced when the boat is out of the water. So this is the time to check them.
Thru-hulls One initial word of warning: Not all thru-hulls are installed below the waterline, but those that are should be fitted with a seacock. Plastic thru-hulls should be inspected carefully for cracks or deterioration. If you see anything suspect, now is the time to replace the thru-hull. For those made of bronze, scratch some bottom paint off so that you can note the color of the metal. It should be hard and gold in color. Softness, porosity, or a red color indicates electrolytic action. Again, if you're at all in doubt, the best step is to simply replace the thru-hull. When you consider the price of the part vs. the price of a salvage job due to an inadvertent sinking, this becomes a no-brainer.
Valves Almost all seacocks are bolted to the hull, which is the preferred method of installation. You'll want to check that the bolts and their nuts are sound and not corroded. You'll also want to ensure that the seacock operates smoothly with minimal effort. Ball valves open and close with a quarter turn like seacocks, but these fittings are merely threaded onto the thru-hull, so check to see that these haven't loosened since their last inspection. Gate valves are what most homes have for their outdoor hose bibs and these are not desirable on boats because you can't be certain that they won't corrode. If you find standard gate valves among the plumbing system on your boat, I recommend you take the time to replace them with stout seacocks or ball valves. Of course whatever valve system you have attached to your thru-hull, make sure that it's functioning smoothly and the valve closes with little effort.
Tapered plug-type seacocks should be disassembled, cleaned, inspected for pitting or wear, lubricated with waterproof white grease, and reassembled once each year. Most ball valves and gate valves are not serviceable. Check that seacock handles are firmly secured, and make sure to replace handles that are lost or broken. For safety, an appropriately sized, tapered wooden plug should be attached to the base of each seacock as a remedy of last resort during an emergency. This is the time to inspect and clean saltwater strainers.
Tanks Tanks should show no evidence of leaks. Black iron, aluminum, and stainless steel are prone to corrosion under straps or where they lie against wet wood. Flexible bladder tanks or those rendered in hard plastic should not be allowed to chafe. Remove the inspection plates and check for accumulations of dregs in the bottom of fuel and water tanks. If you or your boatyard has run nontoxic antifreeze through the potable water system, now is the time to flush the tanks and lines thoroughly, filling the tanks only after this purging.
Run freshwater in the head, shower sump, and bilge and check all the pumps, both manual and electric. Clean the shower sump and add white vinegar to the bilge, head, and sump water to keep them smelling fresh. Head parts may require a little dish detergent to lubricate their seals. Make sure you repair any inoperative pumps. This is also a good time to clean the pressure freshwater screen and replace any drinking water filters.
Depending on their complexity, a vessel's plumbing systems can consist of fresh, or potable, water, salt water, bilge water, gray water, and sewage. In addition, fuels such as gasoline, diesel, kerosene and extremely flammable LPG (propane) are often plumbed throughout the boat. Moving these liquids from one place to another requires the use of the proper hose, tubing, or pipe. Major hose manufacturers list over 100 models that are usually clearly marked. While inspecting plumbing, check for any potentially dangerous misapplication such as the use of a heater hose to transfer diesel fuel.
You'll need to slither through the bilges and check every connection. I like to use double hose clamps just to be sure, and now is the time to replace these if they show any signs of corrosion. Look carefully for chafe where pipes or hoses penetrate bulkheads. Be especially careful with the hose clamps that hold the shaft log hose onto the packing gland. The hose may need replacing if bits of rubber are poking out through the hose clamp's slots indicating that it has been over-tightened. It should be flexible but not mushy or too soft. Twist the hose lightly. Tug gently at each hose to ensure that it is reasonably near its connection point—it should not rotate on the hose barb. And hoses throughout the boat should have no kinks or tight bends that restrict flow.
Copper tubing and rigid PVC pipe is acceptable for some applications within a boat's plumbing system, but be aware that these are subject to vibration fatigue. Check copper tubing for deep greenish pitting corrosion, and use extra caution with brown or gray flexible plastic tubing systems since some have very short life spans in the marine environment.
Engines Of course you'll want to go over the engine carefully. Telltale streaking from the saltwater or cooling system reticulation pumps spells impending trouble. Fuel filters that weren't changed in the fall should be changed now. Connections to hot water tanks and exhaust hoses can be troublesome due to heat expansion and contraction so inspect those carefully. And survey the muffler for cracks, leaks, or burn marks. The other are a to check is the operation of siphon breaks (vented loops) on the engine saltwater exhaust, head discharge, or other pumps fitted with those.
Once your visual inspection is over, use your ears and nose to detect any remaining plumbing problems. Listen for the sounds of dripping liquids. Water systems that hiss or gurgle with air have a leak in the intake (suction) side. A diesel that won't start unless the fuel system is bled each time suffers from the same problem.
The smells of diesel or sewage aboard indicate a leak or improper hose usage. And the odor of propane down below or on deck requires immediate attention. Make sure you pressure-test and sniff-test any LPG system at least once a month. If you follow all these prescriptions, I can't guarantee that you won't encounter problems with your plumbing system, but you'll certainly encounter fewer problems, which means you'll spend more time enjoying your boat.