An anchor windlass is the powerful deck machine that controls a ship’s anchor and the heavy chain attached to it. On large ships and submarines, the chain alone can weigh many tons, so lifting it by hand is impossible. The windlass uses mechanical advantage, strong motors, brakes, and gears to lower the anchor safely and haul it back aboard.
Understanding the windlass shows how physics turns power into controlled force at sea.
When the windlass rotates its chain wheel, called a wildcat or gypsy, the links of the chain lock into pockets around the wheel. A motor supplies torque through gears, allowing the machine to pull with a large upward force at a slow, controlled speed. The chain passes through the hawse pipe and down into the chain locker, while brakes and clutches control whether the anchor is held, lowered, or raised.
The same ideas of torque, tension, friction, and energy appear in cranes, winches, elevators, and many other lifting systems.
Key Facts
- Torque is the turning effect that lets the windlass pull the chain: τ = F r.
- Mechanical power relates force and lifting speed: P = F v.
- The weight of an anchor or chain is W = mg.
- Gear reduction increases output torque while reducing rotation speed.
- Chain tension must be large enough to overcome the weight of the anchor, chain, and friction in the hawse pipe.
- A brake holds the windlass drum or wildcat still so the anchor does not fall under its own weight.
Vocabulary
- Anchor windlass
- A powered deck machine that lowers, holds, and raises a ship’s anchor and anchor chain.
- Wildcat
- A toothed chain wheel on the windlass that grips the anchor chain links as it turns.
- Hawse pipe
- The strong pipe or opening that guides the anchor chain from the deck down through the bow of the ship.
- Chain locker
- A storage compartment inside the ship where the anchor chain piles up when the anchor is raised.
- Torque
- A rotational force effect equal to force multiplied by the distance from the axis of rotation.
Common Mistakes to Avoid
- Confusing force with torque is wrong because the windlass must create turning effect, not just a straight pull. Torque depends on both the pulling force and the radius of the wheel.
- Ignoring the chain’s weight is wrong because on large vessels the chain can weigh as much as or more than the anchor. The windlass must lift the combined weight of anchor, chain, and losses from friction.
- Assuming gears create energy is wrong because gears trade speed for torque. A lower output speed can provide greater pulling torque, but the energy still comes from the motor.
- Forgetting the brake is wrong because the motor is not the only part that controls the anchor. The brake prevents uncontrolled chain runout and holds the load when the windlass is stopped.
Practice Questions
- 1 A windlass wildcat has a radius of 0.35 m and pulls the anchor chain with a tension of 18,000 N. What torque is applied at the wildcat?
- 2 A ship raises an anchor and chain with a combined mass of 4,500 kg at a steady speed of 0.20 m/s. Ignoring friction, what minimum power is needed? Use g = 9.8 m/s^2.
- 3 A windlass motor turns quickly, but the chain moves slowly with great pulling force after passing through a gearbox. Explain how the gearbox changes speed and torque, and why this helps raise the anchor safely.