Adam Farkas wrote in message ...

Thanks Adam, this was just the kind of information I was looking for.

The bad news for you is that trying to use GPS for proving/disproving
your IMS rating with roughly averaging speeds will not tell you how well
you sailed your boat at any moment, it is too slow and inaccurate, so
you can not conclude that your IMS rating is inaccurate. IMS is much
more accurate than what GPS can show you, certainly orders of magnitude
better than 40 sec/m. Sailing to the IMS polars you need much better
calibrated instrumentation, instantaneous data display and absolutely
excellent crew work

Unfortunately we didn't have better instruments. The boat is not mine
and it doesn't yet even have wind instuments. With GPS you can easily
notice errors like 40 sec/mi, but as you said it's not much of a help
during sailing or making polars. I was mainly comparing to other
boats. They seemed to sail quite close to IMS predictions.

We haven't raced much with this boat. It is a new boat, first in
series. Some people have argued to me, that it is impossible to be
competitive with this boat, since it is not designed to IMS and some
other boats from the same designer have not had good success. After
rather poor results, I started to wonder if they were right. I'm now
convinced, that at least most of the 40 sec/mi was caused by poor
sailing or trimming.


The IMS VPP is not based on the average sailors ability to sail the
boat, but sailing the boat at it's optimum at all times. This takes
some very significant effort that is not necessarily obvious to the
average club sailor. Top sailors can sail their boats faster than their
VPP by utilizing other opportunities such as wind shifts, currents,
smart tactical moves etc.

This is obvious to me. There are only a few "top sailors" in IMS in
Finland and the fleet is small as well (three classes, 5-15
boats/class in a race). Some boats race only once a year and do still
very well. Previously it has been quite easy for us to be in the top
half of the fleet. With this boat we have been quite far from that.


There is much literature on this all around.

What would you recommend?

Joakim