So, now the tool is available, the next question is when and how to make use of it. (OK, perhaps that is 2 questions?)
One usage that works all the time (by that I mean, for example, it is not always best to sail max VMC to the Mark) – is to determine which end of the finish line to aim for.
When you are on the final leg, approaching the finish line, quite often there is a question mark over which end to aim for. Sailonline actually uses a single point to describe the finish, and a length value – then it draws a line perpendicular to the rhumbline of the last leg, extending ‘length’ nm either side – that is the finish line you see on the race map.
Now, to determine which end to head for (or sometimes even exactly where on the line to sail to) to finish the fastest you just compute VMC using the next course Waypoint as the target (which is the junction of the finish line and incoming rhumbline)
So, lets say that from your boat the Port pin is at Bearing 270 and the Starboard pin is at bearing 275. If the maximum VMC to the last waypoint is on a heading of 278 – then heading for the Starboard end will get you over the line fastest. Even if, from your current location, that end is farther away! It may be obvious to some, but because sailing on a heading of 278 would make you miss the line, and the Starboard end is the and closest to that bearing, that is why we pick it to head for.
Likewise if the maximum VMC value was 268, you would head for the Port end. Easy huh?
Sometimes it happens, that the optimal VMC will be somewhere between the 2 ends – in this situation, just sail that heading output by the tool – and remember to recompute every 5 minutes or so, depending on how fast you are approaching the line. Perhaps it is better to recompute based on distance, say every 5nm, or 2 – depends on how much time you want to squeeze out
For a more visual discussion of this topic, read 76Trombones’ excellent article: Fastest Route to the Finish Line (actually read all his articles!) The first polar image in that article also gives you a clue on a technique to quickly determine a “rough, best VMC” to any target, using the steering tool in the SOL Race Client.
On a side note, it is funny to look at pictures of the ‘Old’ polar plot from the Sailonline client… Much has changed over the past 14 months 😉
There is even a comment in there by me when I was first starting to write small tools for SOL, confirming that using this tool for that purpose works…. Although at the time it didn’t automate boat and wind updates!
If you happen to discover any tips for how to use this tool for racing, please post here and share.