1. What is Displacement Hull Speed?

Definition: Hull speed is the theoretical maximum speed a displacement hull can efficiently travel through water without planing.

Purpose: This calculation helps boat designers and sailors understand the performance limits of displacement hull vessels.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( HS \) — Hull speed (knots)
• \( LWL \) — Waterline length (feet)

Explanation: The formula calculates the speed at which the wavelength of the boat's bow wave equals the waterline length, creating excessive drag beyond this point.

3. Importance of Hull Speed Calculation

Details: Knowing hull speed helps in fuel efficiency planning, performance expectations, and understanding when additional power becomes ineffective.

4. Using the Calculator

Tips: Simply enter the vessel's waterline length in feet. The waterline length is the length of the hull at the water's surface when normally loaded.

5. Frequently Asked Questions (FAQ)

Q1: Can boats exceed hull speed?
A: Displacement hulls can exceed it but with exponentially increasing power requirements. Planing hulls can exceed it by rising over their bow wave.

Q2: Why is the constant 1.34 used?
A: This empirical constant accounts for the relationship between wave-making resistance and hull length in salt water.

Q3: Does this apply to all boat types?
A: No, it's specific to displacement hulls. Planing hulls and multihulls have different speed characteristics.

Q4: How does load affect hull speed?
A: Increased load lengthens the waterline (increasing hull speed) but also increases drag (reducing actual speed).

Q5: Is this different for fresh vs salt water?
A: The difference is minimal (about 2-3%) due to water density variations.