Very Gusty day down here in Central Texas, winds were 25 to 35 mph from the SSW. Great day to be out on the lake. In a pick up game of rag-tag, I began to really push my boat against a Hunter 320. The Hunter took us up when we were on starboard tack, and just passed our stern as we sparred. After putting the Hunter to rest (they furled their jib and went home) I picked up our GPS (Garmin 12 channel unit) and saw a peak speed of 9.1 knots. There were no swells (inland lake) so we could not have surfed anything larger than a cruiser's wake. My question is this - did we break my all time speed record, or is my GPS on the fritz... We were on a screaming reach just before the race, but the fastest speed I have ever recorded before was 8 knots. Thanks to all my fellow Catalina owners- Rob
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Pete Staehling
Dunno, but ...
I know that my boat is often clocked at above hull speed by a knot or maybe two sometimes. I was out the other day and was amazed that I was making great time, better than ever before. About an hour into the trip I realized that the gps was set to statute miles instead of nautical miles. I had changed it for an automobile trip and not changed it back. I changed it back and realized that I was making good time but not the too good to be true time that I thought I was making. I had a good laugh at my own expense. Pete
I know that my boat is often clocked at above hull speed by a knot or maybe two sometimes. I was out the other day and was amazed that I was making great time, better than ever before. About an hour into the trip I realized that the gps was set to statute miles instead of nautical miles. I had changed it for an automobile trip and not changed it back. I changed it back and realized that I was making good time but not the too good to be true time that I thought I was making. I had a good laugh at my own expense. Pete
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Pete Staehling
GPS Reliability for Speed
The previous post mentioned reliability of readings for very short amounts of time being unreliable. This is true, but most GPS's have a setting that allows you to pick what period of time it averages to get the speed displayed. I forget what setting I use, but I seldom see weird numbers that fluctuate in a manner that doesn't seem correct. If you see them perhaps you can change interval used to calculate current speed (it is never exactly current anyway). If you have erratic speed readings on your GPS, a little trail and error with the settings should resolve the issue nicely.
The previous post mentioned reliability of readings for very short amounts of time being unreliable. This is true, but most GPS's have a setting that allows you to pick what period of time it averages to get the speed displayed. I forget what setting I use, but I seldom see weird numbers that fluctuate in a manner that doesn't seem correct. If you see them perhaps you can change interval used to calculate current speed (it is never exactly current anyway). If you have erratic speed readings on your GPS, a little trail and error with the settings should resolve the issue nicely.
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Tom
GPS speed reliabilty
From what I have read , if you don't have the WAAS enabled GPS units "temporary" (momentary) variations of up to 2 knots speed might be encountered (see link below) Not saying that you weren't going 9.1 kts, just that there might be an inherit error in standard GPS units at times. Though I HAVE seen GPS readings of 11 kts on my old Watkins 27 that I beleive to be accurate. (I just happen to be travelling North of Hells Gate in NYC at the time and the East river current was about 5 kts.........;-) Also go here for more detailed evaluations http://users.erols.com/dmilbert/accur.htm (especially check out the links at the bottom of the page)
From what I have read , if you don't have the WAAS enabled GPS units "temporary" (momentary) variations of up to 2 knots speed might be encountered (see link below) Not saying that you weren't going 9.1 kts, just that there might be an inherit error in standard GPS units at times. Though I HAVE seen GPS readings of 11 kts on my old Watkins 27 that I beleive to be accurate. (I just happen to be travelling North of Hells Gate in NYC at the time and the East river current was about 5 kts.........;-) Also go here for more detailed evaluations http://users.erols.com/dmilbert/accur.htm (especially check out the links at the bottom of the page)
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Robert Moretti
All GPS units are not the same
The newer WAAS-enabled units are much more accurate for speed. This is especially true if they take readings every second or two. My Garmin 76 shows steady, moment-to-moment speed readings that do not fluctuate in any significant manner.
The newer WAAS-enabled units are much more accurate for speed. This is especially true if they take readings every second or two. My Garmin 76 shows steady, moment-to-moment speed readings that do not fluctuate in any significant manner.
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Rob R.
That's what made me wonder..
I have a Garmin GPS 12, and take it traveling with me all the time in my car. It is always dead on as far as speed goes (compared to speedo), and it seems to refresh a couple of times a second. It is not WAAS enabled, but it consitantly shows an accuracy range of 14-20 feet. Thanks for all the responses! Rob
I have a Garmin GPS 12, and take it traveling with me all the time in my car. It is always dead on as far as speed goes (compared to speedo), and it seems to refresh a couple of times a second. It is not WAAS enabled, but it consitantly shows an accuracy range of 14-20 feet. Thanks for all the responses! Rob
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Don
Speed
If you were sailing with a current, then the GPS reading would be the actual boatspeed current speed, since a GPS will only give you Speed Over Ground(SOG) and not actual boatspeed through the water. That is why a knotmeter is more effective in determining actual hull speed.
If you were sailing with a current, then the GPS reading would be the actual boatspeed current speed, since a GPS will only give you Speed Over Ground(SOG) and not actual boatspeed through the water. That is why a knotmeter is more effective in determining actual hull speed.
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Ted O'Connor
Boat speed by Arthur Anderson
I have had three 27's over the years. All were tall rigs with inboards. Two were sailed in Lake Michigan in some extreme wind conditions. I suppose an outboard model would be a little faster but I do not believe the waterline length on the 27s would allow that kind of speed.
I have had three 27's over the years. All were tall rigs with inboards. Two were sailed in Lake Michigan in some extreme wind conditions. I suppose an outboard model would be a little faster but I do not believe the waterline length on the 27s would allow that kind of speed.
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Nate
Maybe?
Rob, I've been thinking about your GPS Speed question. It seems to me that the answer lies in the way that the GPS measures speed. I think that the GPS fixes your location on some sort of time interval- I don't think that it continually tracks you position. I don't know what the interval is, but i would assume that it calculates the boats speed based upon the distance travelled in that time interval. Given the accuracy of these units- I've seen mine at anywhere from /- 300 feet to /- 8 feet. It seems to me that, if at some point during your trip, the GPS took a pair of inaccurate reads fixing the distance travelled at too great a distance- i.e one short of true position followed by one long of true position- it would calculate the speed at a much higher level than your true speed.
Rob, I've been thinking about your GPS Speed question. It seems to me that the answer lies in the way that the GPS measures speed. I think that the GPS fixes your location on some sort of time interval- I don't think that it continually tracks you position. I don't know what the interval is, but i would assume that it calculates the boats speed based upon the distance travelled in that time interval. Given the accuracy of these units- I've seen mine at anywhere from /- 300 feet to /- 8 feet. It seems to me that, if at some point during your trip, the GPS took a pair of inaccurate reads fixing the distance travelled at too great a distance- i.e one short of true position followed by one long of true position- it would calculate the speed at a much higher level than your true speed.
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