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Handling Hull Blocks, Propellers, and Propulsion Shafts

Hull blocks, propellers, and propulsion shafts are the shipyard loads least like one another and least forgiving of a poor lift: a hull block is a large welded structure that has to reach erection without distortion, while a propeller and a shaft are finished components that have to be set down without damage. UTEC Industrial designs, engineers, machines, fabricates, and installs custom material handling systems for aerospace and heavy industry from its Spokane Valley, WA facility, integrating Allen-Bradley PLC and motion control with in-house CNC machining, heat treating, and stress relief. This article works through each load from the yard's side: where a block is picked up, how it is turned and landed, how propellers and shafts are rigged and restrained, what changes aboard a vessel, and what sensing, drives, PLC logic, and energy control the handling equipment needs. That equipment is built along one chain, design → engineering → parts machining → fabrication → assembly → weld fatigue → stress relief → drives → controls → tuning → monitoring, and a pickup point or fixture tolerance set at the first links governs how the drives and controls at the last links have to behave.

Why are hull blocks, propellers, and shafts handled differently from other shipyard loads?​

Arifuddin and Pawara describe steel ship construction in Indonesia as dominated by the hull block construction method, in which the hull is divided into sections or blocks that are worked in parallel to reduce man-hours; once work on the blocks is finished, the blocks are lifted during the erecting process and assembled into the main hull. The lift is therefore not a simple transfer. It is the moment a partly stiffened structure, built to fit its neighbors, carries its own weight from a few attachment points.

The erection sequence also turns every block lift into a schedule event. Shen, Lee, Jeong, and Woo describe the hull block erection network process as frequently delayed because of limited resources, limited workspace, and the block preparation ratio. A block that has to be re-rigged or re-fitted after a poor lift adds one more source of delay to a sequence that is already under that pressure.

Propellers and propulsion shafts pose the opposite problem. They arrive finished, and the handling risk is surface damage, loss of control, or a component that shifts while crews work around it, not structural distortion. Three different handling problems follow:

  • Hull blocks: where to attach, how to turn, and how to keep the structure within its fit-up tolerance.
  • Propellers: how to sling or fixture a heavy, finished casting with sharp edges without damaging it or the rigging.
  • Propulsion shafts: how to support, move, and restrain a long, round part that can roll or shift when rigging goes slack.

The block construction method is what puts the lift, and the pickup points, at the center of the build (Arifuddin and Pawara 2023, Majalah Ilmiah Pengkajian Industri 16-2, abstract; Shen et al. 2021, Journal of Ship Production and Design 37-2, abstract).

How does padeye placement change the stress and distortion in a hull block lift?​

The attachment points decide how the block's structure carries the lift. Arifuddin and Pawara state that the placement of the padeye in the block during the lifting operation plays a vital role in the deformation and working stress of the block structure, and that if it is not observed the result can be misalignment in the welding joint path of the ship block from excessive plastic deformation and stress. A block that distorts in the air does not fit its neighbor at erection, and the fit-up has to be corrected on the berth.

Their study applied the stiffness method in a computer program to 23 padeye positions on a ship block and recorded the deformation and stress in the block structure for each. The optimal position, position 10 in simulation 2, gave deformations of 7 mm, 2 mm, and 7 mm in the x, y, and z directions. The study also reports that, in several positions, the deck girder and longitudinal beam structure was dominantly subjected to high deformation and stress. For a yard, the lesson is that padeye positions are an engineering output checked against the block's own framing, not a choice made on the day of the lift.

OSHA's shipyard rigging guidance adds the practice that goes with that analysis:

  • Each pad eye should be designed for a specific use and able to hold the intended weight or force after it is welded in place.
  • Pad eyes should be inspected for cracks and other defects that affect capacity, and defective pad eyes removed from the work area.
  • When fitting tools pull against a pad eye, everyone should be well out of the danger zone in case the pad eye tears off the surface it was welded to.

