That is undoubtedly a Hectoperm👍 Easily recognisable as the case extends right back to only a thin edge of the brush end cap. The Decaperms have a shorter body and different, wider, brush gear end cap with an earthing tag sticking out.
Pics attached of both Hecto (pic 1) and Decaperm (pic 2) courtesy of Jotika😁. Also of my Decaperm (pic 3), now sitting on the shelf after long since being removed from my 1960s 28" 2kg Sea Scout, where it provided very sedate performance🤔. Pic also shows current fit of a Propdrive brushless. Much zippier😊
I assume that your Hecto is the 6V version, based on your preference for onboard power stated below, and the 6V 6.5(?)Ah SLA battery in the background of your photo.
Therefore it's current draw at max efficiency ON load should be around 8A.
These Marx motors are built for torque and pulling power not for high revs and speed!
So I reckon your 6V Hecto should be fine to get your your 6kg freighter on the move.
Freighters of that era were not known for speed, maybe 16 - 18kn.
Accepted formula for max Scale Speed is the square root of scale x the max speed of the original in knots.
You didn't tell us the scale but I'm assuming 1:100, or 1:96 if imperial units.
For simplicity assume 1:100 and max original 18 kn.
Thus Max scale speed = √1/100x18 = 0.1x18 = 1.8kn.
Which equals a gentle stroll of 2.714mph😉
Or if you prefer 3.33kph, or roughly 1 metre per second😁
That hull can probably take a 6V 7-8Ah SLA without problems (better useful ballast than 'dead lead'😉) so I reckon you'll get well over an hour cruising (like I do with my 1.35m destroyer; 2 540s running on 2 6V 7Ah SLAs in series), or are you a 'pedal to the metal' kinda guy?😁
Hope this helps Mark.
Looking forward to the Sea Trial report👍
Stay safe🤞 and don't run aground!☹️😭
Cheers, Doug 😎