  We derive analytical formulas for the wake and wave drag of a disturbance
moving arbitrarily at the air-water interface. We show that, provided a
constant velocity is reached in finite time, the unsteady surface displacement
converges to its well-known steady counterpart as given by Havelock's famous
formula. Finally we assess, in a specific situation, to which extent one can
rightfully use Havelock's steady wave drag formula for non-uniform motion
(quasi-static). Such an approach can be used to legitimize or discredit a
number of studies which used steady wave drag formulas in unsteady situations.
