Posted by: Libby | June 13, 2009

What’s Faster? Ducking Jetties or Snuggling Up to Sand Isand?

Several days ago, Rick and Milo were talking about racing and had a difference of opinion.  Rick says ducking jetties up the Washington shoreline is the fastest way to get  from the red/green can below Sand Island to the green can outside the mouth of the Lake River.  Milo says that hugging Sand Island is faster.

In an attempt to provoke additional argument on the subject, I talked Rick in to gathering some data and helping me craft this explanation of what we found:

Rick and I took Raven and two GPS units and motored at the same speed up both courses. (We also took some readings going the opposite direction and discovered that the current is ripping along at a whopping 2.5 knots!)

Here’s how it came out:

Milo’s Way:
Distance:2.21 nautical miles
Elapsed Time:35:53.3
Avg Speed:3.7 kts

Milo hugs Sand Island before crossing the channel to rejoin the fleet

Milo hugs Sand Island before crossing the channel to rejoin the fleet

Rick’s Way:
Distance:2.33 nautical miles
Elapsed Time:34:26.3
Avg Speed:4.1 kts

Rick's preferred route past Sand Island

Rick's preferred route past Sand Island

So Milo’s way is shorter, by about 1/10th of a nautical mile.  But with 2.5 knots of current, the jetty ducking method resuts in an average of .4 knots more speed over the bottom, which gets you from Point A to Point B about 90 seconds faster.

There wasn’t any wind the day we took the readings and we were motoring with our sails down.  On a typical summer day, however, the wind would be coming out of the north/northwest and would likely be heavier on Washington than it was along Sand Island, since the tall trees on the island would be a bit of a buffer.

Interestingly, some of the strongest current we measured was along the Washington shore, just outside the jetties.  Running a straight line from dolphin to dolphin puts you right smack in the middle of it.  You have to get  close enough toward shore that you are to the left of the current line.  Just watch the deep-o-meter, and try to minimize the amount of time it takes to duck out around the end and get back inside while keeping the spinnaker flying.  This takes good communication with your crew.

So in last Thursday’s race, we corrected out over Nanuk by 60 seconds. Do you think the result would have been different if Milo had ducked jetties too? Hmmmmm……


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