Après Ski, Let's Dance

In an email to me, Vendée Globe skipper "YR" compares weather routing in the virtual race to playing chess -- it is always important to thnk a few moves ahead.

I agree, as far as that analogy goes.
Here a two more ways to look at it:

• The race is like skiing down a mountain.
  You are starting at the top of the lift.
  You are headed for the lodge.
  There are many trails that will get you to the lodge.
  It is up to you to pick the best one.
  This is your synoptic weather-routing.
  
  But on your way down you encounter details you could not anticipate from the top of the mountain.
  A traverse across a smooth slope might be the equivalent of a beam-reach in a boat.
  A field of moguls requires careful routing [at the wind-cell level].
  Where you exit the mogul field is determined, in large part, by your entry point.
  Selecting that entry point is a crucial decision.
  -- and so is selecting the wind-cell you want to be in at a weather update.
  
  What I like about this analogy is that it reflects the dual-level planning needed for weather-routing.
  Moreover, this dual-level of planning applies in both virtual and real-life ocean passages.
  
• Back at the lodge, a jazz band is playing and it is time to get on the dance floor.
  In this analogy, the wind is the music, and your routing is the choreography you use to dance to the music. 
  
  [A personal note: My Dad was a musician and my Mom was a dancer.  I have played in bands and orchestras.  I have choreographed dances.  It is from this perspective that I offer....]
  
  A jazz band usually plays the first chorus as written in their charts.
  After that, it is time to improvise.
  A big band will stay closer to the original tune than a combo.
  And this is exactly what happens with weather updates.
  The larger the weather system, the less likely that you will be surprised by the way the update has 'improvised' on the prior forecast.
  For light and unsettled winds, however ... well, who knows what those cats will be playing in the next chorus?

Neither analogy is perfect, and the chess analogy still applies.
Taken together, these perspectives help me to wrap my mind around the challenge of weather routing.

Passing by Storms, and Vice Versa

Whether sailing 'virtually' or in real life, storms that pass by can help or can hurt.

In real life, avoiding a potentially dangerous storm usually takes precedence over trying to take advantage of the storm. 

In virtual sailing, the dangers are virtual as well.  With 'real' dangers gone, it is easier to analyze how to use a storm to improve sailing speed.

As I write this, the Vendée Globe sailors [real and virtual] are moving across the Indian Ocean towards the waters to the south of Australia and New Zealand.  The storm pattern looks like this:

 It doesn't take a great deal of analysis to determine that:

• Storms rotate clockwise in the southern hemisphere.
  
• Sailors heading west will do best by bouncing across the top [that is across the northern part] of the storm's wind rotation.

Of course, a sailor's life is never quite that simple.

• Great Circle routing looks at the shortest distances between two points on the globe, and not on a flat map. The meridians [lines of longitude] are much closer together near the poles than they are near the equator.  For example: 10 degrees of longitude is:
   -- 459nm at 40*S latitude
   -- 383nm at 50*S
   -- 298nm at 60*S
  These are differences that a racer must take into account.
  
• The Vendée Globe race committee has established 'ice-gates' to keep the racers from sailing too far south -- and either hitting ice-bergs or freezing to death.

What is the best overall strategy?
That is the topic for the next blog entry.

Practice, Practice, Practice

Javakeda is sailing in the Vendée Globe because this race is one of the best opportunities for amateur weather-routers [of which I am one] to practice their skills.

Where else can you

• read a GRIB file
• make course decisions
• have those decisions confirmed or debunked by the elite skippers of a fleet almost 400,000 strong.

Only in the Vendée Globe.

But, in addition to weather-routing strategy, the race lets me practice the mechanics of routing.
This is the watch-to-watch:

• OK, here are the winds
• Looks like we should go this way for the next watch.
• Looks like we have a handle on the long-term route
  ... or NOT!

Last October, I was the weather-router to the Sea Witch as she made her seasonal passage from New Bedford, CN to the British Virgin Islands [BVI].
I was 'shore crew' -- not on-board, but in regular contact with Captain John and First Mate Dennis.

The first leg of the passage [New Bedford to Bermuda] went well.
Sea Witch set a personal best for that passage.
On the leg from Bermuda to the BVIs, however, the 'routing' became very serious.

We had TS-Patty passing to our west.
We had TS-Rafael, coming at us from the south-east.
Sea Witch was able to pass safely to the west of Rafael within 100nm of the center.
This was less than 24-hours before Rafael became a hurricane.
This was less than 12-hours after Rafael passed over the BVIs, our destination.

Definition:

Experience is what you get, just after you needed it.

Days before, we had made the right decisions regarding our route.
But during the critical time, I wished I had better routing tools and more experience.
In the days after the passage, I resolved to practice
 -- and here I am.







 

 

The Basic VMG Calculation

Understanding VMG (velocity made good) is essential if you want to sail your boat quickly from point to point.  This is true regardless of whether your boat is real or virtual.
VMG values are used in many 'advanced' racing tactics, but the calculation of these values remains the same.

From a 'trig' standpoint, it should be obvious to you that VMG = BtSpd * COS(40*).
Easy enough to let a spreadsheet or scientific calculator tell you the actual value of the Cosine.
You don't need to know the actual values of the trig function.
But the fundamental relationship between BtSpd and VMG should be clear.

If not, you can go to Google for help.
And, of course, you can comment on this blog.