3.1 Ground Tackle: Anchors, Cables, Windlass & Hawse Pipe

Introduction to Ground Tackle & Bower Anchors

Ground tackle is the collective naval architecture term for all equipment deployed in anchoring a vessel, including the anchors, connecting shackles, swivels, stud-link chain cables, windlass machinery, cable stoppers, and hawse pipe fittings. In commercial merchant shipping, the primary anchors deployed at the vessel's bow are designated as bower anchors. Most modern cargo ships carry two operational bower anchors stowed in port and starboard hawse pipes, with an optional spare anchor secured on the forecastle deck.

The standard bower anchor used in commercial shipping is the stockless anchor (such as the Hall, Spek, or AC-14 High Holding Power design). The elimination of the traditional cross-stock allows the anchor shank to be drawn directly up into the hawse pipe for snug sea stowage.

Principal Components of a Stockless Anchor

       [Anchor D-Shackle]
               |
           [Shank]
               |
         [Crown Pivot]
        /      |      \
  [Fluke]  [Tripping]  [Fluke]
             [Palm]

Hawse Pipe, Spurling Pipe & Chain Locker

From the forecastle deck to the seabed, the anchor cable traverses specialized structural conduits:

• Hawse Pipe: A heavy-gauge cylindrical steel casting leading from the forecastle deck through the ship's shell plating. It provides a reinforced channel for the cable during deployment and heaving, and forms a secure housing recess for the anchor head when stowed at sea.
• Spurling Pipe: A vertical cylindrical steel trunk located directly beneath the windlass cable lifter. The chain cable drops through the spurling pipe directly into the chain locker below.
• Chain Locker: A dedicated compartment situated forward of the collision bulkhead beneath the forecastle deck. It provides vertical drop height for self-stowing chain cable. Modern chain lockers incorporate perforated false bottoms (mud boxes) and dedicated bilge suction connections to drain sea water and mud slurry.
• Anchor Wash System: High-pressure sea water spray nozzles mounted inside the hawse pipe casting. Driven by the ship's fire and general service pumps, the wash system blasts mud and benthic sediment off the cable links and anchor flukes as they are heaved aboard, preventing sediment accumulation in the chain locker.

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Anchor Cable Construction, Measurements & Markings

Anchor cables are subjected to immense dynamic loads, cyclic shock, abrasion against rock or coral, and corrosive saltwater exposure. To withstand these forces, commercial vessels utilize stud-link chain cable manufactured from high-tensile forged or cast steel.

Purpose of the Link Stud

Each common link of anchor cable features a solid forged crossbar or "stud" pressed or welded across its internal minor axis. The stud serves three indispensable functions:

1. Kink Prevention: It prevents adjacent chain links from tumbling, twisting, or forming internal kinks that could jam in the hawse pipe or skip across the windlass wheel.
2. Added Weight: The stud contributes to cable weight. The suspended cable forms a catenary curve, which cushions changing loads. Adequate cable length helps maintain a low angle of pull at the anchor; increasing tension straightens the catenary, so horizontal pull is not guaranteed.
3. Tensile Reinforcement: It prevents the sides of the link from collapsing inward (necking down) under heavy pulling loads, increasing the link's ultimate breaking limit.

Maritime Units of Measurement

Anchor cable is manufactured, surveyed, and veered in standardized discrete lengths known as shackles (or shots in naval terminology):

$\text{1 Shackle} = \text{15 Fathoms} = \text{90 Feet} = 27.432\text{ Meters}$

A standard ocean-going merchant ship typically carries between 10 and 14 shackles of cable per bower anchor (roughly 275 to 385 meters per side).

Joining Shackles: Kenter vs. Lugged 'D' Shackle

Individual 15-fathom lengths of cable are connected using specialized joining shackles:

• The Kenter Shackle: The universal standard joining link on modern commercial tonnage. The Kenter shackle consists of two interlocking forged steel halves, a central locking stud, and a machined tapered spigot pin driven diagonally through the assembly. Once seated, a soft lead pellet is hammered into the retaining recess above the pin to lock it permanently in place. Its lugless design and compatible nominal size and pitch allow it to pass over the matching windlass gypsy and through the hawse pipe. Its outside dimensions are not identical to those of a common stud link.
• The Lugged 'D' Shackle: An older style bow-shaped shackle featuring external lugs and a threaded or keyed bolt. Because the bowed head is wider than a common stud link, an anchor cable using 'D' shackles requires enlarged end links and open links (links without studs) to transition from standard dimensions. When assembled, the rounded crown of the 'D' shackle must always face toward the anchor; this prevents the projecting bolt pin from catching on the hawse pipe lip or cable stopper during release.

       KENTER SHACKLE ASSEMBLY
  +-------------+-------------+
  | Half Link A | Half Link B |
  +------+------+------+------+
         |   [Center]  |
         |    [Stud]   |
         |      |      |
         +-[Tapered Pin]-+
         | [Lead Pellet] |

Cable Marking System

To ensure the Officer of the Watch (OOW) and deck ratings know exactly how many shackles of cable have been veered into the water, cables are marked using a systematic pattern of white lead-free marine paint and wire seizings around the studs:

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The Anchor Windlass & Deck Machinery

The anchor windlass is the heavy deck machinery mounted on the forecastle used to heave, veer, and hold the anchor and cable.

