VMG speed is the component of the ship's speed in the direction of the wind. If you sail against the wind, Boat Speed ​​equals VMG. If you navigate through, your VMG will be zero.

VMG and the vicious circle

Don't head towards VMG! If you luff further, you will notice the VMG increase momentarily, but then the boat will slow down and the VMG will be lower than before. You may be tempted to luff again (because it worked last time...), but again a short-term increase will be followed by a long-term reduction in VMG. To compensate for this loss of speed you could drop yourself – but then the VMG would immediately get worse! This is because the ships are relatively heavy and carry significant momentum, it is not an error in the instrument system. The golden rule is to never attempt to navigate to VMG.

It is advisable to check the VMG calculation – by definition, VMG should be zero when sailing at a true 90 degree angle (TWA); If it is not, check your instruments.

Isn't VMG my speed to a waypoint?

The term VMG has been used among motorboaters to refer to the component of speed toward a waypoint. However, sailing sailors resist!… We call the speed towards a waypoint VMG (Velocity Made Good on Course), which is very useful in long runs (dozens of miles or more), but generally not wear in short sleeves.

To be fair to our boating friends, the old GPS units used to call it “Waypoint VMG”. But at some point the expression was shortened to just “VMG” and now this is a cause of great confusion.

And that's the end of our advice for this week, but don't miss the next chapter where we will delve a little deeper into the topic of “Layline”, see you soon.