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Lifting Heeling Arm

Samet Yavuz
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Hi dear Friends,

When we prepare a stability model in the MAXSURF, we first -of course - define the weight items. In these weight items, we define the centers and weight values. 

For lifting operations to the side of the ship,

The Boom and Hook center and the load which to be lifted is entered STB or PT side with the values. 

Here comes the tricky part,

When we open the criteria window and define lifting heeling arm with weight and arms and run the large angle analysis, wouldn't we be adding that moment twice?

So what is the correct way to do it? Because if we remove the load and use only criteria window to apply the heeling moment, the Ship's parallel flotation will change.

This seems very basic question, but I somehow cannot solve it Disappointed

Thanks

Samet YAVUZ

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    Hi Samet,

    I think different class rules calculate this differently. Remember that there are many different types of lifting operations (slewing cranes, slewing cranes with slewing counter ballast, tanks for counter ballast, fixed cranes etc), so different rules are making different assumptions about which type of lifting is occurring.

    My overall view is that any load that is definitely there needs to be included in the loadcase. These are your passengers, cargo etc. Any loads that may be there, such as wind heeling or passenger heeling loads need to be accounted for in heeling arms because they are a transient load that may or may not be there at any given time.

    Taking passengers as an example. Their weight is included in the loadcase at their default position such that the vessel has the correct displacement and trim / heel. However if all the passengers decide to sit on the port side then we account for that potential using a heeling arm.

    A lifting operation where we lift from deck to wharf is similar to the passengers case. We have an initial loadcase with the weight item on deck and then apply a heeling arm of the item weight by the distance from its initial position to the maximum extension position (i.e. from 2m to port to 6m to starboard is an 8m heeling arm). This is what happens in the standard lifting heeling arm:

    Often rules are interested in the dropped load scenario, where the vessel is heeled to maximum and then the weight is dropped and the vessel rolls back, hopefully not capsizing. Most of the time the lifted mass is not significant to the mass of the vessel. However, sometimes class wants to know about the vessel before and after the dropped weight. Unfortunately in MAXSURF we can only model on GZ curve / displacement at a time, so to complete such a rule, you will need to extract the results to Excel and combine them there.

    So - for most cases. Add your lifted weight at its initial or final position and apply a heeling arm based on the maximum extension of the crane hook (change in horizontal and vertical position from initial).

    Regards,

    James

Reply
  • 0 Offline

    Hi Samet,

    I think different class rules calculate this differently. Remember that there are many different types of lifting operations (slewing cranes, slewing cranes with slewing counter ballast, tanks for counter ballast, fixed cranes etc), so different rules are making different assumptions about which type of lifting is occurring.

    My overall view is that any load that is definitely there needs to be included in the loadcase. These are your passengers, cargo etc. Any loads that may be there, such as wind heeling or passenger heeling loads need to be accounted for in heeling arms because they are a transient load that may or may not be there at any given time.

    Taking passengers as an example. Their weight is included in the loadcase at their default position such that the vessel has the correct displacement and trim / heel. However if all the passengers decide to sit on the port side then we account for that potential using a heeling arm.

    A lifting operation where we lift from deck to wharf is similar to the passengers case. We have an initial loadcase with the weight item on deck and then apply a heeling arm of the item weight by the distance from its initial position to the maximum extension position (i.e. from 2m to port to 6m to starboard is an 8m heeling arm). This is what happens in the standard lifting heeling arm:

    Often rules are interested in the dropped load scenario, where the vessel is heeled to maximum and then the weight is dropped and the vessel rolls back, hopefully not capsizing. Most of the time the lifted mass is not significant to the mass of the vessel. However, sometimes class wants to know about the vessel before and after the dropped weight. Unfortunately in MAXSURF we can only model on GZ curve / displacement at a time, so to complete such a rule, you will need to extract the results to Excel and combine them there.

    So - for most cases. Add your lifted weight at its initial or final position and apply a heeling arm based on the maximum extension of the crane hook (change in horizontal and vertical position from initial).

    Regards,

    James

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