Anchor Windlass Working Principle and Key Components

The anchor windlass is one of the most essential pieces of deck machinery on any vessel. It handles the paying out and heaving in of the anchor chain — an operation that seems simple but involves enormous forces, precise mechanical engineering, and strict compliance with classification society rules. Whether you are a marine engineer, shipyard procurement professional, or equipment buyer, understanding how an anchor windlass works and what its key components do will help you make better specification and purchasing decisions.

This guide explains the working principle of both electric and hydraulic anchor windlasses, identifies the critical components and their functions, and covers the classification rules that govern windlass design and selection.

How an Anchor Windlass Works

At its core, an anchor windlass is a powered winch that raises and lowers the ship's anchor and chain through a chain pipe in the vessel's bow. The fundamental operating cycle involves three phases:

Anchoring (Paying Out)

When the vessel needs to anchor, the windlass brake is released and the clutch is disengaged, allowing the anchor and chain to run out under their own weight (gravity). The speed of descent is controlled by the brake. In some installations, the windlass motor is engaged in a low-speed "creep" mode to provide controlled lowering, particularly in deep-water anchorages where chain weight alone may not provide sufficient descent speed initially.

Anchor Recovery (Heaving In)

To recover the anchor, the clutch is engaged to connect the motor drive to the wildcat (chain wheel). The motor — electric or hydraulic — rotates the wildcat, which grips the chain links and pulls them upward through the hawse pipe. The chain feeds down into the chain locker below decks. The windlass must overcome the combined weight of the anchor and deployed chain, plus any bottom suction or fouling resistance.

Securing

Once the anchor is fully housed in the hawse pipe, the brake is applied firmly, the clutch is disengaged (to relieve load on the gearbox and motor), and chain stoppers or devil's claws are engaged to secure the anchor for sea passage. The windlass brake alone is not relied upon for sea-securing — additional mechanical securing devices are always used.

Electric vs Hydraulic Anchor Windlasses

Electric Windlasses

Electric windlasses use an electric motor (typically AC induction) driving through a reduction gearbox to rotate the wildcat. They are the most common type on commercial vessels up to approximately 50,000 DWT.

Advantages:

• Simpler installation — no hydraulic piping, power pack, or oil reservoir needed
• Lower maintenance requirements — no hydraulic fluid changes, filter replacements, or leak repairs
• Faster response time — immediate motor start vs hydraulic system warm-up
• Higher efficiency — direct electrical to mechanical conversion without hydraulic losses
• Cleaner operation — no risk of hydraulic oil contamination on deck

Disadvantages:

• Higher peak electrical demand on the ship's power system during anchor recovery
• Less suitable for very high-load applications (large vessels with heavy chains)
• Motor overheating can limit continuous duty time

Hydraulic Windlasses

Hydraulic windlasses use a hydraulic motor powered by a hydraulic power unit (HPU) consisting of an electric motor, hydraulic pump, oil reservoir, valves, and filters. The hydraulic motor drives the wildcat through a gearbox.

Advantages:

• Better suited for very high loads and large vessels (VLCCs, bulk carriers, offshore vessels)
• Smooth, infinitely variable speed control through hydraulic flow regulation
• Can share hydraulic power with other deck machinery (mooring winches, cranes) from a common HPU
• Inherent overload protection — hydraulic relief valves prevent mechanical damage
• Better for continuous duty operations

Disadvantages:

• More complex installation with hydraulic piping throughout the foredeck
• Higher maintenance burden — oil changes, filter replacements, seal inspections, leak repairs
• Environmental risk from hydraulic oil leaks on deck
• Lower overall efficiency due to hydraulic conversion losses

Key Components of an Anchor Windlass

Wildcat (Gypsy Wheel)

The wildcat — also called a gypsy or chain wheel — is the heart of the windlass. It is a specially profiled wheel with pockets shaped to engage the links of the anchor chain. The wildcat profile must exactly match the chain size (diameter) and type (stud-link or studless) being used. A mismatched wildcat will cause the chain to slip, jam, or damage both the chain and the wildcat.

Wildcats are typically made from cast steel and surface-hardened in the chain contact areas to resist wear. They are mounted on the windlass shaft and can be engaged or disengaged from the drive through a clutch mechanism.

Warping Head (Drum)

Many windlasses incorporate a warping head — a smooth cylindrical drum mounted on the same shaft as the wildcat. The warping head is used for handling mooring lines, towing hawsers, or other rope work. It can be driven by the same motor as the wildcat, providing dual functionality from a single piece of equipment. On combined windlass-mooring winch units, the warping head may include a rope storage drum.

Brake System

The windlass brake is a band brake or disc brake that acts on the wildcat shaft to control the speed of chain deployment and to hold the chain when the anchor is deployed. The brake must be capable of holding the combined weight of the anchor plus the full length of chain deployed — a force that can exceed 100 tons on large vessels.

Classification societies specify minimum brake holding capacity as a function of the chain breaking load. The brake is manually operated via a handwheel or lever on the windlass, allowing the operator to modulate chain speed during anchoring operations.

