pyi vendee ad

diab big

west system fp banner ad 1 15

pyi-kiwi-12-16

Posts Tagged ‘calculations’

Article Separator

tack

Question Of The Week

SA’er ‘Allen’ asks the community to weigh in on his tacking calculations.  

I have been trying to figure out not how long it takes to tack but rather how much time it costs to tack.  My boat is probably not typical as it is old and wood and has a long fin keel with the rudder hung on the end of the keel.  I know it takes about 15 seconds to tack but part of that time is spent going directly up wind, which is the direction I would really prefer to go so there has to be some benefit to that.

I took a GPS track of a tack from our last race in which we did a lot of tacks, mostly on wind shifts, but this particular tack was not on wind shifts so I had a constant bearing before and after the tack.  I then calculated the speed at each second toward a point a long way away. I adjusted the location of that point until the average speed before the tack and well after the boat settled down after the tack was the same.  Next I compared the average speed of the entire sample, which was 200 seconds, to the steady state speed.

The conclusion was that while it took about 15 seconds to tack and my speed dropped from 6 knots to below 4 at the worst point, my average speed to windward only went from 3.9 knots to 3.6 knots.  The net loss was just under 5 seconds or 9 meters to windward.  Clearly the loss of speed was compensated by the almost full 6 knots toward the far off point as I turned the boat before it slowed down.

Has anyone done or seen this kind of analysis? Does my technique seem correct?  How much time do other boats lose when tacking?

For reference, my boat is 36 feet long, 12,000 lbs.

Follow the discussion or weigh in with your own ideas here.

August 11th, 2014 by admin

front-banner

http://www.camet.com/