A crane for a small vessel performs a different function from a crane on a ship. On a fishing boat or a harbour workboat, the deck is short, the crane’s own weight is significant, and the engine has to drive the hydraulics as well as the propeller. The advertised maximum tonnage is rarely the figure that determines whether a crane is suitable for your vessel.
This guide explains the calculations that determine the size of a small boat crane for a fishing boat or workboat. They cover how far you need to reach, what the crane weighs, how much hydraulic power the boat can supply, whether you need a winch, and how the crane is mounted. Achord Chan, Product Operations Director at BOB-LIFT, compiled it from the technical drawings of our nine smallest marine cranes, 0.8 t to 5 t, and from videos our customers sent from their boats. Every crane specification below is reproduced directly from those drawings.
Key takeaways
- Size a boat crane from the load you lift at the furthest point you need to reach, not from its maximum capacity.
- Our 0.8 t knuckle boom marine crane lifts 800 kg at 1.34 m but 220 kg at 4.15 m, so check the required reach over the rail before comparing capacities.
- The crane’s own weight sits high above the deck: ours range from 220 kg (0.8 t) to 2,120 kg (5 t); ask your naval architect to check stability.
- Small cranes require relatively little hydraulic power: from 3.5 kW and 8 L/min for the 0.8 t model to 22 kW and 35 L/min for the 5 t.
- A winch lets the hook go below deck level, into the hold or the water. Two of our smallest models slew 330°, not 360°.
What is a boat crane?
A boat crane is a deck-mounted crane small enough for a fishing boat, workboat or similar small vessel; buyers also call it a boat mounted crane or a small boat crane. The name covers two kinds of machine. First, a davit is a fixed or swinging arm, often manual or electric, used to launch a tender or lift light loads. A hydraulic boat crane has a slewing column and a powered boom, so it can pick a load off the quay, swing it over the deck and set it down where you want it.
This guide is about hydraulic boat cranes: knuckle boom and telescopic boom cranes from 0.8 t to 5 t. If you only need to launch a yacht tender, a davit or tender crane is usually simpler; if you load gear, catch or cargo, read on. For larger vessels, our marine crane buying guide covers the full range up to 25 t.
Another search term causes confusion, because a boat lifting crane is a hoist, travel lift or yard crane that lifts a whole boat out of the water for storage or repair. That is a different machine from a crane mounted on a boat, and we do not build boat hoists. A hydraulic boat crane can lift a small tender or dinghy only if its weight at that reach is within the crane’s load chart.
How far does your boat crane need to reach?
Start with reach, because a crane’s maximum capacity only applies close to the column. Measure from where the crane’s slewing centre will stand to the furthest point you need to lift from: the quay edge when the boat lies alongside, the water beyond the rail, or the far corner of the hold. Then identify the rated capacity at that operating radius.
Consider how steeply the rated load falls: our 0.8 t knuckle boom marine crane lifts 800 kg at 1.34 m, 450 kg at 2.25 m and 220 kg at its full 4.15 m reach. If the crane stands 1.5 m in from the rail and you need to land a load 2 m out over the quay, you are working at about 3.5 m, where it lifts less than 300 kg. Our SQ1ZA3TJ+1 (1,600 kg max) on the same spot lifts about 450 kg; a 2 t knuckle boom lifts over 1,000 kg.
The table below gives the rated load at minimum and maximum reach for our small marine cranes, and each figure is taken directly from the corresponding model’s technical drawing.
| Model | Boom | Max load (at reach) | Load at full reach | Crane weight | Slewing | Winch | Base (bolt holes) |
|---|---|---|---|---|---|---|---|
| SQ08ZA3TJ+1 (0.8 t) | Knuckle | 800 kg at 1.34 m | 220 kg at 4.15 m | 220 kg | 330° | Yes | Ø280 mm flange (12 × Ø14) |
| SQ1ZA3TJ+1 (1.6 t) | Knuckle | 1,600 kg at 1.39 m | 300 kg at 4.23 m | 380 kg | 330° | Yes | 328 × 328 mm (12 × Ø18) |
| SQ2ZA2TJ (2 t) | Knuckle | 2,000 kg at 2.0 m | 750 kg at 5.1 m | 590 kg | 360° | Yes | 780 × 500 mm (20 × Ø21) |
| SQ2SA3T (2 t) | Telescopic | 2,000 kg at 2.0 m | 250 kg at 8.2 m | 830 kg | 360° | No | 500 × 500 mm (16 × Ø22) |
| SQ3.2ZA3TJ (3.2 t) | Knuckle | 3,200 kg at 2.1 m | 680 kg at 7.7 m | 1,236 kg | 360° | Yes | 550 × 550 mm (16 × Ø21) |
| SQ3.2SA4T (3.2 t) | Telescopic | 3,200 kg at 2.2 m | 200 kg at 10.5 m | 1,250 kg | 360° | No | 550 × 550 mm (16 × Ø22) |
| SQ4ZA3TJ (4 t) | Knuckle | 4,000 kg at 2.1 m | 850 kg at 7.7 m | 1,256 kg | 360° | Yes | 550 × 550 mm (16 × Ø21) |
| SQ4SA3T (4 t) | Telescopic | 4,000 kg at 2.5 m | 950 kg at 8.0 m | 1,500 kg | 360° | No | On quotation drawing |
| SQ5ZA3TJ (5 t) | Knuckle | 5,000 kg at 2.1 m | 1,100 kg at 8.05 m | 2,120 kg | 360° | Yes | 680 × 680 mm (24 × Ø22) |
If you have not read a load chart before, our guide on how to read a crane load chart explains reach, boom angle and deductions step by step, and the same principles apply on a vessel. The base sizes matter for mounting: even our 0.8 t crane bolts down through 12 holes, and the deck under it has to carry its overturning moment. Our pedestal crane guide explains flanges, bolts and foundation loads in detail.