Clutch

The clutch connects or disconnects the wildcat from the drive train (motor and gearbox). When the clutch is engaged, motor power drives the wildcat for heaving in. When disengaged, the wildcat is free to rotate independently — allowing gravity-controlled chain pay-out with brake modulation.

The clutch is typically a jaw-type or cone-type mechanical clutch, operated by a handwheel or lever. Engaging or disengaging the clutch while the chain is under load is dangerous and should only be done with the brake fully applied.

Gearbox (Reduction Gear)

The gearbox reduces the high-speed, low-torque output of the motor to the low-speed, high-torque rotation required by the wildcat. Gear ratios typically range from 50:1 to 300:1 depending on the motor speed and required chain speed. The gearbox is usually a multi-stage spur gear or planetary gear design, enclosed in an oil-bath housing for lubrication and protection.

Electric Motor / Hydraulic Motor

The prime mover for the windlass. Electric motors are typically 3-phase AC induction motors rated for marine duty (IP56 protection, Class F insulation, tropicalized windings). Hydraulic motors are typically axial piston or radial piston types sized for the required torque and speed.

Motor sizing is based on the required chain hauling speed (typically 9 m/min per class rules) and the load (chain weight plus anchor weight plus friction). Oversized motors allow faster recovery but increase electrical demand and cost.

Chain Stopper

While technically separate from the windlass itself, the chain stopper is an essential companion component. It is a mechanical device (bar stopper, tongued stopper, or Smit bracket) that locks the anchor chain in position for sea-going, relieving the windlass brake of the holding load during passage. Chain stoppers are required by classification rules and must be rated for the chain's breaking load.

Chain Size Selection and Equipment Number

The size of anchor chain — and therefore the windlass specification — is determined by the vessel's Equipment Number (EN), calculated according to IACS UR A1. The Equipment Number is a function of the vessel's displacement, breadth, freeboard, and windage area, and it determines:

• Anchor weight and number of anchors
• Chain diameter, length, and grade (U1, U2, or U3)
• Windlass type and capacity
• Chain stopper requirements

Common chain sizes for different vessel types:

Classification Society Rules for Windlasses

All classification societies publish rules governing the design, testing, and certification of anchor windlasses. Key requirements include:

• Hauling speed: Minimum 9 m/min at rated load (IACS UR A1)
• Rated pull: Must be capable of hoisting the anchor and a specified length of chain (typically 82.5m for the second anchor) at the rated speed
• Overload capacity: Must sustain 1.5x rated load for a brief period without damage
• Brake holding capacity: Minimum 45% of chain breaking load for the installed chain size
• Stalling torque: Motor must be rated for stalling without damage (for electric types)
• Testing: Factory load test, speed test, and brake holding test required before certification

The windlass must be type-approved by the vessel's classification society, and individual units are inspected and tested during manufacturing under surveyor attendance.

How Hicool Can Help

Hicool sources anchor windlasses and deck machinery components from CCS, BV, ABS, and DNV certified Chinese manufacturers. Whether you need a complete windlass for a newbuild, a replacement wildcat for an existing installation, or spare parts like brake bands, clutch components, or hydraulic motors, we connect you with qualified manufacturers who deliver on specification and schedule. View our anchor windlass range or contact us with your requirements.

Frequently Asked Questions

What is the difference between a wildcat and a gypsy?

In modern maritime terminology, "wildcat" and "gypsy" are synonymous — both refer to the profiled chain wheel that engages the anchor chain links. "Wildcat" is more commonly used in American English and ABS rules, while "gypsy" is more common in British English and LR/BV rules. Some older texts use "gypsy" specifically for wire rope drums, but this distinction has largely fallen out of use.

How often should a windlass be serviced?

Class societies require annual survey of the anchor windlass as part of the vessel's annual survey. Operationally, routine maintenance should include monthly greasing of bearings and gear teeth, quarterly inspection of brake linings, semi-annual inspection of the wildcat for wear, and annual load testing. Hydraulic windlasses additionally require oil sampling and filter changes at intervals specified by the manufacturer.

Can an electric windlass be converted to hydraulic or vice versa?

Technically possible but rarely practical. Converting the drive type requires replacing the motor, adding or removing hydraulic piping and power units, modifying the control system, and obtaining new classification approval. The cost and complexity usually make it more practical to replace the entire windlass. However, replacing an electric motor on an existing electric windlass with a more modern unit is straightforward and commonly done.

What causes a wildcat to wear out?

Wildcat wear is primarily caused by the abrasive action of the chain links as they pass through the pockets. Factors that accelerate wear include: misalignment between chain and wildcat, using the wrong chain size on a wildcat, corrosion from saltwater exposure, inadequate lubrication, and excessive use (frequent anchoring operations). A badly worn wildcat will allow the chain to slip or jump, creating a serious safety hazard. Regular inspection and measurement of pocket dimensions against manufacturer's wear limits is essential.

Need anchor windlass parts or complete units? Contact us or email sales@hiqool.com for specifications and quotations.

Related Resources

• Anchor Windlasses
• Marine Deck Machinery
• Marine Winches & Towing Equipment
• Project Case Studies