A capstan is deck machinery consisting of a vertical rotating drum, used to haul in mooring lines or chain by wrapping the line around the drum and applying rotational power.
How It Works
A mooring line is wrapped several turns around the vertical drum; as the capstan rotates (power-driven), friction between the line and drum allows a crew member to control tension and haul the line in, without the line itself being permanently attached to the machine.
Capstan vs Windlass
- Capstan — a standalone vertical-axis drum, often positioned at various mooring stations around the vessel, purely for line handling
- Windlass — typically combines anchor chain handling (with a horizontal chain wheel/gypsy) and often a mooring warping drum in one integrated unit, usually positioned on the forecastle specifically for anchor operations
Some vessels use windlasses for anchor work and separate capstans at other mooring stations (amidships, aft) where a dedicated anchor-handling mechanism isn’t needed.
Why Powered Line Handling Matters
Mooring lines under load require far more force to haul in than manual effort alone can safely provide, especially for larger vessels — powered capstans and windlasses make line handling both practical and safer than the alternative of relying purely on manual crew effort.
Safety Considerations
Capstan operation involves genuine mechanical hazards — rotating machinery, lines under tension, and the risk of a line parting or a crew member’s clothing or limb getting caught in the mechanism. Standard operating procedures around capstan use reflect these real risks.
Exam Relevance
Capstan operation and its role in mooring line handling are core Ship Knowledge and Deck Operations topics in deck officer competency exams.