A watercraft vessel with at least one planing hull having on one or both sides of a keel region a bottom portion (5s,5b) and a side portion (4s,4p) between a bow and a stern, said bottom portion having at least one downwardly directed water-deflecting surface (9s,9p,10s,10p) which extends rearwardly and obliquely away from said keel region and will interact with the sea water when cruising at a planing speed within at least one predetermined speed range, characterized in that - said bottom portion is V-shaped and rises sideways upwardly from said keel region towards said side portion at a deadrise angle, relative to a horizontal plane, in the interval 5° to 70° so as to form, on each outer side of the vessel, a laterally rising bottom part, which is submerged in relation to an ambient water level at said planing speed and which has an approximately triangular outer boundary located adjacent to said water-deflecting surface (9s, 9p), - said water-deflecting surface (9s,9p), as seen from underneath and along a major longitudinal part thereof, extends at a lateral distance outside and substantially in parallel to said outer boundary of said approximately triangular bottom part of said bottom portion (5s,5p), - said water deflecting surface (9s,9p) faces inwardly towards said keel region and rearwardly towards said stern, and extends, as seen in a cross section through the hull, downwardly from the bottom portion to a lower longitudinal edge located at a higher level than said keel region and also at a higher level than said ambient sea level at said planing speed, so that the entire water-deflecting surface is located above said ambient sea water level, and - the distance of said water-deflecting surface (9s,9p,10s,10p) from said outer boundary is such that, when cruising at said planing speed, there is accommodated, laterally outwardly of said outer boundary, a spray area, which constitutes an additional wetted hull bottom surface area, where a lateral spray water stream is generated when the submerged bottom part meets the sea water at said planing speed and flows laterally outwardly and strikes against said water-deflecting surface, whereby said lateral spray water stream is deflected downwardly and rearwardly so as to generate a lifting force as well as a forward thrust on the hull. - said bottom portion is V-shaped and rises sideways upwardly from said keel region towards said side portion at a deadrise angle, relative to a horizontal plane, in the interval 5° to 70° so as to form, on each outer side of the vessel, a laterally rising bottom part, which is submerged in relation to an ambient water level at said planing speed and which has an approximately triangular outer boundary located adjacent to said water-deflecting surface (9s, 9p), - said water-deflecting surface (9s,9p), as seen from underneath and along a major longitudinal part thereof, extends at a lateral distance outside and substantially in parallel to said outer boundary of said approximately triangular bottom part of said bottom portion (5s,5p), - said water deflecting surface (9s,9p) faces inwardly towards said keel region and rearwardly towards said stern, and extends, as seen in a cross section through the hull, downwardly from the bottom portion to a lower longitudinal edge located at a higher level than said keel region and also at a higher level than said ambient sea level at said planing speed, so that the entire water-deflecting surface is located above said ambient sea water level, and - the distance of said water-deflecting surface (9s,9p,10s,10p) from said outer boundary is such that, when cruising at said planing speed, there is accommodated, laterally outwardly of said outer boundary, a spray area, which constitutes an additional wetted hull bottom surface area, where a lateral spray water stream is generated when the submerged bottom part meets the sea water at said planing speed and flows laterally outwardly and strikes against said water-deflecting surface, whereby said lateral spray water stream is deflected downwardly and rearwardly so as to generate a lifting force as well as a forward thrust on the hull.