In smaller double hull tankers the two longitudinal divisions are omitted from a single centre tank and hence the free surface effect is increased.
Due to the second outer hull the centre of gravity of the cargo is raised causing a reduction in GM.
Oil carriers of 5 000 tonnes deadweight and above and delivered after 1st February 2002 shall comply with the intact stability criteria as specified in MARPOL Annex I, Reg. 27.
For ships loading and or offloading in port only, the GM corrected for free surfaces measured at 0° heel shall be not less than 0.15 m.
In practice the resulting GM in modern smaller size (Panamax) double tankers are very near to the above value.
