With the ever-increasing price of fuel, here are some tips to squeeze even more economy out of your four-stroke outboard – or indeed any marine engine, for that matter.

Marine engines are by their very nature inefficient compared to a road vehicle. Unlike the friction between rubber and tarmac, water is very good as dissipating power, which is why marine engines don’t need a clutch. So how do you make sure that the power you transmit to your propeller makes as much difference as possible?

1. Keep the propeller clean and free from dents

Any marine growth on the blades of your propeller will reduce its efficiency, and burn more fuel. Similarly, any nicks or dents in the leading edge of each blade will cost you power. If the propeller is badly damaged, it will need to be professionally repaired, but small nicks can be filed or hammered out at home. (Make sure the engine is unable to be turned over or started if you are handling the prop)

2. Clean your bottom

Get rid of unwelcome marine growth on your hull. A smooth bottom means less effort for the engine, and a fast planing boat can gain an extra two knots after a bottom scrub. As weed grows faster during the summer months, be prepared to dry the boat out and give it a mid-season scrub.

3. The right propeller

Whilst a clean and undamaged prop is vital, you also need to be sure you have the right prop. Many outboards feature a sail-drive option, particularly on the smaller engines. The propeller that has been designed to propel a dinghy will struggle with a small yacht, as the pitch will be wrong. Ask your dealer about re-propping. You’ll save a lot of fuel, and get better performance.

4. Keep the boat level


How many times have you seen boats waddling along with the nose in the air and the stern sitting heavily in the water? To get the best from your engine, the hull needs to as level as possible, otherwise power is being wasted trying to push the hull up, rather than along. You may need to move your passengers or heavy gear around until the boat is more or less on an even keel. In a small dinghy, with perhaps just one person aboard, try using a tiller extension to move the weight forward. You’ll notice quite a difference in performance – and fuel consumption.

5. Use power trim


Many outboards (and sterndrives) have power-trim as standard. This allows the helmsman to move the angle of the propeller in towards the transom (known as ‘trimming in) or out away from the boat (trimming out.) Trim is used a bit like an aileron on an aircraft – when accelerating, the leg is trimmed in to lift the stern up, and get the boat quickly onto the plane. When she’s there, trim the leg out to the mid-point to lift the nose slightly and find a level point for maximum efficiency. Good trim can increase your range by 8%.

6. Use fresh fuel

Modern fuel contains additives, which can evaporate over time, so your petrol will lose its octane. At the end of the boating season, decant any leftover petrol into your car. Don’t store fuel in the boats tanks over the winter, as condensation will form. When you start to go boating again, refill your tanks with fresh fuel. Your engine will start and run more easily, and give a cleaner burn.


7. Have a regular service

Regular servicing from an authorised dealer will keep your engine in peak condition, and spot any potential trouble early. Fresh oil, clean plugs and a dust free air-filter all help the engine to run more efficiently, and burn less fuel. Savings of up to 5% can be made on a fully tuned and well-serviced engine.

8. Match your speed to the conditions


It’s easy to burn a lot of fuel when bashing into strong headwinds or rough seas. It’s worth throttling back, not only for a more comfortable ride, but also to save a lot of fuel, which you are going to need if you are some way from home when the weather brews up. Similarly, when motoring on shallow inland waterways, you’ll notice that increasing speed will draw the stern of the boat down towards the bottom. It’s possible to burn almost twice as much fuel for just a knot or two of increased speed.

The boat will have a cruising speed where it is happiest, both in terms of ride, and in throttle settings. It may take a little experimentation to find the ideal setting, but it’s worth the effort.

9. Lose unnecessary top-hamper

An excessive amount of top-hamper, such as bimini’s, parasols, dinghies and other ‘air-brakes’ can bleed off up to 10% of your fuel in wasted effort. Without detracting from your boating pleasure, try and create an aerodynamic shape to your superstructure by stowing items below rather than leaving them on deck.