Where a yard lifts the same block family repeatedly, an engineered lifting frame or spreader with fixed, analyzed pickup points takes the padeye decision out of the field (Arifuddin and Pawara 2023, Majalah Ilmiah Pengkajian Industri 16-2, abstract; OSHA Working in the Shipyard Industry: Rigging 2011, p. C-8).

How is a hull block turned from its build position to its erection position?​

When a block is built in one attitude and erected in another, turning it usually means two cranes sharing one load while the load changes attitude. OSHA's shipyard eTool lists the general-industry rules for crawler, locomotive, and truck cranes, 29 CFR 1910.180, that bear on that kind of lift:

  • When two or more cranes are used to lift one load, one designated person is responsible for the operation, analyzes it, and instructs all personnel in the positioning, rigging of the load, and the movements to be made, 29 CFR 1910.180(h)(3)(xii).
  • Side loading of booms is limited to freely suspended loads, and cranes are not used to drag loads sideways, 1910.180(h)(3)(iv).
  • Neither the load nor the boom is lowered below the point where less than two full wraps of rope remain on the drum, 1910.180(h)(3)(x).
  • The operator does not leave the controls while the load is suspended, 1910.180(h)(4)(i).

The rigging guidance records what happens when a turnover goes wrong. In one case, an overhead crane operator set a chain sling in a single choker hitch to pick up and turn over a steel frame lying horizontally on two sawhorses. The sling hook had no safety latch, and the operator was standing between the load and another steel frame leaning vertically against the shop platform. The chain disconnected from the hook, the vertical frame fell toward him, and he was crushed between the two frames. The guidance calls for a working safety latch or a moused hook, daily crane inspection, and keeping every part of the body out of places where it can be trapped.

A turnover fixture or rollover frame gives the block a defined pivot and a controlled rotation, so the load path does not depend on two operators and a changing sling geometry (OSHA eTool: Shipyard Employment, Materials Handling, Hoisting and Hauling Equipment and Use of Gear; OSHA Working in the Shipyard Industry: Rigging 2011, p. C-23).

How should a block, propeller, or shaft be landed and secured after the lift?​

Many shipyard handling injuries happen after the lift, when a load that looked settled moves. Section 1915.116(k) requires pieces of equipment or structure susceptible to falling or dislodgement to be secured or removed as early as possible, and §1915.116(m) requires pallets, when used, to safely support and carry the loads handled on them. OSHA's rigging guidance adds that a load should be set down slowly, that the landing spot should be inspected before the load arrives, and that a load being walked should be kept as close to the ground as possible.

Two of the guidance's case histories show the failure mode:

  • A leaned load. A crane operator set one exhaust stack on its side, leaned a second 3-ton stack against it, and slackened the line so a rigger could reposition the wire rope. The stack fell and killed the rigger. The listed preventive steps are to understand the full sequence of rigging events and the balance point of the material, ensure the drop position is secure, and chock the lifted item where possible.
  • A rolling load. Workers placing support I-beams, each with 24 × 36 in plates welded on its ends, cleared the area after rigging, but a beam rolled and the corner of its end plate fractured the leg of a worker who had fallen. The steps listed are exclusion zones, a sounded lift signal, and keeping personnel out of the lift area.

A propulsion shaft is the rolling case in its purest form, and a propeller set on its hub or a block set on temporary supports is the leaning case. Cradles, chocks, and saddles designed for the part, rather than improvised blocking, are what make the landed load stable (OSHA 29 CFR Part 1915, Subpart G-2026, §1915.116 paragraphs k and m; OSHA Working in the Shipyard Industry: Rigging 2011, pp. C-7, C-20 and C-22).

