Prop Boat Speed Calculator

Prop Boat Speed Formula:

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

Engine RPM (RPM):

rev/min

Propeller Pitch (PP):

inches

Propeller Slip (PS):

Gear Ratio (GR):

dimensionless

Boat Speed (V):

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1. What is the Prop Boat Speed Formula?

The Prop Boat Speed Formula calculates the theoretical speed of a propeller-driven boat based on engine RPM, propeller pitch, propeller slip, and gear ratio. This formula helps boaters estimate their vessel's performance under various conditions.

2. How Does the Calculator Work?

The calculator uses the boat speed formula:

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

Where:

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

Explanation: The formula accounts for the theoretical distance the boat would travel per revolution (pitch), adjusted for slip percentage and gear reduction between engine and propeller.

3. Importance of Boat Speed Calculation

Details: Accurate speed estimation helps in trip planning, fuel consumption calculation, performance optimization, and propeller selection for optimal efficiency.

4. Using the Calculator

Tips: Enter RPM as engine revolutions per minute, propeller pitch in inches, propeller slip as percentage (typically 10-20% for well-tuned boats), and gear ratio from your engine specifications.

5. Frequently Asked Questions (FAQ)

Q1: What is propeller slip?
A: Propeller slip is the difference between theoretical and actual distance traveled per revolution, expressed as a percentage. It accounts for water resistance and efficiency losses.

Q2: What is a typical gear ratio for boats?
A: Gear ratios typically range from 1.5:1 to 3:1, depending on the engine and boat type. Check your engine manufacturer's specifications.

Q3: Why is the result in mph?
A: The formula uses imperial units. To convert to knots, multiply the result by 0.868976.

Q4: What affects propeller slip?
A: Hull design, load, sea conditions, propeller condition, and trim all affect slip percentage. Lower slip indicates better efficiency.

Q5: How accurate is this calculation?
A: This provides theoretical speed. Actual speed may vary due to hull drag, wind, current, load distribution, and other environmental factors.