1. What is a Boat Speed Calculator?

Definition: This calculator estimates boat speed using Crouch's formula based on horsepower, displacement, and a hull-specific constant.

Purpose: It helps boat designers, owners, and enthusiasts predict theoretical hull speed for planning purposes.

2. How Does the Calculator Work?

The calculator uses Crouch's formula:

Where:

• \( S \) — Boat speed (mph)
• \( C \) — Crouch constant (unitless, hull-specific)
• \( P \) — Shaft horsepower (hp)
• \( D \) — Displacement (lbs)

Explanation: The formula relates speed to the square root of the power-to-weight ratio, modified by a hull efficiency factor.

3. Importance of Crouch's Formula

Details: This calculation is essential for boat design, performance prediction, and engine selection.

4. Using the Calculator

Tips: Enter the Crouch constant (default 150 for average planing hulls), horsepower, and displacement. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is the Crouch constant?
A: A hull-specific efficiency factor ranging from 150 (average planing hull) to 220 (high-performance racing hull).

Q2: How accurate is this calculation?
A: It provides theoretical maximum speed; actual speed may vary due to conditions, loading, and hull condition.

Q3: What's a typical Crouch constant for my boat?
A: 150-170 for cruisers, 180-200 for performance boats, 200-220 for race boats.

Q4: Does this work for displacement hulls?
A: No, Crouch's formula is for planing hulls. Displacement hulls have different speed limitations.

Q5: Should I use shaft or brake horsepower?
A: Use shaft horsepower (after transmission losses) for most accurate results.