Eight chart-table calculators in one page: course to steer with the tide allowed for, anchor scope, tide height by the twelfths, passage time and fuel, bridge clearance, horizon and dipping lights, sun times and Beaufort.
Course to steer, done properly
The chart-table vector triangle, solved for you — tide fully allowed for over the leg, leeway and variation included.
One-hour triangle: your water vector plus the tidal vector lands you on the track. On longer legs, run it per hour of tide with each hour's set and drift. This is passage planning, not a substitute for keeping a lookout and a log.
How much chain tonight?
Scope is measured from the bow roller, not the waterline — and it's the depth at high water that matters at 3 a.m.
Rig a snubber on all-chain — it saves the windlass and your sleep. Squally season out here rewards the next scope up whenever swinging room allows. Setting up an anchoring system or windlass? Talk to us — supply and electrical installation are what we do.
Tide where there is no tide station
For anchorages and drying areas between tide stations. Pull the modelled curve for your exact spot, or work a classic secondary-port interpolation from the stations either side of you.
A · Model tide at your position
Heights above chart datum = model sea level + the Mean Level you enter (from the tide tables for your nearest standard port; Kantang is about 1.6 m). Ocean-model estimate — good for planning, not for shaving margins in a drying channel. In narrow channels and marina straits the real turn can lag the open-water model by half an hour or more — and the stream you see at the dock keeps running past the height turn, so slack comes later still. Trust the shape of the curve; treat the minutes as a guide. If you learn your spot’s lag, put it in the time-adjust box — calibrate against the tide board (the level), not the visible flow: at Yacht Haven on 30 Jul 2026 the stream kept ebbing about 95 min after the model’s turn, and the level turned somewhere in between.
B · Between two tide stations (no signal needed)
The classic secondary-port method: take today’s high and low water from the tide table for the station each side of you, then slide to where your spot sits between them.
1 · Today’s tide table figures
2 · Where is your spot between them?
3 · When do you need the height?
Straight-line interpolation between stations — the traditional between-ports approximation. Where official secondary-port differences are published for your spot, they take precedence. Heights are in the same datum as the tables you copied from.
Tide height by the rule of twelfths
Enough water over the bar? Interpolates the tide between high and low the traditional way.
Rule of twelfths assumes a regular semi-diurnal tide (≈6 h each way) — good for planning around most of Thailand and the Andaman, but always check the local tide table and add a safety margin under the keel.
Passage time, ETA & fuel
Distance and speed to ETA — and whether the fuel gets you there with the reserve a prudent skipper keeps.
Fuel check uses the rule of thirds — a third out, a third back or onward, a third in reserve. Guessing what's actually in the tank? Fit a proper sender: our tank sender calculator sizes it from your tank depth in thirty seconds.
Will you fit under it?
Charted clearances are measured from a high-tide datum, not from today's water — so there's usually more room than the chart says. Usually.
HAT on modern charts (MHWS on older ones) — printed in the chart's tidal panel.
Air draft is honest only if you've measured it — mast, then aerials, anchor light and wind gear on top. If the numbers are within a metre, wait for the tide to drop or take the mast route around. No bridge has ever moved for a boat.
How far can you see?
Distance to the horizon from your height of eye — and when a light or landmark should lift over it.
Standard refraction formula (2.08 × √height in metres, answer in nautical miles). A charted light's nominal range is about intensity — the dipping range here is about geometry; you see it at whichever is less.
Sunrise, sunset & daylight
Plan to arrive in daylight — enter where you'll be and when. Defaults to the Andaman coast.
Times are in this device's local time zone. In the tropics darkness falls fast — usable light ends roughly 25 minutes after sunset, so plan the anchor down before that, not at it.
Beaufort & sea state
Turn a forecast number into what the water will actually look like.
Wave heights are open-water typicals — fetch, current against wind, and shallow banks all make it worse than the number suggests. Squalls out here arrive two forces above the forecast.
Weather warnings — what's coming your way
Cross-checks three independent global forecast models (ECMWF, NOAA GFS, DWD ICON) plus a dedicated wave model, and flags anything heading for your position — or anything you're heading into along your course.
Model data via Open-Meteo (ECMWF IFS, NOAA GFS, DWD ICON + Open-Meteo wave model), refreshed every model run. A warning shows when any model crosses a threshold — the agreement count tells you how confident to be. This is decision support, not an official forecast: always check the Thai Met Department (or your local met service) warnings before letting go the lines.