Posted: August 1, 2011
Sea strainers shouldn’t strain to strain.
Raw-water strainers have a vital job aboard the boat, and their need for routine attention is well worth the effort. A sea strainer is a relatively simple device consisting of a removable housing, a clear Lucite shell and a perforated nylon or metal basket insert. Water drawn into the boat flows into the top of the unit and passes through the basket, which is designed to trap debris. The clean water then exits the strainer and flows to its final destination, be it the engine, a livewell, the air-conditioning system or a water-maker pump.
In some applications, a single, large raw-water strainer or a sea chest built into the bottom of the boat will service multiple systems in place of several smaller units. However it is done, the most critical factor is that plenty of water flows all the time to the individual systems to keep them happy and cool.
Strainer maintenance should actually begin at the seacocks, which control the flow of water to raw-water strainers. These valves should be exercised at least once a month by opening and closing them a few times when the machinery is not in operation.
After closing the seacock valve, remove the lid on the top of the strainer. Some strainer lids require a wrench, while others simply unscrew by hand. There will be a gasket in the lid, so be careful the gasket does not fall out or get lost. Pull on the handle to remove the basket, and put it in a small bucket to prevent the debris from escaping into the bilge.
Move out to the dock, dump the basket’s contents, rinse the basket with fresh water and scrub lightly as needed. Reinstall the basket and lid, making sure the gasket is not pinched during reassembly. Be careful not to force or cross-thread any of the parts. Open the seacock, check for leaks and you are done.
If the basket is stainless steel, it is important that the handle touch the metal lid of the strainer for proper bonding. If you have to bend the handle to put the lid on, you are assembling the strainer incorrectly, which could result in leaks or galvanic corrosion to the basket. Try twisting the basket in the housing to be sure it slides into position correctly.
If the boat builder installed the raw-water strainer in a convenient location, you can typically look at it to see how much debris has collected. In a dark bilge, you might need to shine a flashlight on the back side of the globe to see inside.
Finally, be sure to thoroughly inspect your boat’s underwater intake fittings each time you haul out. Apply antifouling paint to the inside of these through-hulls, including external scoops and screens, to repel marine growth and maintain adequate water flow to the raw-water strainers.
