Or did you just mean that it can be ignored?

BTW I'm not being rude.

Editorial stitch in the thread: I believe "neglectable" is certainly a valid word as a combined form using the suffix "-able," and it perfectly fits the definition of "negligible."

Sorry Mary, "neglectable" is not a valid word although at first glance it might seem so. I have tried several online doictionaries and also checked my Oxford and Longman's dictionaries at home in an attempt to prove myself wrong. There is no entry for neglectable, one online site suggested 'negligible' as an alternative.

I understand (I think) what Wouter is saying, I just felt that to be fair to him I should point out that 'neglectable' doesn't exist. If I tried to communicate in Dutch and got it wrong I'd appreciate being corrected.

BTW I never cease to be humbled at how well so many Europeans speak English when we can barely speak it ourselves!!

I can't find "doictionary" anywhere either

I thought that using a WAAS enabled gps eliminated the "built in error" factor? The course I have in mind is at least 1km, probably more, so "minor" errors won't have a large impact on the overall result. The original arguments revolved around a difference of speed of around 10 knots, so we should be able to tell the difference between 20 and 30 knots for instance over a 1 or 2 km distance.
Only another month before the ice is off!
Al

Of course, it is not in the dictionary. Probably can't use it for Scrabble.

It's those dyslexic fingers agaoin....see?

Any GPS, whether differential or not is surely up to the relatively elementary job of average speed over, say, 1nm.
Even if the accuracy is altering it's not going to alter by enough over a couple of minutes to vastly alter the average figure is it? I always believed that GPS (non differential) was only ever 'out' by a max of 50metres or so and that the accuracy didn't wildly swing about with any rapidity.

According to Garmin, the accuracy of waas enabled gps is better than 3 meters 95 percent of the time.
http://www.garmin.com/aboutGPS/waas.html
Now, I'm going to do some work. Really.

More precise; I meant to say that with a good policy (method) you can totally ignore the build-in inaccuracy and even get very very very accurate read-outs.

The trick is to make sure that in the end you subtract the offset from one-another somehow.

You may have to alter your measuring method to make sure this happens but that is easily done.

Wouter

Yes

Exactly. You can find several websites of amatuer that did the swing test. And from memory I think is swung only a few mtr within a few hours. So any Track readout achieved in minutes will be accurate within 10 centimeters. I don't know of any other more conventional method that allows you to measure out a a distance more accurately on water.

But the real trick is to have the GPS log a track and simply look for a 500 mtr stretch of sailing where the average speed was highest. In fact you don't even need a start and end bouy. Just an body of open water, good water and a crew trying for 10 minutes to get the highest speed going for at least 50 seconds.

Later on the PC you can walk through the recorded track and find the track segment with the highest average. As all points on such a small geographical area will all have the same build-in off set it means that the RELATIVE distance between each point on the tack is very accurate and so to the averaged speed. I think we can trust the internal clocks to be very accurate in GPS units.

As a matter of fact the build in error could be 100 km and the results would still be very accurate; just as long as the error changes only very slowly per minute. And this is the case with civilian GPS. The error changes relatively slowly. So any measurement over a short time span will be much more accurate than one would think at first. Just don't intepretate this to mean that MOMENTARY GPS speed is accurate as well as it simply isn't, but it will be to much detail to go into that,

Wouter

Any, "recognised" speed run has to be set up with a fully SURVEYED distance of the course to sub millimetre accuracy, using "light beams" (generally laser) set at 90 degrees across the course at both the start and finish of the "run". These beams are connected to a very precise timing device that is automatically activated when the vessel “breaks” them.
Why do you think that the organizations that are responsible for determining the accuracy of "official", so called "speed records" don't just take the easy way out that is being promoted here, and just use a GPS reading?
Do you imagine for one minute that the GPS system hasn't been fully investigated for this purpose? Fair suck of the sausage, those people are professionals and their results have to be "beyond reproach".
If you want a "comparative" speed reading over some distance or other, then, by all means, use a GPS reading, but it will not be anywhere near accurate enough to rate against any "official" record, regardless of how hard anyone "pushes that barrow". Any GPS readings, especially for distance covered over time, are just too “subjective” and fall down badly when objectively analysed.
It can very easily be shown also, that the “longer the distance recorded, the slower the average will be” that is why it was agreed many years ago that the “standard” run for recording “speed records” for sailing craft, would be over a distance of 500 metres.
(If history is not known then the human race is destined make the same mistakes “ad fin idem”)

Can't a radar gun be used? (I think I may have asked this question on one of the prior speed threads, but, if so, I can't remember the answer.)

A radar gun will only give a "one instant fastest time" mary, and basically what is needed is an average time over a set distance. If a time was recorded with a radar gun in an instant that a boat, for what ever reason, had suddenly accelerated to a way faster speed than it would normally be capable of, and the "gun" recorded that "one off" exceptional speed, it would be an "aboration" and just not truly representative of the potentual of that craft over any greater distance.

