Originally Posted by SURV69
I thought I read once that for slow speed, a larger electric motor
actually(or might), uses less wattage per hour.
Such that a 2k watt motor might push a boat at 3 knots using x wattage, while a 4k watt motor might push that same boat at 3 knots with less than x wattage.
Does anyone know if this might be true, cause if it is, it would give more reason for me to consider what I consider to be an oversized system.
I don't know ... and I'm not sure there are all that many people who do, particularly for small boats. In other words, this is naval engineering question because there are a lot of factors -- wattage, prop size, prop rotation, drag when/if under sail, mass, charge and discharge rates being the obvious but then there ones like balance of mass, wire runs, conversion rates, prop design and loads. All this has been done for years on huge boats but to my recollection it only has been going in earnest for cruising boats since about 2005 with a major industry hit happening since then so I don't think there are many with the combined experience.
Probably the most experienced group of hobbyists are on the Yahoo Electric Boats group
though most are experimenting with a large battery
bank powering the system (hybrid) vs using an generator
(or series of generators) to power the systems as is the case with the huge ships.