550 ft lbs of thrust is one horsepower
Sure you don't mean 55 lbs. thrust?
No, it is 550 ft-pds. per second. So, horsepower measures "work" where thrust only measures a static force . . . like someone leaning against a wall.
I haven't looked at the various converters but one HP = 735 watts. You can compare that to the wattage off numbers provided by Minn Kota and others to see what various sized trolling motors pull.
If you are just trying to figure out max speed, most TMs properly sized for a boat are designed to push around at about 5 mph I think.