Best all around performance is achieved when wide-open-throttle
(WOT) engine operation occurs at the top of (but within) the
wide-open-throttle RPM operating range designated by the
manufacturer for that specific engine. The WOT RPM operating range
can be found in your owners manual. Improperly propping an engine
can not only reduce performance but in fact damage the engine.
An engine that does not reach the rated RPM at wide-open-throttle is
"overproped". This will cause an excessive load through the entire
RPM range from idle to WOT, not just at wide open throttle "WOT".
This "lugging" puts a tremendous load on the pistons, crankshaft, and
bearings.
On the other hand, an engine that revs past the recommended WOT
RPM is "underproped" and can cause damage when operating past the
WOT RPM range. This also creates less speed at cruise RPM.
This is why it is so critical to be sure your engine is propped correctly
for your boat / engine combination and type of boating you want to do.
Using your existing propeller, determine the maximum RPM if you are
able to obtain it (it is best to use a photo tach if possible). If during this
test you begin to exceed the maximum rated RPM of the engine,
reduce the throttle setting to a position where the maximum RPM is not
exceeded. If you can exceed the recommended RPM of your motor,
you need to increase the pitch of your propeller. If you can not reach
your rated RPM's you need to decrease the pitch. Once your
wide-open-throttle RPM's falls within the recommended range of your
engine manufacturer, you have the propeller that is suited correctly for
your boat.
A properly pitched propeller will improve your fuel economy!
Frequently Asked Questions
Q: How much can you change the pitch on my propeller?
A: It truly depends on the individual propeller. Most typically,
propellers can be changed 2" up or down.
Q: Can one propeller give top speed, plus lots of power?
A: No. To gain high speeds involves sizes or pitch ratios unsuited to
load carrying or working conditions. Decide what is most important
and select the propeller accordingly, or change propellers with boating
conditions.
Q: What prop is best suited for MY boat?
A: Much more information is needed before an accurate propeller can
be determined for your application. Call a prop shop for propeller
sizings.
SEA DOCK DIVERS
