Tide Tables and Tidal Currents

Understanding and predicting tides and currents for navigation planning

Tide tables and publications dedicated to tidal currents are essential nautical references whenever navigation depends on changes in water level, times of high and low water, or the direction and speed of tidal streams. Complementary to other nautical documents used on board, they transform astronomical and hydrodynamic phenomena into practical information for passage planning.

Tides influence many aspects of navigation: access to a harbour, crossing a bar or sill, navigating through a shallow channel, calculating under-keel clearance, choosing a departure time, passing through a tidal race or estimating the drift caused by a cross-current.

The Tide Tables and Tidal Currents category at Nautic Way Maritime Bookshop brings together specialist publications from the SHOM – French Hydrographic and Oceanographic Service, the Admiralty – United Kingdom Hydrographic Office, the Canadian Hydrographic Service (CHS) and other nautical publishers. The coverage extends from French coastal waters to major international maritime areas.

What is a tide table used for?

A tide table primarily provides predicted times and heights of high water and low water for reference ports or tidal stations. Depending on the publication, it may also provide tidal coefficients, calculation methods, corrections for secondary ports and other information needed to establish a prediction for a specific location.

This information is particularly important in areas with a large tidal range. In France, the English Channel, Brittany and parts of the Atlantic coast experience significant tidal variations. In these areas, just a few hours can considerably change the available water depth and current conditions.

A sailor preparing an entrance into Saint-Malo, Granville, Cherbourg, Dieppe, Le Havre or Brest must therefore consider not only the depth shown on nautical documents, but also the predicted water level at the planned time of passage.

Understanding water heights and tidal range

Tidal height refers to the elevation of the sea surface relative to the reference level used by hydrographic documents. It helps estimate the available depth of water above a sill, shallow area or critical depth.

The tidal range is the difference in height between successive high and low waters. It varies according to geographical location, the lunar cycle and the local characteristics of each bay, estuary or harbour.

Spring tides occur during periods when the tidal range is greater, while neap tides correspond to smaller tidal ranges. This distinction is particularly important when studying currents: a passage that appears relatively easy during neap tides may present very different conditions during spring tides.

In some areas, tidal current becomes a decisive factor in navigation. The vessel's speed over the ground can then be significantly increased or reduced depending on whether the current is favourable or contrary.

Tidal currents: direction, speed and time of reversal

Publications dedicated to tidal currents provide information that is different from, but complementary to, a tide table. They allow navigators to study the horizontal movement of water masses caused by the tide.

Current information can be used to determine:

• the direction of the current at a given time;

• its maximum speed;

• periods of flood and ebb;

• approximate times of current reversal;

• areas where currents become particularly strong;

• the effect of current on a planned route or arrival time;

• areas where wind opposing the current may produce rougher seas.

This information is essential in narrow passages and exposed areas. In France, it is particularly relevant around the Raz Blanchard, Raz de Sein, Chenal du Four, Passage de la Teignouse, the Iroise Sea, northern Brittany and parts of the Bay of Biscay.

SHOM publications for French coastal waters

The SHOM is the French reference hydrographic organisation for tidal and current data. Its publications and data dedicated to tidal currents cover different coastal areas and provide information on the hydrodynamic characteristics of French waters.

The documentation covers areas including:

• the Strait of Dover and Bay of Somme;

• the English Channel, from Dunkirk to Brest;

• Seine Bay, from Cherbourg to Fécamp;

• the Normandy-Brittany Gulf, from Cherbourg to Paimpol;

• the northern Brittany coast;

• the Iroise Sea;

• the southern Brittany coast, from Audierne to Le Croisic;

• the Pays de la Loire coast;

• the western French coast, from Saint-Nazaire to Royan;

• the Bay of Biscay.

These documents are particularly useful when planning navigation around ports such as Dunkirk, Calais, Cherbourg, Saint-Malo, Paimpol, Roscoff, Brest, Douarnenez, Audierne, Concarneau, Lorient, Quiberon, La Rochelle, Saint-Nazaire, Royan, Arcachon, Bayonne and Saint-Jean-de-Luz.

Admiralty tide tables

The Admiralty, the nautical publishing service of the United Kingdom Hydrographic Office, produces tide publications covering numerous regions around the world. The Admiralty Tide Tables are used to predict times and heights of high and low water for numerous standard ports and secondary ports.

This international coverage is particularly useful for sailors leaving French waters or planning offshore and international passages.

The publications cover areas such as the North Sea, the English Channel, British and Irish coasts, the North Atlantic, Arctic regions and, depending on the volume, other maritime areas around the world.

They are useful for passages and port approaches involving locations such as Dover, Portsmouth, Southampton, Plymouth, Cork, Dublin, Rotterdam, Amsterdam and Hamburg, as well as for longer passages in the Atlantic, Indian Ocean, Asia and the Pacific.

Data for international navigation

Tides are not limited to European coastal waters. They remain an important navigational factor in many regions of the world.

In the North Atlantic, tides are particularly relevant around Ireland, the United Kingdom, Brittany and the Iberian Peninsula. In the North Sea, tidal currents and relatively shallow waters make accurate consideration of tides particularly important.

In the Mediterranean, tidal effects are generally smaller than in the English Channel, but they should not automatically be disregarded in certain local situations. Navigators may also encounter meteorological effects, changes in sea level and specific conditions in harbours and lagoons.

For an ocean crossing, tidal information is mainly critical during coastal approaches, harbour entrances and passages through shallow-water areas.

