Propeller Slip Formula:
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Definition: This calculator determines propeller slip, which is the difference between theoretical and actual boat speed.
Purpose: It helps boaters and marine professionals evaluate propeller efficiency and identify potential issues.
The calculator uses the formula:
Where:
Explanation: The ratio of actual to theoretical speed shows what percentage of potential speed is lost due to slip.
Details: Monitoring slip helps maintain optimal performance, fuel efficiency, and can indicate propeller or hull issues.
Tips: Enter actual measured speed and theoretical speed (from propeller pitch and RPM). Both values must be > 0 and theoretical ≥ actual.
Q1: What is a normal slip percentage?
A: Typically 5-25% for most boats. High-performance boats may be 5-15%, while displacement hulls may be 20-25%.
Q2: What causes propeller slip?
A: Factors include hull drag, propeller design, engine power, water conditions, and propeller ventilation.
Q3: When should I be concerned about slip?
A: If slip exceeds 30% or increases suddenly, check for fouled prop, hull growth, or engine problems.
Q4: How do I find theoretical speed?
A: Theoretical speed = (RPM × Pitch) / (Gear Ratio × 1056). Use our Propeller Speed Calculator for this.
Q5: Can slip be negative?
A: Normally no. If calculated slip is negative, check your measurements as theoretical speed should always exceed actual.