Jeff Richards wrote:

By 'general purpose" I was referring to the features built in to the
typical GPS unit. However, even software like MapTech is not pushing
the bounds of the analysis that's available. Try to find some
details of the software that America's Cup racing boats use, and
you'll be amazed. And it's not difficult to do.

To find out the details of this software, or to develop it? I'd love to see
what they're using! As far as developing it goes...

For instance, it
should be possible to select any part of a track and have VMG to any
nominated point plotted as a line graph. This means that you can see,
for a course that may have included several tacks, exactly when you
were making best time to the mark. Marchaj introduced the polar
performance diagram in the sixties, when sophisticated additional
equipment had to be created to collect the data - now it's all
available from GPS and standard instruments, but I don't know any GPS
software that can produce a polar diagram.

You're right, none of this would be difficult to do. In fact I've toyed with it
as a programming exercise, reading the NMEA string output from the GPS unit, and
drawing a track on a graph. All you have to do is stuff this info into a
database, along with your instruments' output if you want, then you can slice
and dice it however you want. Actually, the biggest obstacle I could see to
developing navigation software is that the file formats for charts are
proprietary, so you have to pay royalties to use them. (A pox on whomever in
government made that deal.)

I'm quite surprised no one has made polar charts a nav software feature -- this
is a no-brainer for racers, or wannabe racers.

BTW, the best personal navigation program is still Maptech 1.0 for DOS! Best
interface and screen design, features, etc. It's just so much more elegant than
the latest stuff, even if it doesn't do as much. It ran better/faster on a 486
than the new stuff does on the latest/greatest. Unfortunately, the charts are
no longer available for it, and it only works at 640x480 screen size. To steal
the words of an old sage, it's amazing how much we've advanced without
improving.

Matt O.


"Matt O'Toole" wrote in message
...
"Amanda" wrote in message
...

I have the opportunity to crew on a racing yacht as tactitician and
would like to learn more about racing with a GPS. Apart from the
obvious (distance and bearing to the next mark) what other uses
can a GPS be put to in yacht racing?

I've raced dinghies and cruised yachts so I'm familiar with general
tactics and how to use GPS, but I need to put the two together.

Jeff Richards wrote:

VMG - velocity made good towards a waypoint. That will tell you
whether pinching (and slowing) or freeing (for speed) will get you
to the windward mark quicker, or exactly what course on a downwind
gybe gets you to the lee mark quickest. You will need a 'relative
bearing' (angle off the bow, or pelorus) device to tell you when to
tack or gybe onto the equivalent course for the mark. You will need
to get all the marks as waypoints, so this may mean visiting each
mark and entering the waypoint before the start.

If you can link the GPS to boat speed and direction then it can
calculate tide set and rate, or you can do it manually if they can't
be electronically connected.

The other useful feature is to be able to save the course sailed for
later analysis, but general purpose GPS software doesn't usually
provide decent analysis tools, so you may have to write your own.
You should be able to replay the whole race or selected parts,
identifying where you gained or lost ground and perhaps working out
why.

How do you mean, Jeff? I find that Maptech, etc., make this pretty
clear. With
my path drawn on the screen, I can see exactly what was going on,
where I gained
or lost ground, etc., better than ever before. A picture is worth a
thousand
spreadsheets!

PC-based navigation programs all have their warts. In fact most of
them are
pretty bad in one way or another. But for the most part they do a
good job
telling you what you need to know.

However, I'm not familiar with the software/firmware in most
self-contained GPS
units.

Matt O.