Enter charted depth, draft, required margin, and high/low tide heights on the same datum. See required tide above datum, clearance at HW and LW, and whether a passage window exists. Optional crude half-window hours (simple sine / semidiurnal approx — clearly labeled). No live NOAA API.
Reach for the tide window planner calculator when a planning number depends on measurements you already have on the boat or trailer. Enter charted depth, vessel draft, required ukc / margin, and high tide height (above datum).
Enter charted depth, draft, required margin, and high/low tide heights on the same datum.
Required tide above chart datum equals draft + required margin − charted depth. Clearance at a tide height equals charted + tide − draft. A window exists when high-water clearance meets or exceeds the required margin (equivalently when HW tide ≥ required tide).
required_tide = draft + margin − charted_depth
clearance_HW = charted + HW_tide − draft
clearance_LW = charted + LW_tide − draft
window ≈ yes if HW_tide ≥ required_tide
Optional half-window uses a simple semidiurnal sine between LW and HW — approximate only, not NOAA times. No live tide API.
Start with the calculator’s default entries: Charted depth = 8; Vessel draft = 5; Required UKC / margin = 2; High tide height (above datum) = 6; Low tide height (above datum) = 0.5; Optional: HW→LW hours (approx) = 6.2.
With those entries the calculator returns:
Window OK at HW
need tide ≥ -1.00 · HW clr 9.00 · LW clr 3.50 · LW already clears — ~all 6.2 h span (approx)
required_tide = 5 + 2 − 8 = -1.00
clearance_HW = 8 + 6 − 5 = 9.00
clearance_LW = 8 + 0.5 − 5 = 3.50
window = HW_tide 6 ≥ -1.00 → yes
LW already ≥ required tide — full HW→LW span clears (approx).
Formula used: required_tide = draft + margin − charted_depth clearance_HW = charted + HW_tide − draft clearance_LW = charted + LW_tide − draft window ≈ yes if HW_tide ≥ required_tide
One input at a time. Raise Charted depth from 8 to 12 and leave everything else alone. The result becomes:
need tide ≥ -5.00 · HW clr 13.00 · LW clr 7.50 · LW already clears — ~all 6.2 h span (approx)
required_tide = 5 + 2 − 12 = -5.00
clearance_HW = 12 + 6 − 5 = 13.00
clearance_LW = 12 + 0.5 − 5 = 7.50
window = HW_tide 6 ≥ -5.00 → yes
Charted depth and both tide heights must share one datum. Mixing datums breaks the math.
We do not invent NOAA tide tables. Pair these clearances with official predictions for your station.
If you enter HW→LW span hours, a crude sine estimate of time above the required tide is shown and labeled approximate.