Views: 20 Author: Achord Publish Time: 2026-09-29 Origin: Site
A marine crane is a slewing crane mounted on a vessel's deck to lift cargo, stores, equipment and small boats on and off the ship. Choosing one starts with three questions: how heavy is your heaviest lift, how far from the crane column does it hang, and how much deck space can the crane take up when it is not working.
This guide explains the two main boom types, how to read a load chart, how to size a crane to your vessel and what the rules say about certification. The figures quoted come from the load charts and specifications in BOB-LIFT's marine crane product manual, which covers 14 knuckle boom models from 0.8 to 25 t and 10 telescopic boom models from 2 to 20 t.
Key Takeaways
Knuckle boom marine cranes fold into a small footprint and place loads precisely in tight spaces. Telescopic boom cranes reach farther in a straight line. In BOB-LIFT's range, the telescopic model reaches farther than the knuckle model at every capacity offered in both types, and from 4 t upward it also has the higher lifting moment.
The headline tonnage is only available close to the column: about 2.0 to 2.25 m for most BOB-LIFT knuckle models and 2.5 m for most telescopic models. At full reach the same cranes lift between 200 kg and 2 t.
Size a crane by the load at your working radius, read from the load chart. Dividing the lifting moment by the radius gives a first estimate, but it overstates the load at long reach.
Check that the vessel can carry the crane's self-weight, base loads and power demand, not just the load.
Since 1 January 2026, SOLAS regulation II-1/3-13 sets rules for lifting appliances on ships it covers. BOB-LIFT marine cranes are not class-certified, so confirm what your vessel needs before ordering.
A marine crane, also called a ship crane or deck crane, is a crane, usually hydraulic or electro-hydraulic, fixed to a pedestal on the deck of a vessel. It slews around its column and lifts with a boom and hook, so the crew can move loads between the deck, the quay and the water without shore equipment.
A work barge with a deck crane, spud poles and a wheelhouse in Tønsberg harbor, Norway. Photo: Wolfmann, Wikimedia Commons, CC BY-SA 4.0. Not a BOB-LIFT crane.
Deck-mounted marine cranes are different from the large gantry and ship-to-shore cranes used at ports, and from heavy offshore cranes built for platforms and construction vessels. For those distinctions, see our articles on the types of cranes used on a ship, the cranes used at docks and the differences between marine cranes and offshore cranes. This guide focuses on vessel-mounted cranes in the 0.8 to 25 t class.
Typical jobs for a crane of this size include:
Loading stores, spare parts, nets and gear from the quay.
Lifting cargo, containers of catch or equipment in and out of holds.
Launching and recovering tenders, workboats or small equipment. Launching lifeboats and rescue boats falls under separate life-saving appliance rules.
Handling tools and components during maintenance and repair.
Illustration (AI-generated from a photo of a BOB-LIFT 8 t knuckle boom crane; the vessel and scene are not a real installation): a knuckle boom crane handling nets on a fishing vessel.
Both boom types are hydraulic, slew on a pedestal and lift with a hook. The difference is how the boom gets its reach, and that shapes how much deck the crane uses and where it can place a load.
A knuckle boom folds at its joints to stow compactly. A telescopic boom retracts its sections and lowers to stow.
A knuckle boom marine crane has an inner boom and an outer boom joined by a hinge, like a finger. Hydraulic cylinders fold and unfold the two sections, and the outer boom usually carries telescopic extensions for extra reach.
The main advantages are:
Compact stowage. The boom folds back against the column, so the crane occupies little deck and is easy to secure for sea.
Precise placement. The folding joint lets the operator reach over a gunwale, into a hold or under an obstruction and set the load down gently. BOB-LIFT's manual describes a double four-bar linkage in the boom that lets it work at a reverse angle, which widens the working range.
Flexible working envelope. The hook can move up, out and down independently, which helps on crowded decks.
The trade-off is more moving parts. Every joint adds pins, bushings, cylinders and hoses to inspect and grease, and all of them sit in salt air.
A 5 t knuckle boom marine crane with the boom folded in its stowed position.
A telescopic boom marine crane has a straight main boom with sections that slide out of each other. A luffing cylinder raises and lowers the boom, and the extension cylinders set the reach.
