Expedition Navigation Software 
1 of 1- Kite
- Expert
Offline - Registered: 1/14/2022
- Posts: 33
Set and Drift
Hello,
I'm experiencing a problem with Set changing from tack to tack (see this screenshot ). When I looked deeper into this it seems that my Heading and COG numbers are fairly erratic too and I'm not sure if there is a connection between that and the Set error:
Am using B&G H5000.
Any suggestions would be gratefully received.
- barne
- Expert
Offline
- Registered: 9/01/2017
- Posts: 47
Re: Set and Drift
Yes, your set and drift is a direct computation of you Heading and COG so if they are erratic, the set and drift values will be subsequently erratic.
Unless your H5000 system is really well calibrated, your set and drift numbers will more be a reflection of calibration errors rather than the actual set and drift. Set and Drift will be subject to:
* Error in boat speed calibration. Both the absolute value as well as the heel and linearity correction. Due to friction in the speedo (assuming you have a paddlewheel) the reading will not be linear so I would definitely populate the speed component of the heel correction whereas the actual heel dependance is more a hit and go thing.
* Error in compass calibration - I would recommend to calibrate the compass before every major regatta.
* Error in leeway - this might be a factor in your case. Check that the leeway is stated in the right direction (i e that your course is lower than your heading) and also doublecheck your leeway factor.
- Kite
- Expert
Offline
- Registered: 1/14/2022
- Posts: 33
Re: Set and Drift
Many thanks for your detailed reply. The actual set and drift numbers (on the whole) seem to accurately reflect what I would be expecting to see and I'm fairly happy with my calibration. I'll look at leeway and see if that is what is causing the problem. The TWA / TWD strip charts are showing spikes now as well which might indicate a problem with the actual compass unit and / or it's connections so I'm going to check that too.
- •
Thread Starter- DuncanR
- Expert
Offline
- From: Up and down East Coast Aus
- Registered: 9/16/2015
- Posts: 465
Re: Set and Drift
Kite, there is certainiy an error there. As Barne suggests, do speedo and compass calibrations as a first step. Until they are in good shape, nothing else matters.
Presuming this to be a recent problem, also find your compass in the boat and check it isn't loose and no metal has mysteriously been placed near it.
- Kite
- Expert
Offline
- Registered: 1/14/2022
- Posts: 33
Re: Set and Drift
I've had some time to study this in more detail and might have found the problem / solution......
I replayed a log file from last weekend and sat and stared at the Set and Drift number boxes for a while and they showed pretty consistent numbers in line with what I would expected to see with no violent spikes. This led me to think that there was a problem with how the strip chart was reflecting the data. On my number boxes I have set and drift damped by 60 seconds. I tried damping the strip chart by the same but also deselected the 'auto-scale' function and manually entered max min parameters as 360 and 0 degrees respectively. I now have a strip chart which looks like this which is what I was wanting to see:
With regards to the TWD issue I'm getting I think it might simply be because we've had a fair amount of northerlies lately and the wind was moving through due north which the strip chart struggles to deal with? (Note that the median TWD of 005 degrees is correct but it looks to me as if the strip chart is struggling to represent the oscillations correctly. Perhaps I have the chart set up incorrectly?)
- •
Thread Starter- Kite
- Expert
Offline
- Registered: 1/14/2022
- Posts: 33
Re: Set and Drift
I forgot to say that the HDG and COG problem was also solved by deselecting auto scale in the strip charts and manually entering max / min of 360 / 0 degrees.
- •
Thread Starter- Lockie
- Expert
Online! - From: Palma
- Registered: 5/07/2021
- Posts: 61
Re: Set and Drift
The TWD looks fine to me. Its just flicking between 295 and 010 or something like that. I always have my TWD on auto scale as its easier to read.