During the life cycle of a vessel a need for increasing the earning capacity of a vessel may arise. This could be achieved by increasing the maximum summer draught, which in many cases is fully possible by simple means! Imagine a medium-sized tanker for chemicals carrying caustic soda in a partially loaded condition. An increase of the maximum summer draught by 0.5 metres corresponds to an increase of approximately six per cent in the deadweight. The business case is even more attractive when there are a significant number of sister vessels in the same fleet and the same study may apply. The return of investment further improves when no structural modifications are necessary.
Assigning to a deeper draught is not considered a major conversion according to the unified interpretation of Annex I in the International Convention for the Prevention of Pollution from Ships (MARPOL). However a multidisciplinary study is still needed which involves freeboard calculations according to the International Convention on Load Lines, a stability analysis according to MARPOL and the International Bulk Chemical Code (IBC), where applicable, as well as a structural evaluation. Port limitations and individual flag state requirements must also be taken into consideration. More in detail, a draught increase feasibility study is initially carried out with respect to the load line, stability, strength and other relevant regulations to ensure safety and regulatory compliance.
A satisfactory result will then be followed by preparation of the documentation required for approval. Finally the approval phase will follow to verify compliance with the statutory and class requirements and issuance of the relevant certificates. Over the last three years DNV GL has handled around 30 draught increase projects. In one of these cases five medium-sized sister vessels of approximately 42,000 dwt capacity, operated by the same company, increased their maximum summer draught from 11.35 metres to 12.06 metres without any upgrading having to be done.
This corresponds to 3,660 tonnes additional load capacity, which means additional earnings – with only a small investment cost for performing the study, preparing the drawings and running through the approval process, all taken care of by DNV GL. Our goal is to help our customers to improve the efficiency and the earnings of their operations without any compromise on the safety standard, and indeed, evaluating the increased cargo capacity is one of them.
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Source: DNV GL, Tanker Update No1 2016