How should a propeller be rigged without damaging it or the rigging?​

A propeller combines a heavy central hub with thin, finished blade edges, and both the casting and the slings are at risk where they meet. Section 1915.116(f) requires slings to be padded with wood blocks or other suitable material where they pass over sharp edges or corners of loads, to prevent cutting or kinking. OSHA's rigging guidance adds a limit on that padding: slings must not be covered with permanent padding that would prevent them from being inspected before each use, and it calls for softeners, padding, chafing gear, or other sling protection as necessary to prevent damage to nylon slings.

Where a propeller or hub is lifted by eye-bolts, §1915.116(e) requires the slings to be arranged, using spreaders if necessary, so the pull is within 20 degrees of the axis of the bolt. Several general-industry sling rules that OSHA's shipyard eTool cites also apply directly:

  • Slings are securely attached to the load, 29 CFR 1910.184(c)(6), and suspended loads are kept clear of all obstructions, 1910.184(c)(8).
  • Hands or fingers are not placed between the sling and the load while the sling is being tightened, 1910.184(c)(10).
  • Shock loading is prohibited, 1910.184(c)(11).

Where a propeller is a sand-cast aluminum bronze, ASTM B148-24 is the specification that covers those castings, alloys UNS C95200 through C95900, with inch-pound values as the standard units. A lifting fixture that seats on the hub bore or on dedicated lifting features spreads the load through surfaces the casting was designed to carry, instead of through blade edges (OSHA 29 CFR Part 1915, Subpart G-2026, §1915.116 paragraphs e and f; OSHA Working in the Shipyard Industry: Rigging 2011, p. C-7; OSHA eTool: Shipyard Employment, Materials Handling, Use of Gear; ASTM B148-24).

What does a propulsion shaft need from its handling equipment?​

A propulsion shaft is long, round, and finished, so it is usually supported at more than one point, drawn into position in small increments, and held while crews work at its couplings and bearings. In a hull, the incremental moves are often made with chain falls and pull-lifts hung from the structure. Section 1915.114(a) requires chain falls and pull-lifts to be clearly marked with their capacity, which must not be exceeded. Section 1915.114(c) requires the straps, shackles, and beam or overhead structure they hang from to be strong enough for the load plus the gear, with the upper hook moused or otherwise secured. OSHA's rigging guidance adds that fitting tools such as come-alongs and chain falls should be used at up to 80 percent of their capacity, and that chain falls positioning a load should be of the same capacity.

Rigging alone is a weak restraint on a heavy round part. In one of the guidance's case histories, a worker was removing a damaged 3,500 lb crane load drum and was driving out the final bolt of the gear-side pedestal bearing. The gear side was secured with rigging, but the drum still shifted forward, and the worker's thumb was caught between the pedestal bearing and the drum assembly and amputated. The preventive steps are a pre-work plan with a hazard assessment and sequence of events, removal procedures approved by experienced personnel, identified pinch points, and securing items where possible.

A shaft handling cradle or carriage provides that positive restraint: adjustable saddles that carry the shaft at its design support points, end stops or clamps that prevent rolling and axial creep, and a controlled drive for the final moves. The saddles' flatness and alignment govern how evenly the shaft is supported, which traces back up the chain to how the cradle frame is fabricated and stress-relieved before its locating surfaces are machined. UTEC Industrial stress-relieves welded frames in-house, including by automated vibratory stress relief, before the frames are machined (OSHA 29 CFR Part 1915, Subpart G-2026, §1915.114 paragraphs a and c; OSHA Working in the Shipyard Industry: Rigging 2011, pp. C-8, C-21 and C-24).

What changes when a component is lowered aboard a vessel or through a hatch?​

Moving a block, shaft section, or propeller onto a vessel adds a floating, moving platform and deck openings to the lift. Section 1915.116(n) requires a section of hatch through which materials or equipment are being raised, lowered, or moved to be completely opened, and the beam or pontoon left in place next to the opening to be lashed, locked, or otherwise secured so it cannot be displaced by accident. Section 1915.116(o) prohibits opening or closing a hatch while employees are in the square of the hatch below.

