Work in progress — not for use. Version of 3 October 2026

Prototype. Slack times can be 15–35 min off on some days. On the water, use the official BoM predictions.

This is a research prototype of a tidal-current model for Port Phillip and Western Port. At the Rip, about 94 % of the model's slack times fall within ±15 minutes of slack times we reconstruct from the Bureau of Meteorology's published peak predictions (typical error about 8 minutes), but some days with a very strong ebb are 15 to 35 minutes off. That reconstruction uses a rule learned from our own model, so this is an internal check, not an independent validation. Western Port has no official current prediction to compare with. Do not use it for diving, boating or any decision on the water: use the official BoM predictions.

Feedback and data to help us improve it are welcome: contact@gansoft.ch

Port Phillip & Western Port tidal currents

The Heads Whole bay Western Port

Depth-averaged tidal current, computed in your browser for the time you pick. Tap the map to read the current at a point; drag along the timeline to change the time.

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Melbourne time

Limits — read before use

Work in progress — not for use. Not for navigation. Check the official Bureau of Meteorology predictions for The Rip.

Timing accuracy is not yet good enough for use on the water. At the Rip, about 94 % of tidal cycles have a slack time within ±15 minutes of slack times reconstructed from the Bureau of Meteorology peak predictions, and about 85 % within ±10 minutes; the remaining cycles, on days with a very strong ebb, are up to about 35 minutes off, because the model underestimates those ebbs. This reference is not an official slack table: we reconstruct it from the Bureau's peak predictions with a rule learned from our own model (about 2–4 minutes of uncertainty), so the 94 % is an internal check, not an independent validation.
Astronomical tide only. No wind, no air pressure, no storm surge. Surge at the Heads is about ±15 cm in calm weather and +40 to +80 cm in storms, about a dozen times a year. Even with the best astronomical prediction, weather can shift the real slack by up to 30 minutes in mild weather and by well over an hour in severe weather, with current errors of up to 2 knots (JakeH5, jake-h5.neocities.org).
How the atlas stores the model: fitted to date slack water rather than peaks (weighted towards low speeds). At the Rip, Queenscliff, Popes Eye, Portsea and the South and West Channels the atlas reproduces the model's slack times within 15 minutes on every cycle; near Point Lonsdale and Point Nepean, where eddies form at the edge of the jet, it is less reliable.
Near slack the current turns fast: 0.15 to 0.70 knots per 10 minutes. A 10-minute error on slack can mean 0.7 knots where you expected none.
Inside the bay the model's tidal range is about 10 % larger than at the Bureau of Meteorology tide gauges, mostly at high water. Currents in the bay are less certain than in the entrance.
Western Port comes from a separate model of the same kind (mesh down to 35 m in the San Remo channel). No official current prediction exists there, so it has only been compared with published studies (a 12-month Delft3D study of the shipping channel, and the published tide delay from Flinders to Stony Point), not with observed slack times. Mud banks that dry are left blank on purpose: there the current of a tidal atlas means nothing.
What holds up: peak times at The Rip fall at a median of 0 minutes from the Bureau of Meteorology published maxima, and the flood/ebb curve has the same shape as Jake's (peak at 0.426 of the half-cycle, against 0.421).
Speeds are averaged over the depth; the surface current in The Rip can be stronger. Particles move about a thousand times faster than the water.

Current slack is not high or low water. The timeline shows both, so the gap is visible. High and low water are computed for open water about 5 km south of Point Lonsdale; they run about 15 minutes (3 to 22 min) ahead of the official Point Lonsdale tide times, which are measured inside the entrance.

Times are Melbourne time (AEST, or AEDT in summer). Speeds in knots, directions in degrees true, towards which the current flows.

More information: contact@gansoft.ch (email)

Sources and credits

What this page takes from each source, and what it does not. The current and tide computations are ours; the input data are these.

Source	What we took	Licence and attribution
AusSeabed · Geoscience Australia	The depths of the bay, the Heads and Bass Strait (AusBathyTopo Bass Strait 30 m, 2022), on which the model mesh is built.	CC BY 4.0 · © Commonwealth of Australia (Geoscience Australia).
SRTM15+ (Scripps, via NOAA ERDDAP)	The global depth base of our bathymetry chain. AusSeabed replaces it everywhere it has data, which is the whole area shown here; SRTM15+ can only remain at the outer margins of the model mesh.	Free to use with citation · Tozer et al. (2019), Earth and Space Science.
Statewide Marine Habitat Map 2023 · DEECA (Victoria), via Seamap Australia	Six seabed classes (reef, sand, sediments…), turned into the model's bottom-friction map (Manning n from 0.025 to 0.045). Friction sets how fast the water can run.	CC BY 4.0 · © State of Victoria (DEECA).
EOT20 · DGFI-TUM	The tidal constituents imposed at the open boundary of our model. And the high and low water times shown on this page, computed from EOT20 just outside the Heads.	CC BY 4.0 · Hart-Davis et al., DGFI-TUM.
OpenStreetMap	The coastline: the model shoreline, and the land drawn on the map (rasterised at 25 m). Positions of the key spots were checked against it.	© OpenStreetMap contributors · database under the Open Database Licence (ODbL 1.0).
SCHISM	The hydrodynamic model, run by us over 40 days. The harmonic analysis that turns it into a current atlas, and the computation in this page, are ours.	Open source (Apache 2.0).
pyTMD	Nodal factors and equilibrium arguments of the tidal constituents, used in the model's boundary forcing, in the atlas synthesis, and for the tide times shown here.	MIT.
Bureau of Meteorology	Nothing is reproduced here. Its predictions for The Rip and its Port Phillip tide gauges were used only to check the model's timing, speeds and water levels. They are not redistributable: use the Bureau's own predictions.	© Commonwealth of Australia, Bureau of Meteorology.
Jake's model (jake-h5.neocities.org)	Nothing is reproduced here. His model was used only for comparison; the weather effects and reversal rates quoted in the limits above are his published figures.	Quoted with attribution; no licence stated.
GOT5.5 (NASA GSFC)	Nothing is reproduced here: used only as a second opinion to check EOT20 on the model boundary (agreement within 3 %).	—
Barlow	The typeface.	SIL Open Font License, via Google Fonts.