I got a Garmin summit gps for xmas but ain't used it on the water yet - a few of my chums have used them at west kirby quite a bit -
people have racked up quite good speeds - my mate ken clocked up 32 kts on a starboard Evo! - windy John got 36 (i think) on an acid -
but so far this year the current record is 37kts........ on some kit I've never heard of.
I followed ken on a few of his 32kt runs (in the dark!) and believe me, it felt really fast, I thought my hair was going to burst into
flame!
If it was not for the fact that I have to buy a new large sail (went through mine last week) I'd buy a GPS as well. Seems like a
brilliant idea to me. I'd love to know how fast I actually sail, I bet its not hlf as quick as it feels.......
yeah - I always thought I'd be doing about 30kts, but having been clocked at 32 (on broad reach, mirror flat water with slightly overpowered 5.0), I realise that I usually sail a lot slower. 32 was scary - cant imagine 46!!!!!
so just how acurate are these things these days ? I know the one on a friends yacht can be a little bit iffy, i.e. it thinks it's 500
yards inland while tied on a mooring, not to mention being 100ft below sea level at times which is worrying on a yacht 
I always fly with one, and often trust life and limb to it when calculating final glides and the like. Believe me, 100ft can make all
the differance between a marginal glide and a major crash. I have used one to get the dimensions of the gliding clubs club house and it
was accurate to within .5 m (it rounds to 1m) everytime.
I guess I'm trying to say I believe they are accurate.
However, I have no idea on the particular models.
I used to use another system (although the name escapes me) which used land based arials. It was accurate to within 500m, and couldn't
cope with speeds over 90knts. Terrible!
Appaently according to the blurb they are accurate to within 0.01 knots. The thing is although they may be slightly off as far as
absolute position goes... Good ones with WAAS (whatever that means) are supposed to give position accuracy to around 5m whereas
slightly lower spec ones say 15m... However, the system is owned by the US Military and they tend to introduce an error which can be as
much as 100m into the system. In some cases they can introduce even greater errors if they wish (I'm sure they have in Iraq)... The US
military obviously have units that correct for these errors....
However, for our purposes it doesn't actually matter how accurate the absolute positioning is as all we need to know is how far we move
in a given time so that we can deduce our speed. As far as this is concerned, the errors introduced my the US Military don't make any
difference, so they are pretty accurate.
Al.
Mine usually sez it's accurate to about 20m. However, I've entered grid refs that have turned out to be several hundred meters out, but
I think that may be a mapping problem rather than accuracy (it's all abit complicated when u want to use it with a map).
I also managed to run at max speed 22.7 mph the other day, which I think would put Linford Christie to shame, so I'm a bit dubious
about that one too esp. considering all the mince pies n stuff weighing me down.
In short - I'm as yet undecided about exactly how accurate these are..... I think having it in a pocket confuses it too.
doesn't it have to be strapped to the top of your head or something so it can see at least 3 satellites ?
That would be ideal - and probably most accurate. However, purely on the grounds of extra wind resistance I'd probably not bother with
that option. The most common idea seems to be to put it in an aquapac and strap it to your arm/boom/mast. I don't think it would work
very well stuffed up your wetsuit sleeve.
Did u all read in boards mag this month that maestro Dunkerbeck himself is bringing out a range of windsurfing oriented GPS systems
which work on 7 satellites and should be spot on, and also have a range of other stuff including an emergency button u can press which
will send your co-ordinates to the mobile phone of your choice for easy rescue...... it's probably worth waiting for one of them to be
honest.
Except that they will no doubt be three times the price of a 'normal' GPS.
Sounds pretty interesting though.
Al.
Hey Wes. Aviation law says your not meant to rely on GPS's for using them as an altimeter for determining your height to avoid
controlled airspace. However, I've often compared them in flight to my altimeter and the GPS is usually fairly accurate with my
altimeter although sometimes the GPS can be a few feet out which is nothing.
I use a Garmin GPS12 thats pretty old now but works well. Must be at least 6-7 years old and cost a fortune in its day. As its not
really worth much anymore. I spose I should purchase an aquapack and just see what speeds I can get windsurfing. One thing to note is
that my dads got an Emap and his GPS positional co-cordiantes are always a few metres out to mine. So it just gos to show that they are
not completely accurate for your positional location but as Al said, thats irrelevant for our use.
Shame the altimeter isn't more accurate though, it would be good if we could work out how high we were jumping as well as how fast we
are going!! 
Al.
quote:
Originally posted by Jonny
However, I've often compared them in flight to my altimeter and the GPS is usually fairly accurate with my altimeter although sometimes the GPS can be a few feet out which is nothing.
Jonny, yep you are right, and I don't rely on it for telling me how high I am. I have a barametric (and arse for sub 100ft!) for that,
but to do final glide calculations, thats when I use it. Its linked to both an L-Nav and palmpilot using Winpilot for the moving map
display both of which give me an estimated arrival height while final gliding damn useful tools as well, definatly a handicap when they
go down!
However, despite having 2 GPS's, map, winpilot and years of experiance of where I can and can't fly, I still took a thermal over Hinton
parachute zone and shut it down for 1/2 hour! The public bollocking I got at briefing next day was more than justified......
Sorry - a little off topic there!
