Sailing: What is VMG?

Velocity Made Good (VMG) is the component of the boat speed in the direction of the wind – if you motor dead upwind then Boat Speed equals VMG, if you are on a beam reach then VMG is zero.

VMG and the vicious circle

Don’t steer to VMG! If you head-up then you will notice the VMG will increase in the short term, but the boat will then slow and the VMG will be lower than before, you may then be tempted to head-up further – because it worked last time – and again a short term increase will be followed by a long term reduction in VMG. In order to compensate for this loss in speed you might bear away – but then the VMG gets instantly worse! This is caused by the fact that yachts are relatively heavy and carry a significant amount of momentum, it is not an error in the instrument system. The Golden Rule is to never attempt to steer to VMG.

It is always sensible to check your VMG calculation – by definition VMG should be zero on a 90 degree (TWA) reach, if it isn’t check your instruments.

Isn’t VMG my speed towards a waypoint?

VMG has been used by the powerboat fraternity to refer to the speed component towards a waypoint, however this is resisted by true sailors! We call the speed towards a waypoint VMC (Velocity Made Good on Course), which is very useful on longer legs of a course (tens of miles or more), but generally not used on short legs.

To be fair to our powered friends, the original GPS units used to call this “VMG Waypoint”, but somewhere along the line it has been shortened to merely “VMG” and now causes wide confusion.

And this is our tip of the week, but don’t miss the next chapter where we will deepen into the “Laylines” topic. See you soon!

⇐ Sailing: True Wind calculation

⇒ Sailing: Laylines