Repowering Your Boat:By Michael Vatalaro
What You Need To Know
Published: April/May 2013
There are many considerations when starting a repower project, including some that are unrelated to the performance requirements of your boat, such as having a local dealer or mechanic nearby for servicing that you like and trust. The following should give you a good starting point from which to plan your shopping list.
Transom Limitations: Space & Weight
The physical limitations of your transom will dictate how much horsepower and weight you can put back there. While modern four-strokes are getting close to their two-stroke counterparts in weight, they still will add to the load at the stern. If you were not running the maximum-rated horsepower in your previous set up, you may have some wiggle room, and be able to absorb some extra weight without impacting seaworthiness. It's a good idea to check with your boat builder what the design limitations were before you start shopping. Weight considerations could limit you to DI two-stroke technology.
Space is more of an issue if you are running twins (or more) because some of the high-horsepower modern four-strokes need more width between the engines, but not always. Honda, for example, designed their four-strokes to fit the standard footprint for easy repowers.
In addition, with the increased horsepower ratings available today, you may wish to switch from twins to a single outboard configuration. For example, swapping twin-150s for a single 300-hp motor, in theory, will reduce both weight and drag, which should increase fuel economy without sacrificing performance. However, boatbuilders caution that the increased power and torque of these modern, power-dense outboards can be too much for transoms that weren't designed for it. A safe bet is to limit horsepower to the highest horsepower single engine configuration offered as original equipment. The boatbuilder should be able to go into greater detail.
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