How heavy is the crane, and can your boat carry it?
On a truck, crane weight is mostly a question of axle loads, whereas on a boat it is primarily a question of stability. The crane is installed on deck, its boom extends well above the deck, and when it lifts over the side the load and the boom both move outboard. That heels the boat and raises its centre of gravity at the same moment.
Consequently, the crane’s own weight is as important as its lifting capacity: our 0.8 t crane weighs 220 kg and our 5 t knuckle boom weighs 2,120 kg. Before you choose, ask the boat’s designer or a naval architect to verify deck strength and stability with the crane at full reach and full load over the side. Your surveyor can confirm which stability rules apply when the boat lifts.
Two design points help here: first, a knuckle boom is usually lighter than a telescopic boom of the same capacity: our 2 t knuckle boom weighs 590 kg against 830 kg for the 2 t telescopic. And a knuckle boom folds low behind the column, so it keeps its weight close to the deck when it is stowed for passage.
Does your boat have the hydraulic power?
A hydraulic boat crane requires a supply of oil at the correct flow and pressure. On a small boat that usually comes from a pump driven by the main engine, a pump on an auxiliary engine, or a separate hydraulic power unit with its own motor. Whichever you use, it must deliver the flow and pressure the crane was designed for.
| Model | Recommended power | Oil flow | Working pressure | Oil tank |
|---|---|---|---|---|
| SQ08ZA3TJ+1 (0.8 t) | 3.5 kW | 8 L/min | 18 MPa | 20 L |
| SQ1ZA3TJ+1 (1.6 t) | 7.5 kW | 15 L/min | 18 MPa | 25 L |
| SQ2ZA2TJ (2 t) | 9 kW | 20 L/min | 20 MPa | 25 L |
| SQ3.2ZA3TJ (3.2 t) | 15 kW | 25 L/min | 25 MPa | 60 L |
| SQ4ZA3TJ (4 t) | 15 kW | 25 L/min | 26 MPa | 60 L |
| SQ5ZA3TJ (5 t) | 22 kW | 35 L/min | 28 MPa | 100 L |
| SQ2SA3T (2 t telescopic) | 8 kW | 25 L/min | 16 MPa | 60 L |
| SQ3.2SA4T (3.2 t telescopic) | 14 kW | 25 L/min | 20 MPa | 60 L |
| SQ4SA3T (4 t telescopic) | 16 kW | 25 L/min | 20 MPa | 100 L |
For example, a pump that delivers too little flow makes the crane slow, while excessive pressure, or an incorrectly adjusted relief valve, can overload hoses and seals. If the boat already has a hydraulic system for a net hauler or a winch, give us its pump flow and relief pressure and we will tell you whether the crane can share it.
One of our customers in Egypt took the separate route, and their photos of knuckle boom marine cranes on harbour workboats show SQ5ZA3T cranes on steel workboats. Each crane stands on a raised pedestal with a seat control station above the deck, and a hydraulic power unit is housed on deck beside it.
Knuckle boom or telescopic boom on a small deck?
Most small vessels are better served by a knuckle boom. It folds into a compact package when it is not working, so it leaves the deck clear for nets, pots, fenders and lines, and its jointed boom can reach down into a hold or over a high rail. Every one of our marine cranes below 2 t is a knuckle boom.
A telescopic boom provides considerable reach for its size, but relatively light capacity at that reach: our 3.2 t telescopic marine crane reaches 10.5 m and lifts 200 kg there. That configuration suits a barge or a quay where operators position light loads far from the crane. It suits a short fishing deck less well, because a straight boom stays long even when retracted and takes more deck length when stowed. For a full side-by-side, read knuckle boom vs telescopic boom; the comparison is written for trucks, but the boom behaviour is the same. If your vessel is a work barge or pontoon, our barge crane guide covers heel and long-reach lifts across a wide deck.
