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Everything You've Always Wanted To Know About Boat
Propellers.
Boat Propellers and finding the "Perfect Prop" for your boat can be
confusing so let's have a quick look at the basics.
How Do Boat Propellers Work?A boat
propeller rotates ... the blades of the boat
propeller push water in one direction causing boat
movement in the opposite direction.
As the boat propeller pushes
water back a vacuum is created on the forward side of each
propeller blade. This vacuum pulls on the boat
propeller blade and helps move the boat forward.
The strength of the vacuum increases
as the boat propeller spins faster ... pushing a
greater volume of water back ... both effects combining to
increase the forward speed of the boat.
How Are Boat Propellers Identified?
Propeller sizes are identified with two numbers ... usualy expressed in inches.
The first number is the diameter of the propellerand the second number is the pitch.
The pitch is the theoretical distance a boat propeller moves forward in one revolution.
So ... if you have a boat propeller with a diameter of 14 inches and a pitch of 18 inches the propeller configuration would be "14x18"
Pitch is the second number listed in the propeller description.
Outboard PropellersThe
centre part of an outboard propeller is called the
"hub." This is the part which connects the outboard
propeller to the propeller shaft.
The image above illustrates a thru
hub exhaust outboard propeller in which the engine
exhaust flows through the outboard propeller.
This is the style of most of today's
outboard propellers including an Evinrude propeller, a
johnson propeller, a Honda propeller, a Johnson propeller, a
Mercury propeller, a Mercruiser propeller, a Mariner
propeller, a Cobra SX propeller, an O.M.C. Cobra 800
propeller, a Suzuki propeller, a Volvo Penta propeller, a
Volvo S.X. propeller, a Yamaha propeller plus a Tohatsu
propeller ... in fact just about any brand of modern outboard
propeller and most sterndrives.
They are easily identified by the
barrel around the hub to which the outboard propeller
blades are attached.
Outboard Propeller Facts.Propeller
design has managed to keep pace with technology over
recent years while the design of boats has changed
significantly and the development of outboard
propellers has been dramatic.
In
spite of those improvements ... the three key factors
affecting the performance of your boat have not changed.
We're talking about weight
... horsepower and the outboard propeller.
Making a boat lighter or buying a
more powerful outboard motor just to improve
performance or economy are options most people would not
consider.
This only leaves the all
important outboard propeller so lets look at the basics
and discover how to find the perfect outboard propeller
for your pleasure boat ... or fishing boat.
The perfect outboard
propeller for you is one which will allow your engine to
develop wide open throttle (W.O.T) RPM with your normal load
aboard while staying within the maximum RPM range recommended
by the manufacturer of your outboard motor.
Engine manufacturers state that
rev-range as part of the engine specifications.
Damage to your outboard motor is
likely to occur if an outboard propeller is fitted
which allows the engine to over-rev, or exceed the
manufacturers specified R.P.M. at W.O.T.
Serious engine damage is also likely
to occur if the installed outboard propeller overloads
the engine making it impossible for it to reach the minimum
specified R.P.M. at W.O.T.
Top speed
and best acceleration is achieved when your RPM at W.O.T. is
near the midpoint of the manufacturer's recommended
maximum RPM range.
That's a good
outboard propeller ... but it may not be the perfect
propeller for your application.
Consider the following ...
Most outboard propellers are
so exposed it's only a matter of time before they become
seriously damaged.
Worse still ...
an outboard propeller is so vulnerable it could even
become totally destroyed ... and very often is.
It's just as well you carry a
spare prop on board your boat ... you do ...
don't you?
CRUNCH ... BEND ...
BREAK.
There it
goes again ... now ... remember where you put that
spare outboard propeller ... that's right ... you
stowed it where you could find it quickly in an emergency ...
didn't you?
Sound
Familiar? ... Thought so.
Considering all
this, no "on-board first aid kit" would be complete without a
spare outboard propeller
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