Spring Tides

Spring Tides

As the seasons roll on and we embrace Spring, we thought we’d look at Spring Tides and their impact on yacht chartering and sailing.

The first thing to know about spring tides, is they have absolutely nothing to do with Spring!

What Are Spring Tides?

A spring tide or ‘springs’ is a higher than average tide, whilst ‘neaps’ refers to a lower than average tide.  A spring tide occurs roughly every fortnight.

What Causes Spring Tides?

Tides are caused by the gravitational pull generated by the Sun and Moon.

As the moon orbits Earth, twice a month, the Earth, Sun and Moon are all in alignment – and this combined gravitational pull is what causes the larger surges of water, or ‘spring tides’ (image source oceanservice.noaa.gov/facts/springtide.html).  These dates coincide with the New Moon and Full Moon phases.

 

Seven days after the Spring Tide caused by the alignments, the Moon and Sun are at their least aligned points within the orbits, and therefore exert a lower combined gravitational effect which is when we see ‘neaps’.

Why are Spring Tides Important?

As a sailor, it is important to know when it is springs and when it is neaps.  In the UK, the tide still changes direction every 6 hours (approximately), but during springs the tide is higher at high-tide and lower at low tide.  Therefore, the tidal range is greater during springs.

 

In addition, for the water to flood to the higher high-tide and ebb to a lower low-tide during the same 6-hour window, it must flow faster during springs than neaps.  In the Solent, the tidal flow is easily twice as fast during springs at HW+/-3.

 

 

If you are chartering a yacht, or planning a sail in the Solent, there are several ways in which spring tides can affect you, all of which can be addressed with sensible passage planning:

  • If your berth is in shallow water or you are visiting a marina which has a sill, during springs you may have a reduced window to arrive or leave from the berth /marina.
  • If you are not moored on a floating pontoon or buoy (for example on a harbour wall) you will need to adjust your lines more frequently.
  • The tidal flow will make a considerable difference to the speed you can make through the water. It is not unusual to see 4 knots of tide through the narrows at Hurst Point and with a gentle breeze or low-powered engine you may only have a boat speed of 4 knots, so you could find you are unable to make headway against the tide, which could delay you for several hours.
  • If you are sailing around the Isle of Wight, consider the overfalls around St. Catherine’s Point which are exaggerated with faster flowing water.
  • Consider the impact of wind against tide – during springs this can affect the sea state and make for a rough crossing, which may not sit well with some of your crew.
  • If you are sailing across the Solent, the rushing tide will sweep you sideways so make sure you calculate and plan for any cross-track error and plot your course accordingly.
  • In addition, the faster flowing water can make berthing challenging for less experienced sailors.

How to Tell When it is Springs and when is Neaps

Any almanac or tide tables contains the details of the times and heights of tides to help you plan your sailing on any given date.  Often, springs dates are highlighted in red, and neaps in blue, although some will show symbols of the full and new moon, so you can work this out yourself.  Alternatively, you can look at the heights and ranges of the tides and calculate when this is greater and therefore springs.

A top tip for Solent sailors, is that when it is springs, high-tide occurs at midday.  So, if you arrive at Hamble Point marina at 6pm to a high tide, you can be sure it is a neaps tide.

If you are uncertain how to read the almanac, calculate tidal heights or would like additional practice at berthing in a spring tide, please contact us and we can arrange for a qualified instructor to join you on board for a day, or you can join one of our many RYA courses.

 

 

 

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