Do you need a winch?
Without a winch, the hook hangs from the boom tip, so the lowest point you can reach is set by how far the boom can go down. With a winch, rope pays out from the drum and the hook can go below the boom tip: into the fish hold, down to a boat alongside at low tide, or to the water to recover gear. On a working vessel, that capability is often the deciding feature.
In our model names, the letter J means the crane is fitted with a winch. Every knuckle boom model in the table above carries the J and is drawn with a winch drum; the telescopic models in the table are not. Ask for the winch’s line pull and rope length when you request a quotation, because the rope must be long enough for the deepest lift you plan.
Slewing range and crane position on deck
Slewing describes the rotation the crane can achieve on its column: our SQ08ZA3TJ+1 (0.8 t) and SQ1ZA3TJ+1 (1.6 t) knuckle boom marine cranes slew 330°; the rest of our marine range slews 360°. A 330° crane has a 30° sector it cannot turn through, so plan its position with that gap facing the wheelhouse or another area where you never need to lift.
Position also determines the reach you need on each side: a crane on the centreline reaches both sides but needs a longer boom to get over either rail. A crane near one rail reaches further over that side and less over the other, so mark the crane’s slewing circle on the deck plan, then mark every point you need to lift from.
Salt water, corrosion and rules for small vessels
Salt spray attacks paint, steel, fittings and electrical parts, so a boat needs a marine version of the crane, not a truck crane bolted to the deck. In our model designations, the suffix T identifies the marine version, so ask any supplier for the coating system, the hose and fitting specification and how electrical parts are sealed. Our marine crane buying guide covers corrosion protection in more detail.
Rules depend on the boat, its flag and its class; in the UK, for example, lifting equipment on ships and fishing vessels must be thoroughly examined before first use and periodically under MGN 332 [1]. SOLAS does not apply to fishing vessels of any size or to cargo ships under 500 gross tonnage (SOLAS Chapter I, regulation 3), but national rules or a classification society can still apply. Our marine cranes are not certified by a classification society, so if your vessel is classed, check the requirements with your flag administration and class before you order.
A six-step boat crane sizing checklist
- Heaviest load. Weigh it, including slings, baskets or a lifting frame.
- Furthest reach. Measure from the crane’s slewing centre to the furthest point you lift from, over the rail and into the hold.
- Load at that reach. Pick a crane whose load chart covers the load at that distance, with margin.
- Crane weight and stability. Give the crane weight and your worst lift to the boat’s designer or a naval architect.
- Hydraulic supply. Confirm that your pump or power unit delivers the crane’s flow and pressure.
- Winch and slewing. Decide if you need to lift below deck level, and where any slewing gap can go.
Frequently asked questions
What size crane do I need for a fishing boat?
Calculate it from your heaviest load and the furthest operating radius. For a fishing boat crane or small boat crane lifting crates, pots or nets close to the rail, a 0.8 t to 2 t knuckle boom crane is often enough. If you lift from the quay several metres away, you will need a larger crane than the load alone suggests.
What is the smallest BOB-LIFT marine crane?
The SQ08ZA3TJ+1 0.8 ton knuckle boom marine crane. It lifts 800 kg at 1.34 m and 220 kg at 4.15 m, weighs 220 kg, slews 330°, has a winch, and needs 3.5 kW and 8 L/min of hydraulic supply.
Can I put a truck-mounted crane on a boat?
We do not recommend fitting a truck crane to a boat, because a truck crane is not built for salt spray, and its controls, slewing and mounting are designed for a chassis, not a deck. Choose a marine version with appropriate corrosion protection.
Can a boat crane lift in swell or at sea?
Load charts assume the vessel is approximately level, whereas swell, heel and trim swing the load and add force to the crane and the hull. Operate in sheltered water whenever possible, and ask your supplier what heel and trim the crane’s ratings allow.
How do I mount a crane on a boat?
Bolt it to a steel pedestal or base that is welded to reinforced deck structure, never to a plain deck plate. Use the base size, bolt pattern and loads on the crane’s drawing, and have the boat’s builder or a naval architect design the reinforcement; our pedestal crane guide, linked above, covers the mounting details.
Why do fishing boats need cranes?
A crane takes the heavy lifting off the crew: on a fishing boat it hauls pots and nets, lands crates of catch onto the quay, and loads ice, fuel drums and stores. With a winch it can also recover gear from the water, which saves time in port and reduces manual handling injuries.
Ready to size your boat crane?
A boat crane that is too small for the reach, too heavy for the deck or too hungry for the boat’s hydraulics costs more to fix after installation than to choose correctly on paper. Send us the boat’s length and beam, a deck plan, your heaviest load and where you need to lift it, and your hydraulic supply. We will then suggest models from our knuckle boom marine cranes and telescopic boom marine cranes, with the load chart and base drawing for each. For larger vessels, see our deck crane guide, or contact us to start.
