Maritime Knowledge Base
Browse questions and answers across marine machinery, merchant navy careers, shipboard operations and maritime glossary terms.
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Marine Machinery
Troubleshooting guides for pumps, boilers, purifiers, compressors and auxiliary systems.
Merchant Navy Careers
Questions about joining the merchant navy, exams, cadetships, ranks and sea-time.
Maritime Glossary
Plain-English definitions of shipping, engine-room, navigation and regulatory terms.
Shipboard Operations
Practical Q&A for watchkeeping, safety, maintenance routines and onboard documentation.
Results for "Propeller"
What is the difference between a controllable-pitch and a fixed-pitch propeller?
A fixed-pitch propeller has blades set at one permanent angle, while a controllable-pitch propeller can rotate its blades to vary thrust and go astern without reversing the engine.
Marine MachineryWhat is cavitation in pumps and propellers?
Cavitation is the forming and violent collapse of vapour bubbles in a liquid when local pressure falls too low — it erodes metal, causes noise and vibration, and reduces efficiency.
Marine MachineryWhat is a thrust bearing or thrust block and what does it do?
The thrust bearing, or thrust block, absorbs the forward or astern thrust developed by the propeller and transmits it to the ship's hull, so the thrust actually drives the ship.
Marine MachineryWhat is the stern tube and stern tube seal on a ship?
The stern tube is the tube through which the propeller shaft passes out of the hull; it carries the aft bearing and a seal that keeps seawater out and lubricant in.
Marine MachineryWhat is a shaft generator and why is it used?
A shaft generator produces electrical power by being driven from the main engine or propeller shaft, so the ship can meet its electrical needs at sea without running separate auxiliary generators.
Marine MachineryWhat is a reduction gearbox on a ship and why is it used?
A reduction gearbox lowers the high rotational speed of a medium- or high-speed engine to the slower speed that turns an efficient propeller, and can combine several engines onto one shaft.
Maritime GlossaryWhat is ballast water and why is it managed?
What ballast water is, why ships carry it, and why it is now exchanged or treated under the Ballast Water Management Convention.
Shipboard OperationsWhat is the man overboard (MOB) procedure on a ship?
When someone falls overboard, immediate, drilled actions — raising the alarm, marking the position and turning the ship back — give the best chance of recovery.
Marine MachineryWhat causes a marine engine turbocharger to surge?
Turbocharger surging is a violent, audible instability of the airflow through the compressor — it signals a mismatch between the turbocharger and the engine's demand.
Marine MachineryHow does a marine diesel engine work?
A marine diesel engine converts the chemical energy of fuel into rotary motion through compression ignition — here is the working principle and the two-stroke and four-stroke cycles.
Marine MachineryWhat is the difference between a two-stroke and a four-stroke marine engine?
Two-stroke and four-stroke marine engines differ in how many strokes complete a cycle, their speed and size, and the roles they play aboard ship.
Shipboard OperationsWhat precautions does a ship take in heavy weather?
In heavy weather a ship reduces speed and adjusts course to ease its motion, secures everything for sea, manages ballast and stability, and guards against dangerous rolling.
Marine MachineryWhat is a governor on a marine engine and what does it do?
A governor automatically controls an engine's speed by adjusting the fuel supply to match the load, keeping the engine at the required revolutions or a generator at constant frequency.
