Sunday, December 2, 2012

Welcome and Voyage Overview

We will use this forum to discuss progress and related matters of navigation and weather for the upcoming OAR Northwest ocean rowing expedition from Dakar to Miami, across the tropical  Atlantic. It will be the longest non-stop, self-supporting ocean rowing venture on record. It is scheduled to depart around the second week of January, 2013 and be underway for about 60 days. The last of the team departs Seattle for Dakar on Dec. 4. The boat is on a ship on the way there, expected to arrive about Jan 4, after several stops.

When we get more specifics on the boat transport, we will post them here. (The first post of this shipment was not right. Storm Sandy had changed scheduling out of NY that not all agents knew about.)

We will address wind, waves, and ocean currents, using the state of the art information.  The boat will be transmitting back the actual data observed, along with much other scientific data, so we can learn how well these modern resources work in practice.

You are invited to post questions and comments here, and we will address them as best we can. It promises to be an exciting event, with much to be learned about ocean rowing navigation, much of which will apply to any vessel transiting the tropics.

Nav Notes, Dakar to Miami

Departure: 14º 38.6'N, 17º 26.0'W

Destination: 25º 45.5'N  080 07.4'W

Distance rhumbline (RL) = 3606.03 nmi on a constant heading of 280.7 T
Distance great circle (GC) = 3561.55, with an initial heading of 291.5 T

At an average speed made good (SMG) of 2.5 kts, this is 60 days. This assumes an average distance per day of 60 nmi.

Currents are variable along the route, but usually less than 0.8. If we could find currents that average a favorable 0.5 kts, then we save about 10 days!  We have notes in this blog on current eddies that will have a dramatic effect on progress, and it will be part of the study to learn about them.

Thus is is difficult to imagine the trip taking less than 50 days under very best conditions.  Over the last several ocean rows, the average speed was 2.5 kts. These trips included times of much more favorable currents, but also times holed up with no speed at all. It is felt that 2.5 kts is a good planning speed for such a trip.  That is, just a bit slower than an average walking speed, so this shows how long it would take to walk to Africa from Miami… which in one sense is not that long. It is a small world after all.

With that said, there are records kept of all ocean rows of all 4-man crews, and those that are mostly in the trades like this tend to average a bit higher, maybe up to 3.0 kts.  For now we are still using 2.5 for our DR (dead reckoning). If we learn different, we will update this.

At present there does not seem to be any route that would favor a direct one (GC or RL) whenever possible. Things that might change this are notably stronger trades to the south of the RL, or the development of anomalous currents.

The Cape Verde (CV)  island group is about 300 nmi from Dakar, right on the route to Miami. The Great Circle route just skims the top of the Cape Verdes. The Rhumbline goes right though 70-mile wide channel over the top of the southern most island. The main first tactical issue (Dakar to CV), however, will be to deal with expected winds that are rather well north of NE. Thus there will likely be a struggle at first just to stay up as close to the GC route as possible.  The wind frees up (goes more NE to E) as they get past CV.

The chart below shows the GC route (blue line) along with the major GC shipping routes (red lines) where they might expect to see some traffic.

The green line is about halfway across, where they will be about 1,000 nmi from land in all directions, and on the way home past that.

Screen cap  from Furuno MaxSea echart program. Furuno is a supporter of the expedition and we are grateful for their valuable contributions in charting and electronics.

We will post a gpx file of these routes as soon as they are tested.... better yet, we will actually set better boundaries on likelyhood of ship encounter based on satellite records of actual ship paths integrated over many years, as shown below.

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