With all this data readily available, it can sometimes be a little overwhelming. Different pieces of data gain and lose significance throughout a sailing passage. For example depth will be less significant when halfway across the English Channel compared to entering a harbour on a falling tide.
It may be necessary to configure a display with multiple pages allowing you to quickly and easily change page to keep a high level of awareness of the relevant information. Dedicated instrument displays such as Triton come with up to eight data pages which gives you the option of customising pages to suit your needs. In addition, some instruments will swap pages automatically if desired. A simple user interface will allow quick selection relevant data.
How do displays derive the data I see?
Instrument systems display 2 types of data. Measured functions consist of (Apparent) Wind Speed and Angle, Boat Speed, Heading and Depth. (Depth is the exception because apart from applying an offset, it is not used in any other calculations.)
Wind Speed and Angle are measured at the top of the mast with a masthead unit comprising a wind vane and cups. The angle that the wind vane is pointing is measured and displayed as the Apparent Wind Angle and is relative to the centre line of the boat. Apparent Wind Speed is measured in knots by calculating how fast the wind cups are rotating.
Boat speed is normally measured with a paddlewheel that is installed through the hull of the vessel. The flow of the water against the blades causes it to rotate – the speed of the rotations is equivalent to the speed through the water or Boat Speed. Depth is measured with another sensor (sometimes combined into the same through-hull fitting as the boat speed sensor) that emits pulses of sound at a high frequency.
The sensor listens for the return echo from the seabed and, similar to radar, the distance can be calculated by measuring the time taken between sending and receiving the pulse.
And this is our tip of the week, but don’t miss the next chapter where we will deepen into the “TWC”- True Wind Calculation -. See you soon!