Race Director's Report
The Doldrums Corridor Rule

14 September 2015

It is possible for a yacht to be becalmed for days on end within the grasp of this windless area. So in order to help preserve the arrival time into Rio at the end of Leg 1, the Clipper Race Committee decided to remove the uncertainty of the ITCZ (Inter Tropical Convergence Zone) or ‘Doldrums’.

The benefits of organising Leg 1 in this way include more certainty for booking flights and accommodation for crew and for friends and family too. It also means that the required time can be spent in port preparing for the next race minimising the knock on effects of a late arrival on the following legs.

The ‘Doldrums’ is a broad belt of shallow pressure and weak pressure gradients, towards which the trade wind air streams of the Northern and Southern hemispheres flow. The expected weather is variable light or calm winds, alternating with squalls and thundery showers. This band of pressure moves North and South on a daily basis according to the seasons and it can be very difficult to predict exactly where the ‘Doldrums’ will occur with any meaningful accuracy until a few days before.

The Course Instructions for Race 1 state that the fleet must pass through a gate which will be at 12°N and between 25°W and 29°W. This will be designated as the ‘ITCZ/Doldrums Corridor’. Within this corridor a skipper and crew can elect to motor-sail for exactly 6° of latitude and for a maximum of 60 hours. The corridor’s southern limit will be at 2°N. A yacht is not prohibited from moving either east or west as long as they stay in the Doldrums Corridor between 25°W and 29°W.

Once 60 hours have elapsed then the team must switch off their engine and continue racing under sail. If they arrive before 60 hours has elapsed then they must wait at that position for the entire 60 hours to elapse before re-commencing racing. For example, if a yacht starts motor-sailing at 12°N then they must stop at 6°N. If they start at 10°N then they must stop at 4°N. If they start at a point south of 8°N then they must stop at 2°N. This is why a yacht must declare passing the latitude of 8°N regardless of whether they are sailing or not, in order for the 60 hours of elapsed time to be calculated.

The ITCZ will still remain a tactical problem. It is the team’s decision on when and where to start motor-sailing depending on the ITCZ position and more importantly where it will be after 60 hours.As its boat speed was falling below 3 knots, LMAX Exchange elected to start its motoring phase at the northern limit of 12°N. This means that it must stop at 6°N or when 60 hours has elapsed, whichever occurs first.

So to recap;

  • -The doldrum corridor is defined by four virtual waypoints (you can see this on the race viewer);
  • 12°N /25°W in the north-east corner
  • 12°N /29°W in the north-west corner
  • 2°N /25°W in the south-east corner
  • 2°N /29°W in the south-west corner

  • -Each yacht may elect to motor-sail for 6° of latitude or 360 nautical miles within the Doldrum Corridor.

  • -Each yacht has 60 hours to complete the 6° of latitude or 360 nautical miles.

  • -If a yacht completes the 6° of latitude or 360 nautical miles before 60 hours has elapsed they must wait at that position until 60 hours has passed. This is to make it fair for all yachts.

  • -A yacht can move either east or west in the corridor.

  • -All yachts must declare their time of crossing 8°N so that 60 hours elapsed can be calculated. This is because all yachts starting their motor-sail below 8° must cease at 2°N which clearly means they cannot travel the full 6° of latitude.