The most important piece of data you need when you're underway is depth. If you run aground, knowing that you're 250 metres from the layline or that you should be able to achieve a VMG of 5.3 knots is pretty irrelevant, so a good depth sounder should be high on your list.

Depth sounders are very reliable and rarely give erroneous data. However, due to their importance to the safety of the boat and crew, it is advisable to check them from time to time. Important things to pay attention to:
• Is the depth reading varying?
• Does the depth reading appear accurate?

Typically, in waters deeper than 100m a standard depth sensor will fail to find the bottom. But depth gauges have a secondary application: They can be used to detect an inaccurate GPS position. If your chartplotter says you should be at 30m, but your echosounder shows you are at 10m, be on the alert: either you have a tidal range of 20m, or your chart is inaccurate, or your GPS position is inaccurate – either way, you should be concerned!

Modern GPS devices are incredibly accurate, but they are not infallible. The “disclaimer” warnings that all of these units now display are there for a reason and not just to limit the manufacturer’s liability. Over-reliance on navigation aids is not good practice and can get you into serious trouble. Your eyes and common sense are the most important navigation tools you will ever have.

Course

You know the depth of the water. Now you need to know where you're headed. A heading is a crucial tool whether you're using it as a reference for wind direction or for dead reckoning across a channel, bay, or just in a zone of reduced visibility. The simplest example: If you're sailing south and later find yourself surrounded by fog, you know that to get home you need to head north, and you can navigate with this basic information.

Ship speed (Log)

If you know your heading, the ship's speed, and a time reference, you can use the dead reckoning method to calculate your position fairly accurately. This is the method, along with celestial navigation, by which ancient ocean navigators found their routes.

We now generally refer to Speed ​​Log as Boat Speed, and use the word “Log” to indicate speed.
car miles sailed (like the odometer on a car). Accurate boat speed is, and has always been, key to achieving an accurate measurement of navigation and performance.

Royal wind
True wind is the wind experienced by a person or object when stationary relative to the surface of the water.

Apparent wind

Apparent Wind is the wind experienced by a person or object while it is in motion. If you stand still on a windless day, you will not notice any breeze. However, if you go for a ride on your bike, you will notice the wind rushing past you. This is the Apparent Wind effect. Apparent Wind not only differs from True Wind in speed, the angle is also different.

And that’s all for our tips for this week, but don’t miss the next chapter where we’ll go a little deeper into the topic of “Wind.” See you soon.