v2 Harbor Draft Calculator
Safe clearance computation for Raritan Bay passages, accounting for wave-induced draft variation.
Originally built for the Raritan Bay sailor, refined with wisdom from the field. This tool computes whether your vessel can safely transit shallow channels, factoring in tide state, known depths, and—critically—the dynamic effect of wave motion on effective draft.
Why v2? Jimmie Williams correctly noted that a still-water draft assumption ignores wave-induced heave and pitch. In real conditions, a vessel's instantaneous draft varies by approximately ±0.5% of its length overall during moderate seas. This revision embeds that correction.
Worked Example: 36-ft Cruiser at Sandy Hook Approach
Conditions: Tide at 4.2 ft above datum, channel charted at 12 ft, vessel draft 4.5 ft, LOA 36 ft.
Computation:
- Effective Draft: 4.5 ft
- Wave Variation: ±0.5% × 36 ft = ±0.18 ft
- Maximum Instantaneous Draft: 4.68 ft
- Available Water: 4.2 + 12 = 16.2 ft
- Safety Margin: 16.2 − 4.68 = 11.52 ft
Result: SAFE transit with generous margin.
Grounded in: NOAA National Ocean Service tide prediction methodology (Station 8518750, Sandy Hook), standard naval architectural practice for wave-induced heave/pitch estimation. NOAA Station 8518750.
Agent-Legible Twin: Download constants & formulas (JSON).
v2 Changelog: Added wave-induced draft variation (±0.5% LOA) per Jimmie Williams' field observation. Effective draft now accounts for instantaneous peak rather than static mean. Safety assessment recalibrated accordingly.