Primary Windlass Components

• Gypsy (Cable Lifter): A heavy cast-steel wheel formed with contoured perimeter pockets ("snugs") shaped to grip the exact links of the ship's stud-link chain. Each vessel's gypsy is custom-cast to match its specific cable diameter.
• Jaw Clutch (Dog Clutch): A sliding mechanical coupling that engages or disengages the gypsy from the windlass drive shaft. The clutch must be engaged when using the motor to heave or walk back the cable, and disengaged when letting go on the gravity brake.
• Friction Brake Band & Handwheel: A heavy-duty steel band lined with heat-resistant, asbestos-free friction material wrapping around the outer drum of the gypsy. Operated via a threaded spindle and handwheel (or hydraulic cylinder), the brake holds the gypsy stationary or regulates speed when dropping anchor.
• Warping Head (Warping Drum): Smooth, barrel-shaped drums keyed to the outer horizontal ends of the drive shaft, used for handling synthetic or fiber mooring lines during docking operations.

Cable Stoppers

Mounted on the forecastle deck between the hawse pipe and the windlass, the cable stopper secures the chain while riding at anchor, relieving the windlass motor, shaft, and brake band from severe dynamic shock loads. Common designs include:

• Guillotine / Pawl Stopper: A heavy hinged steel bar or hinged pawl dropped across the vertical link of the cable, bearing against the following horizontal link to prevent outward movement.
• Roller Stopper: Integrates a grooved roller that supports the chain during heaving, combined with a hinged clamping pawl or screw-down compressor clamp.

The Bitter End Connection

The final link of the anchor cable inside the chain locker is termed the bitter end. It is secured to a heavy reinforced deck-pad eye on the chain locker bulkhead using a quick-release slip hook (pelican hook) or a collapsible hinged clench pin.

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Anchoring Operations & Bridge Communications

Anchoring maneuvers require precise coordination between the Master or OOW on the bridge and the anchor party on the forecastle (typically headed by the Chief Officer and assisted by GP ratings).

Methods of Deployment: "Walk Back" vs. "Let Go"

1. Walking Back the Anchor (Lowering Under Power):
   • The windlass jaw clutch is fully engaged, the brake is opened, and the windlass motor is driven in reverse to lower the anchor slowly under power.
   • Deep-Water Anchoring: Follow the vessel’s anchoring plan and windlass limits. Walk the anchor and cable out under power as required; on very large ships, walk out at intervals or all the way to avoid overloading the brakes and bitter end.
   • Also standard practice for walking the anchor out of the hawse pipe to 1 meter above the water line before a controlled "let go".
2. Letting Go (Dropping Under Gravity):
   • The anchor is cleared from the hawse pipe, the jaw clutch is disengaged, and the anchor is held entirely on the friction brake band.
   • Upon receiving the bridge order "Let go port / starboard anchor!", the operator releases the brake and controls the running speed of the anchor and cable with it, following the ship’s procedure.

Reporting Protocol from Forecastle to Bridge

During anchoring operations, the forecastle party must provide continuous, standardized reports to the bridge covering three critical variables: Lead, Strain, and Status.

      REPORTING CABLE DIRECTION (CLOCK CODE)
                   12 o'clock
                  (Ahead/Bow)
                       |
      10 o'clock       |       2 o'clock
           \           |           /
            \          |          /
             \         |         /
   9 o'clock ----------+---------- 3 o'clock
  (Port Beam)          |         (Starboard Beam)

1. Cable Lead (Direction): Reported using the 12-hour clock code relative to the ship's head, accompanied by the vertical lead:
   • "Cable leading at 12 o'clock, growing forward."
   • "Cable leading at 2 o'clock, medium lead."
   • "Cable leading up and down" (hanging strictly vertical from the hawse pipe; anchor directly beneath the bow).
   • "Cable leading under the bow / under the hull" (report immediately with the strain, so the bridge can control vessel movement and avoid damaging the cable or hull).
2. Cable Strain:
   • "Strain slack" (cable hanging loose in a deep catenary).
   • "Strain moderate" (cable straightening smoothly with steady load).
   • "Strain heavy" (cable rigid, vibrating, bar-tight).
   • "Cable surging / checking" (cable jerking violently as the brake slips under peak wave loads).
3. Operational Anchor Milestones:
   • Anchor Aweigh: The anchor has broken out of the seabed mud and is suspended freely in the water. At this exact instant, the vessel is legally underway under COLREGs.
   • Anchor Up and Clear: The anchor crown and flukes have reached the surface, fully visible, clean and clear of any obstruction.
   • Anchor Foul: The anchor flukes are entangled with submarine cables, abandoned wire ropes, rocks, or discarded fishing nets.