What we would need first is a standardized method of determining what top speed is.

Land speed records are measured over a measured distance(a mile?). Of course they get up to speed before reaching the accurately placed measuring devices,most likley placed by a surveyor.

Drag Racing used to measure top speed over a 120' with two light beams. A beam placed at 60' past the first was the win-loss light. Now they do it with two 30' apart, the first starts the mph clock and the second stops it and is the win-loss light.

In both cases average speed through a measured distance is used.

Soooo. What distance shall we use? Hummmmm.

Hi again. Just for clarification on my part, on the original speed thread there were individuals arguing that a beach cat can't go more than 22mph (or was it knots?), and that to me seemed quite low, so I'm interested in experimenting myself to see what I can average over a fixed distance on a good day. From some gps discussions, it would seem that at least some people would discount the gps accuracy for measuring speed out of hand, and maybe they're right (and I don't own a waterproof gps). My idea was to use the gps to measure the distance (using a powerboat, excuse my french), then use a stopwatch to measure the time. I don't expect that anyone would consider the results official, and I'm only really interested in accuracy to the extent that I'm able to tell the difference between 22mph and 30mph with a high degree of confidence. So that's my perspective, and it would be interesting to see others post results measured in a similar fashion. 500 meters would be a great distance to use, maybe I'll break down and set my own marks (when the ice melts). OR, set the marks BEFORE the ice melts, use my truck to measure the distance . . . naw, wouldn't work.
Al

Wouter WHY do you always assume that my replys are pertinent only to you (which they aren't) I am not critisizing you, I am only answering to the "general forum"
By the way, for 10 years I did work as a surveyer AT sea (as you call it) doing harbour and channel surveying as well as mining survey where it is one of the most difficult and critical areas of establishing PRECISE (more than accurate) datum points, so I would appreciate it if MY qualifications were not called into doudt thank you. Why do you seem so aggressive? or is it just my imagination? Chill out and enjoy life as it passes you, don't always fight with it, we will all be a long time dead.

I understand that your post are only to me. I choose only to react to your post because your methode has serious drawbacks that can easily create far bigger errors than you think you are making. Also GPS units are far easier to use that two laser beams perfectly aligned on some spot on the shore that is at water level. I appreciate your background but like I said I don't take anybodies background as a garantee that they are right. That includes my own background. I've seen to many high profile characters drop a few balls at different times.

I'm sorry if I come across agressive but I think it is a real pitty that a bunch of people are now of track due to this post. There are talking about laser guns and setting up lasered courses. How is a normal human being going to do that. The laser gun methode is inherently problematic as the shooter needs to be directly in front or behind of the record speeding craft to get the best measurement. How do you align yourself like that without knowing the exact fastest heading. An angle between shooter and heading of only a few degrees will give an error of 0.1 to 0.5 knots ; worse than a GPS track readout.

My point is only that GPS is both the most practical way and pretty accurate (if not to most accurate) if you handle the data right and make sure that deduction or feedback takes out the very much present error.

It is as easily as getting a tracking GPS. set the GPS to storing 1 point per second and start sailing for about an hour trying all headings and than read the track into a PC and determine the fastes 500 mtr track. Windshifts and such do not distrubt the readout as the 500 mtr track can also be a curve with a GPS. WAAAY easier and more practical than setting up a laser course and lasergun and less problematic to implement. And this is using a 150 US$ non-differential (waas) GPS

Sorry Darryl,I respect you but I don't agree with your views even if you are a land surveyer.

Wouter

darryl, Don't waste your time,some people just don't get it.

Wouter
Don't waste your time. Some people just dont get it.
So, what is the error over 500 nautical yards anyway?
Seriously, if we can establish (agree on) a maximum error, I for one am quite happy to subtract it from the measured average speed and call that the speed. Right now we seem unsure if a Tornado or H16 have the record at 24 or 32 knots!
I am not worried about cheating, because in practical terms there seem to be few people who can really make a boat move, so it should be pretty obvious who is dreaming up numbers and who isn't. this is not an entry for the Guinness, but more for the Heineken. HA Ha.

I would not rely on a hand held GPS to be very accurate with speed. I don't know why but for some reason if I run across the street with mine, held out in front, aimed up to get a good signal, it says I did 54 mph! I ran from the house to the beach one time, 50 yards, it said 35 mph! (no, I'm not that fast)

I have a much more expensive unit for aircraft (also by Garmin, like my handheld) that is very accurate on speed, it never puts out wild numbers, but it has a much better antenae system. I think that's the problem with the hand helds, the antenae don't get good signals all the time and that is reflected in bogus speeds. We need to develop a better antenae, maybe one that you could stick to the top of the hull forward of the beam, that would eliminate the mast tip motion problems.

