Engine and Boat Performance

Propeller Selection
Select a propeller that will allow the engine to operate at or near the top of the recommended full throttle RPM range with a normal load.
If the RPM is above the specified RPM, a propeller of the next higher pitch should be installed and tested.
If full throttle operation is below the specified RPM, a propeller of next lower pitch should be installed and tested.
For better acceleration, such as is needed in water skiing, propping to next lower pitch is recommended. However, do not operate continuously above the specified maximum RPM.

Common problems, which cause loss of RPM, may require a lower pitch propeller be installed.

a. Warmer weather and greater humidity.
b. Operating in a higher elevation.
c. Operating with dirty boat bottom.
d. Operating with an increased load (additional passengers,
        pulling skiers, etc.).

Refer to your Operation and Maintenance Manual for propeller removal and installation.

Propeller Repair

If your propeller should become damaged, it can usually be repaired at one of the authorized propeller repair stations. Your authorized servicing dealer can advise location and procedure for shipping propeller to be repaired.

IMPORTANT: When a stainless steel propeller is installed on your product, it may increase the potential for galvanic corrosion action. If a stainless steel propeller is used, some type of corrosion protection should be provided, especially in salt or brackish water. See your authorized dealer for more details.

Conditions Affecting Operation

Positioning of weight (passengers and gear) inside the boat has the following effects:

Shifting weight to rear (stern).

  • Generally increases speed and engine RPM.
  • At extremes, can cause boat to porpoise. Causes bow to bounce in choppy  water.
  • Increases danger of the following wave splashing into boat when coming off  plane.

Shifting weight to front (bow).

  • Improves ease of planing off.
  • Improves rough water ride.
  • At extremes, can cause boat to Veer back and forth (bow to steer).


To maintain maximum speed, the following conditions of the boat bottom should be observed:

  • Clean, free of barnacles and marine growth.
  • Free of distortion, nearly flat where it contacts the water.
  • Straight and smooth, fore and aft.


In some areas, it may be advisable to paint bottom to help prevent marine growth. Anti-fouling paints with a tri-butyl-tin-adipate base can be applied safely to the boat bottom. See your dealer for recommendations for your boat.

IMPORTANT: Do not use anti-fouling paints which contain copper
                         or mercury compounds, as they will increase the
                          rate of corrosion.

IMPORTANT: Do not paint anodes or Cathode system's anode and
                         reference electrode, if so equipped, as this will
                         render them ineffective as galvanic corrosion
                         inhibitors. Leave a 1" taped, break line between
                         bottom paint and drive units, trim tabs, sensors, etc.


Cavitation occurs when water flow cannot follow the contour of a fast moving underwater object, such as a gear housing or propeller cavitation permits the propeller to speed up but boat speed is reduced. Cavitation can seriously erode the surface of the gear housing or propeller. Common causes of cavitation are:

  • Bent propeller blade or damaged gear housing skeg.
  • Raised burrs or sharp edges on propeller or gear housing.
  • Weeds or other debris snagged on propeller or gear housing.


Ventilation is caused by surface air or exhaust gases which are introduced around the propeller, resulting in propeller speed-up and reduction of boat speed. Excessive ventilation is annoying and usually caused by:

  • Stern drive trimmed out too far.
  • A missing propeller diffuser ring.
  • Damaged propeller or gear housing which allows exhaust gases to escape between propeller and gear housing.

How Elevation and Climate Affect Performance

Elevation has a very noticeable effect on the wide-open throttle power of an engine. Since air (containing oxygen) gets thinner as elevation

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