A number of incidents have occurred recently involving failure of the slew bearings of ships’ cargo deck cranes, resulting in crane losses and serious injury to personnel.
These failures have been caused by undetected excessive wear in the slew bearings.

Rocking tests
Crane manufacturers generally recommend that ‘rocking tests’ are carried out every six months in accordance with their instructions, and that the results are recorded and monitored in order to ensure the wear tolerances remain within the limits permitted by the designers.

Cranes which are particularly at risk are those with single ball race slew bearings. Cranes fitted with this type of slew

bearing must have rocking tests carried out, in accordance with manufacturer’s instructions, to determine that the amount of wear in the bearing races is within permitted limits.

Although cranes with single ball race slew bearings are considered to be most at risk, rocking tests on all deck cranes,

where recommended by the crane manufacturer, must be carried out and the results must be recorded.

Lloyd’s Register surveyors are being instructed to review the results of rocking tests at all future Annual Thorough Surveys.

If no rocking test has been carried out in the previous six months, the crane in question will not be certified for further use.

It will also be recommended that the crane is taken out of service and the Lifting Appliance Register will be endorsed accordingly.

Measuring proceadures for wear in slewing bearings for rope luffing cranes.

The slewing bearing is an essential part of the crane and must be well maintained.
Over the years the slewing bearing will have some wear, and to be able to know if there is a need for changing the slewing bearing it is needed to keep a record of the wear.

The measurements should be taken reqularly, every 6 months.
Measurements can be sent to the Maker for evaluation.

Note When measurements are to be taken the ship shall have as little list/trim as possible.

Attached you may find proceadures for Cranes Rocking test service information.
 

Infomarine On-Line Technical Library

File	Description	File size
Mac-GregorRocking.pdf		222 Kb
Rocking Test procedure - Tsuji Cranes.pdf	Rocking Test procedure - Tsuji Cranes	1978 Kb
rocking-test classification-letter.pdf	LR Classification News letter Deck crane slew bearing rocking tests	121 Kb