4.1 Cargo Handling Appliances: Derricks, Cranes & Safe Working Load (SWL)

4.1 Cargo Handling Appliances: Derricks, Cranes & Safe Working Load (SWL)

Safe and efficient cargo handling operations are central to merchant vessel operations, crew safety, and maritime trade. General Purpose (GP) ratings play an essential hands-on role on deck during port stays: rigging derrick booms, monitoring crane movements, inspecting loose lifting tackle, and serving on cargo watch. A deep understanding of lifting appliance mechanics, operating geometry, safety limits, statutory safety factors, and discard standards is necessary to prevent catastrophic equipment failures and ensure full compliance with international maritime conventions.

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1. Shipboard Derrick Systems

Shipboard derricks are traditional lifting booms pivoted at their heels on masts, kingposts, or derrick houses. While many modern vessels are equipped with deck cranes, derrick rigs remain widely used on general cargo ships and heavy-lift vessels due to their rugged simplicity and exceptional lifting capacity.

The Union Purchase Rig (Married Falls / Yard and Stay)

The Union Purchase rig is the most widely utilized conventional derrick arrangement for breakbulk and general cargo. In this setup, two derrick booms are fixed in rigid operating positions throughout the loading or discharging operation:

• Hatch Derrick: Fixed directly over the open cargo hatch square.
• Yard (Outboard) Derrick: Fixed over the ship's side, plumbing the quay, jetty, or receiving barge.

                     UNION PURCHASE RIG SCHEMATIC

                TOPPING LIFT                 TOPPING LIFT
                    /                             \
                   /                               \
          HATCH DERRICK BOOM               YARD DERRICK BOOM
                /       \                      /      \
               /      HEAD                    /      HEAD
              /       BLOCK                  /       BLOCK
             /          \                   /          \
      SCHOONER GUY -----\-------------------/---- SCHOONER GUY
           /             \                 /            \
          /             RUNNER          RUNNER           \
         /               WIRE            WIRE             \
    PREVENTER GUY          \              /          PREVENTER GUY
        /                   \   (Angle)  /                 \
       /                     \  <--0--> /                   \
   MAST TABLE                 \        /                 MAST TABLE
   GOOSENECK                   TRIANGLE                   GOOSENECK
   & HEEL BLOCK                 PLATE                     & HEEL BLOCK
                                  | 
                             CARGO HOOK
                                  |
                             [ CARGO LOAD ]

Key Rigging Components and Functions

1. Gooseneck Assembly: A heavy forged steel pivot pin and universal swivel joint fitted into a bronze-bushed socket at the boom heel on the mast table. It permits simultaneous vertical topping (luffing) and horizontal swinging (slewing).
2. Spider Band (Spider Hoop): A heavy circular steel collar shrunk and welded around the derrick boom head. It provides four forged eye lugs for securing the topping lift block, cargo runner gin block, working guys, and heavy preventer guys.
3. Heel Block: A heavy single-sheave lead block mounted immediately adjacent to the gooseneck at the boom heel. It directs the cargo runner wire from the deck winch drum cleanly up along the axis of the boom, eliminating fleet angle distortion.
4. Head Block (Gin Block): A single-sheave block suspended from the spider band at the boom head that guides the cargo runner wire down to the cargo hook.
5. Runner Wires (Cargo Falls): Flexible steel wire ropes ($6 \times 24$ or $6 \times 36$ construction with fiber or independent wire rope cores) led from independent cargo winches. The two runner wires are "married" by shackling them to a heavy triangular steel plate (known as a monkey face or union swivel plate) connected to a common cargo hook.
6. Preventer Guys: Heavy steel wire ropes rigged directly from the boom head spider band to certified deck eyeplates. The preventer guy is set up taut alongside the lighter fiber-tackle working guy to take the primary tensile load, protecting the working guy from parting.
7. Schooner Guy (Intermediate Guy): A span connecting the heads of the two married derricks to limit their separation. The outboard working and preventer guys control the booms in the approved union-purchase arrangement.

