Created by: Sophia Bennett
Last updated:
Compare a user-entered tide-gate or access window with departure ranges, speed scenarios, delays, contingency, arrival times, and feasible departure intervals.
Compare user-verified access times with departure and speed scenarios—the calculator does not predict tides.
Enter from current official predictions, notices, or operational information.
A Sailing Tide-Gate Arrival Window Calculator compares an entered departure range with an entered gate opening and closing time using slow, planned, and faster speed scenarios. It reports travel time, earliest and latest arrival, feasible departure intervals, waiting before opening, missed-window status, and arithmetic speed required from the latest departure.
The tool does not predict the tide. A “gate” can represent a user-verified tidal stream window, depth threshold, bridge or lock access period, marina restriction, daylight constraint, or other operational interval. Its times must come from current authoritative information using the correct station, datum, corrections, date, and time zone.
Arrival arithmetic is only one part of the decision. A route may contain hazards, traffic, changing current, weather, waves, visibility, speed restrictions, waiting limitations, and no safe holding area. Required speed is not a recommended or safe speed; it is simply the constant average that would satisfy the entered close time under the model.
A sound passage plan considers what happens if preparation takes longer, the boat is slower, the gate changes, the crew becomes unwell, weather deteriorates, or the route cannot be completed. Entered alternatives and a safe cancellation point matter more than squeezing an optimistic ETA into a narrow window.
For each speed, underway time equals distance divided by speed. Percentage contingency is applied to that underway time and fixed delay is added afterward.
The earliest and latest entered departures each receive the same modeled travel duration, creating an arrival range.
Subtracting travel duration from gate open and close creates the departures that would arrive within the gate. Intersecting that with the entered departure range gives the feasible interval.
Required speed from the latest departure is calculated only when positive travel time remains after fixed delay. It is labelled arithmetic, not a safe-speed recommendation.
Travel = distance ÷ speed × (1 + contingency fraction) + fixed delay
Feasible start = max(departure start, gate open − travel)
Feasible end = min(departure end, gate close − travel)
Required speed = distance × (1 + contingency) ÷ available underway time
An 18-nautical-mile route at six knots takes three hours before added delay. Departing between 08:00 and 09:00 gives arrivals from 11:00 to 12:00. For a 12:00–14:00 gate, later departures can arrive inside the entered window.
At two knots, the same route takes nine hours. The entered morning departure range cannot reach an early-afternoon gate. The correct interpretation is to reconsider the plan, not to assume the tide gate will wait.
If the earliest scenario arrives one hour before the entered opening, the calculator reports arithmetic waiting. The skipper must separately determine whether a safe, lawful waiting location exists in the expected conditions.
Record the exact source, station, datum, correction, date, time zone, and access notice used to create the gate window. Recheck it immediately before departure.
Use route-specific speeds and current effects rather than one optimistic boat speed. Add explicit harbour, manoeuvring, bridge, lock, and preparation delays.
Define a safe waiting area, refuge, return point, later window, and cancellation trigger. Do not chase the calculated close time when conditions or crew readiness deteriorate.
No. The opening and closing times are entered by the user from an authoritative current source or a separately verified operational constraint. The calculator only compares those times with departure and travel scenarios. It does not calculate tide height, current, depth, bridge operation, lock status, weather, or a safe transit window.
For each speed scenario, the calculator subtracts modeled travel time from the gate opening and closing times, then intersects that result with the entered departure range. The overlap is the arithmetic departure interval that reaches the gate inside the entered window. A feasible time is not approval to make the passage.
The entered percentage increases the distance-over-speed underway time before fixed delay is added. This creates a transparent conservative scenario, but it does not model a specific head current, sea state, equipment problem, traffic restriction, or weather event. Those should be handled with route-specific scenarios and alternatives.
Every date and time must use the same clearly understood basis. Tide tables, almanacs, bridge schedules, lock notices, GPS displays, forecasts, and crew watches may use UTC, local standard time, or daylight-saving time. The browser interprets datetime entries locally, so write the intended zone beside the operational passage plan.
Treat the scenario as infeasible. Do not increase speed merely to chase the gate if vessel limits, visibility, traffic, sea room, weather, fuel, wake restrictions, or safe-speed requirements make that inappropriate. Consider an earlier departure, later window, alternate route, safe waiting location, or abandoning the passage.
A range exposes operational flexibility and shows the latest arithmetic departure under each speed scenario. It also makes clear when a slower plan still works if departure moves earlier. Passage planning should include alternatives because crew, preparation, weather, mechanical, and access delays can move the actual departure.
Gate times are user-entered. This calculator does not predict tides, depths, currents, bridge or lock operation, safe speed, safe waiting, weather, or whether a transit should be attempted.