Unlike land-based cranes, marine cranes must address eight unique offshore hazards simultaneously: load safety, mechanism limit stops, vessel roll and trim, heave motion caused by waves, explosion protection, emergency stop, anti-collision, and anchoring & wind resistance. The complete system is governed by mandatory standards including SOLAS, CCS/ABS/DNV, and API 2C, and consists of eight subsystems: load moment protection, travel limit control, braking safety, emergency cut-off, environmental & anti-collision protection, electrical explosion protection, dedicated marine stability systems, and monitoring black box.
I. Load and Moment Safety Protection System – Mandatory Core System for Marine Cranes
1. LMI Load Moment Indicator
-- Standard safety fitting for all marine cranes of 5t and above; high-precision moment sensors are mandatory for units exceeding 20t.
-- The LMI collects real-time data of lifting load, luffing angle, and boom length, and calculates the actual moment via the formula: Actual Moment M = Load × Radius. It then cross-checks the value against the Safe Working Load (SWL) corresponding to the current radius:
• 90%~95% rated moment: Audible and visual pre-alarm with red text alert on display screen
• 105% rated moment: Hazardous movements interlocked (lifting, luffing out, and slewing outward prohibited; only luffing in and lowering hook for load discharge permitted)
• 110% SWL: Complete power lockout and crane shutdown; manual reset is required for restart
-- Small hydraulic cranes adopt pressure sensors for indirect load measurement.
-- Offshore cranes are equipped with dual redundant moment sensors with a measuring error of ≤2%.
2. Multi-Mode Load Switching
For marine cranes supporting multi-condition operations with lifting hooks, grabs, or container spreaders, independent overload thresholds are set for each working mode to prevent false protection triggering under full grab load conditions.
3. Real-Time Weight Display at Operator Console
The operator cabin of the YFM Crane is fitted with a moment display screen, providing full visualisation of the live load and maximum allowable lifting capacity at the current radius. Disabling LMI operation is strictly prohibited.
II. Multi-Travel Limit Protection
Dual-stage redundant design to prevent over-hoisting, over-luffing, and over-slewing
Every moving mechanism of the YFM marine crane is equipped with dual protection: primary operational limit + secondary ultimate emergency limit:
1. Hoist Height Limit
- Primary limit: Automatically stops hoisting when the hook approaches the jib head;
- Secondary ultimate limit: Cuts off hoisting power forcibly if the primary limit fails, avoiding the pulley striking the jib top.
2. Lower Depth Limit
Restricts the lowest unwinding position of wire ropes to prevent full rope disengagement from the drum and hook falling overboard.
3. Luffing Limit (Jib Lifting & Lowering)
- Minimum radius limit (fully retracted jib);
- Maximum radius limit (jib extended to the farthest position, where the Safe Working Load (SWL) drops significantly; over-luffing will immediately activate moment protection).
4. Slewing Angle Limit
Limits the maximum left/right slewing range to avoid collision of the jib with superstructures, hatch coamings, and masts;
YFM full-slewing marine cranes are fitted with 360° buffer deceleration limits.
5. Override Bypass Switch
For maintenance use only, secured with a key or protective cover. Strictly prohibited during normal operation. Continuous audible and visual alarm is activated when the bypass is engaged.
III. Brake Safety System
For marine cranes requiring classification society certification, closed-spring brakes must be fitted to hoisting and luffing mechanisms, which automatically engage upon power or hydraulic pressure loss, with a safety factor of no less than 1.5:
- Main Service Brake: Used for normal start-stop and deceleration braking;
- Emergency Safety Brake (Secondary Brake): Instantly engages in the event of main brake failure, power cut-off or hydraulic pressure loss;
- Manual Emergency Brake Release Device: Manually releases the brake to lower loads slowly to a safe position during offshore power failures, eliminating risks of suspended loads left unattended;
- Slewing Damping Brake: Restrains inertial slewing of the jib under vessel rolling motion to prevent load swinging;
- Additional Fittings for Traveling Marine Cranes: Rail clamps plus rail anchoring wedges, providing wind resistance and anti-slip protection against vessel list.
IV. Emergency Stop & Safety Cut-off System
1. Multi-position Emergency Stop Buttons
Hard-wired cut-off circuit for marine cranes, independent of PLC control.
- Red mushroom-head emergency stop button on main control console in operator cabin;
- Auxiliary emergency stops installed on crane base and both sides of walkway platform;
- Directly cuts off the overall hydraulic power and main power supply upon fault triggering, engaging all brakes to full lock-up.
2. Main Power Supply Protection
Automatic full crane shutdown in case of short circuit, electric leakage, motor overload or excessively high hydraulic oil temperature; Dual pressure protection with high-pressure overflow and low-pressure loss monitoring for hydraulic system.
3. Mechanical Interlock Protection
Electrical interlock for hoisting, luffing, and slewing motions of the crane. Simultaneous operation of multiple mechanisms under extreme limit conditions is prohibited to avoid composite moment overload.
