|
This
is due to differences in lower unit gear ratios. Stock outboards
are geared so that the propeller shaft turns at a slower speed than
the rpm at the powerhead. This is usually expressed as a ratio such
as 12:21 or 14:28, referring to the number of teeth in the drive
gears. In the first example, the crankshaft gear has 12 and the
propeller shaft gear has 21. This means the propeller shaft turns
only 57% as fast as the indicated rpm at the powerhead.
The
lower the gear ratio, the larger the propeller that can be used
and vice versa. |
