Mercury 30 Service Manual page 28

After initial propeller installation, the following
3.
common conditions may require that the propel-
ler be changed to a lower pitch:
Warmer weather and great humidity will
a.
cause an RPM loss.
Operating in a higher elevation causes an
b.
RPM loss.
Operating with a damaged propeller or a dirty
c.
boat bottom or gear housing will cause an
RPM loss.
Operation with an increased load (additional
d.
passengers, equipment, pulling skiers, etc.).
90-826148R2 MARCH 1997 IMPORTANT INFORMATION - 1C-5