Working Angle Limitations and Tension Physics

For a symmetric static lift, with both runners equally inclined to vertical, the tension in each runner is given below. During transfer the inclinations and tensions can differ; the actual rig must remain within its certified union-purchase SWL and rigging limits.

$T = \frac{W}{2 \cos(\theta / 2)}$

where $W$ is the suspended load’s weight and $\theta$ is the included angle between the equally inclined runners. Each runner is at $\theta/2$ to vertical.

Swinging Derricks (Single-Boom Systems)

Swinging derricks use a single heavy boom that tops and slews dynamically while carrying the cargo load:

• Hallen Derrick: A swinging derrick operated by a single winchman using dual joystick controllers. It features twin topping lifts rigged to an unstayed Y-shaped bipod mast or outrigger cross-trees. The topping lifts act simultaneously as stays and slewing tackles, eliminating independent guy wires. Use the marked, certified Safe Working Load (SWL) of the actual rig.
• Velle Derrick: Utilizes a distinctive T-shaped boom head and dual topping-slewing winches with continuous tackle reeving. Provides fast, stable slewing and topping control directly from an enclosed operating cab.
• Stülcken Heavy-Lift Derrick: A heavy-lift swinging rig mounted between two unstayed, outward-canted bipod mast towers, with capacities ranging from 100 to over 450 metric tonnes. The boom can swing through (traverse) between the two canted mast legs in a fore-and-aft direction. This allows a single heavy Stülcken derrick to serve two adjacent cargo holds (such as Hold No. 2 and Hold No. 3) without unrigging or re-reeving tackle.

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2. Shipboard Electro-Hydraulic Deck Cranes

Modern bulk carriers, container ships, and multi-purpose vessels rely primarily on electro-hydraulic deck cranes mounted on tall cylindrical pedestals along the centerline or ship's side.

               ELECTRO-HYDRAULIC DECK CRANE ANATOMY

                           [ HOIST SHEAVE ]
                                /    \
                               /      \ [ OVERHOIST LIMIT SWITCH ]
                              /        \
                             /        HOIST WIRE
                            /            \
                           /              \
                   CRANE JIB (BOOM)     [ HOOK BLOCK ]
                         /                  |
                        /                 SAFETY
                       /                  LATCH
     [ LUFFING        /                     |
       CYLINDER ]    /                  [ CARGO ]
             \      /
              \    /
             [ CAB ]
         [ SLEWING RING ]
         [ PEDESTAL POST ]

Core Mechanical Components

• Jib (Boom): Welded high-tensile steel box-girder or tubular lattice structure supporting the hoisting sheaves.
• Slewing Ring & Bearing: A heavy-duty internal ball or roller bearing ring with gear teeth, bolted between the revolving superstructure and stationary pedestal with pre-stressed high-tensile bolts. Driven by hydraulic motors through reduction pinions, equipped with spring-applied, hydraulically released fail-safe disc brakes.
• Winch Units: Dedicated hydraulic hoisting and luffing winch drums driven by variable-displacement axial piston hydraulic motors powered by an electric prime mover.

Mandatory Crane Limit Switches

Deck cranes are equipped with fail-safe electro-mechanical and hydraulic limit switches that prevent equipment over-travel. Trainee ratings must understand their functions and verify that they are never bypassed:

1. Overhoist Limit Switch (Anti-Two-Block Limit): A weighted trip lever or proximity sensor suspended beneath the jib head sheave. If the cargo hook block is hoisted dangerously close to the jib head, the block displaces the counterweight, breaking the electrical circuit. This immediately cuts off hoisting power while keeping lowering power operational, preventing the block from striking the sheaves and snapping the wire.
2. Lower Limit Switch: Positioned on the hoisting winch drum to monitor wire unspooling. It cuts winch power when the hook reaches the lowest permissible operating depth (such as the tank top of an empty hold at low tide), ensuring that a minimum of 3 full safety turns of wire rope remain on the grooved winch drum to prevent shearing of the drum wire clamp.
3. Luffing High Limit Switch: Disengages hydraulic topping power before the jib reaches vertical dead center (typically at an elevation of $75^\circ$ to $80^\circ$ above the horizontal), preventing the jib from toppling backward over the crane cab in heavy swells.
4. Luffing Low Limit Switch: Stops jib lowering when the boom reaches its minimum certified working angle (typically $20^\circ$ to $25^\circ$), where extreme overturning moments and structural bending stresses occur.
5. Slewing Limit Switches: Restrict rotational travel when crane slewing could strike ship structures, such as bridge wings, radar masts, or an adjacent deck crane.

