It’s an unfortunate fact of boating life that boats occasionally sink. While raging storms, navigational errors, structural failures and collision at sea account for some of these events, most powerboat sinkings, in my experience, occur right at the dock, on the mooring, or even while the boat sits on its trailer.

For today’s purposes, when I write about a boat sinking, I’m referring to what happens when a powerboat takes on enough water to submerge the machinery or electrical harnesses or both.

Boats sink when they take on water faster than the scuppers and bilge pump(s) can get rid of it, and this can happen in any number of ways. For example, a boat can swamp dockside or on a trailer when it fills with rainwater. This happens dockside when a poorly covered boat stands in heavy rains and the bilge pumps shut down after poorly maintained batteries run down. Boats sink on their trailers under similar circumstances after the owner has allowed the boat to stand with its drain plug firmly in place. (Marine surveyors in our area call this latter phenomenon “sinking on land” as opposed to “sinking on water.”)

The rising water in a sterndrive or inboard-powered boat eventually will submerge the starter and alternator, soak the electrical harnesses and finally enter the engine. If the water gets high enough in a slipped or moored boat, it will become unstable and roll or downflood. That’s the usual way outboard motors get dunked.

As I write this month’s column here at Rex Service Center in Norwalk, yard workers all along the Connecticut shore are attempting to save boats that sank in this manner during the heavy rains associated with two late-summer tropical storms. There is hope for those that sank in fresh water, but the prognosis is poor and, certainly, expensive for those that suffered the same fate in salt water. Repair of these engines and electrical systems is difficult and expensive.

After any sinking, the general rule is to get the boat out of the water and to begin repairs immediately. Time is the enemy. Rust and other forms of corrosion begin as soon as oxygen in the air becomes available.

Don’t forget to notify your insurance company early on. They’ll expect you to do everything you can to prevent further damage, and that expectation effectively authorizes yard work to reduce their ultimate cost. Check the engine service manual, too. Most engine makers offer complete instructions for dealing with submerged engines, although in some cases especially modern outboard motors stuffed with microprocessors—the instructions boil down to “remove the motor, disassemble it completely and put it back together replacing all electrical harnesses and components with new items.” On one modern four-stroke outboard, the harnesses and other electronic parts cost about $5,000. By the time you add the cost of labor to remove the powerhead, disassemble it, then put it all back together and test it, the best bet might be to scrap the motor. You’ll need to get your insurers and a good surveyor involved. If the immersion has been in salt water, your chances of a quick inexpensive fix are grim.

Typically, on sterndrives and inboard powerboats, the boat is hauled, blocked and drained, and everything that had been under water is thoroughly flushed with lots of clean fresh water. Next, you (or more probably the yard technicians) must drain all the fluids from the engine and put them aside in clean containers for inspection. Remove spark plugs or igniters, spray oil directly into the cylinders and rotate the crankshaft slowly to push any water out of the cylinders. Then repeat that process several times. (The plugs are removed to allow the engine to turn over with minimal resistance and prevent damage from hydraulic lock.)

Change the oil as you would under normal circumstances and take a good look for water in the old oil. If you see water in the pan, you’ll need to change the oil at least twice during the recovery operation.

All electrical components should be blown dry and then sprayed with a corrosion inhibitor approved for use on electrical devices. Corrosion X and Corrosion Block are good. Some engine makers recommend their own products. Take special care to spray terminal blocks, harness connectors and the ends of wire bundles. Keep in mind that water probably has wicked up under the insulation, and will continue to corrode the conductors and terminals unless the corrosion inhibitor works.

If your starter, alternator and other critical electrical devices and cabling have been submerged in fresh water, the actions described above may suffice. These items sunk in salt water are usually doomed, though they may operate normally immediately after the clean-up process and fail a month or two later. That’s been our experience at Rex Marine Center with saltwater sinkings in Long Island Sound. If the boat has sunk in salt water toward the end of the season, we usually suggest that customers keep the old starter and alternator (assuming we can get it running at all) until the season ends and then replace them during the winter lay-up. Alternatively, if the boat sinks in salt water at the beginning of the boating season, we recommend an immediate replacement of the alternator and starter so the boater’s season isn’t interrupted.

Replace the batteries. Chances are good that old, neglected batteries sank the boat in the first place. Check the fuel for water contamination. Change the fuel filter. Before you attempt to start the engine, double check that (1) all spark plugs have been cleaned and reinstalled with the ignition wires on the correct plugs; (2) that all electrical connections have been dried, cleaned, inspected, and sprayed with a corrosion inhibitor; (3) that all external metal parts have been similarly dried, cleaned, inspected and sprayed, and (4) that belts are correctly adjusted.

Now, start the engine, run it long enough to get the oil fully circulated and up to operating temperature and then shut it down. Change the oil and do the start-run-stop cycle once more. Change the oil again. During the run times, you should check all engine instrumentation. Be sure you spray the electrical contacts on the back of the instrument panel with the corrosion protective agent. When you believe you are done, run the engine for at least 30 minutes—one to two hours is preferable—to drive out remaining pockets of water from bearings and other hidey-holes. Continue to monitor closely engine fluids for signs of water contamination over the course of the season. After 20 engine-hours of clean check-ups, and with good fortune, you may find the consequences of immersion will be behind you.

If your boat has sunk in salt water, talk the situation over carefully with the insurance adjuster, technicians you trust and a competent surveyor. Permit no short cuts. Do exactly what the factory recommends. Don’t forget that gensets, windlass motors, air conditioning compressors and electrical panels will need specialized care too.

Of course, you can avoid all of this hassle. Be sure to keep your batteries, bilge pumps and float switches well maintained; cover your boat; follow the weather reports and double-up lines in anticipation of big blows, or consider hauling the boat. If you have to be away for a while, ask the yard to check on your boat regularly. Close all the sea cocks when you are away. And, if you keep your boat on a trailer, don’t forget to remove the drain plug.