The crane

Crane regulations and capacity ratings

Before using a land-based mobile crane in a vessel application, review the applicable regulations and standards where the application will take place.

Crane manufacturers may have or create special capacity ratings for their cranes when being operated on vessels. These ratings might permit the crane to operate at a greater incline than when operating on land.

It is recommended to consult the crane manufacturer to get the capacity rating of the crane and any configuration limits for the lifting operations on the vessel. If a crane manufacturer’s capacity ratings are unavailable, a qualified person should be consulted. They should provide appropriate capacity reductions and any changes to the allowable configurations of the land-based capacity charts. Local regulations are to be followed.

List and trim angles

A manufacturer’s special ratings take into account the effects of greater list and trim angles that may effect the crane while being operated on a vessel.

The crane list will induce:

• lateral forces on the boom
• superstructure
• slewing mechanism.

Example of list causing an offset load

The crane trim may increase the operating radius of the load in relation to the crane. This increases the minimum attainable load radius. Increasing the minimum attainable load radius decreases the allowable capacity of the crane.

When used on vessels, these ratings may also limit the use of:

• specific boom lengths
• crane configurations
• attachments.

Example of trim causing an increase in load radius

During planning, it is important to analyse the resultant of the list and trim changes to the vessel and the crane. A list/trim measuring and indication device should be visible to the operator. This is to make sure the crane is not operated outside of the allowable inclinations as given on the special capacity chart.

Crane operation, such as lifting/lowering load or slewing, impacts list and trim angles of the vessel. This also has an influence on the actual crane radius. If the inclination of the vessel increases, although the luffing gear is not operated, the crane radius increases and vice versa.

Slewing the crane

Slewing the crane can also influence the radius. For example, if the loaded crane slews from a position with the boom parallel to the longitudinal vessel side (more stable side) to the transverse side (less stable side), the crane radius increases. The image below shows this effect:

Relation between radius and vessel heel

This sometimes means that when working at a high rated capacity use, the limitation of the crane’s rated capacity system could be activated during rotation.

For cranes that have slew limiting available, there is also a risk that the following crane functions may stop due to a rated capacity system limitation:

• the slew motion
• boom hoist
• load hoist.

Indications from the rated capacity system should be monitored. Corrective action should be taken when necessary.

All changes in inclination caused by the operated crane should be adjusted to minimise side and/or longitudinal pull that could result in a possible load pendulum during lift off.

Relation between load movements and vessel heel

Preserving the crane

Cranes used in seaport areas or inland areas near shore can become corroded. The negative effect of corrosion on exposed crane parts needs to be taken into account.

It is recommended to take protective measures against corrosion. These methods could include:

• wrapping machine parts
• applying protective coating.

An increase in the inspection and maintenance schedules may also be required. As an extra measure, and if not already required, the functioning of the following parts should be checked on a daily basis:

• limiting switches
• load sensors
• anemometers.

Multiple crane operation

Multiple cranes operating on one vessel at the same time can impact vessel inclinations. The vessel becomes unpredictable for the single crane operator. When multiple cranes are on a vessel, only one crane should be operated at a time.

Multiple crane operation of two or more cranes on two or more different vessels (for example, tandem lift from two different vessels) may result in unpredictable horizontal forces to the boom head. It is not recommended unless special preparations are in place.