Request for GPS Data

In your data, do you have any real speeds, as in straight line, spinnaker run speeds on each leg, or are they VMG type speeds? Does it show actual speed on different angles and points of sail? Or is it calculated by the total distance vs. the total time?

My Garmin Etrex handheld (taped to the boom) only records

max speed

and at that time I'm usually too busy trying to keep the boat upright to see what it is! At the end of the day it will only show total distance and total time for an

average speed

which is useless, as I'm sailing slower as I come in to the beach.

I would like to try running at different angles downwind to see which is fastest, raw speed wise, and then do the geometry to see where the breakover point is for sailing

low and slow

on a shorter course vs.

high and fast

over more distance, for the best VMG from A to C mark.

Oh, and I can tell you how one boat beat the other even without GPS data. The skipper on the winning boat is usually better. He knows when to go high and fast vs. low and slow. He see's the puffs coming and is ready and waiting to use them to extend his lead. He's looking back, upwind, watching for those puffs to come, while everyone behind him is looking foreward at him, not looking for the puffs behind them.

There is a lot of skill involved, it's not all about the math.

Maybe in the upcoming F16 Global Challenge, Nov. 9-14, Gulfport, Fl, we can get some data if enough people are carrying GPS units that you can get tracks downloaded from. I've never downloaded any off my Etrex.

Timbo,
The Etrex will show speed between data points. Open the track log in Mapsource, and look at the properties of the track log. It will give you a ton of valuable information.

As an added note, do not save the track log at the end of a sail. Wait until you save it to the computer. If you save the track log using the Etrex, it will truncate the data and make it useless for the information you are seeking.

.

Is that the

around the island

course?

Speaking of Garmin Etrex ..
Do you think its a good unit for sailing in genreal?
worth $75 (used?)

Yes to your question on Round The Island and yes the Etrex Series is a great product. I now have the HCx series (mapping, navigation, etc.)and it rocks. HCx is a high sensitivity GPS and it works great. It will even acquire inside my house. The HCx also comes in very useful in city streets with skyscrapers, heavy wooded forests, steep canyon walls, etc.

cool, thanks for the info

I've got some RTI and other race data if you want it.

We killed three Etrex Legends during the Worrell.... seems they're not waterproof enough.

I use a Garmin 76S and love it. Sadly they've not come out with a newer model like it except for the color ones.

I have a 76MAP and its great except that during this year's T500 the screen got cracked.

I'm still a fan of the foretrex for catsailing. It has everything you need on it and out of the way.

Hi Timbo,

I get lat/long data every second. With that you can calculate a lot of useful information. Right now I have 24 different metrics that I look at. Time on tack, time tacking, mark rounding time, speed on tack/gybes, various parts of the course, etc.

I found out, for example, that tacks to port were a real time killer for me. Specifically, my time to accerate after the tack. Over vacation, I must have done 50-75 port tacks and now I look at the data and I have improved my time on that metric about 33%.

Agreed its not all about the math, but the math can help identify and quantify some of the things the good skipper did compared to everyone who finished behind him/her.

BTW, I use a SpeedPuck. I like the big readout and some of the features, but too expensive. You can get 90% of the real value from these other units being discussed. Gathering lat/long every second as opposed to larger increments is very important for accuracy.

I'm using a Decathlon GPS watch since beginning this year and I'm very happy with it.

I check the files with GPSAR (freeware) which enable you to draw speed statistics easily and also a polar.
I have learned a little from the tracks, but could use some more input on how to analyse and what to improve based upon the tracks.

Gill

You can get most of what you want to analyze from GPSActionReplay...but it takes some effort.

Here are a set of tracks recorded on the Tornado during the MidWinters regatta out of Mission Bay San Diego (I could not attach this 800+ kb file to this post...100 kb limit...you can save the file from your browser)

Link to GPX file for 3 race tracks

These tracks can be replayed on-line thru GPSAR here:

Mid Winter '09 Races 4, 5 & 6...Tornado Full Tilt

Thanks.