Darryl,

You should realize that I'm not some hack here. My field is control engineering and sensor offsets or non linearity is such a serious factor that we continiously account for that. To put it in simple terms. No sensor is truly accurate of dependable. Most of the time you only get accuracy by devising a methode that subtracts the error from the desired result. I'm sure that landsurveying technics are based on the same principle. Why simply because you can't make tools THAT accurate and not spend heaps and heaps of money. Often the same result can be achieved for far less cost if you are just smart in the way you do it.

Also you reply is both wrong and misguiding in several points. I'm sorry that I have to say that.





Do some landsurveying on the sea, please Darryl. Not having a stationary point there makes things difficult. Also you can set up those lasers on the water for the same reasons; so they have to be set-up on some nearby land. In most cases this can easily be some distance away for it is difficult to have the wind blow strongest near land or have it blow in exactly at the right angle to the land.

No I REALLY want to see ANYONE point out a location TO THE SUB MILLIMETER with complications like that. YOU may THINK that you are accurate the sub milimeter because that is what you've been told or that is what the tool says but that DOESN'T mean you are accurate the that level. Will have have to set up you beamer to at least 1/1000 of a sub millimeter to get that accuracy at say 1000 meters away. You CAN'T do that out there in the open. Hell the elasticity in the tripod and its footing (soil, dirt) will cause a greater deflection when the tripod is experiencing a gust. I know of cases where a man standing next to measurement setup caused enough deflection in the earth to cause an unacceptable off set. Yes the ground is an elastic body as well and WILL deflect under weight bringing the tripod with it.

Besides you method is totall misguided. What if the wind is so aligned that the fastest heading is say 1 or 2 degrees of the surveyed track ? THAT will give a far greater error still. In short it is IMPOSSIBLE for a sailing crew to closely approximate the layed out straight track. Also your method assumes that teh surveyer knows exactly (to the same accuracy) what the optimal speed heading is. I doubt that very much. GPS on the other hand lets the crew decide and just records.

I dare say that a GPS unit with tracking (storing location points in memory) can easily be MORE accurate in determining the highest average speed over 500 mtr than you method. I even consider it. Simply because of the limitations described above.




I've met more than a few people out there that are simply dumb. Engineers and scientist are also just people. I've been dumb on several occasions so I have no illusions there but it has taught me to look closely at what is at hand. The best lesson I got was when I was shown and realize that accuracy is frightingly dependend on side conditions and often alot less than your tool says or claims. True accuracy comes from smart measuring methodes.



And it IS being used in record verification. How else do YOU think they determine 24 hour distance records ? You never know when and where you are going to break that. Lasers and such are old technologies of a pre-GPS time, but now time has moved on and we have more options. Slowly these will be introduces in the various area's. Besides GPS is more and more used in landsurveying as well. If it is good enough there !



This is just nonsense Darryl. Quite frankly; your laser method falls down quicker. Sorry.

And the fact that GPS is a new technique doesn't mean that the old technique is more accurate.

Wouter

This thread is rapidly heading towards the top of the table for popularity in terms of numbers of replies. It's obvious I suppose that because we sail fast boats, speed particularly interests us. So, where are we going with this debate? Measurement methods aside, it would appear that we are all keen to see some form of 'record' for catamarans - possibly by class/type or length?

Say a series of records based on the 'F' measurements? F14 through to F20?

IF WE COULD AGREE a measurement method, record attempts could possibly be grafted onto a regatta by RC's for those people that wanted to have a go. Or are we talking about a specific event(s) set up in an 'ideal' area (known for good breezes and flat water).

I'd be interested to know what people's thoughts are and where this thread is really headed.

Obviously you would not learn anything with one shot. I was thinking in terms of taking a whole series of radar gun shots over a specified period of time or over a designated course length and then averaging all the radar gun readings.

So my question was whether a radar gun is accurate enough. If so, that seems like an easy way to do it.

Its accurate enough to stand up in a court of law!

Bushnell has a low cost radar gun. We bought one for our speed shoot outs but have yet to try it out.

http://www.bushnell.com/products/digital/specs/10-1907.cfm

and what is wrong with getting the fastest instantaneous speed? That is what we are trying to get isn't it? Not an average over 500 metres which will be less.

Dave
http://www.westlakesailingclub.com

Most people seem to agree that some beach cats are capable of short bursts of speed above 24 knots (or is it mph?), as when surfing a wave or when a big gust hits right before the pitchpole. The argument seems to be about whether they are capable of sustaining such speeds over a given distance or certain number of minutes.

Therefore, the people who do not believe it is possible to sustain higher speeds for more than a few seconds are not going to be swayed by one radar gun reading giving the speed for one instant in time.

I wish I could tell that to the judge.

I think it would be great to come up with a simple, standardized, economical, credible way of clocking speeds for the small cats so it could be done as an ongoing fun thing and goal for fleets and individuals around the world.

Problem seems to be that there is no agreement on how to do it.