The main advantages are:
Longer straight-line reach. The boom extends directly toward the load, which suits lifts over the side or onto a quay. In BOB-LIFT's range, the telescopic models reach 8.0 to 22.3 m, against 4.2 to 18 m for the knuckle models.
More lifting moment per tonne of rating. From 4 t upward, the telescopic model at each capacity has a higher lifting moment than the knuckle model, for example 25 against 21 t·m at 10 t.
Simpler boom geometry. There is one boom and one pivot, so there are fewer joints to maintain.
The trade-off is stowage. A telescopic boom cannot fold, so it needs a clear run of deck or a boom rest when lowered. The sliding sections and their wear pads also need regular attention in a marine environment.
A 6.3 t telescopic boom marine crane with its boom extended over the water.
Knuckle boom | Telescopic boom | |
|---|---|---|
How it reaches | Folds and unfolds at one or more joints | Slides boom sections out in a straight line |
Stowed footprint | Small, folded against the column | Longer, boom retracted and lowered |
Best at | Tight decks, placing loads into holds or under obstructions | Clear decks, lifts over the side, longer straight reach |
Maintenance focus | Pins, bushings, hoses at each joint | Sliding sections, wear pads, extension seals |
BOB-LIFT range | 14 models, 0.8 to 25 t, reach 4.2 to 18 m | 10 models, 2 to 20 t, reach 8.0 to 22.3 m |
A marine crane's headline rating, such as "10 t", is the most it can lift, and only close to the column. What decides the load at longer reach is the lifting moment, the load multiplied by its horizontal distance from the slewing center, quoted in tonne-metres (t·m). The load chart turns that into a rated load at each working radius.
For a first estimate, divide the lifting moment by the radius you need:
estimated load (t) ≈ lifting moment (t·m) ÷ radius (m), never more than the rated capacity.
The load chart then gives the real figure. Take the 10 t knuckle boom marine crane, model SQ10ZA6TJ, rated at 21 t·m. Its chart gives 10 t at 2.0 m, 4.65 t at 4.5 m and 3.08 t at 6.49 m, close to the estimate of 3.2 t. At its full reach of 14.68 m it gives 1.15 t, well below the 1.4 t the estimate suggests, because the boom's own weight counts for more as it extends.
Rated load against working radius, from load chart points in the BOB-LIFT marine crane product manual. The dashed line is the simple moment estimate for the 10 t knuckle model.
Telescopic cranes add one more variable. Their load charts are tables by boom length and boom angle, not a single curve. For the 10 t telescopic model, SQ10SA4T, the chart gives 5.7 t at a 4.3 m radius with the 5.6 m boom at 30°, but only 4.3 t at a 4.4 m radius with the 9.02 m boom raised to 60°. The radius is almost the same, but the longer boom weighs more, so it lifts less. Read the row for the boom length you will actually use.
For a lift plan, always use the manufacturer's load chart for the exact model and boom configuration. Our article on the lifting moment of a crane explains load charts and moment limiters in more detail.
We read the load chart of every model in BOB-LIFT's marine crane product manual. Three patterns stand out:
Full rated load stops close to the column. Most knuckle models lift their full rating out to 2.0 to 2.25 m (the 0.8 t and 1.6 t models to about 1.3 to 1.4 m). Most telescopic models reach 2.5 m at full rating, and the 2 t and 3.2 t models 2.0 and 2.2 m.
Telescopic models reach farther. At every capacity offered in both types, the telescopic model has the longer maximum working radius, from 8.0 against 7.7 m at 4 t to 22.3 against 15.9 m at 16 t.
Loads at full reach are small. At the last point on each chart, the cranes lift between 200 kg (the 3.2 t telescopic model at 10.5 m) and 2 t (the 25 t knuckle model at 18 m).
Maximum working radius of each BOB-LIFT marine crane model, taken from the last point on its load chart. Source: BOB-LIFT marine crane product manual.
