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Hi have been told that gps recivers will give accurate speed on the water however there seems to be alot on the market do they all do the same job ? are some no good what is the best solution ? tried a car tom tom but dont think speed was relieable at 4mph The handheld garmin look better but are they ? your thoughts experience will be very helpfull.

Sandy & Bob :Stinky

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An argument that has been raised on a number of occasions, anything allowing 12 satalites to be read will be the most accurate peice of equipment for measuring speed over ground, whilst on the water, available, even at 4 mph.

Some claim to be more accurate at locating a position than others from 5m down to 1m but due to the way the satalites are used this should have no bearing on the speed over ground, unless you are dead set on just doing a couple of meters at a time. even your Tom Tom should be giving accurate speed readings.

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:-D I use the Garmin E/Trex H and can't fault it, tried my prat nav and is wasn't up to much and gave wrong speed readings,

the Garmin is accurate to tenths of a mph, and has lots of other usefull features most of which I havn't worked out yet, like plotting your course, moon phases and a best time for fishing thingy wherever you are, I use the Energizer Ultimate battery's in mine and get about a weeks usage from them, like Perry I'd recommend it, for such a small thing it does one hell of a lot,,

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Hi All,

At the low speeds used on the broads no form of sat nav is accurate enough to give a reading acceptable for a prosecution.

SOG as displayed by the best form of DGPS does not have the repeatability reqd to give an accurate reading at such low speeds.

Sat Nav (even the best systems in use today) will only give an indication of SOG at the low speeds that we use on the broads.

Sat Nav (all forms ) does not even come close to the 76% repeatability error that is requred in the most basic forms of navigational systems (Decca on a good day will come within the 98% repeatability error that is allowed).

When one uses road type mapping on the rivers (which use a totally different form of data base) Road Sat Nav at worse is no better than useless and at best an indication of SOG.

Sorry to be so blunt but the best form of speed control on the broads is still the MK 1 eyeball and if any misguided River Ranger tries to give you a b*******king based on GPS speed simply tell him/her to take a hike.

I would not even bother to employ a Lawyer if I found myself in court on a GPS based speeding charge.

Trouble is with all this is that the issue is subjective, but I will hazard a guess that if you are puled over by a ranger (apart from the aux rangers) you will probably have been speeding so you really should know better.

As far as I know there is no defence againt being caught in a radar gun ( police officers please comment) or being done simply on speed distance calculations ie He passed Reedham at x time and he passed Berney at y time so he must have been doing at least z MPH.

Sat Nav on the broads gives an indication of speed and no more.

Rod

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:-D Rod! no doubt your right about GPS and Sat Nav, but I think all anyone wants is an indication of speed, I don't think there is such a thing as accurate speed reading on any boat, if there is I've never found one, you know yourself that the difference between 4mph and 5mph is barely noticable, but get the wrong ranger and you could be done for speeding, I was going to fit a rev counter, but after reading how tide and wind can affect your speed at the same revs I gave it a miss, even my through hull speedo thingy is way out and it was a very expensive one when it was fitted, at least with GPS your speed is measured over the water or land so tide and other factors don't really affect it, even though I know my GPS is pretty accurate on speed, I still keep an eye on my wash, because on the main rivers I can throw up as much wash at 4mph going against wind and tide than I do flat out across Breydon, So I'd still recommend a handheld GPS, but like you use your eyes as well, it's not about speed it's about the wash you create in my book,,, cheers

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Hi everyone ,

Thanks for your info on this , Rod I know nothing will give really accurate speed on water at low speeds, We spend most of the time on the river being overtaken and some times undertaken so guess we mus be some where near the porper speed and always keep an eye on our wash. However thought it would be usefull to have someting else to go on but there is so many options that I thought I would ask for other peoples experience. The Garmin etTrex H was on my list also looked at the eTrex Hcx but reveiws on Amozon are not so good? :Stinky

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Hi Guys,

Dont get me wrong GPS or Sat Nav is a first class piece of kit.

Its just that I have had this discussion so many times :cry

If an indication of speed is all you want then Sat Nav or GPS is good enough. But it is not as accurate as some try to make out and the errors are compounded when using it as a device to measure low speed.

It is claimed to have an accuracy of between 5 and 12 metres when position fixing so why then do we not trust them to navigate a 40m wide ship along a 150m wide channel.

Even experienced ships officers will look at the GPS display when we are preparing to swing a ship and believe what it says when by actually looking out of the window will reveal that the land is moving past too fast/slow for the readout to be believable.

IMHO the only accurate measure of speed over the ground is with a doppler log and I think it will be a long time before these devices drop in price enough to be fitted to leisure craft.

Rod

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I have sat nav and a indic8tor speed camera detector in the car. both use gps and both give the same speed but the indic8tor is more visable and you can set a max speed which it will beep when you go over. You can also mark locations (speed cameras) and will be given a count down each time you approch them :naughty: I bought this bit of kit of ebay for about £35 a lot cheeper than handheld gps and it came with cig lighter plug and mag dash mount. Indic8tor is the name not some text talk if you want to search.

Jonathan :Stinky

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Hi Sandy & Bob

We have a Garmin GPS72, it is nothing flash but suits our needs on the Broads. I mainly got it for it's large speed display and it's trip functions, although you also have compass, map and waypoint functions. You can also purchase it with a marine kit that includes a robust fixing bracket and cigar lighter type power lead which avoids burning out batteries.

As far as accuracy of speed goes It is reliable enough for the BA Rangers as they use these as there main speedo.

Col

:Stinky

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