The sea is a tough place, where a combination of wave impacts, exposure to the elements and salt corrosion can create big problems, especially for poorly maintained hardware. Electric connections in particular can suffer if not regularly checked, and should such a connection fail, the uninitiated can be left helpless by what they deem to be an irreversible breakdown. And yet, the various breakdown services assure us that in the vast majority of cases, a boat can be made useable again with just a few simple steps - and often without even getting out the toolbox.

Man working on outboard engine

The sea is a tough place to break down - regular maintenance is key.

But before we attend to that, a quick caveat - if your engine fails, then in the first instance, you should ignore your spanners and attend instead to your own safety. What will happen if you can’t get started again? Will you be swept onto rocks or into a busy shipping lane? If the situation is in danger of becoming hazardous, forget the engine and call for emergency assistance. But if all is likely to remain safe for the foreseeable future, then it is time for some trouble-shooting…

Boat being towed home

Not everything can be fixed - sometimes there's not option but enlist some help to get home.

Reassuring basics

All internal combustion engines function by sucking a fuel/air mixture into the cylinder. The mixture is then compressed and burned, causing an expansion, which generates the power. If your engine isn’t working, it is because one of these things is not happening - and as an internal breakage is very rare, an intact engine with a functioning cycle has no choice but to run. The electrical side of things is similarly straightforward. If there is power in the battery and it is applied to a functional starter motor, it has no choice but to turn - and these happy facts allow us to set about checking the two main causes of breakdown (electrics and fuel) with a good degree of confidence.

diesel engine wiring

Wiring is a common problem.

Electric Avenue

If a previously functional engine is refusing to restart and won’t turn over on the key, you have a basic electrical problem. Check your dash equipment. If it shows no signs of electrical input, either the battery is flat or its volts aren’t reaching the boat’s main wiring system. Either way, there’s no need for panic. Check that the main battery switches are on - and turn them on and off several times to help clean the contacts. If that brings life to your electrical equipment but the motor still won’t turn over, then electricity isn’t getting to the starter motor. Again, check the simple things. Is the gear lever in neutral? Is the kill cord connected?

If all is well but you still get no success, could it be corrosion of the electrical contacts? If so, you can bypass these by connecting a jump lead between the main terminal of the starter motor and the positive post on the battery (in that order). If you’ve got ignition, the engine will start. If it still won’t start, it’s time to call for assistance.


You could be out of fuel or there could be a blockage.

Fuel issues

If the engine turns over but refuses to start, don’t simply keep trying indefinitely or you’ll flatten your battery. Instead, visit your tank and find out if you have any fuel. If you don’t, call for assistance. If you do, check the primer bulb. If it stays squeezed when you let go, there’s a fuel blockage between it and the tank. If all is good, disconnect the fuel line from the motor and see if it flows freely into a container. If not, you have a blockage in the pipe between the bulb and the motor.

Next up, check to see if there is any water in your fuel - and if there is, cleaning out your fuel filters may be enough to get you home. If you have a secondary fuel tank, then this is the time to hook it up. Turn the engine over at wide-open throttle to clean the dirty stuff away and all should be well.

Finally, if you are sure that good fuel is reaching the engine, but you’re still getting no joy then your ignition is likely to be the problem. If your engine is quite old (say 15 years or more), you can start by checking the ignition light, followed by the circuit breakers or the fuses on the engine itself. But if your engine is relatively modern, your prospects of doing much about it as a regular boating enthusiast are limited. Despite your best intentions, it’s time to admit defeat and call for assistance.


There are marine equivalents to the AA or RAC.

The safety net

There is no doubt that maintaining your boat well and knowing your engine will bring big dividends in terms of reliability. And given that more than 80 % of breakdowns at sea are the consequence of either fuel problems or faulty electrics, a working knowledge of the simple steps outlined above will radically improve your chances of remaining self-sufficient and mobile in the event of an incident.

Nonetheless, if you want to feel just that bit safer, you would do well to buy some RAC-style marine breakdown cover from a company like SeaStart or ShoreGuard. Prices are very reasonable and both the service and the area of coverage are getting better all the time.

In addition, you can help make your boat as safe as it can be with an RNLI Sea Check. This free service involves an RNLI expert taking a look at your boat and giving you recommendations. It’s not a pass or fail situation - just a face-to-face advice service that takes place on board your own boat. You set the time, they visit your craft and they tailor their input to the type of boating you do. It’s a great chance to ask any questions you have about your equipment or about what to do if things go wrong. As long as you live in the UK or the Republic of Ireland, Sea Check is free so call 0800 328 0600 (or for those in Ireland, 1800 789 589) and get yourself booked in. See the RNLI for more.

For more on diesel engine problems, maintenance and repair, see Diesel engine repairs: fuel, air, starting, wiring or Diesel engine overheating and charging repair, and for outboards see Outboard motor problems: starting, fuel, shear pins.

Written by: Alex Smith
Alex Smith is a journalist, copywriter and magazine editor with a long history in boating and a happy addiction to the water. He’s worked on boats, lived on boats, bought boats, sold boats and – when he’s not actually on board a boat – he can generally be found in his Folkestone office, tapping away at the computer and gazing out to sea.