This calculator helps determine the required bridge deck clearance for multi-hull vessels to minimize wave pounding. Based on your triangular platform design with submerged NACA-wing legs.
Expected significant wave height in your operating area
Typical wave period in your operating area
Distance from waterline to bottom of main platform
Distance between outer legs (platform width)
Your planned cruising speed (4 MPH ≈ 3.5 knots)
Your desired pounding frequency target
Interpretation: With your current clearance, you can expect approximately 0.02 wave pounding events per day, which meets your target of less than 1 event per day.
Maximum Wave Height at Clearance: 8.4 feet (waves above this height will cause pounding)
To achieve your target of less than 1 pounding event per day in 7-foot significant waves, we recommend a minimum bridge deck clearance of 16.7 feet.
This provides a safety margin above the 1/1000th highest waves expected in your operating conditions.
The calculation uses established naval architecture formulas adapted for multi-hull vessels:
1. Maximum Wave Height (Hmax) for given probability:
Hmax ≈ 1.86 × Hs (for 1/1000 probability in open ocean)
2. Required Clearance (C) to avoid Hmax:
C = Hmax + Safety Margin (typically 20-30% of Hmax)
3. Pounding Probability (P) based on Rayleigh Distribution:
P = exp(-2 × (C/Hs)²) × (Time Period / Wave Period)
4. Speed Correction Factor (for vessel motion):
Effective Clearance = C - (0.5 × Speed² / g) [where g = 32.2 ft/s²]
These formulas account for the statistical distribution of wave heights, vessel motion, and the non-linear nature of extreme waves.
Diagram showing relationship between waves, platform, and clearance (not to scale)
Red dashed line shows current clearance level. Waves reaching above this line would cause pounding.
| Clearance (ft) | Pounding Events per Day | Pounding Events per Month | Max Wave Avoided (ft) | Risk Level |
|---|
Given your specific design with NACA-wing legs and low speed operation: