Spring and Neap Tides Explained – What Every Boater Should Know

Spring and neap tides are a fundamental part of tidal navigation. Understanding the difference is essential for sailors, powerboaters, ocean rowers and anyone planning activities on tidal waters.

The height of the tide and the strength of tidal streams change throughout the lunar month. A lunar is defined as the time from one new moon to the next and is 29.53 days (29 days, 12 hours, 44 minutes, and 2.8 seconds). On some days, the difference between high water and low water is considerable, while on others it is much smaller.

These variations are known as spring tides and neap tides.

What Causes Spring and Neap Tides?

Tides are caused primarily by the gravitational influence of the Moon, with the Sun also playing an important but lesser role

Although the Sun is vastly larger than the Moon, the Moon is much closer to Earth and therefore has a greater gravitioanil pull (tide-generating effect).

As the Moon orbits Earth, the relative positions of the Sun, Moon and Earth change. Their combined tidal effects produce a regular cycle of larger and smaller tidal ranges.

What Is a Spring Tide?

A spring tide occurs when the Sun, Moon and Earth are approximately aligned This occurs at either a new moon or a full moon. At these times, the tide-generating effects of the Sun and Moon reinforce one another, working together and produe a greater tidal range.

During spring tides:

• High waters are usually higher than average.

• Low waters are usually lower than average.

• The range between high and low water is greater.

• Tidal streams are usually stronger, particularly in narrow channels and estuaries.

Despite the name, spring tides have nothing to do with the season of spring. They occur throughout the year, approximately every 14–15 days.

What Is a Neap Tide?

A neap tide occurs when the Sun and Moon are approximately at right angles to one another as viewed from Earth. This happens around the first and third quarter phases of the Moon.

Their tide-generating effects partially oppose each other. The high tide still follows the moon, but the sun reduces its effect, producing a smaller tidal range.

During neap tides:

• High waters are usually lower than average.

• Low waters are usually higher than average.

• The range between high and low water is smaller.

• Tidal streams are generally weaker than during springs.

Neap tides occur approximately halfway between successive spring tides.

The Spring and Neap Tidal Cycle

The complete lunar phase cycle lasts approximately 29.5 days, during which there are two sets of spring tides and two sets of neap tides.

●	◐	○	◑
New Moon	First Quarter	Full Moon	Third Quarter
SPRINGS	NEAPS	SPRINGS	NEAPS
Day 0	Day 7.	Day 15	Day 22

Illustrative lunar cycle. Actual maximum spring and minimum neap ranges may occur a day or more after the corresponding Moon phase, depending on location.

Comparing Spring and Neap Tides

Example: How Spring and Neap Tides Affect Water Depth

Consider a harbour with the following illustrative heights of tide, measured above Chart Datum.

For a vessel approaching a shallow harbour, there may be more water available around spring high water, but considerably less at spring low water. This is why understanding the tidal range is just as important as knowing the time of high water.

Why Do Spring and Neap Tides Matter to Boaters?

1. Under-keel clearance

Spring low waters can expose rocks, sandbanks and other hazards that remain covered during neaps. Conversely, spring high waters can provide additional depth over shallow harbour entrances and tidal sills.

2. Tidal streams

Tidal streams are generally stronger on springs. This can make passage planning more important, particularly through narrow channels, harbour entrances and around headlands.

3. Mooring and anchoring

A greater tidal range means allowing sufficient scope when anchoring and ensuring mooring lines accommodate the full rise and fall of the tide.

4. Launching and recovering boats

Slipways can be considerably more exposed at spring low water, potentially making launching or recovering small craft difficult or impossible.

5. Sailing and passage planning

Stronger tidal streams may help or hinder a passage. A fair spring tide can substantially improve progress over the ground, whereas an adverse stream can slow a vessel considerably.

Spring and Neap Tides in Southampton Water and the Solent

The Solent is a particularly interesting area for studying tides because the tidal streams and tidal heights are influenced by its complex geography.

Southampton is well known for its double high water and young flood stand, both of which can affect the shape of the tidal curve.

Although spring tides generally produce greater tidal ranges and stronger streams, high water does not necessarily mean slack water.

In some parts of the Solent, tidal streams can continue running strongly around high water. The timing of tidal-stream changes also varies considerably between the eastern and western Solent.

Boaters should therefore consult both tidal-height predictions and tidal-stream information rather than assuming the stream turns at high or low water.

Do Spring Tides Always Occur on a Full or New Moon?

Not necessarily.

Although spring tides are associated with the new and full moons, the largest tidal range at a particular location often occurs a day or two afterwards. This delay is sometimes called the age of the tide. It results from the way the oceans respond to the astronomical tidal forces and the influence of local geography. Consequently, the date of the largest spring tide should always be obtained from local tidal predictions rather than simply looking at a lunar calendar.

Frequently Asked Questions

Are spring tides only in spring?

No. Spring tides occur approximately every fortnight throughout the year. The name is unrelated to the season.

Are spring tides always higher than neap tides?

Spring high waters are generally higher than neap high waters, but spring low waters are generally lower. The key difference is the greater tidal range.

Are tidal streams stronger on springs?

Generally, yes. However, the actual strength and direction of tidal streams depend on local geography and other factors.

Are neap tides safer for boating?

Not necessarily. Weaker tidal streams may make some manoeuvres easier, but lower high-water levels can restrict access to shallow harbours and moorings.

How many days are there between springs and neaps?

Approximately seven days. The average interval between successive spring tides is about 14.8 days.

What are equinoctial spring tides?

Equinoctial spring tides occur around the spring and autumn equinoxes, in March and September. In many UK locations, these periods are associated with some of the larger tidal ranges of the year.

Can the weather affect spring and neap tides?

Yes. Strong winds and changes in atmospheric pressure can raise or lower observed sea levels relative to astronomical predictions. Consequently, the actual water depth may differ from that shown in tide tables.

Learn More About Tides and Navigation

Understanding spring and neap tides is an important part of safe navigation. At Chieftain Training, we teach tidal heights, tidal streams and passage planning on our RYA Day Skipper Shorebased, the RYA Yachtmaster Offshore Shorebased and many of our practical boating courses.

Author:

Doug Innes  BA (Hons), MCA Master 200 CoC & RYA Navigation Instructor Trainer.

For further reading, see our guides to Tidal Heights,  Southampton Tides and the Rule of Twelfths.