Fuelled Up: Should You Choose A Diesel Engine For Your Seagoing Craft?

A powerful engine is practically a must-have for any seagoing boat or ship, whether it's a high-powered inboard engine or a small, emergency engine for a yacht or sailboat. However, with a vast variety of engine types, powers and configurations to choose from on the marine engine market, it can be difficult to know what is best for your nautical needs.

One particularly tough decision you will have to make is whether to opt for a petrol or diesel-powered engine. While petrol-powered engines are generally more commonly used, diesel engines have a number of unique advantages that are singularly suited for use at sea. However, using a diesel boat engine also comes with a few inherent drawbacks, so weigh the pros and cons of choosing diesel carefully before you make your decision.

What are the advantages of choosing a diesel engine?

Fuel economy: The main reason for diesel's popularity on the road also applies at sea since diesel engines do not use spark plugs to ignite fuel, they tend to burn much leaner than equivalently-sized petrol engines, giving your craft significantly longer range. This quality makes diesel particularly suited for powering auxiliary engines, where range and reliability are far more important than raw power. 

Increased torque: Both land and sea-based diesel engines also have superior torque compared to petrol equivalents, a particular boon when fighting against strong undercurrents or tacking into the wind. Added torque also requires the engine to work less hard in rough conditions (particularly when propelling heavy-hulled ships), which can help lengthen the working life of your engine.

Durability: Having said that, a diesel engine can usually be expected to last longer than a diesel engine in any circumstances. This is because they are generally much more robustly built and suffer less internal wear as a result of handling a less volatile and corrosive fuel.

Safety: While diesel fuel is flammable, it is far less volatile than petrol; for instance it will not immediately ignite in the presence of fire.

But what about the disadvantages?

Initial cost: Over the long-term, a diesel engine is still the most economical option, but the trade-off for improved fuel economy is a high initial purchase cost. Diesel engines can also be more expensive to fit (or retrofit) to an existing boat hull than petrol equivalents, due to their overall larger size.

Weight: This increased size naturally translates to increased weight, and you should be careful that a powerful diesel engine doesn't permanently alter the trimming characteristics of your craft. However, modern, high-end diesel engines can boast a better power-to-weight ratio than some petrol-powered equivalents.

Noise: Diesel engines are generally significantly noisier than petrol equivalents; this may not present much of an issue when mounted to a larger, steel-hulled ship, but noise and vibration from a diesel engine can make the lower decks of a smaller fibreglass craft a very loud place to be.