Alabama Boaters Engine Basics 4 — Questions and Answers
Question 1: What does engine 'trim' refer to on a boat with an outboard or stern drive?
- Adjusting the throttle sensitivity
- Changing the angle of the engine/drive unit relative to the transom (Correct answer)
- Setting the idle fuel mixture
- Balancing the weight of passengers fore and aft
Correct answer: Changing the angle of the engine/drive unit relative to the transom
Trimming the engine adjusts the vertical angle of the lower unit, affecting the bow angle and performance of the boat.
Question 2: Which of the following is a sign that a spark plug may need replacement on a marine engine?
- Smooth idle with consistent RPM
- Engine misfires, rough idle, or difficulty starting (Correct answer)
- High oil pressure reading
- Consistent fuel consumption
Correct answer: Engine misfires, rough idle, or difficulty starting
Misfiring, rough idling, and hard starting are common symptoms of worn or fouled spark plugs that are failing to ignite the fuel mixture reliably.
Question 3: What is the purpose of a shear pin or slip clutch hub on a propeller?
- Increase propeller pitch automatically
- Protect the engine and gearcase by breaking or slipping when the prop strikes an object (Correct answer)
- Lock the propeller at high RPM
- Prevent reverse gear engagement
Correct answer: Protect the engine and gearcase by breaking or slipping when the prop strikes an object
The shear pin or slip hub absorbs the shock when the propeller hits an object, preventing damage from transferring to the gearcase and engine.
Question 4: What causes 'pre-ignition' in a marine gasoline engine?
- Fuel igniting before the spark plug fires due to a hot spot in the combustion chamber (Correct answer)
- Air entering the fuel line before the carburetor
- Engine oil burning in the combustion chamber
- A lean fuel mixture at idle
Correct answer: Fuel igniting before the spark plug fires due to a hot spot in the combustion chamber
Pre-ignition occurs when the fuel-air mixture ignites prematurely from a hot spot such as a glowing carbon deposit before the spark plug fires.
Question 5: After striking a submerged object, what should you check on an outboard motor before restarting?
- Battery charge level
- Propeller for damage and the shear pin or hub for failure (Correct answer)
- Fuel tank vent cap
- Navigation light wiring
Correct answer: Propeller for damage and the shear pin or hub for failure
Striking an object can shear the prop's pin, bend blades, or damage the lower unit, so the propeller and its drive mechanism must be inspected before restarting.
Question 6: Which statement about ethanol-blended fuel (E10) and marine engines is correct?
- Ethanol improves power output in all marine engines
- Ethanol can absorb water and cause phase separation, harming fuel systems (Correct answer)
- E10 extends the life of rubber fuel components
- Ethanol reduces the octane rating below safe levels
Correct answer: Ethanol can absorb water and cause phase separation, harming fuel systems
Ethanol in fuel absorbs moisture from the air; when enough water accumulates, phase separation occurs, sending corrosive water into the engine.
Question 7: What does 'WOT' stand for in the context of marine engine testing?
- Water Over Transom
- Wide Open Throttle (Correct answer)
- Warning On Tachometer
- Weight Of Transom
Correct answer: Wide Open Throttle
WOT (Wide Open Throttle) refers to operating the engine at maximum throttle, which is used to verify that the engine achieves its rated RPM with the installed propeller.
Alabama Boaters Engine Basics 4
What does engine 'trim' refer to on a boat with an outboard or stern drive?