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The Delicate Balance Between Blade
Area & Pitch
In order to achieve maximum performance it is necessary to balance
the blade area with the effective pitch of the propellers.
The propeller must produce sufficient Thrust to move the vessel. Thrust
is like torque in a car engine. Torque is necessary to get the wheels
turning and to keep them turning once the car is moving. Blade area
on a propeller produces the thrust that gets the boat moving and keeps
it going once underway.
Insufficient blade area will result in excessive slip, lost efficiency,
poor performance, and increased fuel consumption.
Blade area is directly related to diameter and number of blades and
is often referred to as D.A.R.
As diameter increases so does blade area. Because of hull limitations
sometimes the correct diameter propeller is impossible to install.
In these cases additional blades will accomplish the same purpose.
Thrust is not speed. Pitch is speed. Pitch is like the gear
box on your car. There must be enough pitch to achieve the speed and
performance a vessel is capable of. Both pitch and blade area combine
to load the engines. A balance must be achieved so that enough thrust
is generated to move the boat while enough pitch is present to attain
the design speed.
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| Blade
Area and Pitch |
For any given engine, vessel, gearbox combination there is an optimum
pitch, diameter, and blade area propeller. If the correct
propeller is not available or impossible to install it then becomes
necessary to compensate in pitch for any change in diameter
or blade area. As this occurs the propeller becomes a compromise
and efficiency begins to degrade.
For instance say the optimum propeller for a the F/V SPEED KING is
a 32 RH 35 x 3” 4-blade 0.80 D.A.R. propeller [That is 32”
diameter x 35” pitch x 3” bore]. Now, if the largest diameter
propeller that can be installed is a 30” diameter then pitch
must be added to compensate for the loss in diameter or a propeller.
Pitch will never compensate entirely for loss of diameter. At
some point too much diameter or blade area will be lost decreasing
thrust which in turn will increase slip to the point that propeller
efficiency plummets. On the other hand too much blade area will generate
induced drag and reduced pitch which slows the boat down.
Boating
Magazine |
| “We picked up 1 mph at top
the top end and nearly 3 mph at the boat’s cruising
speed of 1900 rpm. In addition, we were able to run similar
speeds at lower rpm, which helped fuel consumption.” |
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Power
& Motor Yacht |
| “Computerized scanning can make your props
more efficient and your boat perform better.” |
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Shallow
Draft |
| “Ignoring the propeller on
today’s sophisticated vessels is ignoring the most important
piece of equipment on your vessel.” |
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Marine
News |
| “Combined with vessel performance and
engine loading information the Prop Scan EPS software can
calculate changes that will decrease propeller slip and match
engine loading requirements thus increasing vessel performance.” |
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Contact WildCat Props!
Custom propeller configurations are also available on request. Should you
require assistance in selection of a new propeller suited to your vessel,
restoration-repair of your existing propellers or prop tuning-maintenance
please contact WildCat Props. |
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Read How WildCat Props Exceeds the
Expectations of Our Customers!
A quick note to thank you for your excellent work over the last 5 years
(those being years Wildcat worked on Backlash wheels), we have placed in
the top three (first, second, third) for six tournaments. The smaller three
blade wheels allow us to go slow for winter rockfish trips. And we like
the economy of 20 knots/20 gallon/hr (combined). But I really get excited
with the 24x27 ZF 4 blades. Your recommendations were right on: 30 knot
cruise, 35 knot top end, zero cavitation, super smooth and (best of all)
fuel economy!!! Right after we put the 4 blades on in Hatteras, we won the
2007 Hatteras Village Open with a 613# Blue Marlin and another release.
If someone thinks you are too high - don't forget -you are saving them money
on fuel. And that fuel expense is not likely to change!!!
Thanks again, Troy and Team,
Capt Steve Richardson owner/operator "Backlash"
Read more customer testimonials here |
Also read customer propeller case studies |
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