So, i've got a nice vintage Graupner Scimitar Speed boat (24 inch speedboat, shallow vee), with a horrible original Graupner 7022 setup, Speed 600 8.4v brushed motor with a really noisy 2:1 reduction gearbox. The motor gear has broken and beinh discontinued, i just cannot find a replacement anywhere. Performance with this setup, and using a 3 cell lipo is acceptable, but could be better. According to what i have found online, this motor is good for 15,500 rpm off load, producing 70 watts. This gives me 7,750 rpm at the shaft, again no load. The boat is running a graupner x35 prop.
My maths tells me that, eliminating the noisy gearbox, a 1000kv motor using the same 3 cell lipo should give me more final rpm i.e. better performance. And rather than 70 watts my guess is i need to look at 200 watts at least, on the assumption that the brushless motor, unlike its older brushed ancestor, will do its best to reach its designed rpm. Speed controller around 50A to be safe.
Are my workings ok here or am I missing something. I am also tempted to replace the ancient shaft with better Raboesch water lubricated shaft to do away with greasing, so open to prop suggestions as well.
Thank you
Chris from the little sunny island that is Malta.