My S29 came with a 9.9 Yamaha 4-stroke. The previous owner used her on a lake. I've found that the 9.9 is underpowered in a coastal area especially with a lot of current.
Just purchased a 20hp Yamaha w/remote control and will install in the next week or so. I've also changed the prop to a lower pitch as recommended by Yamaha for heavier boats.
The Yamaha 20 hp motor is a little heavier than the 9.9, but probably not as heavy as the 25 hp 2-stroke motor originally installed. I am concerned about the overall length of the shaft fitting in through the door opening when raised, but I'm willing to make a modification to the stern if necessary in order to gain the needed horse power.