From: Pallard, Robert [Rob.Pallard@nrc-cnrc.gc.ca]
Sent: Wednesday, January 21, 2004 10:55 AM
To: 'jim@tytech.org'
Subject: IMS Heavy Displacement Series - Canoe Body Only

Dear Jim,
Please find attached three .tnk files containing the results of the canoe
body only tests with the USSA/IMD Heavy Displacement Series.
There is a problem with the data for M2 as when the model was pulled, we
discovered that the third row of stud tape had come loose. From examining
the photos, it is clear that the third row of stud tape was loose on the
windward side part way through the 15 deg set. It is not possible to detect
when it occurred on the leeward side of the hull because the shutter speed
of the camera blurred the spray coming off the hull and thus we could not
see through it.
A better indicator of when it may have occurred were the roughups for day2
where the drag was down by slightly over 1% - enough that we double checked
the drag calibration (it was OK) but I was too stunned (Newf for stupid)to
look further. At the roughup speeds, the third row of studs is worth about
1N of drag (12N full scale) which was about what we were looking at.

During the upright line, on the first day, the drag was a little lower as we
came through FR=0.325 than it had been on the last roughup but was certainly
within the variation that we dread/expect. This value was very close to what
was measure during the 2nd and 3rd roughups on Day2 which might argue the
case that the stud tape was loose very early on.

My recommendation, and I admit that it is just a guess but a similar thing
happened during the VO70 test, is that you analyze the results of the data
measured on Day 1 using 86 studs, while for Day 2 you will need to use only
41 studs. I don't think that we were getting laminar re-attachment due to a
favourable pressure gradient when yawed. 

I abbreviated the yaw sweeps by simply doing yaw 2,4 and 6 deg. If trends
had looked bad, we would have filled in at the odd angles but I though it
looked pretty good. I used the time saved, to embed a trim study, nominally
1/2 deg additional trim by bow or stern though the set at Fr=0.325 and
Heel=25 have a few extra points because the wrong trim moment had been
called for initially which was noted by the discontinuity in the trim vs
speed plot. I had made an error in inserting data into the test plan.

The tests with M1 and M3 did not have problems with studs blowing off but
there were enough repeats and scatter in the results to make the M2 test
look pretty good.

Best Regards
Rob 

