Boat 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 move through the water and the actual distance it travels. It represents the efficiency loss due to water slippage and is expressed as a percentage.

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 (%)
\( V \) — Boat speed (mph)
\( RPM \) — Engine revolutions per minute (rev/min)
\( PP \) — Propeller pitch (inches)
\( GR \) — Gear ratio (dimensionless)
1056 — Conversion constant

Explanation: The formula calculates the theoretical speed based on propeller pitch and engine RPM, then compares it to the actual speed to determine slip percentage.

3. Importance of Propeller Slip Calculation

Details: Propeller slip is crucial for optimizing boat performance, fuel efficiency, and engine health. Ideal slip ranges from 5-25% depending on boat type and conditions.

4. Using the Calculator

Tips: Enter actual boat speed in mph, engine RPM, propeller pitch in inches, and gear ratio. All values must be positive numbers for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is a good propeller slip percentage?
A: For most boats, 10-15% slip is considered excellent. Planing hulls typically have 5-15% slip, while displacement hulls may have 20-25% slip.

Q2: Why does propeller slip occur?
A: Slip occurs due to water viscosity, cavitation, hull drag, and propeller design factors that prevent the propeller from achieving its theoretical advance.

Q3: How can I reduce propeller slip?
A: Proper propeller sizing, maintaining clean hull surfaces, optimal trim adjustment, and choosing the right propeller design can reduce slip.

Q4: Does slip vary with boat speed?
A: Yes, slip is typically highest at low speeds and decreases as the boat reaches its planning speed, then may increase again at very high speeds.

Q5: What affects propeller slip calculation accuracy?
A: Accurate speed measurement, proper RPM reading, correct propeller pitch specification, and accounting for current and wind conditions are critical.