The crane itself changes when it works from a vessel:

  • Derricks and cranes that are part of, or regularly placed aboard, barges, other vessels, or the wingwalls of floating drydocks, and that transfer materials to or from a vessel or drydock, are tested and certificated under Part 1919 by accredited persons, §1915.115(a)(1).
  • OSHA's shipyard eTool lists wave movement, barge size or stability, and a shifting crane as the reasons for special precautions when a crane is placed on a barge.
  • When ship's gear is used to hoist materials aboard, a competent person determines that the gear is properly rigged, in safe condition, and not overloaded by the size and weight of the lift, §1915.117(a).

The rigging guidance adds the edge hazards: riggers should avoid putting themselves between a load and a deck edge, where a sudden swing can knock them through the railings; guardrails removed to land a load require other protection against falls overboard; and workers over water must be provided with approved personal flotation devices under 1915.71(j)(3) (OSHA 29 CFR Part 1915, Subpart G-2026, §1915.115 to §1915.117; OSHA 29 CFR Part 1919-1974; OSHA eTool: Shipyard Employment, Materials Handling, Hoisting and Hauling Equipment; OSHA Working in the Shipyard Industry: Rigging 2011, pp. C-9 and C-10).

What sensing and PLC controls belong on block, propeller, and shaft handling equipment?​

Each of the failures above has an engineered counterpart. The rules assume people keep a turning block balanced, a landed shaft still, and a load within its rating; sensors and interlocks can hold those conditions directly:

  • Load sharing at each pickup. The padeye study shows that the stress in a block depends on where, and how evenly, it is carried. Load cells at each pickup point of a lifting frame or at each hoist of a multi-hoist system let the PLC compare the measured share with the planned share and stop the lift when they diverge. The same measurement helps keep the slings, shackles, and hooks within the safe working load that §1915.111(b) forbids exceeding for the gear covered by §1915.112 and §1915.113.
  • Synchronized motion. In a turnover fixture or a two-hoist lift, encoders on each axis let the controller hold the axes in step instead of relying on two operators. Servo drives such as Allen-Bradley Kinetix 5700 close position, velocity, and current loops on encoder feedback and have safe torque-off built in.
  • Deterministic logic. Logix 5000 controllers organize code into continuous, periodic, and event tasks, so synchronization and interlock logic can run at a fixed period rather than whenever the processor has time.
  • Positive-restraint permissives. Switches that prove a shaft clamp, cradle stop, or turnover lock is engaged before a drive can move, or before lifting gear can be slackened, turn the leaned-load and rolling-load lessons into interlocks.
  • Safety functions that cannot be bypassed. Emergency stop, zone entry, and safe speed belong in a safety controller. Rockwell Automation rates a GuardLogix 5580 primary controller with a safety partner for safety applications up to SIL 3 and PL e, Cat. 4, and without one up to SIL 2 and PL d, Cat. 3.

The frameworks are ISO 12100:2010 for risk assessment and risk reduction, ISO 13849-1:2023 for the safety-related parts of the control system, and IEC 60204-1:2016 for the electrical equipment of machines. UTEC Industrial, a Rockwell Automation Recognized System Integrator, builds this Allen-Bradley control into UL 508A panels for the handling systems it fabricates (OSHA 29 CFR Part 1915, Subpart G-2026, §1915.111 paragraph b; Arifuddin and Pawara 2023, Majalah Ilmiah Pengkajian Industri 16-2, abstract; Rockwell Automation 2198-UM002E-EN-P, 2018, Kinetix 5700; Rockwell Automation 1756-RM094N-EN-P-2025; Rockwell Automation 1756-RM012J-EN-P-2025; ISO 12100:2010; ISO 13849-1:2023; IEC 60204-1:2016).