The practical lesson is simple. If you need "3 t at 6 m", you need a crane with at least 18 t·m and a load chart that confirms 3 t at 6 m. In BOB-LIFT's range, the 10 t knuckle model gives 3.08 t at 6.49 m and the 8 t telescopic model, SQ8SA5T, gives 3.1 t at 6.0 m with its 8.8 m boom at 40°. The 8 t knuckle model, at 16.7 t·m, falls short, and its chart gives 2.47 t at 6.49 m. A 3.2 t crane, at 6.8 t·m, is nowhere near. Our guide to ways to calculate crane capacity covers the arithmetic step by step.
Size the crane from the job, then check that the vessel can carry the crane.
The four core checks. Power, slewing and options follow in the list below.
Heaviest single lift. Weigh the heaviest item you will lift and add the hook block, slings and any lifting beam. This sets the capacity class.
Radius of that lift. Measure the horizontal distance from where the crane column will stand to where that load must be picked up and set down, including over the side to the quay. Then check the load chart at that radius.
Deck space and stowage. Check where the crane can be mounted and where the boom will rest at sea. A tight deck or a need to reach into a hold points to a knuckle boom. A clear run of deck and lifts over the side point to a telescopic boom.
What the vessel can carry. BOB-LIFT marine cranes weigh from 220 kg for the 0.8 t knuckle model to 6,950 kg for the 20 t telescopic model. That weight sits high on the deck, and the crane's base and the deck beneath it must take the lifting loads. Ask a naval architect or the vessel's designer to confirm the mounting position and the effect on stability.
Power supply. Across the range, BOB-LIFT lists a recommended power of 3.5 to 55 kW, hydraulic flow of 8 to 80 L/min (80 + 63 L/min on the 20 t telescopic model) and system pressure of 16 to 35 MPa. BOB-LIFT's manual shows both electric and diesel hydraulic power units. Confirm whether your vessel's own hydraulic system can supply the crane instead.
Slewing range. All BOB-LIFT marine cranes from 2 t upward slew 360° continuously. The 0.8 t and 1.6 t knuckle models slew 330°. Check that the crane can reach every position you need from its mounting point.
Options and controls. Decide early whether you need a winch, a grapple or a work basket, and whether the operator will work from an overhead seat or a wireless remote. BOB-LIFT also adapts the mounting arrangement to the vessel on request.
A 3.2 t telescopic boom marine crane with its control cabinet and power unit beside the column.
The table below is a general guide to where each capacity band fits. The right model always depends on the load at your radius, not the headline rating.
Illustration (AI-generated from a photo of a BOB-LIFT 6.3 t telescopic boom crane; the barge and scene are not a real installation): a telescopic boom crane lowering cargo onto a work barge.
Capacity class | BOB-LIFT models | Typical fit |
|---|---|---|
0.8 to 3.2 t | Knuckle 0.8, 1.6, 2, 3.2 t; telescopic 2, 3.2 t | Small workboats, yachts and fishing boats handling stores, gear and light equipment |
4 to 8 t | Knuckle 4, 4.6, 5, 6.3, 8 t; telescopic 4, 5, 6.3, 8 t | Fishing vessels and workboats lifting catch, nets, tenders and heavier equipment |
10 to 16 t | Knuckle 10, 12, 16 t; telescopic 10, 12, 16 t | Barges and larger work vessels handling cargo and equipment |
20 to 25 t | Knuckle 20, 25 t; telescopic 20 t | Barges and larger vessels with the deck strength and space for a heavy crane |
Salt spray attacks paint, steel, hydraulic fittings and electrical connections, so a marine crane needs better protection than a crane that works on land.
BOB-LIFT's manual states that its marine cranes use several anti-rust processes designed for the marine environment. The product pages for several telescopic models, including the 2 t, 16 t and 20 t, specify an epoxy zinc-rich primer and a polyurethane acrylic topcoat to resist seawater corrosion, and sealed electrical components to keep moisture out. When you compare suppliers, ask for the coating system and film thickness, the hose and fitting specification, and how electrical parts are sealed.
Sea conditions also matter. The rating of a shipboard crane assumes the vessel is close to level. Lifting while the vessel heels, trims or moves in a swell swings the load and adds dynamic force to the crane and the vessel. Ask any supplier what heel and trim its ratings allow, and plan lifts for sheltered water whenever you can.
A 20 t knuckle boom marine crane in the factory.
For a closer look at pedestals, booms, winches and counterweights, read the structure of marine cranes.