How to use a tide table on board

Using a tide table generally begins by identifying the reference port corresponding to the navigation area. When the required port is not a standard port, the publication may provide corrections that allow a prediction to be established for a secondary port.

When planning a harbour entrance, the navigator can proceed methodically:

1. identify the relevant port or reference station;

2. determine the time and height of high or low water;

3. establish whether the tide is rising or falling at the planned time;

4. apply any corrections provided for the location;

5. check the available depth and the vessel's draught;

6. integrate the tidal current into the route calculation;

7. take weather conditions into account, as they may modify the actual sea level.

This method is particularly important when a vessel has a deep draught or must cross a sill with limited under-keel clearance.

Tide tables and under-keel clearance

Under-keel clearance is the amount of water maintained beneath the vessel's keel. Its calculation depends on the vessel's draught, available depth, tidal height and possible variations caused by meteorological or hydrodynamic conditions.

A tide table therefore allows the navigator to incorporate tidal height into the calculation of this safety margin.

A typical example is a sailing yacht entering a shallow harbour on a falling tide. The arrival time must be selected according to the available water depth, but also according to the time required to sail through the approach. The navigator therefore needs to consider how water depth will change throughout the manoeuvre rather than relying solely on the water level at departure.

Tidal currents and route planning

Tidal currents also have a direct influence on navigation under sail or power.

A favourable current can increase speed over the ground and reduce passage time. Conversely, a contrary current can significantly reduce progress. In a narrow passage, the effect may become substantial enough to completely alter the optimum crossing time.

This is particularly apparent in the English Channel, between France and England, but also around Brittany, in the Bay of Biscay and in parts of the North Sea.

Current information should be interpreted together with wind direction. Wind opposing the current can produce shorter, steeper seas, while following wind and current can create considerably different conditions.

Nautical documentation complementary to charts

A tide table does not replace a nautical chart. The two documents answer different questions.

A chart shows depths, hazards, channels, buoys, shoals and geographical features. A tide table provides time-related information about water level. Current publications add the dynamic dimension of water movement.

For comprehensive passage planning, the navigator can therefore combine:

• depth information;

• predicted times and heights of tide;

• tidal currents;

• harbour and approach information;

• weather conditions;

• vessel draught and speed;

• the required safety margins.

This approach provides a more complete understanding of coastal navigation and makes it possible to build a coherent passage plan.

Useful documentation for coastal and offshore navigation

Tide tables and tidal current publications are useful to recreational sailors and professional navigators alike.

They are relevant for a coastal sailing trip in Brittany, a Channel crossing, navigation in the Bay of Biscay, a North Sea passage or the preparation of an international voyage.

Hydrographic organisations and publishers such as SHOM, Admiralty, CHS and other international nautical publishers provide complementary geographical coverage. The appropriate publication therefore depends primarily on the navigation area, the type of tidal information required and the level of accuracy needed.

Conclusion

Tide tables and tidal current publications make it possible to incorporate both time and water movement into navigation planning. They are particularly important in areas subject to a large tidal range or strong tidal streams, such as the English Channel, Brittany, the Iroise Sea, the Normandy-Brittany Gulf, the North Sea and parts of the Atlantic.

From calculating available water depth to studying a tidal current, these publications provide essential information for selecting a departure time, crossing a difficult passage, planning a harbour entrance or optimising a coastal route.

For accurate navigation, they should always form part of a comprehensive planning process combining hydrographic data, depth, vessel draught, weather information and local conditions.

FAQ – Tide Tables and Tidal Currents

What is a tide table used for?

A tide table provides predicted times and heights of high and low water for different ports and reference stations. It is used to plan harbour entrances, passages through shallow areas and under-keel clearance.

What is the difference between a tide and a tidal current?

A tide primarily describes the vertical variation in sea level. A tidal current describes the horizontal movement of water. The two phenomena are linked but require different types of information.

Why are tidal currents important in the English Channel?

The English Channel has significant tidal currents, particularly around the Cotentin Peninsula, the Breton coast and narrow passages. These currents can substantially affect speed over the ground and navigation conditions.

What is a tidal coefficient?

A tidal coefficient is a value used particularly on French coasts to characterise the amplitude of the tide. It helps distinguish periods of spring tides from periods of neap tides.

Are tide tables intended only for professional navigators?

No. They are useful for recreational sailors, offshore navigators, fishermen, maritime professionals and anyone planning a passage where water depth or tidal current is an important factor.

Does SHOM publish tidal current information?

Yes. SHOM provides publications dedicated to tidal currents in different areas of the French coast, from the English Channel to the Bay of Biscay.

Why use an Admiralty publication?

Admiralty publications offer extensive international coverage and are particularly useful for navigation around the United Kingdom, Ireland, the North Sea and many other maritime regions.

Does a tide table replace a nautical chart?

No. A tide table provides time-related information about tides, while a nautical chart describes geography, depths, hazards and navigational aids. The two types of documentation are complementary.

How do you calculate the available water depth in a harbour?

The calculation generally starts with the charted depth or hydrographic reference depth, to which the predicted tidal height is applied. The vessel's draught and required safety margin must then be considered. Local corrections should also be applied where necessary.

Do tidal currents depend on wind?

Tidal currents are primarily generated by the tidal phenomenon, but wind can modify actual conditions at sea, including water levels, sea state and the interaction between wind and current.

Why should a tide publication correspond to the navigation area?

Tides and currents vary considerably from one region to another. A publication covering the English Channel does not provide the same information as one covering the North Atlantic, Arctic waters or another maritime region.