V. Marine Special Stabilization & Environmental Safety Systems - Exclusive to Shipboard Cranes
1. Vessel Heel & Trim Interlock Protection
Shipboard cranes are equipped with built-in vessel inclination sensors:
- For standard deck cranes: Lifting capacity is automatically restricted, and travel speed reduced when vessel heel exceeds 5° or trim exceeds 2°;
- The hoisting function will be fully locked once the allowable inclination angle is exceeded to prevent crane capsizing.
Offshore AHC cranes are fitted with Active Heave Compensation (AHC) systems, which counteract wave-induced vertical motion in real time to maintain a constant hook height relative to the sea surface and eliminate dynamic overloads.
2. Anti-Sway Control System
The electric control system automatically adjusts acceleration and deceleration ramps for hoisting, slewing, and luffing motions, limiting cargo sway within ±0.5° to avoid cargo collisions with the hull or personnel injuries.
3. Wind Speed Safety Protection
Wind speed sensors continuously monitor deck wind velocity:
- An alarm is triggered when wind speed surpasses the safe threshold (typically 12 m/s);
- Hoisting and slewing operations are prohibited under extreme wind conditions, and the jib must be retracted to the minimum radius for anchoring.
4. Wind Resistance Anchoring Device
When the ship crane is out of service, four-layer composite securing is implemented: jib retraction, hook lowering to ground, slewing lock pins, rail clamps, and wind guy cables, providing reliable storm resistance.
VI. Anti-Collision Safety Subsystem
1. Laser/Ultrasonic Area Scanning Anti-Collision System
When multiple ship cranes operate on the same deck, or when approaching hatches and superstructures, the system scans obstacles to trigger speed reduction in advance. It will shut down the crane immediately if equipment intrudes into the safety zone.
2. Physical Hard Limit Stops
Mechanical stoppers fitted at the end positions of slewing and luffing movements, serving as the final physical backup for electronic limit switches.
3. Hatch Zone Operation Restriction Program
The maximum allowable load will automatically decrease once the jib moves above the hatch opening.
VII. Electrical & Explosion-Proof Safety System
Marine cranes installed on oil tankers and chemical tankers are mandatorily equipped with Ex explosion-proof features.
- The whole electrical control system has an ingress protection rating of IP54~IP66, resistant to salt spray, rainwater, and deck splashing.
- Explosion-proof models for Zone 1 / Zone 2: Ex d flameproof motors, explosion-proof solenoid valves, explosion-proof control boxes, and intrinsically safe sensors.
- Earthing, lightning protection, and surge suppression devices, plus insulation monitoring for lightning-prone offshore environments.
- Multi-point temperature & liquid level alarms for oil temperature, hydraulic oil contamination, motor temperature, and hydraulic fluid level; the crane will automatically stop for cooling when overheating occurs.
VIII. Audible & Visual Alarms, Video Surveillance and Safety Data Black Box
1. Graded Audible & Visual Alarms
- Pre-warning: Amber light + intermittent buzzer (triggered when near rated load, approaching limit positions or under excessive wind speed)
- Fault & Hazard Alarm: Red light + continuous high-decibel siren (triggered by overload, excessive luffing angle, emergency stop activation and ultimate limit actuation)
Mobile marine cranes emit continuous audible and visual warning signals during travelling to alert deck crew to keep clear.
2. Visual Surveillance System
Multiple cameras are installed in the marine crane cabin, including overhead hook view, jib tip view, and deck operation zone view, eliminating all blind spots.
3. Safety Data Recorder
Mandatory for all marine cranes. It continuously records lifting load, outreach, movement timelines, overload alarms, emergency stops, luffing angles, and wind speed data with a storage retention period of no less than 90 days.
Complete recorded data must be provided for maritime accident traceability and annual surveys by classification societies.
IX. Supporting Mechanical Safety Accessories
Passive Protective Devices for Ship Cranes
- Rope anti-drop devices and rope breakage protection
- Hook safety latches and pulley guards
- Overload buffer relief valves to prevent structural damage caused by instantaneous impact loads
- Walkway guardrails, anti-slip platforms, and emergency escape routes
- Maintenance locking pins: mechanically lock the jib and slewing mechanism during maintenance to eliminate accidental movement
X. Applicable Codes & Standards
- International standards: SOLAS Chapter II-1 Regulation 3-13, ISO 10245, API Specification 2C (Offshore Cranes)
- Classification society rules: CCS Rules for Ship Lifting Appliances, ABS Rules, DNVGL-ST-0378
- Electrical standards: IEC 60204-32 Safety of machinery – Electrical equipment of machines – Part 32: Requirements for lifting machines
Operating Logic of Complete Safety System for Ship Cranes
Prioritization sequence (from highest to lowest):
→ Mechanical hard limit switches/Emergency stop (highest priority, power cut-off directly)
→ Load moment overload protection
→ Vessel heel/trim & wind speed environmental limitation
→ Electronic travel limit switches
→ Interlocks for mechanism movements
→ Audible & visual pre-alarm signals
→ Full-cycle data logging & storage
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