Whether your marine crane needs certification depends on the vessel, its flag and its class, so check this before you order.
SOLAS regulation II-1/3-13. The International Maritime Organization added this regulation on lifting appliances and anchor handling winches, and it entered into force on 1 January 2026. It covers design, construction, operation, inspection, testing and maintenance. Its design, construction and installation requirements apply to ships built on or after 1 January 2026, while its operation, inspection, testing and maintenance requirements apply to all ships it covers (IMCA Information Note 1657, January 2024). Lloyd's Register notes that new lifting appliances must be certified before entering service, including plan appraisal, material verification, inspection and a load test once installed (Lloyd's Register class news 12/2025). For appliances with a safe working load below 1,000 kg, the flag state decides how far the design, construction and installation provisions apply (IMCA).
Which ships SOLAS covers. Unless a regulation says otherwise, SOLAS applies to ships on international voyages, and its general exceptions include cargo ships under 500 gross tonnage, fishing vessels, pleasure yachts not engaged in trade and ships not propelled by mechanical means (SOLAS consolidated edition, Chapter I, regulations 1 and 3). National rules, the vessel's classification society or a charterer can still require a certified crane on a vessel outside SOLAS.
Where BOB-LIFT fits. BOB-LIFT marine cranes are not certified by a classification society. They are intended for vessels and duties where a class-certified lifting appliance is not required, such as many fishing boats, workboats, barges and yachts. If your vessel is classed or falls under SOLAS, including when you add a crane to an existing ship, confirm the requirements with your flag administration and classification society before you order.
A marine crane is only as safe as its mounting and its daily care. The deck must be reinforced for the crane's base loads, the pedestal bolted or welded to an approved design, and the hydraulic and electrical connections protected from spray.
In service, keep these habits:
Check the load chart for every lift. Know the load weight and the radius before you lift. BOB-LIFT marine cranes carry a dedicated moment limiter, but it is a safeguard, not a substitute for planning the lift.
Keep people clear. Never stand under the boom or a suspended load.
Stow and secure the boom at sea. An unsecured boom can swing as the vessel rolls.
Inspect before use. Look at hoses, cylinders, pins, the hook latch and the slewing ring bolts, and grease the joints as the manual specifies.
Rinse and touch up. Wash salt off after use and repair paint damage before rust spreads.
Our guide to safely putting marine cranes on ships covers installation planning in more detail.
The crane figures in this guide come from BOB-LIFT's marine crane product manual, and the table below summarizes the main ones for each model. The maximum working radius is the last point on each model's load chart, with the rated load at that radius. Self weights are as printed in the manual, so confirm the weight of your exact configuration with BOB-LIFT before a deck-load or stability calculation. Links go to the product page for each capacity. Some product pages still show earlier model codes or figures, so ask for the current load chart when you inquire.
Model | Type | Rated capacity | Lifting moment | Max. working radius (load there) | Self weight |
|---|---|---|---|---|---|
SQ08ZA3TJ+1 | Knuckle | 0.8 t | 1.3 t·m | 4.15 m (220 kg) | 220 kg |
Knuckle | 1.6 t | 2.2 t·m | 4.23 m (300 kg) | 380 kg | |
Knuckle | 2 t | 4.2 t·m | 5.1 m (750 kg) | 590 kg | |
Knuckle | 3.2 t | 6.8 t·m | 7.7 m (680 kg) | 1,236 kg | |
Knuckle | 4 t | 8.4 t·m | 7.7 m (850 kg) | 1,256 kg | |
BLZ90K5TJ | Knuckle | 4.6 t | 9 t·m | 11.7 m (590 kg) | 1,520 kg |
Knuckle | 5 t | 10.5 t·m | 8.05 m (1,100 kg) | 2,120 kg | |
Knuckle | 6.3 t | 13.2 t·m | 10.2 m (1,190 kg) | 1,740 kg | |
