asic apparatus

The basic instrumentation is intended for motorboats and small sailboats, intending to take day long coastal journeys. It is composed of a logspeedo, to know the surface speed of the vessel and a vane/anemometer to know wind direction and force. A digital sounder (numbered, nongraphic information,) completes the equipment. They are simple and have a read out dedicated to their function, except for some bi or tri-data models; a single screen for two or three sensors. Note that the log-speedo may also indicate water temperature.



Central navigation

If you are looking for more information and want true values (wind speed, drift, heading etc.) you must refer to a navigation unit. These central systems are designed for sailing, to find relevant information, or performance. On a regatta vessel, one puts the emphasis on a model
giving as much information as possible on the actual wind (speed and direction) with the possibility of returning to the ship, specific data (polar) and displaying it…On a cruiser, it is often limited to actual and apparent (wind speed) and course display(electronic compass.)
Generally, centrals are composed of a calculator (black box) on which sensors are connected and displayed. These are programmable (not dedicated) capable of displaying all information centrally. They are placed at different points on a sailing boat (helm, for example…) for which they display all information. The capacity of calculation of the central is important. That is what will determine the relevance and frequency of information displayed.

The sensors and their installation
The speedometer
This is the sensor that indicates the speed of the boat on the water. It consists of a wheel and magnet. When the boat moves, the mobile equipment turns. It then simply counts the revolutions to deduce the speed and distance. On a sailboat this sensor should be mounted in a through-hull forward of the keel in the axis of the boat to give the same information from one side to the other. It must be located in a zone where the water is not disturbed.


Wind vane-Anemometer
This is the sensor that measures wind speed. This is essentially the same principle but with an aerial that can be mechanical (cups that rotate) or electronic (static ultrasonic sensor). For wind direction, it uses a wind vane which is placed in the wind. The vane-anemometer (both sensors are combined, the weathervane on top of the anemometer) installed on the mast head on an arm which holds the sensor to the front so it is not disturbed by the sails and works in the breeze.


The Sounder

This is the sensor that measures the depth under the boat. The sounder works on the frequency 200 kHz (range 200 m). Via its probe installed in the hull, it sends an echo and measures the time it takes to come back. Taking into account the propagation of sound in water depth is deduced. On a sailboat, the sonar sensor must be at the front of the boat in line and always in the water. On a boat with inboard engine, it is placed in front of the engine, between the middle and 2 / 3 of the hull. With outboard motor, one chooses a rear sensor ensuring that the probe is an extension of the hull bottom, to avoid turbulence. The electronic compass The sensor indicates the compass heading. It must be calibrated so that it memorises north. The compass is installed on a vertical partition inside the boat. One must ensure that the area is cleared of all metallic mass which may affect the compass. If the compas  may be utilised by the central navigational unit, it will provide the basic information of the autopilot.

Professional advice

“By day the screens must be legible even with polarized sunglasses, night lighting should not blind the crew.”