I have seen these in catalogs. They look like a cylinder with a prop on each end. They fasten to your stern board and help control the back end of boat . I see stern thrusters for very large boats in the catalogs , but not what im looking for . I really dont know what they would call them . If anyone knows where i could find one , who makes them ,and what they call them. The last one isaw was a minnkota. But that has been a long time ago. Any help would be appreciated