CONTINUOUSWAVE

Q1: will a recent model year Yamaha F25 long-shaft engine with power trim and tilt be a good choice for use on a 1987 SPORT 13?

I am replacing a Johnson 40-HP [two-stroke-power-cycle engine] that has seen better days. A believe a SUPER SPORT 13 weighs 580-lbs.

BACKSTORY
I may buy a used [unspecified model year] Yamaha [F25 four-stroke-power-cycle] engine that a seller states has only 50-hours of run time, has power tilt and trim, and is selling for $3,000.

While growing up I knew several people who had 13-foot Boston Whaler boats with 25-HP engines.

Also, in some jurisdictions the maximum [boat] engine horsepower that can be operated without possessing a license is 25-HP.

I believe that in the state of New Hampshire if you are over 12-years-old you are "fine" driving a boat with 25-HP.

pufferfish wrote:Q1: will a recent model year Yamaha F25 long-shaft engine with power trim and tilt be a good choice for use on a 1987 SPORT 13?

If your goal is to buy an engine for the 1987 SPORT 13 so it will be powered by no more than 25-HP, and also you want a four-stroke-power-cycle engine, the Yamaha F25 is probably a good choice. However, in changing to a 25-HP four-stroke-power-cycle engine from a 40-HP two-stroke-power-cycle engine, you should prepare for a significant decrease in performance.

The classic Johnson 40-HP engine most likely provided a wider RPM range for its power rating, and, most significantly, could produce more power at lower engine speeds than the typical modern four-stroke-power-cycle engine that is using natural aspiration, that is, no forced air induction.

Also, if the engine weight of the new engine is greater than the old engine, the added weight will also tend to reduce performance. You may have a double-negative: more weight and less power. The effect will be most noticeable in the ability to get on plane with added persons aboard, as well as reduced top speed.

pufferfish wrote:While growing up I knew several people who had 13-foot Boston Whaler boats with 25-HP engines.

I would expect that if your were growing up more than 20-years ago, most of those 13-footers would have had two-stroke-power-cycle 25-HP engines.