How are the drives tuned and the controls proven before a block or shaft is lifted?​

A controlled axis is only as good as its tuning at the load it actually carries. The Kinetix 5700 commissioning procedure includes a tuning step for each axis, and autotuned loop bandwidths depend on the application and can require adjustment once the motor and load are connected. A shaft carriage or turnover axis tuned empty can overshoot or oscillate with the shaft or block on it, which is exactly the uncommanded movement the load drum case history shows is dangerous near a pinch point. Tuning is therefore checked at representative load during commissioning and again when a heavier block family or shaft size is added.

Proving the controls follows the same logic:

  • Each positive-restraint switch and load-sharing limit is tested by forcing the fault it guards against, not only by observing normal operation.
  • Warning devices stay connected. The rigging guidance records a newly assigned crane operator who silenced alarms he did not understand; with the anti-two-block disconnected, there was no warning before the headache ball broke free and fell on the worker below. The guidance's lesson is to leave safety and warning devices on and functioning.
  • Drive fault history, motor current, and axis following error are trended from the first lift, so wear or binding in a cradle, turnover bearing, or hoist shows as a change against the commissioning baseline.

A handling system proven this way at factory acceptance and again at site commissioning arrives at the berth with limits that mean what the specification said (Rockwell Automation 2198-UM002E-EN-P, 2018, Kinetix 5700; OSHA Working in the Shipyard Industry: Rigging 2011, pp. C-18 and C-21).

How is hazardous energy controlled when this equipment is serviced in a shipyard?​

A raised turnover frame, a cradle holding a shaft, or a hoist holding a block by its brake is stored energy, and servicing it needs an energy-control program. In shipyard employment the governing rule is 29 CFR 1915.89, which covers servicing machinery, equipment, and systems when energization, startup, or release of hazardous energy could endanger an employee. It applies to servicing in any landside facility that performs shipyard employment work and on any vessel or vessel section, paragraph (a)(2)(i). Its core requirements are:

  • A written lockout/tags-plus program and procedures, paragraph (b).
  • All energy sources identified and isolated and the equipment rendered inoperative before servicing, paragraph (c)(1).
  • A lock wherever the energy-isolating device can be locked, unless the employer demonstrates that tags-plus gives full protection, paragraph (c)(2). A tags-plus system is a tag on the isolating device plus at least one additional safety measure, paragraph (c)(4).
  • After October 31, 2011, energy-isolating devices designed to accept a lock whenever equipment is extensively repaired, renovated, modified, or replaced, or new equipment is installed, paragraph (c)(5). The requirement does not apply when the shipyard employer does not own the equipment or builds or services a vessel or vessel section to customer specifications.
  • A fixed sequence when locks come off temporarily to test the equipment or position a component: clear tools and materials, remove nonessential employees, remove the lockout/tags-plus system, restart and test or position, then shut down and reapply all systems before servicing continues, paragraph (h).
  • A lockout/tags-plus coordinator and log when several systems, or several crews on one system, are serviced at the same time, paragraph (c)(7).

A marine manufacturing plant whose work is not shipyard employment follows the general-industry rule instead: 29 CFR 1910.147 excludes employment covered by Part 1915 under paragraph (a)(1)(ii)(B), and defines push buttons, selector switches, and other control-circuit-type devices as not being energy-isolating devices. A PLC stop is not an isolation point under either rule (OSHA 29 CFR 1915.89-2011; OSHA 29 CFR 1910.147-1989).

What should a yard specify before ordering block, propeller, or shaft handling equipment?​

A request that gives only a capacity leaves out most of what drives the design. A complete specification covers the chain from design through monitoring:

  • Load envelope: the weight range, dimensions, center-of-gravity location, and fit-up tolerance for each block family, and the weight, hub geometry, and finished surfaces of each propeller and shaft.
  • Pickup points: analyzed padeye or lifting-lug positions for each block, checked against the block's girders and longitudinals, and the lifting features on propellers and shafts.
  • Motion: turnover angle and axis, lift and traverse strokes, landing speeds, and whether the equipment works ashore, from a barge, or aboard a vessel, which triggers Part 1919 certification under §1915.115(a)(1).
  • Restraint: cradles, saddles, chocks, and clamps for every landed position, and the positive-restraint switches that prove them.
  • Controls: load sensing per pickup, synchronized axes, safety functions in a safety controller, and alarms that cannot be silenced from the operator station.
  • Energy control: lockable energy-isolating devices on new equipment, consistent with §1915.89(c)(5) in a shipyard or 1910.147 in a general-industry plant.
  • Acceptance: factory and site tests at representative load, safety-device tests, and the records the yard's inspection program keeps.

