The Complete Guide to Buying a Boat Engine

Views 2 Likes Comments Comment
Like if this guide is helpful
The Complete Guide to Buying a Boat Engine

Boats allow people to spend spare time in natural environments, including on rivers, lakes, and the sea. Boat owners have vast opportunities for enjoyable experiences. Fishing, snorkeling, water skiing, and travelling to remote islands are only some of the activities that can be undertaken with a boat. Although it is possible to combine boating with a workout, as when using a rowing boat that requires some muscular strength, most people prefer motor boats over rowing boats. Motor boats are power-driven vessels that contain a combustion engine, which drives the propeller or the jet pump to make the boat move. Motor boats range from small speed boats to large yachts. Even an inflatable boat is classified as a motor boat if it uses an engine.

As the engine generates the power that allows for use of the motor boat, it is a vital part of the vessel. Boat engines can be bought from high street shops that specialise in boat parts and accessories, and they are also available on large online auction sites such as eBay. Boat engines can be regarded as investments, and therefore their types and features should be studied carefully before making a purchase.

Types of Boat Engines

Boat engines are divided into two basic types according to their location on the boat. Outboard boat engines are located outside the boat, clamped or bolted at the back of it. Inboard boat engines are located inside the boat. Outboard boat engines are further divided into three: two-stroke, direct injection two-stroke, and four-stroke engines. Inboard boat engines include jetboat engines.

Two-Stroke Boat Engines

A two-stroke boat engine has a power cycle that is completed in two strokes, meaning that the piston only has to move up and down once in order to complete the cycle. The piston is either a short cylinder or a disc inside the engine, and it moves up and down against the fuel inside the internal-combustion engine. This is what causes the boat to move. The two-stroke boat engine is the most fuel-consuming boat engine among the outboards, but it can also provide a power boost, thanks to its short power cycle. This engine emits the most harmful gases. The fuel and oil used for the an ordinary two-stroke engine need to be mixed separately, and this makes such engines time-consuming to operate. However, if the outboard engine is equipped with oil injection, the mixing does not have to be done separately.

Direct Injection Two-Stroke Boat Engines

As with two-stroke boat engines, the power cycle in a direct injection two-stroke outboard is completed in two strokes, meaning that the piston simply has to move up and down once. Compared to ordinary two-stroke boat engines, direct injection two-stroke boat engines consume about 35 per cent less fuel. This is because the fuel charge is injected directly into the chamber where the combustion takes place. Direct injection two-stroke boat engines are also lighter than four-stroke boat engines. These outboard engines may require computers.

Four-Stroke Boat Engines

The power cycle of the four-stroke boat engines consists of four strokes: intake, compression, combustion, and exhaust. Because of the longer power cycle, the four-stroke boat engine is suitable for slower boats. Compared to two-stroke boat engines, four-stroke outboards are the heaviest. However, they are also the most economical.

Inboard Boat Engines

An inboard boat engine is located inside the boat, usually in the middle. A drive runs from the engine to the propeller, which is located at the rear, and power is transferred with a transmission. Compared to outboard boat engines, inboard engines are more difficult to operate and maintain, and the initial costs are also higher. Thanks to their heaviness, however, they provide great balance and torque, and are suitable for wakeboard boats. Inboard engines run either on diesel or gasoline. An inboard engine that runs on diesel is heavier than a gas engine and is therefore best suited for large vessels. Diesel engines also run at lower RPMs than gas engines. The main benefits of a diesel engine include low running costs, long life-expectancy, non-explosiveness, and no carbon monoxide emissions.

Jetboat engines are a subtype of inboard engines. These engines do not have a propeller, and therefore they pose less risk to the marine environment and to people. They take in water and then discharge it at high pressure, propelling the boat forward. These boat engines are not suitable for shallow water, because the boat cannot be steered if there is no stream of water.

Comparison of Boat Engine Types

The four boat engine types have different characteristics that should be considered before making a buying decision. The following chart outlines these characteristics for purposes of comparison, to aid in the decision-making process.

