A vessel of 8000 tonne displacement has 75 tonne of cargo on the deck. It is lifted by a derrick whose head is 10.5 m above the centre of gravity of the cargo, and placed in the lower hold 9 m below the deck and 14 m forward of its original position. Calculate the shift in the vessel's centre of gravity from its original position when the cargo is: (a) just clear of the deck (b) at the derrick head (c) in its final position.

A vessel of 8000 tonne displacement has 75 tonne of cargo on the deck. It is lifted by a derrick whose head is 10.5 m above the centre of gravity of the cargo, and placed in the lower hold 9 m below the deck and 14 m forward of its original position. Calculate the shift in the vessel's centre of gravity from its original position when the cargo is:

(a) just clear of the deck

(b) at the derrick head

(c) in its final position.

Reference: REED'S NAVAL ARCHITECTURE FOR MARINE ENGINEERS (4^th edition), Exercise – 4.7

 

Solution:

a)

Shift in KG = mass moved*distance moved/displacement

                   = 75*10.5/8000

                   = 0.098 m up

b)

Rise in KG = 0.098 m

c)

Change in KG = mass moved*distance moved/displacement

                        = 75*9 / 8000

                        = 0.0844 m down

Change in LCG = mass moved*distance moved/displacement

                          = 75*14 / 8000

                          = 0.1313 m FOR