I've been trying to find some information about the accuracy of the
time allowances in a IMS certificate. Haven't found any!

The boat I've been racing has it's certificate he
http://www.avomeripurjehtijat.fi/ims...003/L-9791.txt The
boat is a fast cruiser (http://www.se-ra.com/29cd/alku.htm), that has
been designed without any consern to IMS-rating.

How many sec/mi would you expect the individual time allowances to be
off? How many sec/mi benefit can a "good" IMS boat like X-332 have?
How bad can an non-IMS-optimized boat be?

Here is an example:

After the most recent race (36 nautic miles) I compared the time we
lost to our competitors in different conditions. It seemed that we
were OK in light (4-6 kt, 12,5 miles) beat and medium (6-12 kt, 12,5
miles) run. After these 25 nautic miles we were in a very good
position. Then started the problems. On a 3 mile ~90 degree (just
without spinnakers) leg in a 12 kt wind other boats near us (X-342,
X-332, Doufour 334, the new Dehler 34) were much faster. One actually
passed us rapidky on leeward side just about a boat lenghts distance.
According to IMS these boats should have been 0-40 sec/mi faster but
we lost 40-80 sec/mi to them, quite accurately 40 sec/mi too much to
all of them. There were only small waves and I think there was nothing
wrong in our sailing, just couldn't go faster.

On the following 3 mile beat in a 12-14 kt wind we still kept loosing
at least 40 sec/mi more than we should have. This I could understand,
since we had to keep the main quite far leeward in order to keep the
boat from not heeling too much and we were only three onboard (250 kg
vs 450 kg in certificate). I looked our GPS-track and calculated, that
we were doing about 900 sec/mi VMG instead of 808-828 according to
IMS. How many sec/mi would you expect to loose with those 200 kg
missing?

The last leg was in 45-100 degree 10-14 kt wind, most of which we
could keep the full power in our sails. We were passed by a number of
boats that should have been only 10-30 sec/mi faster and a boat that
should have been 15 sec/mi slower came closer all the time. According
to my calculations we lost 40-70 sec/mi more than we should have to
ALL the other boats.

There are a couple of things in our certificate that caught my eye:

1. The keel is defined as "FIXED KEEL with WINGLETS". The keel is a
modern keel with a round bulb (http://www.se-ra.com/29cd/alku.htm,
press MITAT). According to IMS regulations, this definition increases
the effective Draft (D) in VPP. I guess that would increase the
calculated L/D-ratio for the keel???

2. The mast has not weighted. The defaults are quite low, I would
guess the ast weights 70-100 kg. How much effect it has? On what wind
speeds and directions?

3. The RM of the boat is very low, 45 kgm/deg. A typical value for
other boats in the same size and sail area range is about 60 kgm/deg.
I have been told, that IMS VPP assumes a very little speed decrease on
a boat with a lower than "normal" RM. Any insights?

4. This boat is, according to IMS, surprisingly much faster than
Dehler 29 (IMS-certificate:
http://www.avomeripurjehtijat.fi/ims...002/L-9028.txt) ,
which has about the same dimensions and sails. Actually I don't know
any other 29-footer with a GPH around 670 at least with a displacement
of over 3000 kg.

Joakim