Boat Propeller Slip Calculator

Propeller Slip Formula:

\[ PS = 100 \times \left(1 - \frac{V}{\frac{RPM \times PP}{GR \times 1056}}\right) \]

Speed (V):

mph

RPM:

rev/min

Propeller Pitch (PP):

inches

Gear Ratio (GR):

dimensionless

Propeller Slip (PS):

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1. What is Propeller Slip?

Propeller slip is the difference between the theoretical distance a propeller should advance through the water and the actual distance it travels. It represents the efficiency loss due to factors like water resistance, cavitation, and propeller design.

2. How Does the Calculator Work?

The calculator uses the propeller slip formula:

\[ PS = 100 \times \left(1 - \frac{V}{\frac{RPM \times PP}{GR \times 1056}}\right) \]

Where:

\( PS \) — Propeller slip (%)
\( V \) — Actual speed (mph)
\( RPM \) — Revolutions per minute (rev/min)
\( PP \) — Propeller pitch (inches)
\( GR \) — Gear ratio (dimensionless)
1056 — Conversion constant

Explanation: The formula calculates the percentage difference between theoretical and actual propeller performance, indicating efficiency.

3. Importance of Propeller Slip Calculation

Details: Propeller slip measurement helps optimize boat performance, fuel efficiency, and propeller selection. Ideal slip ranges typically fall between 5-15% for most recreational boats.

4. Using the Calculator

Tips: Enter actual speed in mph, RPM in revolutions per minute, propeller pitch in inches, and gear ratio (dimensionless). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is considered good propeller slip?
A: For most boats, 5-15% slip is ideal. Values below 5% may indicate measurement error, while above 25% suggests poor propeller efficiency.

Q2: How does propeller pitch affect slip?
A: Higher pitch propellers generally have lower slip at cruising speeds but may struggle at lower speeds. Proper pitch matching is crucial for optimal performance.

Q3: What factors influence propeller slip?
A: Hull condition, load distribution, water conditions, propeller condition, and engine trim all affect slip percentage.

Q4: Can slip be negative?
A: Negative slip indicates the boat is moving faster than theoretical maximum, which is physically impossible and suggests measurement error.

Q5: How often should I check propeller slip?
A: Regular checks help monitor performance changes. Check after propeller changes, hull cleaning, or when noticing performance degradation.