Marine Propulsion & Propeller Systems Flashcards
7 cards from real MST practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Marine Propulsion & Propeller Systems flashcards as text
How do you verify that a replacement propeller has the correct pitch for a given engine?
Answer: Confirm the engine reaches the manufacturer's rated wide-open throttle RPM range under full load
The correct pitch allows the engine to reach the manufacturer's specified WOT RPM range under full load, confirming the engine is neither overloaded nor under-loaded.
What is a counter-rotating propeller system?
Answer: Twin propellers on concentric shafts rotating in opposite directions to cancel torque effects
Counter-rotating systems use two propellers on concentric shafts spinning in opposite directions, which cancels torque and P-factor effects, improving efficiency and reducing steering pull.
What physical process causes the characteristic pitting (erosion) seen on cavitating propeller blades?
Answer: Micro-shockwaves from the violent collapse of vapor bubbles on the blade surface
Cavitation erosion pitting is caused by the violent collapse of vapor bubbles on the blade surface, generating intense micro-shockwaves that mechanically remove material from the metal.
What is propeller rake?
Answer: The angle at which propeller blades are swept forward or backward relative to a perpendicular plane through the shaft
Rake is the fore-and-aft sweep angle of propeller blades relative to a plane perpendicular to the shaft, affecting bow lift, ventilation resistance, and overall performance.
How does a folding propeller primarily benefit a sailboat with an auxiliary engine?
Answer: Its blades fold parallel to the shaft when not in use, greatly reducing drag under sail
A folding propeller's blades collapse streamlined along the shaft when not motoring, dramatically reducing hydrodynamic drag that would otherwise slow the vessel under sail.
What is the primary purpose of a sacrificial zinc anode installed on a propeller shaft or strut?
Answer: To corrode preferentially and protect the propeller and shaft from galvanic corrosion
Zinc is less noble than aluminum, bronze, or stainless steel in the galvanic series, so it corrodes preferentially when connected to those metals in an electrolyte, protecting the more valuable components.
Why is anti-seize compound applied to the splined shaft before installing a propeller?
Answer: To prevent galvanic corrosion between dissimilar metals and ease future removal
Anti-seize compound prevents galvanic corrosion where dissimilar metals contact each other (e.g., aluminum propeller on stainless shaft) and ensures the propeller can be removed without damage in the future.