Frequently Asked Questions
Q: How do I know if my propeller can be
repaired?
A: A maximum of one third of the blade can be replaced. Contact
us for further information regarding your particular situation.
Q: How much can I change the pitch on
my propeller?
A: It really depends on the individual propeller. Typically,
most propellers can be changed 1" up or 1" down.
Q: Can one propeller give top speed, plus
lots of power?
A: No. To get the highest speed possible, this may involve sizes
or pitch ratios that are unsuitable for the load carrying capabilities
or working conditions. Decide what is most important and select
the propeller accordingly, or change propellers with boating conditions.
Q: What is the purpose of the rubber cushion
hub in an outboard propeller?
A: The "hub" in the propeller protects the lower unit
parts by cushioning the shock of propeller impact. If impact is
severe enough, this "hub" can slip, and may have to
be replaced.
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
us for a FREE propeller sizing.
back to top
Common Propeller Terms
- LEADING EDGE - The edge of the propeller nearest to the boat
cuts through the water first, starting at the hub it extends to
the blade tip.
- BLADE TIP - This is the farthest point that a propeller extends
from the center of the hub to the outer radius of the blade.
- TRAILING EDGE - The edge of the propeller farthest away from
the boat where the water leaves the blade.
- CUP - The cup on a propeller is designed to help lock the propeller
in the water to reduce slippage and prevent cavitation. The cupped
area is located on the trailing edge of the blade starting approximately
1" from the hub extending outward to the blade tip.
- PUSHING FACE - This is the face of the propeller blade away
from the boat. More commonly called the PITCH FACE which faces
the pitch block when being repaired.
- NEGATIVE FACE - This is the face of the propeller blade toward
the boat.
- BLADE ROOT - The thickest area of a propeller where the blade
and the hub are joined together.
- HUB - The center of the propeller that fits over the propeller
shaft.
- OVER HUB EXHAUST - Exhaust gases flow over the hub and blades.
- THRU HUB EXHAUST - Exhaust gases flow through the hub to prevent
exhaust gases from flowing over the blades of the propeller.
- RUBBER HUB - Inner hub bushing made of hard rubber, moulded
to a splined spindle to protect the drive train when shifting.
- ACR/DIFFUSER RING - The flared ring used on through hub exhaust
propellers. The ACR/Diffuser ring prevents the exhaust gases from
backing up on the blades which produces cavitation during take-off.
- CAVITATION - The introduction of air on the propeller blades
resulting from running a damaged propeller, or from sucking air
from the surface of the water. A cavitating propeller is actually
slipping and produces very little thrust.
- PITCH - The theoretical travel of a propeller through a mass
per revolution. EX: A 19" pitch propeller moves forward approximately
19" per revolution.
- STRAIGHT PITCH - The pitch is constant or the same from leading
edge to the trailing edge of the propeller.
- PROGRESSIVE PITCH - The pitch increases from the leading edge
to the trailing edge. EX: Leading edge measures 17", trailing
edge measures 20" pitch - this is a 3" progressive pitch.
- VARIABLE PITCH - The pitch increases from the leading edge
to the trailing edge, and from the hub to the outer tip.
- RAKE - The angle of the propeller blade in correspondence with
the propeller shaft.
- FORWARD RAKE - Blades are angled toward the boat. Commonly
used for inboard propellers and small outboard propellers.
- AFT RAKE - Blades are angled back or away from the boat. This
type of rake is used to help lift the stern of the boat on take-off,
and on top end will help to lift the bow up - improving performance.
- PARABOLIC RAKE - The off center development of a propeller
blade used to make the rake concave or convex.
- DIAMETER - The overall width of a propeller.
- RIGHT HAND ROTATION - The propeller turns clockwise on the
shaft.
- LEFT HAND ROTATION - The propeller turns counter-clockwise
on the shaft.
back to top
How To Select A Propeller
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. Incorrectly propping an engine can not only reduce performance,
but, in fact, may damage the engine.
An engine that does not reach the rated RPM at wide-open-throttle
is in an "overpropped" condition.-- This will cause
an excessive load throughout the entire RPM range from idle to
WOT, not just at wide open throttle. This "lugging"
puts a tremendous load on the pistons, crankshaft, bearings and
the entire driveline.
On the other hand, an engine that revs past the recommended WOT
RPM is "underpropped" and can cause damage when operating
past the WOT RPM range. This also creates less speed at cruising
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 you
are able to obtain (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, you need to decrease the
pitch. Once your wide-open-throttle RPM falls within the recommended
range of your engine manufacturer, you have the propeller that
is best suited for your boat.
And remember that a properly pitched propeller will improve your
fuel economy and extend the life of your engine!
back to top
Useful Links
back to top |
