Thursday, 21 June 2012

Lifting Operations in ship

 Lifting Operations in ship
Lifting Operations in ship
The following contains subjective comment on lifting operations with the Grove AT1500, telescoping crane with flyboom It does not constitute a set of instructions and does not supersede in any way LOLER of other lifting operation regulations. In addition there are several factors such as outrigger extension, outrigger pad size and ground state which have been specifically excluded as they apply only to a shore based lift. We assume that the counterbalance weight is fixed and that the stability area of the load capability chart does not apply
In addition not considered here is the trim of the vessel although this will have an effect and should be considered

Crane Mounted Load Computer

The Grove Crane has a load computer which measures the load weight, Boom Extension and Boom angle. Form this it can compare computed load against a model stored within its memory. As the load approaches overload alarms are sounded. The computer has an extra mode which takes into account operation with the flyboom. This load computer is there as a safety factor and in no way should be considered to replace proper planning.

Lifting operations.

    To carry out a safe lifting operation a set of variables must be known; these consist of the following
      The weight of the lift.
    • The height of the lift
    • The Radius of the lift
    • Obstructions within the lift area
    • The Sea State

Weight Of lift

This may be either a known weight i.e. a weight which is certified and clearly marked, or an unknown estimated weight- in which case the weight is estimated and a factor of safety applied
    To be added to the lift weight is the weight of the hook and lifting accessories before calculations are carried out. For the hook this is given as a test weight of
    • 0.20 tonne for 10t hook and headache ball
    • 0.65 tonne for 50t 3 sheave block
Note that unless the lift weight is certified it is always classed as estimated in all circumstances.

Height of the Lift.

Note this is measured form the boom pivot point and not the deck. The height of the pivot point above the deck is 4.2m

Radius of Lift

In a similar fashion the radius is measured from the pivot point and not the centreline of the crane. The distance from the pivot to the centreline is 2.1m

Obstructions within lift area

The area not only where the load will be lifted and put down, but also the area covered whilst the crane is slewing. Should this be of particular concern a lifting plan should be created and discussed with the crane driver highlighting areas of concern and how best the Crane drive may avoid them. It should be understood that the crane driver may be unsighted of some of these obstructions therefore where this is considered to be a high risk a lift supervisor should be designated to guide the crane driver at all times. Special consideration has to be given to lifts of unusual shape or where spreader bars are in use.

The Sea State

Vessel lift operations differ from shore based operations in that dynamic load forces have to be taken into consideration. The worst sea state condition considered to occur during the whole operation should be used and lift calculations based on that The Dynamic Loading factor stated in QGPS Lifting Equipment Regulations is 2.4 times for routine loading/unloading. A factor of 1.35 may be applied after written consent. maximum wind speed is given as 25knots and maximum wave height of 2m

Lifting tackle Inspections

A lifting tackle inspection by a competent person is required on all lifting accessories every 6 months. However, it is also required that all lifting accessories are examined for defects before use and this includes all crane operations. Appendix C gives a listing of the failure parameters applicable to typical lifting accessories

Worked Example

A load of estimated weight 3 tonne is to be lifted from a platform at a level of 20m above sea level. The vessel can manoeuvre so that the base of the centreline of the crane is within 20m of the lift. The sea state is calm

Lift Weight

The weight is a estimated 3tonne lift with a 100% factor of safety this gives a weight of 6 tonne for calculation. The 10 tonne block is fitted adding 0.2 tonne. The lifting accessories are estimated at 0.1 tonne. This gives a total weight to lift of 6.4 tonne

Lift Height

The height of the lift above sea level is 20m. The freeboard is 1.5m and the crane pivot is 4.1m above the deck This gives a lift height of 14.4m

Lift radius

The Lift is 20m from the centre line. The pivot is 2.1m behind the radius therefore the lift radius becomes 22.1m


The lift is clear of obstructions. However to clear the lift and ensure that the accessories are properly placed the Gib head has to be 2m above the lift. This changes the height of the boom to 16.4m

Calculation of Boom extension

The easiest way to do the following is with graph paper with suitable scaling

however it is possible to calculate the required boom length.

