GPS

[JimC]

Steve Clark, the American Catamaran (Cogito the C Class) and IC Sailor has gone on record as saying that GPS VMG without true wind data is at best very misleading. Apparently he found when working up Cogito that settiing up VMG to the leeward and windward mark or even VMG to three miles upwind was useless due to the amount of variation that apparent wind and all the rest of it puts in the mix.


On the other hand there's considerable potential for explaining how your day went to your mates... See this by 12 (footer) sailor EdB posted on Sailing Anarchy...





I wouldnt want to see GPS readouts visible on boats I sailed against, but I like the idea of capturing the data for playback later. Prove that the only reason fred got ahead was that atrociously jammy shift on the last beat, that sort of thing...

[rick perkins]

It appears if we wish to make this change to accomodate GPS then we need 11 others who think the same to discuss it at the AGM.

If you'd like to see GPSs permitted then please drop me an email on rick@force5marketing.co.uk

PS: How do you make email addresses clickable?

[jammy dodger]

I agree with Rick, let's get real and allow technology on board. We use them while yachting and they are a great aid on big courses on the Solent. Have to say it will be a complete waste of time at Spinnaker, as is the tactic, but it sure as hell will help wind up those lasers and solos!

[rick perkins]

Email me then ... seems you need 12 people ...

[grazz]

[philipcosson]

Rick, this seems to work <a href="mailto:philipj.cosson@ntlworld.com">mail me</a> use Spam-me-not to encode the email first if you want to avoid spam.

Philip

[hairy dog]

None of the detractors have so far put forward a case for how a GPS will improve their (or any one elses) performance during a race.

Yes, GPS or VMG instuments are used on yachts but the most succesful helmsmen (including ex 505 world champions) I have sailed with rarely, if ever, use them round the cans.

[rick perkins]

Graham,

You raise a number of interesting points.

I don't think a GPS is ever going to give a dinghy a sensible measure of startline position.

The accuracy is only so good and the bouys move on the wind & tide ... so I don't think starting will be impacted.

On your wish list for GPS features I think the Velocitek unit already hits many of these ... have a look at their site.

The layline feature would be handybut I can see how we may not like those types of feature impacting decision making.

Perhaps a good starting point is to allow data collection but not viewing during a race ...

Thats the benefit of a forum to get all these issues on the table ...

[grazz]

Just found time to read up on the Velocitek and unfortunately I think the VMG calculation is flawed. You have to manually enter a wind direction. Now in all the places I've sailed in the last 20 years the wind has never stayed in the same place, shifts of 5 degrees are common, 10 frequent and 15+ not unknown during a race.

From the Velocitek website:
"In VMG mode the S10 combines GPS data with a user defined wind direction to calculate your upwind or downwind VMG once every second. In speedometer mode the S10 shows your current speed over ground and can also instantly recall both your maximum and best 10 second average speeds. The S10 has made some of the best sailors in the world faster and we are confident that it will work for you."

My basic trigonometry tells me that a 5 degree wind shift will lead to a 9% error in VMG. Not sure it's worth $299 dollars to get a VMG of that accuracy, it really needs to be combined with a proper wind indicator.

Time to develop our own I think, then get ISAF to change the RRS and we'll be rich . . .  

[rick perkins]

I think if you understand the limitations of the tool then you can make sensible use of it ...

[John Thornton (Guest)]

Just to add some more fuel to the fire of this debate, which I thought I understood before Grazz confused me ...

I can see the benefit of logging GPS data for training and also for having some fun post race analysis,  and with the current generation of GPS devices I see little risk in doing this. My experience leads me to believe that GPS only measurements are not accurate enough to 'tune' the boat in realtime race conditions (wind shifts will still be easier to spot with a compass), and I am not sure that even Grazz will be get anything more than a sore head from post race analysis - developing a bigger beer belly would surely be more effective.

However I have no doubt that it will not be very long before compact devices that combine GPS and INS data with some simple wind direction measurement will provide very effective VMG and hence relative performance measurements. As several people have mentioned I feel this would not be appropriate for N12s, these are seat of the pants boats.

So I am for having GPS in the boat to record data, but the rule change needs to be carefully thought out to prevent a future arms race.

Rick, How many names have you got?

John
N3443

[Jimbo41]

My approach to all this is somewhat "old-mannish". Forget GPS for all the reasons given above.

My strategy would be to choose a different marker - one that works. Take Graham and Zoes' or Tom and crews' boats for examples. If you need to choose a good course, try staying with them at least some of the way. They also give more reliable data on wind shifts than any other electronic device. They have their tacktick eady and waiting so you don't even need your own. The secret is to secretly snag them with a long length of green shark line, and then you'll be up there permanently on their tail, almost effortlessly.  

I realise I'm going to be critisised heavily by some of you guys and girls, but seriously, my approach would be to be less concerned with knowing where I was on the water electronically and more by using simple visual techniques to check out my competition and knowing where the currents and wind were. These are easy to see at the start line since the bias is quite obvious from the way the boats are positioned.  I wouldn't need anything more than my Tacktick and perhaps a hand held bearing compass. AND I prefer the beer and good company afterwards to my laptop.....

Cheers!

Jim.

[rick perkins]

[quote by=John Thornton (Guest) link=Blah.cgi?b=Cool1,m=1175205580,s=40 date=1176860421]

Rick, How many names have you got?

John
N3443 [/quote]

5 ... I am only going to push this along if there seems to be support.

So far seems there is quite a bit of resitsance so I suspect it will not make it onto the agenda ...

Funning that there is such resistance given that there are other electronic aids that have been is use for some time ...

However, I know a GPSs have been used by people at previous opens and this is a breach of the rules that is unhealthy ...