Continuing the maintenance masterclass, we take a look at the engine, stern drive and underwater fittings.

Engines

It is quite astonishing that the RNLI are regularly called out to help motor boats that have simply run out of fuel. A motor boat has no sail to drive it along if the engine stops, and in most cases it's impractical to paddle or row. So common sense dictates that you don't go anywhere, especially offshore, without carrying out a few simple checks to minimise the risk of a breakdown. Do you have enough fuel for the trip, plus a reserve in case of delay? Is the engine cooling system working? Are fuel and water filters clear? Are engine and gearbox oil levels correct?

Most of the above applies to sailing boats with auxiliary engines. If the engine fails and it's not a flat calm you can always get back home under sail, but you wouldn't want to be tacking back into your marina berth.

Increasingly nowadays in our crowded waters, boats run the risk of getting a rope round the propeller. With outboard engines and most outdrives, this isn't too much of a problem: you can lift the prop out of the water to clear it. With shaft drive transmission, it's less simple because the propeller is under the hull and you may have to call in a diver - not very practical offshore, and one more good reason for having a twin engine or a get-you-home auxiliary. Canal boats, which tend to collect weed round the prop, frequently have the ideal solution built in - a weed hatch accessible from the inside of the boat.

Sterngear and underwater fittings

The bits of the boat that you rarely get to see include some of its most vulnerable points. Because they are below the waterline, any failure can have catastrophic effects.

You might not be able to see the outside of a skin fitting, but you can usually check its integrity from the inside. Any sign of a leak, either from the skin fitting itself or from the seacock, should be dealt with immediately.

For shaft-engined boats, the other significant point of vulnerability is the sterngear. The sterntube is moulded into the hull, with the propeller shaft rotating inside it, and the gap between the two is sealed with either a cutless bearing or a sterngland packed with grease. If the latter, the packing needs to be topped up from time to time, whenever there is any sign of seepage.

All metal underwater fittings are at risk from galvanic corrosion. Ignore this at your peril! There are essentially two points to watch out for: one, that all fittings are connected to an internal bonding system, and two, that enough sacrificial anodes are fitted. Check the state of the bonding wires, and also check that the anodes still have some metal left on them to sacrifice.

Follow our Maintenance Masterclass each month in our Features section.