Crane Attachments: Grabs and Spreaders

• Clamshell Grabs: Electro-hydraulic or radio-controlled grabs used for discharging dry bulk commodities (coal, grain, iron ore fines). When operating with a grab, the crane's Safe Working Load is derated (typically to $70\%$--$80\%$ of hook SWL) to account for heavy dynamic shock loads and grab weight.
• Container Spreaders: 20-foot and 40-foot semi-automatic or fully hydraulic spreaders fitted with corner twistlocks to lift ISO freight containers.

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Signals During Cargo and Stores Lifts

Before lifting stores or machinery, agree the signal code, radio channel, designated signaller and stopping procedure with the operator. The signaller must see the load and remain in communication with the operator, concentrate on the lift and keep people clear. If the signal or communication becomes unclear, stop the motion until communication is restored. Obey a stop signal from anyone who sees danger.

These examples illustrate a common crane/hoist hand-signal code; use the agreed chart for the equipment:

For a stores lift, inspect the load for loose items, use certified gear within its limits and keep everyone out from beneath the suspended load. Lower it onto the prepared landing area before releasing the sling; then secure the stores against movement.

3. Safe Working Load (SWL) & Statutory Lifting Regulations

For Indian-flag SOLAS ships, SOLAS II-1/3-13 and Merchant Shipping Notice 02 of 2026 govern the covered lifting appliances from 1 January 2026. New installations need approved design, testing and certification; existing installations must comply by their first SAFCON renewal survey on or after that date. Valid earlier ILO 152 or Indian dock-work certificates are accepted through that transition. Appliances below 1,000 kg retain SWL marking/documentation and risk-based SMS inspection and maintenance requirements.

Engineering Load Definitions

• Minimum Breaking Load (MBL): The certified breaking load at which a new, undamaged wire rope, chain, sling, or metal fitting fractures under tensile laboratory testing.
• Proof/Load Test: A controlled test above SWL, witnessed by a competent person, checks integrity. Under MSC.1/Circ.1663, minimum lifting-appliance test loads for port or sheltered-water use are:
  • For appliance SWL $\le 20\text{ t}$: $\text{Test load} = 1.25 \times \text{SWL}$.
  • For $20\text{ t} < \text{SWL} \le 50\text{ t}$: $\text{Test load} = \text{SWL} + 5\text{ t}$.
  • For appliance SWL $>50\text{ t}$: $\text{Test load} = 1.10 \times \text{SWL}$. Loose gear has separate item-specific proof loads in Table 2; do not apply this appliance table to shackles or slings. Open-sea appliance test loads require Administration/RO approval accounting for dynamic loads.
• Safe Working Load (SWL): The maximum statutory working load certified by a competent person that may be safely hoisted, suspended, or handled under normal operational conditions.

Design Safety Factors

The Safety Factor ($\text{SF}$) is defined as:

$\text{SF} = \frac{\text{MBL}}{\text{SWL}}$

Use the marked certified SWL. The applicable design standard determines the safety factor; ILO Convention 152 does not impose one 5:1 factor on all cargo gear. ILO ports Appendix E gives the following guidance unless a recognized standard provides otherwise:

Given-value calculation: With MBL = 100 t and factor = 5, SWL = 100/5 = 20 t. This calculation does not change an appliance’s certified rating.

The Register of Lifting Appliances and Cargo Handling Gear (Chain Register)

Certified appliances and their test/examination records must be entered in the onboard Register of Ship’s Lifting Appliances and Cargo Handling Gear (often called the Chain Register). Records must contain the required information and be authenticated by a competent person; approved formats can differ. Common ILO certificate examples include:

• Form No. II: Certificate of Test and Examination of Winches, Derricks, Cranes, and Their Accessory Gear.
• Form No. III: Certificate of Test and Examination of Loose Gear (shackles, blocks, hooks, swivels, chains, rings).
• Form No. IV: Certificate of Test and Examination of Wire Ropes.

