Call Yourself a Navigator?

CALL YOURSELF A NAVIGATOR?

from the Chief Sailing Officer

Most of us who cruise, especially those of us who own cruising yachts, consider ourselves to be competent navigators - but just how thorough, and thus safe, a navigator are you, really?

 

Earlier this year one of Australia's top offshore yachts on a fairly routine offshore night race out of Sydney was lost, with the loss of two lives. At around 0200 local time and thus in darkness the yacht hit rocks close inshore on an islet that was being used as a rounding mark.  Within a very few minutes and in the heavy but by no means unusual or extreme swells the mast came down, the keel bulb broke off, the yacht was flung on its side and broke up. Most of the crew were able to scramble on to the islet, but three went into the water.  Of these one was rescued alive but two - the yacht's skipper and another - were dead when their bodies were recovered.  Both were numbered among Australia's most experienced and respected offshore racers.

 

The organisers of the race, the Cruising Yacht Club of Australia, have recently published the report of its own internal committee of inquiry - and it makes salutary reading.

 

While very properly placing no blame the report offers some hard-to-escape conclusions about how the accident came to pass and, inter-alia, how it might have been avoided.  The section on navigation is particularly telling.

 

The yacht was apparently being navigated entirely from on deck and entirely relying on GPS and its related cockpit display. This display was of a type found widely throughout our own Royal Thames fleet. The report draws attention to possible initial set-up and initialisation errors that I know from my own experience to be not uncommon, to put it no more strongly. The report also draws attention to system errors to which I know from my own experience many of us pay little attention - indeed of which many of us are probably blissfully unaware. Do you know what Horizontal DOP is? (It is an indication of the likely error in a GPS fix obtained from two or more satellites that are temporarily, because of the juxtaposition of their orbits, in line or nearly so.)

 

There are other system errors to which frequently we pay little attention, but which lurk ever-present when we go to sea relying only on GPS not the least among them being the very rudimentary one of where our aerial is positioned, and the errors induced by the fact that inevitably it wafts about like a leaf in a thunderstorm.  From the report:

 

'A GPS aerial on a yacht is a very different situation [from those land-based, fixed aerials used to assess system accuracy] with its low height and angle of heel, which affects the horizontal plane of the aerial, plus an environment cluttered with the rig, deck hardware and crew.  The errors... would be exceeded on board a yacht and especially in the conditions of working to windward in a 20-knot breeze, a lumpy sea and at about 20o angle of heel.'

 

The full report of the inquiry may be found here and in particular I take the liberty of commending to all our navigators and owners pages 26 to 31.

 

The paper chart and the hand-bearing compass are still far from redundant.

 

Malcolm McKeag

Chief Sailing Officer.