Q: When using #TANKER why do I sometimes get current and wind forces in a direction opposite of what I expect?
REV 5.03

A: This is a function of the OCIMF data. #TANKER uses the curves proposed by the Oil Companies International Marine Forum (OCIMF) which were based on extensive wind tunnel and tank tests on typical tankers and published in the book, "Prediction of Wind and Current Loads on VLCCs" (now in its second edition, 1994). We have incorporated digitized versions of these curves into MOSES; therefore, what is derived is essentially what was measured. The question now becomes why are these forces in a direction which surprise you - the answer is probably lift, but this depends on your expectations. The hull will behave like an aerofoil where the flow does not separate immediately at the bow (and particularly if it is cylindrical as far as wind loads are concerned). As a consequence, the longitudinal force components may be "negative"; i.e. up current or upwind, for some directions. Rest assured, however, the resultant force is always downweather - there is a net drag!