Got home from work and my GPS had arrived, so quickly read how to switch it on and reset the Max Speed and then headed off to the
beach. I checked the current speed reading on the GPS against my vans speedometer and it seemed spot on. I was pretty amazed at how
little movement you need to make before it picks up on it.
The wind was around 25 knots and the sea pretty rough so I rigged my 5m sail and big board, reset the max speed on the GPS and got out
there. The conditions were just perfect, I was well powered up and flying off the waves, with some massive jumps at times. The sea was
pretty lumpy even right out the back where there were some monster waves. Just perfect.... Not great for full-on speed with my GPS, but
still an amazing session.
Got back to the beach to check my Max speed and realised I didn't actually know how to do that, so after derigging had to drive all the
way home at less than 15mph to make sure I didn't exceed the speed I had done on the water.
I've since read the instructions and found out that my max speed was 28.7mph... Not great, but in 4 foot lumpy seas not too bad either
I don't think.
Al.
Time to pout, stamp my feet and start shouting
want one! want one! want one!
Damn I need more money!
Justal, what is the make and model of the GPS you got? Also where did you carry on whilst windsurfing? also how much was it and where
did you buy it from?
Sounds like a fun thing to have which could make the whole experience even more interesting.
[Edited on 7-1-2005 by Bananaman]
Its a Garmin Etrex which I got from thenavigationcompany.com for £84.95
I put it inside an aquapac which I got from eBay for £1.99 and then put the aquapac around my neck and stuffed the whole thing
inside my wetsuit.
About to got out and play with it again in a mo!!
Al.
silly question I know, but how does it work if it's inside your wetsuit ? don't these things need to be able to confirm their position with a satellite.
I guess so, but it doesn't have 'eyes' so isn't doing it visually!! I don't know what it does use, but it seems to work from within my
wetsuit. It works inside my van as well, but doesn't work inside the house, although it does sometimes just pick up a signal from
within the house.
I guess the weather conditions will make a difference as well, but it doesn't get much worse than it was today weather wise and it
worked OK.
Al.
Al - you've got to be loosing some accuracy when it's inside yer suit and an aqua pac - mines an etrex too and it barely works in my coat pocket! It will work in the car though (if near a window). I've used mine with no bag, tied around my spreader bar - it's not let any water in so far & i've had some excellent high speed wipe outs with it. I reckon the safest bet would be the aqua pak and then tie the lot to yer mast or boom or spreader bar..... One of the guys at kirby has doctored an old boom front end so it's attached to the boom right under his nose, and the etrex clamps into that so he can see how fast he's going all the time (if he dare look at it).
GPS works on similar Radio Frequencies to mobile phones so if you've got inside your wetsuit you still should get a signal. Difficulties will arise when you're inside metal containers (the back of a van with no windows). One thing to be aware of is that your GPS performance will deteriorate as the batteries get low.
I'm not convinced mate... They don't even work very well under trees. I'll give it a try in my suit though, just to be sure...
[Edited on 10-1-2005 by shawn]
Ah - and I have just found out that garmin actually make a neoprene holder for the etrex..... maybe it can see through yer wetsuit afterall!
It does work inside my wetsuit, but not as well as outside of it. I was having trouble getting a signal with it inside my wetsuit
yesterday. I need to find a way of fixing it to my harness really.
Al.
Al, is there an option to plug in an external aerial? If so you can tuck the GPS away and strap the aerial outside your wetsuit - should be ok as long as you keep the GPS watertight where you pass the aerial cable out of the bag.
I don't think there is, but I shall hav a go at somehow fixing it to my harness I think. I just don't want it to get in the way or flap
about at all, and I don't want it too exposed to heavy landing.
It has worked OK inside my wetsuit, but I guess it will be better outside of it.
The wrist mounted versions obviously have an advantage from this point of view, but they are a little more expensive and I'm not
convinced that I wouldn't break it in no timne with it on my wrist.
Having the GPS has certainly added a new dimension to me time on the water though. I'd never been too bothered with going fast before,
but now I have a reason... I'm even in the process of getting a faster board (2nd hand Sputnik).
Al.
I was amazed at how much ground we cover in a day!! As a result I'm considering doing a sponsored 250 mile sail when it warms up a bit
- shouldn't be to diff given some decent wind......
It does give u an urge to push out those extra few knots doesn't it - my wave board seems a bit inadequate when looking at the 35kt
barrier. How fast are wave boards meant to go d'ya think?
I'm not sure really, but it didn't feel safe at 33 knots!!!
I'm looking forward to one of those summer days with Westerly winds where I spend the whole day blasting back and forth from Tywyn to
Borth, with a 7 mile long reach I should even get a decent average speed as well.
Al.
They see through wetsuits ok you just have to make sure that you have got a lock on the sats before putting it in there.
quote:
Originally posted by justal
Having the GPS has certainly added a new dimension to me time on the water though. I'd never been too bothered with going fast before, but now I have a reason... I'm even in the process of getting a faster board (2nd hand Sputnik).
Al.
Al,
I used to have a hollow Sputnik 280, it was faster than the 275. I maybe able to get hold of a hollow 270 if your interested.
Dunk
Maybe .... Although I can't afford anything at the moment!!
Al.