Knuckle | 8 t | 16.7 t·m | 14.68 m (850 kg) | 2,730 kg | |
Knuckle | 10 t | 21 t·m | 14.68 m (1,150 kg) | 2,920 kg | |
Knuckle | 12 t | 27 t·m | 14.5 m (1,000 kg) | 4,350 kg | |
Knuckle | 16 t | 34.8 t·m | 15.9 m (1,450 kg) | 4,500 kg | |
Knuckle | 20 t | 42.3 t·m | 16.6 m (1,910 kg) | 4,900 kg | |
Knuckle | 25 t | 53 t·m | 18.0 m (2,000 kg) | 6,474 kg | |
Telescopic | 2 t | 4.2 t·m | 8.2 m (250 kg) | 830 kg | |
Telescopic | 3.2 t | 6.8 t·m | 10.5 m (200 kg) | 1,250 kg | |
SQ4SA3T | Telescopic | 4 t | 10 t·m | 8.0 m (950 kg) | 1,500 kg |
Telescopic | 5 t | 12.5 t·m | 11.8 m (600 kg) | 2,100 kg | |
Telescopic | 6.3 t | 15.75 t·m | 12.6 m (600 kg) | 2,200 kg | |
Telescopic | 8 t | 20 t·m | 18.5 m (400 kg) | 3,250 kg | |
Telescopic | 10 t | 25 t·m | 15.5 m (1,050 kg) | 3,250 kg | |
Telescopic | 12 t | 33 t·m | 16.2 m (1,200 kg) | 4,050 kg | |
Telescopic | 16 t | 40 t·m | 22.3 m (1,050 kg) | 5,800 kg | |
Telescopic | 20 t | 50 t·m | 22.0 m (1,500 kg) | 6,950 kg |
For photos, full specifications and inquiries, visit the BOB-LIFT marine cranes category.
A knuckle boom is usually the better fit for a small or crowded deck. It folds against its column when stowed and can place loads into holds or under obstructions. A telescopic boom needs a clear run of deck to lower and rest its boom, but it reaches farther and, in BOB-LIFT's range from 4 t upward, has a higher lifting moment at the same rated capacity.
The first figure is the rated capacity, the most the crane can lift, available only close to the column. The second is the lifting moment, the load multiplied by its radius. On BOB-LIFT's 10 t knuckle model, SQ10ZA6TJ, the load chart gives 10 t at 2.0 m, 3.08 t at 6.49 m and 1.15 t at 14.68 m. Always read the load chart for the radius you need.
It depends on the model and boom type. In BOB-LIFT's range, the knuckle boom models reach 4.2 to 18 m and the telescopic boom models 8.0 to 22.3 m. At full reach they lift only a small part of their rating, between 200 kg and 2 t, so check the load at the reach you need.
It depends on the vessel. SOLAS regulation II-1/3-13, in force since 1 January 2026, sets certification, testing and maintenance rules for lifting appliances on ships covered by SOLAS. Many smaller cargo ships, fishing vessels and pleasure yachts fall outside SOLAS, but national or class rules can still apply. BOB-LIFT marine cranes are not class-certified, so confirm your vessel's requirements first.
BOB-LIFT marine cranes are hydraulic. Each model lists a recommended power, from 3.5 kW for the 0.8 t knuckle model to 55 kW for the 25 t knuckle and the 16 t and 20 t telescopic models, plus the hydraulic flow and pressure it needs. BOB-LIFT offers electric and diesel hydraulic power units, or you can check whether the vessel's own hydraulic system has the capacity.
Send the heaviest load, the radius you need it at, the vessel type and size, the planned mounting position and deck space, and the power available on board. With those details, BOB-LIFT can recommend a model and send its load chart. You can send an inquiry or contact the team.
The right marine crane is the one that lifts your heaviest load at your working radius, fits your deck when stowed and suits what your vessel can carry.
Choose a knuckle boom for tight decks and precise placement, or a telescopic boom for clear decks and longer straight reach.
Size by the load chart at your radius, not by the headline tonnage.
Confirm deck strength, stability, power supply and certification requirements before you order.
About the author: Achord is Product Operations Director at BOB-LIFT and has spent decades working with construction machinery products. The figures in this guide come from the load charts and specifications in BOB-LIFT's marine crane product manual, checked on 29 September 2026. Learn more about BOB-LIFT.
Tell us your heaviest load, working radius and vessel type, and BOB-LIFT will recommend a marine crane and send its load chart. Send an inquiry to get started.
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