Ship's Log, Depth sounder, Wind speed and direction
A depth sounder transmits an ultrasonic signal from a transponder mounted on the the hull.
A signal is transmitted towards the sea floor and the time taken for the signal to return is used to calculate the depth.
They are less accurate over soft mud, when going astern due to propeller wash, fish, the wake of another vessel, and large variations in water temperature.
When on an unfamiliar vessel, use a lead line to verify the sounder's accuracy.
Depth sounders can be set up to read from the bottom of the keel, the location of the transducer, or the waterline.
There are advantages and disadvantages for each way of setting up the echo sounder.
a) Set to read from the deepest part of the vessel.The skipper knows when the reading is zero the vessel will touch the bottom.
Disadvantage:The draught of the vessel has to be added to the reading to obtain the actual depth.
b) Set to read from the transducer.There is no scope for introducing artificial error as you rely on the instrument's own calibration.
Disadvantages:Calculations have to be made for finding the clearance under the keel and to find the depth of water.
c) Set to give the actual depth.The information displayed will match.
Disadvantages:A calculation will be needed to allow sufficient depth for the draft of the vessel.
The log measures the speed and calculates the distance that you have through the water.
There are various types including through hull mounted, and trailing logs. The one shown
opposite is a through hull version and uses an impeller that spins as the water moves past it, sending pulses to the instrument. The instrument
calculates the speed of the vessel from the pulses.
The impeller should be cleaned regularly and checked for accuracy over a measured
distance. In some areas, dedicated surveyed markers have been installed that clearly define one nautical mile.
Being able to monitor wind direction and speed is helpful not just for sailing yachts, but all vessels. It allows the skipper to monitor the progression of weather forecasts and evaluate the conditions to be expected for any potential passage. On their own, they measure apparent wind which is the combined effect of your boat speed and direction, and the wind speed and direction.
