Westsail Performance Metrics

  • April 07, 2017 17:30
    Message # 4735705

    found this: https://www.fastseas.com/#

    Looks like a terrific planning tool, that would be made even better if I knew how to tweak the performance metrics for this to fit a Westsail a little better.

    Anyone have any ideas?


  • April 10, 2017 11:27
    Reply # 4739936 on 4735705

    Good day Steve:

    A couple of notes; the "create simple polar" is ok+/-  use 29.5 for waterline (I know it is not that) but that is about best we can do. I used 55deg which is optimistic +/- Probably should use 60 deg

    I recommend "edit my polar" 

    edit down the 2kt data if you don't have lite air sails by (about 1 Kt)

    add 1 kt all of the 15kts data  (if you have good sails)

    add 0.5 to all the 20kts data

    leave the 25kts data

    subtract 0.5 kts from the 30kts data (wave and wetted surface - bluff bow and a big bottom)

    On a passage from SFO to Hawaii it looks about right with the above (note 5.5kt motor speed and do that below 2kt.;  puts it at 15.5 days which is about right if you motor 15 Hr+ @5.5 and are ontop of the sails all of the time and clean bottom (i.e as good as Dave King). For older sails and mostly clean bottom cut all the polar data above by 0.25 to 0.5 Kt depending = 16.7 days or 17.3 if you sail down to 1Kt, but for old and worn sails and average bottom cut 1.25Kt off all #'s including motor speeds then you are 21 + days. 

    All of this looks good kind of ( but from my experience the routing from the program is not what I would use)  and even ? using it for a race. Here is why, if you do the above today (you would not be using the high and low as you should, i.e. not south enough on the first 2 days), I can go on, but but that would be a page long.  I would encourage you to become proficient at weather forcasting and prediction YOURSELF!. Based on a test drive of the above, I would give the FastSeas site; a C+ for a grade, but an A+ if compared to doing no planing at all. 

    PS. if you have a wind instrument and OpenCPN you could get your very own Polars and they would be 100% correct not a guess.

    Hope this helps:


    opps All of the above is true if you have faired the rudder (if not, all of the above 4kt speeds mentioned above are going to be 0.2 to 0.3Kts slower)

    The one part I would love to know, how real is there current data? it seams way to detailed to be real (maybe averages for locations, but a model to predict what they are showing is ? in my opinion.)

    Just in my opinion from weather faxes; NOAA wind speed conversion

    predicted 5k will be 3 or less could be 0;

    predicted 10 will be 6+/- ;

    predicted 15k will be 7-8 with gusts to 13;

    predicted 20 will be 15 to 22;

    predicted 25K will be 28 +/- :

    predicted 30K will be 35-45

    predicted 35 will be over 40

    when they predict 40Kt be ready for 50 +

    This is what noaa 45Kts looks like https://www.youtube.com/watch?v=hQ-svmgOxqw

    Last modified: April 10, 2017 16:46 | Anonymous member
Powered by Wild Apricot Membership Software