Hampton-to-St. John: The Route

Two weeks from tomorrow, weather permitting we will be under-way from Hampton VA to St. John USVI.  You can use Google Earth to see the route.  In a subsequent post I'll describe what this leg of the trip means to me.  This post describes the facts.

The total distance along the rhumb line route is 1280 nm (nautical miles, about 6076/5280 = 115% of a statute mile).  It:
-  departs Hampton and crosses Hampton Roads,
-  passes over the Chesapeake Bay Bridge Tunnel (at 10 nm into the route),
-  turns southeast at Cape Henry onto a course of 161 degrees magnetic, and hugs the coast of North Carolina (passing 15nm off of Nags Head),
-  hits the west wall of the Gulf Stream (at 142 nm into the route),
-  makes landfall at Cruz Bay St. John (at 1280 nm into the route).
(All this route planning is done in about 10 minutes on my laptop using Raytech RNS software.)

A useful rule-of-thumb is that one travels a distance of 200 nm in 24 hours at an average speed of 8.3 knots (nm/hr).  A more typical average cruising speed for Heron is 7.75 kn, so 186 nm/day.  Sometimes we do 10.5 knots for days at a time.  Sometimes we sail in light winds, hating to turn on the engine, doing 5 or 6 knots.  We'll have to conserve fuel on this trip in case we have too many light-air days, so let's assume 7.5 knots, or 180 nm/day.

If we leave at 0800 on Monday November 7, and travel along the rhumb line route at an average speed of 7.5 knots, we:
-  pass over the Chesapeake Bridge Tunnel at 0922,
-  enter the Gulf Stream at 0300 on Tuesday morning,
-  arrive at Cruz Bay at 1030 on Monday November 14 --just over 7 days on the ocean.

But that's the theory that won't happen.  Typically, boats follow a more easterly route to a point just south of Bermuda.  They do this to "gain their easting" while north of the easterly trade winds that appear at around 22-24N lattitude.  A very good explanation for why hundreds of boats follow this general route to the Caribbean can be found here:
http://www.worldcruising.com/carib1500/route.aspx
http://www.worldcruising.com/carib1500/featuresarticle.aspx?page=S634514213858597422&ArchiveID=4&CategoryID=145&ItemID=23819&src=
Some years it is more of a downwind sleigh ride, gybing down the rhumb line.  More commonly, boats sail a close haul course, tacking over onto port tack when the wind goes more easterly.  But whatever the optimal route is for each boat in the actual wind conditions, the distance travelled is more likely to be 1500 nm (than 1280), hence the name "Caribbean 1500 Rally".  So.... we don't expect to get there until 8.3 days --sometime Tuesday... or Wednesday... or.... and the weather could delay our start by a few days...  I am told that the USCG assumes an average speed of only 3 knots before it considers a vessel overdue on its plan.

The riskiest part of the trip is getting past Hatteras and across the Gulf Stream.  You don't want to be there in bad weather.  Fortunately, this is a very short-range (reliable) forecast for our departure from nearby Hampton.  But unless the forecast is ideal, we are likely to give it wide berth (head more easterly).  We are likely to keep our speed up over 8 knots (with the engine as necessary) to get the heck out of Dodge.  Once we are a few hundred miles from Hatteras, we'll have the sea room to deal with surprises.

So we'll plan our actual route using the forecast on the day of departure, and we'll adjust it to reality when we get out there.

Jay