Mandatory Statutory Survey Intervals

• Load Testing: Covered lifting appliances must be retested at least once in every five years, and after major repairs, modifications or alterations. Testing and thorough examination are also required before a new installation enters service. Apply the approved appliance test procedure and load.
• Annual Thorough Examination: A certified competent person must conduct a comprehensive visual and operational survey of all lifting appliances, limit switches, brakes, sheaves, and loose gear every 12 months.
• Pre-Use Visual Inspection: Conducted by the ship's officers and GP ratings before every cargo operation.

Marking Requirements

• Booms and Cranes: The certified SWL must be painted in bold, high-contrast block lettering on the boom heel or jib side (e.g., SWL 35 MT (GRAB 28 MT) R=3.5-28m).
• Loose Gear: Clearly and permanently mark the SWL and unique identification, with any additional information required for safe use. Keep proof-test dates and results in the linked certificate/register; a proof date is not a universal required stamp on every item.

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4. Loose Gear Inspection & Discard Criteria

GP ratings must inspect loose lifting gear prior to use and immediately remove any defective items from service.

Shackles: Types and Inspection

       BOW (OMEGA) SHACKLE                 DEE ('D') SHACKLE
             Crown                               Crown
            /     \                             |     |
           |  (O)  |                            | (D) |
            \     /                             |     |
           Pin Lug                               Pin Lug
          [=======]                             [=======]
             Pin                                   Pin
      (Multi-leg / Angular)                 (Inline Axial Only)

• Bow (Omega) Shackle: Features a rounded, wide crown profile. Designed to accommodate multi-leg sling bridles and angular pulls up to $45^\circ$ without pinching sling eyes.
• Dee ('D') Shackle: Features narrow, parallel sides. Strictly designed for straight, in-line axial tension pulls. Must never be subjected to angular or side loading.
• Screw Pin vs. Safety Bolt: Select the type approved for the connection and loading. A safety-bolt shackle uses a bolt, nut and split cotter pin. For permanent rigging, prevent pin loosening with the approved securing method, such as mousing a screw-collar pin or fitting the cotter to a nut-and-bolt pin. Inspect the security before use.

Cargo Hooks and Swivels

• Cargo Hooks: Must be fitted with an operational spring-loaded safety latch. Discard if:
  • The throat opening has stretched or widened by more than 10% of its original manufactured dimension.
  • The hook body is twisted by more than $5^\circ$ out of its original plane.
  • Any gouge, crack, or unauthorized weld repair is detected.
• Swivels: Must rotate smoothly under hand pressure without binding, axial slack, or gritty resistance, relieving line twist generated during hoisting.

Wire-Sling Inspection and Discard

Use the applicable manufacturer, recognized-standard and RO retirement criteria for the sling and its terminations. Withdraw suspect gear and report it before further lifting.

• The ILO ports guidance identifies more than 5% broken wires over six rope diameters, concentrated breaks in one strand or a short length, breaks in splice tucks, and more than one broken wire beside a compressed termination as replacement indicators.
• Withdraw slings showing kinking, bird-caging, crushing, core failure or heat damage.
• Severe corrosion, pitting, damaged ferrules or unsafe eyes and end fittings also require withdrawal.
• Inspect the whole sling, including beneath movable protection where permitted. Record defects and apply the specified disposal procedure; do not rely on an invented universal broken-wire count.

Synthetic Webbing Slings

Webbing slings must be condemned and destroyed if:

• Cuts, tears, punctures or snags damage the load-bearing webbing, including its edges or eyes.
• Acid, caustic, or chemical attack has dissolved or softened fibers.
• Fibers are melted, glazed, or charred from hot work or friction.
• Load-bearing stitching is broken, frayed, or pulled loose.
• The manufacturer's statutory identification tag showing the SWL is missing or unreadable.