Tack Loss


The Tack Loss is a way to rate a tack (and to patentially bark at the driver).

It will enhance three major areas in the tack:

  1. Going head-to-wind
  2. Crossing the wind
  3. Recovering speed

Going head-to-wind

The boat has speed, and comes up. As a result, the VMG increases, because the boat speed remains as the true wind angle becomes smaller.

Crossing the wind

At this point, only the momentum given by its previous speed is moving the boat. As the speed can only diminish, this step must be kept as small as possible.

Recovering speed

Once the tack actually happened, the boat now needs to recover the speed it lost during the previous step.

Rating the tack

This idea is to find a geometrical way to rate the tack. The goal is to loose as less speed as possible, at to recover what's lost as fast as possible.
Instead of the boat speed (BSP), we will rather consider the VMG, as the goal is to progress upwind.
The three steps of the tack can be represented this way:

Tack Loss

The idea we found to rate the tack is to compare:

Tack Loss
this area in grey
Tack Loss
with this one

This way we compare a "no-loss" tack, with the area representing the VMG along the tack. Having a ratio of 1 is reaching the perfect tack.
An interesting parameter will be to know when to begin the measuring of the VMG, and when to finish it, relatively to the point where the boat is head-to-wind. After our experience, it looks like 10 to 15 seconds before and 30 seconds after are ok.

But, this only has a sense when the conditions before and after the tack are similar. If, for example, you tack to escape the bad gas another guy is sending you, you will probably do better on the new tack than on the old one. In which case the Tack Loss will probably reflect a gain...
Tack Loss is to be used when the two tacks are similar.

2003, Oliv Cool Stuff Soft Strikes Again !
Any comment ?