I recently tried to use my short shaft 9.9 Merc. 4 cycle on my V21. I was not happy with the results. The motor sat so low in the water on the lower mount adjustment that water was all the way up to the bottom of the engine, the mount is not stable, it moved side to side and the tiller was at such a angle that steering at anymore than half throttle would have been a problem. What has worked for you guys? Maybe the upper notch on the mount would be better? I know a smaller engine with a long shaft would be the best answer but I do not have a extra thousand laying around. I have seen some boats with a fixed motor mount that extends maybe a foot away from the transom, was this custom made?