200221 Compass Error

Compass Error
Report No. 200221

Compass errors are one of my "things" and at the beginning of every voyage I have a difficult few weeks reviving the simple and correct routines for confirming and recording the performance of the Standard and Gyro compasses. The Standard compass in particular is the only machine we have at sea which is almost 100% reliable and I do wish this was recognised. I now understand that someone has devised a frightening new technique for obtaining errors and it works like this:

1. A buoy is seen on the radar.
2. The position of the buoy is taken off the chart by dividers and entered in the GPS and saved as a waypoint.
3. The course to go to this waypoint is then obtained off the GPS and considered as the True bearing.
4. This is compared with the radar bearing of the same target.
5. The difference is the compass error. Job Done!!

Admiral Lang's last MAIB Summary had, as a theme, machines are only as good as the men in control. I feel we are reaching the stage where technology is getting beyond the capacity of the present generation. I used to be proud of what I did, now I just look forward to the safety of retirement.

Readers Comment

I was appalled to read about the 'new' method of obtaining a compass error in MARS 200221 (May 2002). Are Seamanship and Navigation not taught these days? Has no-one told the exponents of this method that the position of a buoy is always in doubt and, even if it is correct, the position given is that of the anchor, clump or weight which holds the buoy. Has no-one explained the movement of anchored or tethered objects? The position of the buoy on the chart is never the true position, it depends on the length of chain, depth of water etc.