Boat Engine Type






Most fuel-consuming, uses a gas-oil mixture

Easy to remove and maintain

Direct Injection Two-Stroke


35 per cent less fuel than two-stroke, uses a gas-oil mixture

Easy to remove and maintain


Heaviest outboard

Most economical outboard, uses gasoline

Can be removed for maintenance



Runs on diesel or gas, economical

Comparatively difficult to maintain because it is located inside the boat

The type of engine also depends on the specific boat the engine is bought for. Usually the type can be determined by checking the type of the previous engine on the boat or by reading the boat specifications.

Boat Engine Features

Besides choosing the type of the boat engine, a prospective buyer should consider several other features. These features include PTT, horsepower, the fuel delivery system, and foldability.

PTT on a Boat Engine

"PTT" is an acronym for "power trim and tilt" and it refers to a feature of some outboard boat engines. The PTT is a ram that lifts the leg of the outboard engine out of the water. Although this feature is useful, it can add to the overall cost of the boat engine.

Horsepower of a Boat Engine

The power of an engine is measured in terms of horsepower. One unit of horsepower is equal to about 750 watts. The horsepower of the boat engine should be chosen according to the weight and size of the boat, and the required horsepower is usually stated in the boat's specifications. The weight of the boat includes the fuel, the equipment, and the passengers. It is best to opt for the maximum possible horsepower compatible with the size of the boat when choosing an engine. If the boat is underpowered, the engine has to work harder and wears out more quickly. If the boat is overpowered, the boat may go too fast and may be unsafe.

Fuel Delivery System of a Boat Engine

Boat engines that run on gasoline can use any one of three fuel delivery systems: electronic fuel injection, carbureted fuel system, or direct fuel injection. An electronic fuel injection system uses an electronic pump that helps to maintain constant pressure, while another sensor measures the amount of air required in order to burn fuel efficiently. An electronic system offers great fuel economy combined with low emissions.

An engine with a carbureted fuel system has a carburetor on the top, which controls the fuel and air flow into the engine. The whole process is mechanical, and therefore this system is not very economical, although it is the cheapest and simplest by design.

In a direct injection system, the fuel is inserted directly into the engine's cylinders. As a result, the fuel compression ratios are optimised. The emissions from such a system are low, and the system can adjust automatically to air and water temperatures as well as to altitude.

Foldability of a Boat Engine

Some very lightweight outboard boat engines can be folded and stored in compact spaces. Foldable engines are great for day-sailers and dinghies, as well as for tenders, which are small boats that are usually used for recreation or racing. Foldable boat engines can also act as reserve engines in case the main engine of the boat fails.

Buying a Boat Engine on eBay

If you want to buy a boat engine on eBay, first consider what kind of engine you need. The more specific the keywords you type into the search box, the easier it is to choose. It is advisable to specify the type, whether inboard or outboard. After you receive the initial search results, you can narrow them down by sorting the results in terms of price or auction time. You can also click on related searches. Read the item listings carefully, paying attention to the horsepower and engine sizes in order to find a boat engine that is compatible with your boat.

If you have any questions, feel free to contact the seller. You can enquire about payment methods, delivery, packaging, refunds, and exchanges, among other things. Boat engines are big and heavy, so you may want to opt for local sellers who can arrange a pick up, as sending an engine by post can be quite expensive.


Motor boats open up a world of opportunities, from fishing to water skiing. They are powered by boat engines that drive the propeller, which, in turn, makes the boat move. When buying a boat engine, it is important to choose the appropriate type and to consider the features according to the boat.

Fundamentally, boat engines are divided into outboard and inboard engines, according to their location in relation to the boat. Outboard engines, which are further categorised into two-stroke, direct injection two-stroke, and four-stroke engines, are located outside the boat. Compared to inboard engines, which are inside the boat, usually in the middle, outboards are easier to maintain. Fuel economy varies by type, with four-stroke boat engines being the most economical.

Features that should be considered when buying a boat engine include PTT, found in some outboards, horsepower, which is a measure of the engine’s capacity, foldability, and the fuel delivery system. The fuel delivery systems available include carbureted, direct injection, and electronic fuel systems. They vary in terms of emissions and fuel economy.

Have something to share? Create your own guide... Write a guide
Explore more guides