The easiest solution to powering a self-launching boat would be for an upright motor at each corner and a separate means of propulsion altogether, as is common among a number of eVTOL designs. The alternative appears to be some number among which are motors able to be tilted to the horizontal for the purpose of hovering.
I think the latter is our preferred solution as things stand, because aviation invariably evolves as does nature toward a minimum of appendages, with apologies to millipedes who may be reading.
There is a precedent too for four-engined reconnaissance craft that shut down two of them to improve endurance, that being the military version of the first jet airliner in the shape of the Nimrod. Pilots of its forebear had been known to shut down two of the four engines in flight to conserve fuel and while it was debarred for commercial practise, the RAF continued the practise.
Above all however what I like about a 'leg' in each corner is that it means the airframe is perfectly balanced, which is a key desirable at the outset.
And consider the one successful VTOL jet fighter in the Harrier had... four nozzles.
