An engine failure at sea can be much more than an inconvenience. It could be dangerous. There are a number of common causes of failure, and a little planned maintenance and preventative work can prevent those situations.
By far the most common problems are in electrical systems. Before you go, simply checking for loose wires may seem like a no-brainer, but it’s rarely done. A common cause of electrical problems on some fast sports boats is water in the bilge. As the boat speeds up, bilge water can flow to the rear of the boat and splash onto the steering wheel. The spray can then hit the starter motor, stopping it in its tracks. Making sure the bilge is empty before you leave, and occasionally checking (and emptying the bilge if you’re loading water) while you’re away can prevent this from happening. Another common problem (on flybridge boats) is failure to start when stopped after a cruise. This may be due to the upper helm controls not fully disengaging after stopping. These boats have systems to prevent starting from the lower helm if the upper assist controls are not FULLY disengaged.
Failures also occur in batteries and disconnectors. Smaller boats often experience this particular problem because parts are often partially exposed to splashing. Having spare isolator switches on board is a simple solution. Batteries may be low on fluid or have sagging cells, or simply be too old to manage any longer. The terminals are also a source of battery failure, often due to unscrupulous use of a hammer to hit the connectors there! Avoiding these problems is as easy as having a spare (fully charged) battery on the boat. Products such as portable power supplies are also available.
Problems with fuel systems are the second most common source of failure. Unfortunately, this is often simply due to running out of fuel. As basic as it sounds, making sure you have enough fuel for your excursion is vital. Too many boaters rely on their onboard fuel gauge to be accurate. Marine fuel gauges are notoriously inaccurate and cannot be counted in the same way as a car gauge. Always make sure you have at least a half tank when you’re out at sea. Submerge the tanks to be sure.
A problem that is becoming more common is system fouling due to bug growing at the diesel/water interface. The bug seems to be propagating. There are a number of treatments available for this. Some work well by turning dead bugs into a combustible material that simply burns along with the fuel. But some of them just drop dead lime to the bottom of the tank, and that stuff clogs the fuel filters. Keeping spare filters on board can save a lot of time and hassle, provided you’ve taken the time to learn how to replace them.
Other sources of trouble are found in gearboxes, steering gear and sail transmissions. Clutch wear will eventually wear out the gear. This is often caused by the carrier. Riding the clutch or allowing it to slip during maneuvers is often the reason the clutch fails. Making sure your saildrive propeller is installed correctly and securely after replacing the annular anodes at the start of the sailing season is obviously critical. But those falling propellers are one of the notable causes of breakdowns. Hydraulic steering systems also fail due to normal wear. A thorough visual inspection of cables and fittings, and checking for hydraulic leaks can schedule those maintenance tasks before you leave.