Terms of Use

Slack Water – Port Phillip · Gansoft SARL

These terms apply to the Slack Water app ("the App"), published by Gansoft SARL, Switzerland. By using the App you accept them.

What the App is

The App predicts tidal currents and slack-water times in Port Phillip and Western Port, Victoria, Australia, from a tidal model, on your device. With the Complete plan it also shows the next 48 hours of wind, gusts, storm risk and waves. It is a planning aid.

Limits of the predictions

• A planning aid, not a navigation aid. Slack Water helps you plan. It is not a certified navigation aid and does not replace official charts or your own judgement.
• Currents: astronomical tide only. Wind, swell, air pressure, storm surge, rain and river flow are not included in the current, and they can change the real current a lot.
• Wind and storms from a global model. Wind, gusts, storm risk and offshore swell come from the NOAA GFS global model, about 25 km wide: sea breezes, gusts off the cliffs and squalls are not resolved, and storm risk is not a warning. Check the Bureau of Meteorology's marine forecasts and warnings.
• Waves are an estimate. Waves are worked out on your phone from that wind, the fetch, the depth, the tide and the current, and checked against the five wave buoys in Port Phillip (typical error 0.13 m). Western Port has no buoy to check them against. Breaking waves at the Heads can be bigger than shown.
• A simplified bay. The model sees Port Phillip on a grid about 90 m wide at the Heads and 300 m elsewhere, and Western Port on a grid about 60 m wide in the San Remo channel and 250 m elsewhere. Piers, reefs, small channels and eddies behind points are not resolved: near the shore and at dive sites the real current can be quite different.
• Averaged over the depth. The current shown is averaged from surface to bottom. At the surface and at depth it can differ in speed and direction.
• Times are approximate. Slack times can be off by tens of minutes, sometimes more. Allow a margin and watch the water.
• Slack is not zero current. The slack window is when the modelled current stays under your own threshold. Its length changes a lot between neaps and springs, and on some days there is no window at all.
• Not an official prediction. The official references are the Bureau of Meteorology tide tables and Australian Hydrographic Office charts.
• Western Port is less proven. No official current predictions exist for Western Port, so the model there has only been compared with published studies, not with observed slack times. Mud banks that dry are left out of the model.
• The map is not a chart. The background map shows no hazards, depths or navigation marks.
• Alerts can be late or missed. Battery saving, muted notifications or not opening the app for a week can stop alerts. Don't rely on them alone.
• Your spots. Positions of your spots are the ones you entered or imported.
• Your dive, your call. Follow your training, your dive plan and your club's rules, have surface support, and check conditions on site. The Rip is dangerous whatever the predicted slack.

No warranty

To the extent permitted by law, the App and its predictions are provided "as is", without any warranty of accuracy, completeness or fitness for a particular purpose. Nothing in these terms excludes, restricts or modifies any consumer guarantee or right you have under the Australian Consumer Law or any other law that cannot be excluded.

Limitation of liability

To the extent permitted by law, Gansoft is not liable for any loss, injury or damage arising from the use of, or reliance on, the App or its predictions, including decisions about diving, boating, paddling or fishing. Where liability cannot be excluded but can be limited, it is limited to supplying the service again or refunding the price you paid for the current subscription period.

Your responsibility

You decide whether and when to go on or in the water. Check official sources, the weather and the conditions on site, and follow your training and your club's rules.

Subscriptions

The yearly subscriptions (Currents and Complete) are sold by Apple or Google. On iOS, Apple's standard licence agreement also applies. It renews every year unless cancelled at least 24 hours before the end of the period; manage it in your store account. Refunds are handled by Apple or Google.

Data and licences

The current atlas, the wave tables and the weather forecast in the App are derived from third-party data used under their licences, listed in the App under Settings › Credits & licences. Your data stays on your device: see the Privacy Policy.

Changes and law

We may update these terms; the App asks you to accept a new version when the substance changes. These terms are governed by Swiss law, without prejudice to the mandatory consumer protection law of the country where you live.

Contact

Gansoft — contact@gansoft.ch

Version 1 · 23 September 2026