Checking the Cranes Capability

We now look at the Lifting capacity chart for the crane

. Here we can see that at 20m radius/28.04m boom extension the lift capability is 11.9 tonne. For a 22m radius with same boom extension the lift capability is 10.5 tonne. As are lift is 6.4 tonne the crane is suitable.
We therefore instruct the crane driver to Gib Up and Boom out to 27.5 m placing the Gib 2 metres above the lift
These instructions may also be used for shore crane operations. On the capability chart a darkline denotes the limit of stability and refers to lifting weights with the boom at right angles to the bed rather than over the cab. For shore operations the capability chart refers to full outrigger extension only and a separate chart must be in place if half outrigger extension is to be used

Effects of sea state

A set of Class approved Guidance charts indicate the effects of seat state on the lifting capabilities of the vessel. These supersede the lifting capability chart although they are for guidance and care must be taken to observe additional factors given by the crane manufacturer.

Fly Boom Extended

Extending the flyboom creates a special case. The flyboom is only used with all the sections at maximum extension. For this crane that is a boom extension of 42.76m. The lifting capacity chart now changes from a radius/boom length relationship to a boom angle/fixed boom length relationship. Again the required angle to check the capability of the crane can be found by either by use of graph paper or by calculation It should be noted that great care when operating with the flyboom extended must be taken to ensure that the crane is not overloaded something which is entirely possible even with no load on the hook when Gibbing down
In addition a Swing Away may be used which takes the form of a fixed boom that bolts to the jib head and generally sits at an angle to the boom.

The Effects of Dynamic Loading on the Lifting Capability of a Crane

For this document 'Dynamic loading refers only to the effects of movement of the vessel due to rolling only. The effects of Pitching, lift and lower acceleration and deceleration, relative movement between vessel and platform from which weight is being lifted or lowered to is not considered.

Effects of Heel Angle

As the crane comes under load there is a tendency for the vessel to heel towards the load. The effect of this is to increase the lift radius. This effects increases with increasing boom length.

Increase in Lift Radius = New Lift Radius R2 - Original Lift Radius R1
= LCos Ø2 - LCosØ1
= L ( Cos Ø2 - Cos Ø1 )
It can be seen that this effect increases with increasing boom angle.
For example with an original boom angle of 20o a heel of 5o will increase lift radius by about 3%
At 65o the same heel will increase lift radius by about 8%
Lift radius is computed as a function of Boom angle and Boom Extension only; no compensation is given for Heel. In such conditions Overload may occur and proper planning including a reduction in the Lift capacity should be made.

Effects of Rolling

The effects of rolling are two part;
Firstly they increase the Lift radius in the same fashion as described under 'Effects of Heel'.
Secondly they accelerate and decelerate the Gib head and thereby the Lift weight, as well as the main structure itself. All of which adds up to increased load on the crane. Considering the effect of the lift weight only

For example a max heel angle of 10o, radius of gyration 40m and a period of oscillation of 6s would cause acceleration of the head of about 0.4g increasing load due to weight by 2.5 to 3.5% dependent on Boom Angle
This effect increases with increase boom length and boom angle and worsening weather condition
The effect of this will be rapid transients in the indicated load on the computer; the effect of increased radius of lift would not be accounted for. In such conditions Overload may occur and proper planning including a reduction in the Lift capacity should be made.

Pendulum Effects on Weight during Rolling

The effects of this is to increase the radius of Lift as the weigh moves away from the Gib Head as well as to impart forces onto the Gib head for which it was not designed.
This action tends to increase with increased distance between gib head and load as well as rolling severity.
Please note that the above information is given without guarantee but based on my training as an Appointed Person.


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