A rough guide to choosing the right propeller for your boat. Propeller Pitch & Diameter, Prop slip, Propeller Cupping, Propeller slip, Hole shot,

1. Propeller Diameter & Pitch
A rough guide to choosing the right
propeller for your boat.
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2. Considerations
•
•
•
•
•
Engine type
Horsepower rating
Boat weight
Hull type
Current prop - number of blades, diameter &
pitch
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3. Props are measured in two sizes:
Diameter
Pitch
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4. What affects can it have?
INCREASED or DECREASED:
• Boat performance
• Acceleration
• Torque
• Top speed
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5. What is Prop pitch?
• # inches prop moves
through water in one
revolution
• The steeper the angle the
greater the pitch.
• Pitch affects RPM level
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6. High vs. Low Pitch
High Pitch:
Low Pitch:
• Reduced RPMs
• Higher top end speed
• Similar to low bike
gears that are harder
to pedal at first but
eventually achieve
higher speeds.
• IncreasedRPMs
• Improved hole shot
• Similar to high bike
gears that are easier
to pedal at first but
won’t achieve high
speeds.
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7. What is hole shot?
• When you go from neutral (dead stop) to
Wide Open Throttle (WOT) – the time it takes
to ‘get out of the hole’ and onto the plane.
Some factors affecting hole shot:
• Hull design
• Boat weight
• Prop pitch & diameter etc
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8. Rule of thumb (pitch)
• The higher the pitch, the faster the top end
speed but the lower the rev's.
• The lower the pitch the faster the acceleration
and the higher the rev's
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9. Theory vs. Reality (Prop Slip)
THEORY:
Each prop revolution propels the boat
forward a distance equal to the prop
pitch
I.E. 15 inch prop = 15 inches of
forward motion per revolution.
REALITY:
Due to prop slip we are going
approximately 10-20% slower at top
speed on high speed craft.
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10. Prop diameter
• The distance across a circle
swept by the tips of the
blades.
• Generally correlated to size
of boat (& engine)
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11. Prop Diameter – Small vs. Large
Small diameter:
Large diameter:
• Low weight boats
• Low engine
mounting height
• High performance
racing boats
•
Heavier weight boats
•
Higher engine
mounting height
Incorrect diameter = Under-powered/increased RPM (too small). Increased
resistance/decreased RPM (too big)
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12. Cupping
• Upturn of trailing edge
• Reduces cavitation
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13. 4/5 blade
3 Blade
•
Slightly higher top end speed
•
Faster hole shot
•
Slower to plane
•
Better holding in rough seas
•
Cheaper
•
Better low speed handling
•
Better performance in mid-range RPM
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14. Activity dependant choice…
Engine type
Outboard /
Stern drive
Use?
Cruise
Ski
Race
Loads
Low pitch
Low pitch & 4/5 blade
Higher pitch, cupping, smaller diameter
Low pitch
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15. Aluminum VS. Stainless Steel
•
Painted with protective coating
•
Improved perf. Due to thinner blades
•
Cheaper / Common
•
Last 5x longer than aluminum
•
Repairable (but will suffer loss of
strength)
•
Doesn’t flex under pressure
•
Repairable (no loss of strength)
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16. For more tutorials visit
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Or follow us on:
www.Facebook.com/i
nstructorresources
@marineeducation
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17. References/Credits:
www.propellerpages.com
www.hhscott.com
www.mercurymarine.com
www.brianrogers.net
www.boatdesign.net
www.propellerworld.co.uk
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