A lot depends on the particular type of Graupner motors - they made a wide range of sizes, and quite a few variations for each size.  Gearboxes speak of displacement hulls like tugboats, a fast boat like a PT really needs direct drive.<div>Ballast?  In a fast boat?  Only as a very last resort if it can't be trimmed any other way by resiting the battery or batteries.</div><div>A previous owner might have had the idea of running the wing motors off one ESC, and fitting a brushless motor to work the center prop that he never got round to fitting.  That could have been a bit of a handful off 2 channels.</div><div>Running 2 motors off one ESC is quite feasible providing the 2 motors are closely matched and the ESC is up to the job.  Running 2 ESCs off one Y lead is also feasible, provided that they both have closely similar responses.  With very basic 2.4GHz sets having 4 channels, separate control for 2 motors is a good option, shouldn't knock too big of a hole in the budget.</div>