Blue Sky (Nordic Tug 42) came with a Twin Disc trolling valve. As idle speed is approaching 4 knots, if I have folks fishing in the cockpit I engage the valve to bring the speed down to around 2 knots, which makes them happy. The throttle is not touched until the valve is disengaged, and fortunately I also have an indicator light at the helm that lights up when the valve is engaged.
Talking with a seasoned Lugger repair shop owner, I was told that as long as I kept the engine RPMs low there should be no problem.
Another not so seasoned mechanic suggested that I could use the trolling valve for low speed maneuvering at the dock. A really dumb idea.
Campbell River BC