Since the resistance of water at zero speed is virtually zero, it takes almost no thrust to actually move a boat of any size. What you can't get with a small motor is acceleration and speed. As soon as the boat starts to move the resistance goes way up. However consider this. Most people would have a VERY hard time pushing with a100 lbs of force against a piling. Now imagine that you could do that, and do it continuously too. I think the reality is that even a small trolling motor will spin a 40 foot boat around a whole lot quicker than you might think! All of the issues come down to how to mount the thing. You only need to mount it sideways, and use forward and reverse if you just want to steer. It doesn't have to be centered either. So if you had a permanent stainless bracket with a wedge slot on one side of the bow, and a plug for the unit on deck, you could reach over the side and drop the motor into the bracket and plug it in when you needed it.