Hyper-local tidal currents: the Solent, Puget Sound, Scotland and other complex waters

Savvy Navvy uses hyper-local current models in a number of regions where standard tidal models are not detailed enough. This article explains what that means, why it matters, and what to expect when you are planning a passage through complex water.

The short version

• Tidal heights (how deep the water is) are predicted from celestial mechanics and are reliable months or years ahead.
• Tidal currents (how the water moves) are much harder to predict, because wind and barometric pressure affect them.
• In places with complex geography such as the Solent, Puget Sound, Scottish waters and the Norwegian fjords, global and regional current models are too coarse to capture what is really happening.
• For selected regions like these, we have built hyper-local current models using high-resolution seabed data and fluid dynamics simulation, so we can model flow through narrow channels, around islands, and in eddies far more accurately.

Tidal heights, tidal currents and tidal streams

These three terms get used interchangeably, but they describe different things.

Tidal heights

• The water level at a specific tidal station at a given time.
• Driven by celestial mechanics: the moon, the sun and other bodies.
• Because those movements are predictable, heights can be published far in advance, months or even years ahead.

Tidal currents

• How the water actually moves: speed and direction.
• Influenced by atmospheric and barometric conditions as well as the tide, so they cannot be predicted precisely a long way out.
• Reliable forecasts generally only extend a few days ahead.
• "Current" also covers ocean currents and river or estuary flow, not just the tidal element.

Tidal streams

• A long-range pattern rather than a forecast.
• Built from roughly 27 to 29 years of historical tidal current data, which gives the likely pattern for any point in the year.
• Useful for planning ahead, but because atmospheric pressure varies, the real world will not match it exactly on the day.

Where our current data comes from

• Our baseline is a global current model from Copernicus, which gives worldwide coverage.
• In some parts of the world, higher-resolution regional models are available and give us considerably more detail. The north-western European shelf model is a good example.
• Both are excellent over open water. Neither was designed to resolve what happens inside a mile-wide channel between two islands.

Why standard models struggle in complex waters

Global and regional models work on a grid. If the grid squares are larger than the features you are sailing through, the detail disappears.

That becomes a real problem in places like:

• The Solent, with its double tides, strong channel flows and the Isle of Wight splitting the stream
• Puget Sound and the Seattle area, with deep inlets, narrow passages and strong tidal exchange
• Scottish waters, with islands, sounds and some of the fastest tidal races in the world
• Norwegian fjords, where flow is funnelled through long, narrow, steep-sided channels

In water like this, a coarse model can miss eddies entirely, average out a strong channel flow, or point a current in broadly the wrong direction. Before we introduced hyper-local modelling, current predictions in these areas were often too coarse to be genuinely useful.

How hyper-local current models work

For selected regions, we have built dedicated models that combine:

• High-resolution bathymetry, meaning detailed seabed shape and depth data
• Fluid dynamics simulation, which models how water actually behaves as it moves through that geography

The result is a far better picture of:

• Current speeds through narrow channels and passages
• Flow direction as water is funnelled around islands and headlands
• Local eddies and back-eddies close to coastlines

What this means for your passage planning

• In hyper-local regions, the currents shown in Savvy Navvy reflect real local behaviour rather than a smoothed regional average.
• Smart routing uses this data, so your route and timings account for how the water is genuinely moving.
• Current forecasts are most reliable a few days ahead. If you are planning weeks out, treat the picture as indicative and check again closer to departure.
• Even the best model is a prediction. Conditions on the day, especially strong wind or unusual barometric pressure, will shift things. Always keep an eye on what you are seeing on the water.

Frequently asked questions

• Does this change tidal heights too? No. Tidal heights come from tidal station predictions and are already highly accurate. Hyper-local modelling addresses currents, which is where the difficulty lies.
• Why is my area not covered by a hyper-local model? Building one takes detailed bathymetry and significant simulation work, so we prioritise regions where complex geography makes standard models least useful. We are continuing to expand coverage.
• The currents still do not look right in my area. Please tell us. Send the location, the date and time you were looking at, and what you expected to see, and we will investigate. Reports from local sailors are genuinely one of the most useful things we get.

Need help?

If you have any questions or feedback please contact our team at ahoy@savvy-navvy.com OR via our in-app chat and we will be happy to assist you!

Updated on: 20/08/2026