Hello,
I have yet to measure current draw with the 45mm/#174 prop. If weather permits I might be able to do this on Sunday.
You are indeed right that the motor itself requires quite some power to get moving. With the 40mm/#147 prop, at 40-45% throttle (my usual sailing speed) current draw is 1.7A (2.20A total - 0.50A idle power draw for BEC and ESC fan). And from spec sheets it is not uncommon to have 1-1.5A at no load. So yes you're probably right that the first amp or so is eaten up by the motor itself. And slow speed can be seen as "no load".
I'm going with bigger motor because most low-KV motors on HK tend to be bigger. On my future twin-screw springer with 4240-620kv motors I'll probably end up with 2x2A of "base" draw. Current plans call for a 10AH battery. In terms of weight/ballast I could probably afford twice as much but I might have form factor/battery shape issues. And even with a 10AH battery I think I'll be able to pull of over an hour of constant sailing.
Robbe has smaller (36mm) slow-kv motors: 100kv, 300kv, 500kv.
They also have a nice small 28mm 750kv which would be ideal for a springer. Problem is: they 2 or 3 times as expensive as HK's "bigger" motors ...
Under usual conditions (ie: sailing alone, recovering stranded / flipped boats at the pond) I can't see any difference between the 45mm/174 and the 40mm/147. We didn't have enough time at
Bateaux en Fête to experiment with different props towing mengam's
Spirit where I think the prop type would make a difference.
On the other end of the spectrum, I'm working on a micro-springer, around 18.5cm x 8cm. Will be 3D printed. Brushless powered of course !