UTEC Industrial performs factory acceptance testing and on-site commissioning, so these acceptance criteria can be written into the purchase order and demonstrated before handover (OSHA 29 CFR Part 1915, Subpart G-2026, §1915.115 paragraph a.1; OSHA 29 CFR Part 1919-1974; OSHA 29 CFR 1915.89-2011; OSHA 29 CFR 1910.147-1989; Arifuddin and Pawara 2023, Majalah Ilmiah Pengkajian Industri 16-2, abstract).

Related Articles

References​

  • Arifuddin AMN, Pawara MU (2023). "The Influence of Padeye Placement on Ship Block Lifting." Majalah Ilmiah Pengkajian Industri, 16(2), 53-61. DOI 10.29122/mipi.v16i2.5255
  • Shen, H., Lee, Y., Jeong, Y.-K., Woo, J.H. (2021). "Analysis on Hull Block Erection Process Considering Variability." Journal of Ship Production and Design, 37(2), 67-77. DOI 10.5957/jspd.07190036.
  • OSHA 29 CFR Part 1915, Subpart G-2026: Gear and Equipment for Rigging and Materials Handling. U.S. Department of Labor, 2026.
  • OSHA. Working in the Shipyard Industry: Rigging (Safety and Health Injury Prevention Sheets). U.S. Department of Labor, 2011.
  • OSHA. eTool: Shipyard Employment — General Requirements — Materials Handling (including Gear and Equipment for Rigging). U.S. Department of Labor, 2026 (undated web documentation, accessed September 2026).
  • OSHA 29 CFR Part 1919-1974: Gear Certification. U.S. Department of Labor, 1974.
  • OSHA 29 CFR 1915.89-2011: Control of hazardous energy (lockout/tags-plus). Occupational Safety and Health Administration, 2011.
  • OSHA 29 CFR 1910.147-1989: The Control of Hazardous Energy (Lockout/Tagout). Occupational Safety and Health Administration, 1989.
  • ASTM B148-24: Standard Specification for Aluminum-Bronze Sand Castings. ASTM International, 2024.
  • IEC 60204-1:2016 (Ed. 6.0): Safety of Machinery -- Electrical Equipment of Machines -- Part 1: General Requirements. International Electrotechnical Commission, 2016.
  • ISO 12100:2010: Safety of machinery — General principles for design — Risk assessment and risk reduction. ISO, 2010.
  • ISO 13849-1:2023: Safety of machinery — Safety-related parts of control systems — Part 1: General principles for design. International Organization for Standardization, 2023.
  • Rockwell Automation 1756-RM012J-EN-P-2025: GuardLogix 5580 and Compact GuardLogix 5380 Controllers Safety Reference Manual. Rockwell Automation, 2025.
  • Rockwell Automation 1756-RM094N-EN-P-2025: Logix 5000 Controllers Design Considerations. Rockwell Automation, 2025.
  • Rockwell Automation 2198-UM002E-EN-P (2018): Kinetix 5700 Servo Drives User Manual. Rockwell Automation, 2018.

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UTEC Industrial designs, engineers, machines, fabricates, and installs custom material handling systems for heavy industry, from the stress-relieved structure and drives to the Allen-Bradley PLC controls, tuning, and monitoring that run them, at its Spokane Valley, WA facility. Send UTEC the application, loads, and duty cycle to start a system review.

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