Open Sea Race Conditions

The majority of the races on the Leinster Open Sea calendar are open sea races in the Irish Sea (the other races are open water races in lakes). Conditions at each open sea race will be different because of tide, wind and weather and can only be assessed at the race location before the race.

How difficult or easy it is to compete in an open sea race depends on many factors:

  • distance of the course
  • shape of the course
  • location of the course
  • weather and wind
  • water temperature
  • fresh water or salt water
  • tidal streams

The strength and direction of the tide is a more important factor in determining the difficulty or ease of competing in an open sea race than the distance of the race. Therefore to judge or grade an open sea race based on the distance of the race on its own is misleading.


The Irish Sea is a moving body of water and is subject to tidal movements. An incoming tide flows in a different direction to an outgoing tide. The strength of the tide varies from day to day depending on the tidal range before high water and low water.

Height and time of tides are available online, for example at

Rule of Twelve (Tides)

There is six hours between high and low water and low and high water. The tide flows at its strongest at the midpoint between high and low water and is close to slack when the tide turns at high or low water (see Wikipedia article on tides).

If the race is run within an hour either side of high or low water there may be very little tidal current, whereas if the race is run two hours to an hour before high water there may be a substantial tidal current.

That is why the start times of races are important so that swimmers have a chance to “catch the tide” when it is going in the direction of the race.

How Tides Affect Swimming in the Open Sea

If the tide is going in the same direction as the race course, a swimmer will swim 1,600 metres faster than they would in a heated indoor swimming pool. However if the tide is in full flow in the opposite direction to the direction of a race, it may be next to impossible for a swimmer to swim 400 metres against the tide.

It is the job of the organising clubs to check the time, direction and strength of the tide when planning races. Clubs often set courses so that swimmers benefit from tidal streams.

Check out this article on swimming and tides.

Shape of the Course

If a course is straight (point to point) swimmers should get the full benefit of the tide. If however the race is a rectangular course or triangular course, swimmers may end up having the tide push them on one leg of the course and slow them down on the next leg of the course.

Swimmers new to open sea swimming often find it easier to navigate along a straight line (point to point) course, and find it difficult to adapt to courses where they have to learn to navigate and swim to a buoy. This is one of the skills which swimmers must acquire in open water swimming.

Where a swimmer swims will also determine how much gain or loss they obtain because of tides. The tide will run at different strengths close to shore or out from the shore. Swimmers need to determine what line to take, to benefit most from tides.

Weather and Wind

Open sea races like other maritime sports are dependent on the Irish weather. When setting a course in the sea on the day of race, the club must take into account prevailing sea and weather conditions. It is therefore not possible to publish in advance an absolute guarantee that an open sea race will be a given distance. Clubs may need to change courses to take account of the prevailing wind and sea conditions.

Location of the Course

Courses such as those at Seapoint and Windsurfers Pier are in the lee of the wind (except from east winds) and therefore afford greater protection to swimmers than more exposed courses.

Temperature of the Water

Clearly racing in early June when the water is colder is harder then mid July or August when the temperature of the sea rises.

Fresh Water or Salt Water

Swimming in lakes can be more difficult than sea swimming as swimmers do not have the benefit of the buoyancy of salt water.