Mixed Deck — All MST Topics Flashcards

When inspecting a through-hull fitting, a technician finds the seacock is stiff and difficult to operate. What is the correct action?

Answer: Apply marine grease and exercise the seacock; replace if operation does not improve

Seacocks must operate freely for emergency use; they should be greased and exercised regularly, and replaced if they remain stiff or corroded.

What ABYC standard governs the installation of gasoline fuel systems on recreational boats?

Answer: ABYC H-24

ABYC H-24 (Gasoline Fuel Systems) establishes minimum safety standards for fuel tanks, lines, fittings, and ventilation on recreational vessels.

What is the maximum distance at which two VHF radios at sea level can typically communicate using line-of-sight propagation?

Answer: Approximately 20–25 nautical miles between two vessels depending on antenna height

VHF radio is line-of-sight, and the range between vessels is limited by antenna height above the waterline — typically 20–25 nm vessel-to-vessel at normal antenna heights.

What does a manifold vacuum test on a marine gasoline engine primarily indicate?

Answer: Overall engine health including valve sealing and timing

Manifold vacuum readings reflect combustion efficiency, valve seating, timing accuracy, and cylinder sealing simultaneously.

When adjusting trim tab position on an outboard, moving the trim tab to port will cause the boat to turn in which direction?

Answer: Starboard (right)

Moving the trim tab to port deflects water flow to the right side of the lower unit, creating a force that steers the stern to port and the bow to starboard.

What is the correct procedure for checking injector spray pattern on a port-fuel injected marine engine?

Answer: Remove injectors and test on a bench injector tester

Bench testing removed injectors on an injector tester allows direct visual inspection of spray pattern, atomization quality, and leak-down rate.

On a marine vessel, what is the MAXIMUM distance the main DC overcurrent protection (fuse or circuit breaker) should be located from the battery positive terminal per ABYC standards?

Answer: 7 inches (18 cm)

ABYC E-11 requires the main overcurrent protection to be installed within 7 inches (18 cm) of the battery positive terminal to protect the unguarded conductor from the battery to the fuse.

When flushing a saltwater outboard engine after use, what is the correct procedure?

Answer: Attach a flush muff to the water intakes with the engine running in neutral and flush with fresh water for 5–10 minutes

Running the engine with a flush muff circulates fresh water through the entire cooling system to remove salt deposits that cause corrosion and blockage.

A stern drive engine overheats only at high RPM and normal operating temperature is maintained at idle. What is the most likely cause?

Answer: Partially clogged cooling water passages

Partially clogged cooling passages restrict flow sufficiently at high demand (high RPM) but allow adequate flow at idle, causing overheating only under load.

A technician is about to sandblast antifouling paint on a vessel hull. Which hazard requires the highest priority personal protective equipment (PPE)?

Answer: Toxic heavy metals such as tributyltin and copper in old paint dust

Old antifouling paints often contain toxic biocides like copper and historically tributyltin; airborne dust during sanding or blasting requires respiratory and skin protection.

A technician installs a new battery bank on a vessel. Under ABYC E-10, what is required to prevent accidental shorting of the battery terminals?

Answer: Insulated battery terminal covers or boots on all exposed terminals

ABYC E-10 requires that all exposed battery terminals be protected with insulated covers or boots to prevent accidental short-circuit contact.

Water in the outboard gear oil is most commonly caused by what condition?

Answer: A failed propeller shaft seal or damaged prop shaft

Water enters the lower unit most often through a failed propeller shaft seal, especially if the prop has hit an obstruction and damaged the seal.

A technician is diagnosing a fuel-injected outboard that runs rough and has a lean misfire code. Fuel pressure is within spec. What is the next logical diagnostic step?

Answer: Check for vacuum leaks in the intake manifold

Lean misfire with correct fuel pressure suggests unmetered air entering the intake; vacuum leaks allow air to bypass the throttle and MAF sensor, causing a lean condition.

Why is it important to inspect the marine engine’s exhaust system?

Answer: To prevent blockages or leaks that affect engine performance and safety

Inspecting the marine engine’s exhaust system is critical for both engine performance and safety. Blockages, such as carbon buildup, can restrict exhaust flow, reducing engine efficiency and potentially causing overheating. More importantly, leaks in the exhaust system can allow dangerous carbon monoxide fumes to enter the boat's cabin, posing a severe health risk to occupants. Regular checks ensure proper gas expulsion and prevent these hazards.

Which agency administers the Oil Pollution Act (OPA 90) for vessels operating in US waters?

Answer: USCG and EPA jointly

OPA 90 is jointly administered by the US Coast Guard (for vessel compliance) and the EPA (for facilities and response planning).

When reinstalling a marine engine cylinder head, what is the correct sequence for torquing head bolts?

Answer: Inside to outside in a spiral pattern from the center

Head bolts must be torqued from the center outward in a spiral pattern to evenly distribute clamping force across the gasket and prevent warping the head.

What does the term 'stray current corrosion' refer to in a marine context?

Answer: Accelerated corrosion caused by DC electrical current leaking into the water from the vessel or marina

Stray current corrosion is caused by DC current leaking from the vessel or marina electrical systems into the water, which dramatically accelerates metal corrosion on underwater components.

Osmotic blistering on a fiberglass hull is caused primarily by what process?

Answer: Water migrating through the gel coat into the laminate

Osmosis occurs when water molecules permeate the gel coat and react with water-soluble compounds in the laminate, forming acidic fluid-filled blisters.

Which type of fire extinguisher is most appropriate for an engine compartment fire involving fuel and electrical components?

Answer: Type B:C dry chemical or CO2

B:C rated dry chemical or CO2 extinguishers are approved for flammable liquid (B) and electrical (C) fires common in engine compartments.

After completing a fiberglass hull repair, what is the correct sequence of finishing steps?

Answer: Wet-sand, compound, polish, wax

Wet-sanding levels the repair, compounding removes sanding scratches, polishing restores gloss, and waxing provides UV protection.