Originally Posted by kiltym
To use in routing software for longer trips.
I received a 20kt polar from FP, out of the original FP Tobago
brochure. It's a start. I have attached it here.
Would like to make my own, and looking for some software to help out with the process since a computer should be able to build a decent one given enough time on the water
Yep, most racing
software will build them for you provided your data (wind, compass
, log, etc.) is fed into the software. Then you must sort the outcome by the sail choice used and you may sort it out by the sea-state.
I use polars of various boats for weather
routing. Remember you will want RT (not delayed) gribs in regular intervals - the less the interval, the more accurate the result. It also takes quite some time to learn the specific software and its quirks and limitations to use wx routing functionality effectively. Most boats, if sailed by actual VMG fare at least nearly as good as those that are wx routed. But it is fun, and some people are simply pressed for time (or else scared by the weather) and so it is a great thing that such things as gribs and polars and PC's exist. Other pieces of software you may like to have onboard are a wefax receiver, a digital pilot charts
atlas, and a good grib downloader. I have not yet found a good digitized support for ocean currents but there is good information strewn on the web. Get it - you do not want to get that extra 0.5 of a knot
from your wx routing skills only to be wasted by an opposite ocean current
that could otherwise be avoided!
A good starting point is to extrapolate from the polar you attached and while observing your boat you will be able to make some very educated guesses into what speed is likely in any given conditions and which gybe/tack takes you to the best location for tomorrow's conditions. Two generalizations that can help you upfront will be that in light conditions, as soon as the boat starts going, you will achieve good speeds close hauled and up to beam reach but not on the 'very broad' reach and running; as the wind
builds beyond her comfort zone, you will still be able to upkeep good speeds broad reaching and running but not beating and close hauled. Most polar data of manufacturers omits this fact - they all think out there in the design office that we are sailing on a lake, really ;-) Another general rule
is that you are sailing a cat and so you will be sailing broad reaches rather than runs and so you must tell your routing software this is the case; otherwise, right out-of-the-box, most software will think a run is such a fast track, which actually it is not.
Finally, do not miss the big picture - features you will see on wxfax, but not in the gribs - they may make you chose a track contrary to wx routing advice in many cases - to avoid some wx features or else to seek them.
Bueno. My two cents. Have fun using the toys and sail safe!