Tracker Details

[tiger beetle]

For a tutorial on options for wind map, there's a tutorial that covers some basic functions-
http://www.maccinfo.com/Introduction_to_Windy.html

Thanks for the pointer to windy.com - I'd never seen that application before, fun to play around with.

- rob/beetle

 

[pogen]

Carliane said her monitor was being a "stubborn beast" and had her wandering off course. I hope she isn't going to have a problem tomorrow with the direction she's currently heading?

She jibed since this post, now headed SW.

I'm not sure why she even has a windvane as primary autopilot. I believe she upgraded her electrical system significantly prior to the race, added solar panels and maybe a new battery system and alternator. An electric AP will steer well even in very light air -- getting through very light air patches is very important, and a windvane won't do it well and it is too tiring for a human.

 

[tiger beetle]

I believe she upgraded her electrical system significantly prior to the race, added solar panels and maybe a new battery system and alternator.

Carlianne mentions "...I’ve been shutting fridge off during day to save power...", which suggests either she's low on power or doesn't yet trust the onboard power management system. I do not know which autopilot(s) she might have, nor do I know how much power is needed to steer a Freedom 38.

I have an Alpha Spectra pilot (two of them) and that unit uses 4-5 amps/hour to keep a 45' boat moving along. I also have a ComNav 1500 backup pilot and it pulls a steady 5-6 amps to keep the boat moving. That's a lot of power they go through in a 24 hour cycle. To keep everything going you have to learn to love your batteries

My guess is that the windy reach placed maximum power draw on the system to support the autopilot and her charging circuit didn't keep up with the pilot draw as much as she had hoped, so she switched over to the Monitor to preserve power on board. It's also possible an autopilot failed, though she hasn't mentioned such an occurrence. With a large single sail swung way off to one side weather helm would be something of an issue, particularly when running deep.

- rob

 

[pogen]

I had a Nexus hydraulic ram with would draw > 6A when the motor was on, which might be 50% of the time. I supplemented with a Pelagic which drew far less power . When I did the SHTP, my fridge wiring failed sometime before the race, to the decision to save power by not running the fridge was made for me! I had AP failures on two of the three longer ocean races I did. My hydraulic ram was also damaged beyond use twice when I owned my own boat, and once with the new owner.

 

[CindyS]

Carliane explained in racer news about the crazy turns, so I'm not as worried. She's doing amazing!

 

[tiger beetle]

How is tracker 24 hour run distance calculated?

COG/SOG question
I was looking at the tracker data today, and it strikes me that the trackers are supplying position data - but the speed/course (SOG/COG) data appears to be calculated. Is this in fact the case, or do the COG/SOG values depend on the type of tracker and how it is configured? In my case, the inReach tracker does send out the COG/SOG as part of its position report; perhaps the tracker on Double Espresso does not.

24 Hour Run question
I was looking at Kynntana's most recent 24 hour run, from 29 June 23:26 to 30 June 23:28. Reported positions are:

29 June 23:26 - 32 deg 59' 15.51''N x 137 deg 28' 55.77''W
30 June 23:28 - 32 deg 12' 14.89''N x 139 deg 02' 23.25''W

based on an arbitrary point off Hanalei (where I am anchored right now) located at 22 deg 13.902'N x 159 deg 30.203'W, the 24 hour distance made good towards the finish line point is 91 miles. I need to go look up the actual line the boats are racing towards.

The distance between the the 29 June and 30 June position reports is 92 miles.

The tracker display reports the 24 hour run as 118 miles. This is entirely possible if the tracker is counting the distance actually sailed through the water as Kynntana advances along. If that's the case, a tracker reporting once every 24 hours would have shown a 24 hour run of 92 miles.

does anyone know how the tracker is calculating 24 hour distance run - e.g., distance between 24 hour points, or cumulative distance between all points in the past 24 hours? It might be fun to use the data to compute distance made goods towards the finish.

- rob/beetle

 

[CindyS]

I watched Double Espresso's speed go down to around 4.5Kts awhile ago, it's now at 2.64Kts. I hope he's ok?

 

[Aussie]

All trackers supported by Jibeset do not provide COG and SOG. COG and SOG shown on the track for point N are calculated from the time and position at point N and the time and position at point (N-1).

The last 24 hours data {Last: 24 HRS 161.4 NM at 6.7 KTS} is the sum of the distances between the reporting points in the last 24 hours = distance sailed.

On the Estimated Finish screen, the DMG is the change in DTG in the selected (6, 12, 18, 24) hours. The SMG is the DMG / Time Selected. The estimated TTG is the DTF / SMG.

 

[sleddog]

All trackers supported by Jibeset do not provide COG and SOG. COG and SOG shown on the track for point N are calculated from the time and position at point N and the time and position at point (N-1).

Any explanation why DOUBLE EXPRESSO's SOG and COG is so erratic, varying from .2 knots to 17 knots and back?
Worrisome for supporters and RC. Can that be fixed?

 

[pogen]

Erratic COG and SOG from a GPS are due to sampling errors. Speed and course are estimated from successive position calculations. If the error in position is large, the fluctuations in velocity will be very large as well. It doesn't mean anything much. Look at the average speed over the course of an hour instead.

 

[Aussie]

There is no way to "fix" this. All we have to work with is the data received from the boat. In this cases it appears that DE send an incorrect position on 6/30 at 4:49AM. The following position at 8:48 having the correct position - hence the variation in the reported COG and SOG around those two points.

 

[BobJ]

Ray, thanks for all this new info! More to watch.

 

[tiger beetle]

Look at the average speed over the course of an hour instead.

That would work if the trackers actually worked; Double Espresso's tracking device certainly isn't performing up to snuff and produces various interesting position reports which in turn confound the folks trying to make sense of the data. It's also time-consuming to go backwards through the tracker data to locate the position reports for a specific time in order to make the calculations on a time average that's useful. But it's hardly the tracker display page's problem that Double Espresso's tracker is acting up.

The tracker data page is supplying two data elements that aren't relevant, and in my opinion are incorrect: COG/SOG (presented as if it were at the moment the tracker sent a report), and 24 hour run (presented as if it were distance made good towards the finish).

for example:
247 Degs at 6.71 Kts
Last: 24 HRS 183.1 NM at 7.6 KTS

What would be useful is COG/SOG at the time of position report - that would tell the audience something about current conditions on board. As it is, COG/SOG is just a calculation to handle advance over time between two points and doesn't contain any additional information beyond the Lat/Lon position reports. If the tracker messes up (as Double Espresso's does) then you get silly COG/SOG results.

The relevant 24 hour run data on a long race like this with various course options is distance made good towards the finish. The 24 hour run as presented in the tracker can tell you how much water the boat has sailed through; an artifact of this approach is that the more tracking points a boat produces the further that boat will have sailed through the water. But that doesn't tell you anything about how the boat has performed relative to any other boat in terms of getting to the finish line. Distance made good does provide data that can be compared across boats.

As an aside, I run Beetle's instruments on 8-second rolling averages, the value displayed in the cockpit are those rolling averages - this seems to be enough to dampen out changing GPS COG/SOG, boat speed, course, and wind speed/angle to produce information I can work with (though I do miss out on the high and low values).

- rob/beetle

 

[dolfinbill]

"Tracker Details" seems like a good place to post this. Jacqueline was giving Dolfin the "doggy handshake" pretty much all the way across until pulling ahead at the end. I could see Mike on AIS the whole race but I don't transmit so he couldn't see me yet stayed right on my tail. Two days before the finish he crossed my track just 100 yards ahead after 1900 miles at sea. Here are some of the screen shots I took after realizing I couldn't shake him.