I was unable to resist a major purchase: a Garmin eTrex Venture HC hand-held GPS unit, which I thought would be fun to play with on my windsurf. It wasn't the first time I'd bought a GPS for windsurfing. Back in the day when I lived in Virginia I went through a couple of similar eTrex units. (They are not nearly as waterproof as advertised.) This time I'm keeping the thing in an Aquapac to be on the safe side.
Some of my motivation to get back into sailing with a GPS came from reading Peter Richterich's blog, "The Windsurf Loop." Peter is savvy about analyzing his speeds and tracks on the computer, using a program called "GPS Action Replay." Looking at the nerdy gloriousness of that program, I knew I had to try it. Today there was a good side-offshore breeze and the waves were very small, so I got my gadgets together to do a GPS-recorded speed session. I used a 106 liter freestyle-wave board and a 6.8 meter squared wavesail, which is not a particularly fast setup, but whatever. Here's a screenshot from the gspar program with an analysis of part of my track.
The program said my max speed was 23.4 knots (26.9 mph), which is a little lower than what the GPS itself said was my max speed (27.9 mph). I'm not sure why there's a discrepancy, but it might be that there are too few "bread crumbs" in the track file saved in the GPS and uploaded to the computer for analysis. I think I can change the GPS settings so it records at a higher frequency, and that might help.
Another cool stat that gspar can calculate is your minimum speed in jibes. My maximum minimum speed was 9.8 knots (11.3 mph). I'd say that's planing, but barely.
Heh. As if the GPS data logging wasn't obsessive enough, I also filmed the session with my GoPro camera and made it into the video below, set to a song by The Brother Kite.
James,
ReplyDeleteWondering why you didn't buy one of those GT31 units they use in the speedquest?
http://www.midwestspeedquest.com/page31/page31.html
Cost?
Hi Brian- It was the instant gratification factor. I could get the Garmin right then and there, but I would have had to order and wait for the GT31. Also, the Garmin has a color display screen and some features for hiking and orienteering and stuff that the GT31 doesn't have. If I get crazily into speedsailing maybe I'll change GPS models, but I doubt I'm going to get that serious about it.
ReplyDeleteIt would be fun to put the straps outboard, try a few more runs and see what the speed diff is; and the wave maneuverability. Of course, the wind variability would almost certainly make it unreliable, but still.... Many of my friends can't understand my nerd obsessiveness of reviewing GPS logs, speed through jibes, etc. but I'm glad someone else does! I haven't use a GPS for quite a few years, but mainly because I lost the unit overboard and haven't felt justified to use a work one. Those Shadowbox look like the ultimate windsurf geek toy -- for now!
ReplyDeleteI think 9.5 knots or so is a pretty solid plane - whats the max displacement speed of the board - something like 1.3 times square root of waterline length in feet, I think? It probably about 4 knots. But were any of your jibes those special and rare (for me they are!) jibes where the boom falls into your hands and you step straight into the straps and think "I'm going almost as fast as when i started the jibe!"? They must be 15 knots or more I'd guess
Morley- I am seriously jonesing to test and compare with the outboard straps, but there hasn't been any planeable wind since I changed them. Doh! Maybe late this afternoon, though it's likely to be onshore and choppy. That's interesting about the max displacement speed calculation. None of my jibes on the recorded session were those magic, "faster out than I went in" types, but I'm eager to see what one of those looks like in the analysis. :)
ReplyDeleteWhat you failed to mention in the post was the discussion a few weeks prior to this where you talked about having a gps/speed tracker before and how you didn't feel like you really needed one now...
ReplyDeleteImpulse buy ftw! Kid...candy store...
But seriously, I'm loving the epic nerdery going on here. Especially the set up with the satellite pic of your track relative to the shoreline. That's really neat to see.
Definitely looking forward to more. Hopefully Rocktober will pan out with a few more windy sessions!
Epic Nerdery Powers Activate, form of gopro and gps watch! I do this too, lol, but I use the garmin 910xt set to 1 second recording and just use the garminconnect website for track analysis, not as great as gpsreplay, but it uploads automatically as soon as I get home and takes no time. Here w some recent vid, the youtube description has the links to the gps tracks:
ReplyDeletehttp://www.youtube.com/watch?v=NCWmKLEDnm4