Tidal or Non-Tidal : What’s it all about?

You may come across the terms ‘tidal’ and ‘non-tidal’ with reference to RYA sailing certificates. Here’s some information about exactly what this means. I hope it will tell you a few things you didn’t know before …

Most of the oceans of the world are subject to tides, which are caused by the combined effects of the gravitational forces exerted by the Sun and the Moon and the rotation of the Earth. Tides cause the water level to rise and fall and, in doing so, the water is moved around causing a tidal stream which can sometimes be pretty fast!

When the water is at its highest point it’s called High Water. When it’s at its lowest it is called Low Water. The difference in height between High and Low Water is known as the tidal range. The bigger the tidal range, the stronger the tide. The highest tidal range in the world occurs at the Bay of Fundy in Canada with over 53ft (16m) difference between High and Low Water. The second highest range is in the Severn Estuary in the UK; this can be as much as 50ft (15m) with a tidal stream of up to 8 knots.

Did you know that tidal forces affect the entire Earth, not just the seas, although the movement of the solid Earth is only centimeters?

There are different types of tide:

• Diurnal tides are those where one High and one Low Water occur each 24 hours. Diurnal tides are mainly experienced in the Pacific Ocean.
• Semi-Diurnal tides have two High Waters and two Low Waters in a 24 hour period. These are mainly experienced in the Atlantic Ocean. This is the type of tide you’ll find around the coast of the UK, France, and the East Coast of the USA.
• Mixed tides have characteristics of both Diurnal and Semi Diurnal tides and are found in areas such as the Indian Ocean, Gulf of Mexico, and Australia.

Some bodies of water (the Mediterranean, Baltic, Black Sea, Caspian Sea, and Caribbean) don’t respond strongly to tidal forces. The reasons for this are a bit complex but basically it is due to their size and geographic nature. These areas are described as Non-Tidal. Although they do actually have small tides they are not strong enough to be taken into consideration when navigating.

If you like detail, Non-Tidal areas are those where the tidal range is less than 1ft or 0.3m. There are a few spots in the Mediterrean that have slightly bigger tides, although these are small compared to most places in the world. There is a 1m tide at Gibraltar, due to the Atlantic tide spilling into the Mediterranean at that point. There is also a 1m tide at Venice as the top end of the Adriatic and the largest tide in the Mediterranean is in the Gulf of Gabes, Eastern Tunisia, with a 1.5m tidal range.

Anyway, interesting as it may be to know Venice has a tide, it doesn’t affect the fact that the whole Mediterranean is classed as a non-tidal sea. This makes navigation easier.

Sailing boats are subject to the natural forces of both wind and tide. If there is no tide to consider, passage planning is a lot simpler. For example, we used to have a 31ft yacht on the west coast of Scotland, where tides could be 5 or 6 knots. Our little boat rarely exceeded 6 knots, flat out. Get your timing for the trip wrong and you’d be sailing hard but going nowhere … except possibly backwards!

If you take an RYA Day or Coastal Skipper course anywhere in the Mediterranean or Adriatic you’ll be issued with a Non-Tidal Practical certificate. This is fine for chartering in any of the non-tidal areas mentioned above.

Those who want to be able to sail elsewhere in the world – the UK or USA for instance, may well want to convert this to a Tidal version. In order to do that, you’ll first need to study some more theory to ensure that your tidal knowledge is up to scratch. You can then take a 2-day conversion course at a school in a Tidal area.

Here’s some RYA schools where you can take your tidal update:

• Hamble School of Yachting
• East Coast Offshore Yachting
• Plas Menai Sail Training
• UKSA
• Allabroad Sailing Academy

There are other schools that offer the tidal update as well.

Whether you learn in a tidal or non-tidal is only relevant once you start learning to navigate. At Competent Crew level the syllabus and course are identical in both areas – so why not take your Comp Crew in the sunshine with us?

If you intend mainly to sail in the Med or other non-tidal waters, there isn’t much point taking a tidal Day Skipper course, where you’ll spend a lot of the time making calculations you’ll never need here. The Tidal and Non-Tidal Day Skipper courses are both 5 days. Without tides to worry about you can spend a more time boat-handling and learning skills like ‘Med mooring’ – or of course you can just take a longer lunchtime and swim. 🙂

You definitely need tidal knowledge and experience to sail in tidal waters but I’ve become a great fan of learning in a non-tidal area first and then adding tides on as an extra layer of knowledge.

That’s one reason why we’re running our second tidal Highland Adventure in the spring. Find out more about this great trip by clicking

Best regards

Melody

PS: If you intend to sail with us in 2014 you can save money by booking and paying your deposit before the end of November. All bookings made within the next three weeks will be at 2013 prices. More information coming soon …