VMG is the component of boat speed in the direction of the wind. If you are sailing into the wind, Boat Speed ​​equals VMG. If you are sailing across, your VMG will be zero.

VMG and the vicious circle

Don’t head towards VMG! If you luff more, you will notice that the VMG increases momentarily, but then the boat will slow down and the VMG will be lower than before. You might 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 down – but then the VMG would immediately get worse! This is because boats are relatively heavy and carry significant momentum, it is not a fault in the instrument system. The golden rule is to never try to sail towards VMG.

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

Isn't VMG my speed to a waypoint?

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

To be fair to our motor boating friends, older GPS units used to call this “Waypoint VMG”. But somewhere along the line the term was shortened to just “VMG” and this is now causing a lot of confusion.

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 “Layline.” See you soon.