Fleet sizing for offshore supply vessels

Supply vessels provide offshore installations with necessary supplies on periodic basis from an onshore base according to weekly sailing plans. Each plan is built for a certain time horizon to guarantee required level of service to offshore installations at least cost. In a sailing plan several voyages are assigned to each vessel. The execution of sailing plans is affected by stochastic weather conditions. A vessel may not perform all visits within the planned voyage duration because of bad weather influencing vessel’s sailing and service time. In such cases, additional vessels may be needed. Deciding on the number of supply vessels to hire on the long-term basis is an important part of the strategic fleet size planning. We present a discrete-event simulation model that evaluates alternative fleet size configurations of vessel fleet size for an annual time horizon.