thank you Martin Sir..
the used bow thruster was inspired by centrifugal pumps.. its one of my old idea.. its so effective in slow moving crafts.. its so easy and can add from things around us.. here i am adding the detailed step, of my new lobster boat, is also intended for rail model city.. its also slow.. so, you can see a motor is driving a gear, inside the hull, a brass rod is downed to the hull through a brass tube.. these brass rods are welding rods, that in 2mm dia, costing 20 Rs/- here.. for railings i use 1mm brass welding rods.. so no rusting issues.. then you can see a round base made of foam board, then a circle inside the foam board base, with four blades as an impeller.. then a casing with P V C pipe, with an opening at the front side.. this can also fix at back side, to avoid any induced drag.. but this craft is so slow, no problem with opening at front.. and last, a covering for the P V C pipe.. now time to function.. when the impeller start to rotate, water must throws through the opening, to the direction of the impeller.. so it makes a counter torque, that turns the craft.. more clearly.. if we looks from above the boat, and if the impeller rotating to star board direction, water will expelled through the star board side, forcing craft to turn to port side.. its so easy to add..