Hi guys
Can only agree to some contributions above: Deca was a "Mercedes" --- 25 years ago.
And is an old overpriced grandfather...
For myself, long time I prefered van motors from the junkyard.
(Nowadays it's not easy to get a cheap one there...)
In meantime i'm using industrial Buehler motors. Some shootings at ebay, and some bought here:
http://www.hobby-lobby-modellbau.com/onlineshop/product_info.php/info/p2893_B-hler-BB-Power-f-r-Gro-modelle--12-Volt.html/XTCsid/0b9b671ebfee2024dd501a9a6ed612bbIf you have enough mounting space and ballast of ~700gr : First choice!
No gear, no noise, 12pole-collector, 3300rpm. @12V (IMHO: 35W netto, 50W max)
Starts softly at ~3V/250 mA.
I'm using them in 2 ships, each with 2x 24V-types. and 70mm/75mm Raboesch props.
Each about ~65" and ~32 kg.
No heating, no problems. Current (combined, both motors) : Full throttle ~3A, if ship is fixed: ~4A
I think, this motor could easily drive your 3"4 blade. And 3300rpm is much enough for such a monster-blade ;-)
Pete