The one on the Airboat came from BRC Hobbies and is an A2814-5T 1660Kv 350W and turns a 7X4 prop, guessed about right with this one as the boat goes like s--t off a shovel, well it did till I hit a buoy
( new boat nearly finished )
The one in the MTB well I didn't guess very well with this one, the boat is very light being made of balsa and the XYH35-30 1400Kv 340w from Giant Cod makes the boat leave the water. Going to try it with less volts tomorrow and see how that is, if still to fast I will get a smaller prop at Blackpool, if all fails to slow it down to something I can handle I will have the plans enlarged by 50 per cent and build a bigger boat
Brushless motors are a big learning curve for me
The ones in your post seem Ok at that price, water cooled as well, just turn my boats upside down for cooling
Alan