Harbour Cranes

The harbour crane is a lynch pin of any port facility and as the fundamental purpose of each facility varies, so to do the basic models and functions of the harbour cranes present.

Depending on the cargo being handled, the cranes installed on a particular port facility would be tailored for the application. However, an attempt maybe made to generalize the different type of crane designs commonly found (the following is meant as a general summary).

Gantry Type

These cranes are best described as having a fixed air draft with their booms in the horizontal (or operational) position. The boom itself does not move relative to the vessel's holds, instead the crane would move the spreader (or grab bucket) to the cargo via a system of trolleys that move along the boom. Container cranes and bucket type shipunloaders are common examples.

Level Luffing Types

The main characteristic of these cranes are the fact that the hook platform remains at the the same level while the hook platform moves in or out relative to the rest of the crane (this movement is what is refferred to as luffing). Again, the air draft is fixed. These crane are commonly found with slewing rings to enable a versatile functioning unit. Typical of the catergory are the "horse head" design.

Shiploaders

These cranes take many forms and are usually custom built for the cargo to be loaded. For solid bulk cargoes, the basic design entails a conveyor belt along a boom that usually leads into a loading chute which is lowered into the cargo hold. Liquid bulk cargoes tend the have pumps and loading arms that transfer the cargo into the vessel's cargo storage tanks. Depending on the loading requirements, the air draft may vary.

Technical Knowledge

The following are some of the basic technical knowledge that is usually applicable to the above mentioned crane classes.

Mounting

Harbour cranes maybe either rail mounted or fitted with rubber tyres depending on the intended role and functions in a port.

Main Power

A harbour crane maybe powered via a high volatge power source or via diesel (liquid) fuels. Certain manufactueres also provide the option for both sources of power. Power to the winches maybe either AC or DC current.

Winch Motors

Many cranes use either AC or DC current to power their winches. In the latter half of the 20th century there was the belief that DC motors were better suited for winch applications over AC motors. However, with the advent of VFD's and well written PLC programmes, AC motors have gained ground. When both systems are compared to each other however, there are distinct benefits and drawbacks for each one. Eventually cost and application are the main deciding factors for most ports seeking a crane.

Brakes

Braking systems are a critical part of the crane and are the main safety system.