Join Date: May 2002
Thanked 32 Times in 30 Posts
Rep Power: 14
You should get a motor that is matched to the task. A motor that is too powerful will cost you more when you buy it, and it'll use more fuel throughout it's lifetime. A small motor will push a displacement boat up to hull speed fairly easily, but it takes an inordinate amount of power and fuel to make it go any faster than hull speed. Your boat's hull speed is a little over 6 kts., and the 15 hp. motor won't push it any faster than the 9.9. The extra 5 hp won't help you.
I had a 7.5 hp motor on a 25 ft boat that I'm sure is heavier than your C&C, and it pushed the boat to hull speed (slightly over 6 kts.) with power to spare. The 9.9 would be more than enough. I suggest you get the 9.9 with an extra long shaft.
I wouldn't be surprised if you would occasionally encounter 6 kt currents in your area, and in that much current, the 15 wouldn't be any more likely to get you through than the 9.9. I tried to pass through a bascule bridge in Florida once, and the 38 ft. boat's 55 hp diesel was barely able to push the boat through, against about a 7 kt. current. If you steer the boat out of the deeper water, and into as shallow water as you dare, the current will be weaker, and you might be able to get through.