So we're back to measured distance and a watch then?

Why not just put a fast cat in the French Ditch the next time they are doing speed runs there? It's measured from shore.

Whew....can you imagine that capsize? Yikes. It's bad enough on water but to cartwheel on land would be quite ugly.

All you'd need is a suit of armour and someone else's boat.

No...Wait...put wheels on a Tornado, take it to the Bonneville Salt Flats when it's blowing 40 and...

Hey, it's blowing 20G30 out on my lake right now, I'm going to take my kid's Hobie 14 (non-turbo, unfortunately) and my Garmin hand held, see how fast I can go before I swim, I just hope I don't lose the hand held...or a hand.

Do you really want to know ? Because the speed in a GPS is calculated by differentiating momentary travelled distance. This is very suspective to signal noise. This is also why all electroics and feedback systems try to transform "cirquits" so that only INTEGRATORS are included and no differentiators. Integrator are NOT so suspectable to signal noise. Now if you have a GPS with tracking ability you will find that the path and traveller distance recorded on your sprint WILL have been logged quite accurately. If you use this later in your PC software to calculate average speed THEN the read-out will be much more accurate.

Like I said the used method of acquiring a measurement can be and often will be very important in determining what accuracy you get.

So don't believe the GPS momentary speed read-outs as these are indeed very unreliable. Use the stored tracks and process these in the PC software and do get accurate measurements.




It is not the antenna system is the the implemented internal software that has been burned in a low energy consumption hardware chip. They don't use elaborate way of calculation here both for reasons of expense and energy consumption. Having said this ALL GPS units use about the same location hardware and internal software so these ARE accurate (within the specified 3 to 5 mtr accuracy)

So log the basic position data with a cheap handheld GPS (Garmin Geko 201) and use PC software to proces the raw data into speeds and travelled distances etc. You'll be surprised hpow accurate you can get.

Wouter

OK, I just got back in from an hour on the Hobie 14 in 23G28 (I just called the local airport to check). To get the most accurate GPS speeds possible I didn't even turn it on until I had the sail up, ready to go. The unit I have is a Garmin Legend ( the little blue, $200 one) I tied it to the hiking strap and laid it down face up, reset all the speed/track data, then launched.

After 4 reaching blast runs back and forth across my lake (about 2 miles each way) it said the distance was 8.2 knotical miles with a max speed of 16.5 knots. These numbers seem realistic. I turned it off as soon as I got back to the beach so as to not mess up the numbers while moving it around on the beach. The tracks looked right on.

So, with my lazy, fat (185lb.) butt on the little, very old H 14, it will go about 16.5 knts. With someone who has bigger balls, is lighter and actually good at racing a newer H 14, with a new sail and foot straps, probably a couple knots faster. An Olympic Gold Medal crew on a Tornado, same wind, probably twice as fast, maybe 30+ knots?

It was all I could do to keep the lee hull tip out of the water and they both went uner on a couple of waves. I was trapping all the way at the back, rear foot on the hull at the top of the rudder and the other on the rear corner peice of the tramp, slipping and sliding every time I took a wave over the hull. I am going to add some footstraps and non skid to that thing before I try that again!

I did manage to do something I've never seen before, I'll call it a wheelie capsize. As I was tacking at the end of the second run (I did a jibe on the first and third) as I passed under the boom, the thing stood right up on the sterns! It actually blew over backwards!

I'm thinking WTF?? as I quickly crawled up the tramp, came down on the inside of the now sideways hulls, reached through the tramp lacing to uncleet the traveler and main, flipped the righting line over the top hull and waited for it to spinn around so the wind would help right it. As the mast came up I jumped up onto the low side tramp to keep it from going all the way over the other way. But I never got my hair wet .

Even though I stopped about 5 minutes for this drill and I had to stop once to get a rudder back down, the moving average showed 10.9 kts. Great fun but I wish I had something with straighter, fatter hulls to play on! That rocking chair nose dive with every gust is a real pain in the butt!

Ah the beauty of a hobie 14! The only boat I have capsized in all four directions on the same day. Put on a dry suit and try it in January in Newport, RI and we call it frostbiting!
Chris
www.acceleratedchaos.com