I am using GPSar to view, but now I'm dumping the data out of it for the analysis due to the

effort

you mention.

I started out identifying and logging the key data points (beginning of tack, end of tack, etc.)and speed data manually. Once I got the data points I needed and the metrics down, I started to try to automate it. From the tracks I have studied so far, mathematically you can identify these points, then do the calculations to determine time on tack, speed, etc.

The end goal is to feed in the GPS data, supply a few required data points (race start time, etc.) and have the program automatically produce the analysis. Again, there are commercial programs out there, but I don't think the analysis is granular enough nor do they do a good job summarizing the data.

Any chance I could get Smilemaker's tracks for the same races?

You can, but that Smilemaker (I20) GPS was only recording one point every 10 or 15 sec so the tracks look very smoothed out...you miss all the tacking/gybing performance details. On the Tornado tracks we were recording at 1 sec intervals...you can actually see oscillations as we hit waves every other second.

Paths the same as the first one...File names for R1-R3 are: MidWin-09-R1.gpx ; MidWin-09-R2.gpx ; MidWin-09-R3.gpx

perhaps half the functionality of the etrex, or any gps really, comes from just what's on the screen while you are using it. instantaneous speeds, max speed etc. don't forget to try and save your race buoys as waypoints and create a route that goes from each one to the end. then you can set the display to large, and select, speed, max speed and VMG, to experiment with sailing angles

another huge area of functionality comes when you download the track data to a computer. mapsource is garmin's gps program but as garmin are the defacto standard of small gps there are also many freeware programs out there

GPS action replay is my current fav.

http://www.youtube.com/watch?v=BNAsxV1ltMU

with the HCX etrex series you get H high sensitivity, C color screen to make reading map detail much faster and X expandable memory. the memory also stores track data so you can put in a cheap 2GB microSD card, set track data record points to

most often

and then get very detailed plots

You're right, every 10-15 seconds won't allow the kind of detail I'm trying to analyze.

I am working with your race 4 data for now. Do you recall the wind speed that day?

Has anybody done a trawl of the gliding sites for suitable software, they have been using GPS data for analysis and scoring since the early 90's, there are some really very mature and sorted programs available ?

Here are the ones I have downloaded and played with the demo versions:

Velocitek Speedplay
GPS Action Replay
Visual Sail

I also looked at the description on Tack Tracker.

Maybe I missed it, but none of these programs show summary metrics around time tacking/gybing, accerlation after tacking/gybing, mark roundings, etc.

My analysis shows that about 19-20% of the time on the courses I've run is related to turning the boat. Maybe to more experience sailors, this isn't a big deal, but right now, that is where I am focusing my efforts to improve.

A year ago I also tried to make some tracklog analysis in excel.

What I found:

1. It toke a lot of time until my boat reached the speed she had before the tack. t = 60 sec.

2. the acceleration is not continuous, poor helming...

3. My speed went down dramatically (21km/h --> 4km/h)ds = 17km/h = 4.7 m/s

4. This tack cost me (measure the blue area, just approximately ) ds x t / 2 = 4.7 m/s * 60 s / 2 = +- 140m.

5. So If I make an unwind leg with 5 tack instead only 3, it cost me nearly 300m. So I really need a good reason to do this.

Of course all of this depend on the wind/wave conditions, and just one tack is not representative. Based my practice the loosing should be much less. I hope...

Interesting. I will add some charting to my program.

I identify when the tack has begun (combination of drop in average speed and/or change in lat/long) to when the tack

ends

(increase in average speed). Two of my metrics are time to reduce speed or decelerate and time to accelerate.

Given your input, I think I will add distance covered on tack as well. Maybe I can work the math to show angle or arc of the tack as well.

Given comments on this board, I have begun doing more wide tacks. This increases deceleration time, but reduces acceleration time.

My guess is you will find technique even more important on the lighter boat. It is awfully easy to make an atrocious tack. Don't ask me how I know.