Attaching Outboard Engines: A Guide For Boat Owners

Outboard engines are a popular choice for propelling small watercraft. They are self-contained units that include an engine, gearbox, and propeller, and are designed to be affixed to the outside of the transom (the part where the sides of the hull join at the rear of the boat). Outboard engines are all-in-one marine engines that provide propulsion and steering control. They are usually mounted on a bracket on the transom to one side, with the bracket consisting of a thick board that emulates a dinghy transom, on which the motor is clamped.

Outboard engine mounting hardware

There are several types of mounting brackets available, including:

• Adjustable outboard motor brackets: These brackets can be mounted to the transom or swim step of a boat and allow the outboard motor to be lowered into the water for use or raised out of the water for storage. They are versatile and can usually accommodate both 2-stroke and 4-stroke motors.
• Rail-mount outboard brackets: These brackets are designed to attach to the railings of a boat, providing a secure and space-saving solution for storing the outboard motor.
• Transom support plates: These plates are used to reinforce the transom and provide added stability for mounting the outboard motor. They are typically made from stainless steel or powder-coated steel.
• Swim platform outboard motor brackets: These brackets are designed to be mounted on swim platforms, providing a convenient location to keep the outboard motor ready for use. They are typically made from powder-coated aluminium.

When installing an outboard engine, it is important to consider the shaft length to ensure it is a good match for the transom thickness and dimensions. Additionally, the mounting height and trim angle of the motor should be adjusted to optimise performance and prevent ventilation, which can cause the engine to race and the propeller to spin uncontrollably.

The transom

To attach an outboard engine to the transom, first, measure the height of the transom. The mounting height of the outboard will affect the speed of the boat. If the height is too high, cavitation may occur, leading to a slowdown, energy waste, and propeller damage. If the height is too low, water resistance will reduce speed and energy efficiency. The optimal mounting height will depend on the specific conditions of the boat, and it may be necessary to test different heights.

Next, find the appropriate shaft length for the outboard motor. Different transom heights require different shaft lengths. A simple chart can help determine the suitable shaft length based on the range of transom height. If the motor is still hard to reach the water, an outboard motor bracket may be needed.

Finally, place the outboard on the centre line of the transom and tighten the transom clamp bolts firmly. This will ensure the boat is well-balanced and prevent the outboard motor from falling off or moving on the transom, which could cause a loss of control and serious injury. It is important to check the clamp screws for tightness occasionally, as they may become loose due to engine vibration. For added security, a cable can be used to avoid complete loss of the outboard motor in case it falls off the transom.

Steering control

Outboard engines provide steering control by pivoting over their mountings to control the direction of thrust. The skeg acts as a rudder when the engine is not running.

Outboard motors are steered in one of two ways: tiller steered or controlled from the helm. Small outboard motors, up to 15 horsepower (11 kW) or so, are affixed to the boat via clamps and thus easily moved from boat to boat. These motors typically use a manual start system, with throttle and gearshift controls mounted on the body of the motor, and a tiller for steering.

Larger outboards are affixed to the transom using clamps and are either tiller steered or controlled from the helm. Generally, motors of 100 hp plus are linked to controls at the helm.

There are a variety of steering kits available for outboard motors, including:

• Hydraulic steering kits
• Rotary steering kits
• Zero torque feedback tiller steering systems
• Wireless remote control steering systems

Engine maintenance

Outboard engines are a self-contained unit that includes an engine, gearbox, and propeller or jet drive, designed to be affixed to the outside of a boat's transom. They are the most common form of propulsion for small watercraft.

Cleaning and Maintaining the Motor:

• After each outing, flush out the engine with fresh water, even if you've been in freshwater.
• Check the water pump for good water flow. Ensure the output is strong and the water is warm, but not hot.
• If the output is weak, shut down the engine to prevent overheating and damage, then clear any debris from the outflow tube with a small piece of wire.
• After flushing, disconnect the fuel line and let the engine burn the remaining fuel in the carburetor.
• Turn off the engine and, if applicable, the battery switch.
• Remove the engine cowling and check for fuel or water leaks. Consult a mechanic if leaks are found.
• Wipe down and spray all accessible mechanical components and moving parts with an anti-corrosive like WD-40. Lubricate all moving parts.
• Replace the cowling, wipe it down, and keep a canvas or plastic cover on the engine between trips.

Regular Maintenance:

• Replace spark plugs and plug wires as needed. There is no set lifespan for spark plugs, but they will wear out faster with frequent use or poor maintenance.
• Check for water in the fuel regularly. Ethanol fuel additives can cause this issue, so try to avoid them.
• Check the fuel line fittings to ensure they are properly seated and leak-free.
• Replace the water pump impeller annually if used in saltwater, or every two years for freshwater use.
• Always use fresh fuel. Drain your tanks and dispose of fuel at the end of the season.

Additional Tips:

• Read your owner's manual for specific maintenance procedures and schedules.
• Avoid fuel and battery problems by using non-ethanol gasoline and regularly checking battery connections.
• Complete annual servicing, either yourself or with a professional technician.
• Winterize your engine if used in colder climates to prevent freezing and damage.
• Check the propshaft for fishing line or debris, which can lead to costly repairs.

Engine cooling systems

Outboard engines are almost always water-cooled, with very few exceptions. Water is used to cool the engine as it has greater mass and is a better conductor of heat than air. The water is pumped up from below the waterline into the engine through the lower unit. The water pump is the heart of the cooling system, with an offset impeller that pressurises the water to one side of the pump, allowing it to enter and be pumped out.

The water is drawn up through a seacock fitting and pumped through the engine's water jacket and ports by a mechanical water pump. This cooler water absorbs heat from the engine and is then pumped out through the exhaust. This is known as a "raw water" system. Most newer marine engines use an enclosed cooling system, which has a small tank on top of the engine that uses a combination of freshwater and coolant. The freshwater is circulated through the engine and a heat exchanger, absorbing heat from the engine. The raw water is pumped through the heat exchanger, where it absorbs heat from the freshwater, and is then pumped out.

The advantages of an enclosed system are significant, especially in saltwater, as saltwater tends to build up a corrosive scale when the engine operates above 140°. In a raw water system, this scale builds up inside the engine, and when it restricts water flow, the engine will overheat. In an enclosed system, the water that flows through the engine is freshwater and coolant, so the scaling occurs in the heat exchanger, which is cheaper to replace than the engine.

Other components of the cooling system include the seacock, sea strainer, hoses and clamps, belts, and water pump impeller. The seacock is a through-hull device with a handle that allows you to shut off the water flow if there is a problem. The sea strainer is a device that filters out debris, sand, and leaves from the raw water before it reaches the engine. Hoses, clamps, and belts should be checked periodically for wear and corrosion, and replaced if necessary.

The water pump impeller should be changed annually, and engines used in saltwater should be regularly flushed with freshwater to prevent corrosion and scaling. Problems with the cooling system can lead to serious engine issues, such as a blown cylinder head gasket or complete engine seizure.

Frequently asked questions