New Posts New Posts RSS Feed: VMG display, app ?
  FAQ FAQ  Forum Search   Register Register  Login Login

VMG display, app ?

 Post Reply Post Reply Page  <123
Author
Riv View Drop Down
Far too distracted from work
Far too distracted from work


Joined: 23 Nov 13
Location: South Devon
Online Status: Offline
Posts: 338
Post Options Post Options   Quote Riv Quote  Post ReplyReply Direct Link To This Post Posted: 11 Aug 21 at 11:37am
Check out all the instrumentation in this. A really good listen.https://youtu.be/bVfY0yRxmgY
Mistral Div II prototype board, Original Windsurfer, Hornet built'74.
Back to Top
eric_c View Drop Down
Far too distracted from work
Far too distracted from work


Joined: 21 Jan 18
Online Status: Offline
Posts: 359
Post Options Post Options   Quote eric_c Quote  Post ReplyReply Direct Link To This Post Posted: 10 Aug 21 at 9:36am
Originally posted by Sam.Spoons

I think you need a waypoint to get a VMG readout, the wind direction alone wonít work (and will vary from minute to minute)

VMG means different things to different people.
On some yacht GPS systems you can set up readouts for VMG to 'windward'.
I have a little old Magellan GPS which reads out VMG to a waypoint.

VMG to windward sounds more useful than it is. It's a trap because you can always get a higher VMG in the short term, by heading up a bit, it then collapses as the boat starts to slow down.
Also the calculation of 'true wind is usually not accurate enough due to errors in wind sensors, compasses etc etc.

And then there's the question of what kind of true wind you want your VMG relative to?
Instantaneous?
Average over the beat (in retrospect?)?
Average over some other period?
And if the wind has a bend in it so it's a few degrees different further up the course?

Because we are interested in small differences, a boat length or two over a beat, we need VMG readouts to be very accurate if they are to be at all useful.


Then, if you are using a GPS based VMG instead of water-referenced speed, you have all the complication of tide making VMG different on either tack and hour by hour.


My Laser seems to tack through about 85 degrees. So VMG to windward is about (boat speed)*(COS 42.5) i.e. 74% of boat speed. That's crude bur probably more accurate than you'll get from an app or most instruments.
Back to Top
L192444 View Drop Down
Really should get out more
Really should get out more


Joined: 30 Apr 12
Online Status: Offline
Posts: 500
Post Options Post Options   Quote L192444 Quote  Post ReplyReply Direct Link To This Post Posted: 09 Aug 21 at 11:50am
Originally posted by PeterG

I think you need a waypoint to get a VMG readout

Is that true? I agree about rapid changes in wind making it unlikely to be useful as a method of calculating VMG. Realistically you need a wind direction transducer, which is likely to be tricky, and expensive on a dinghy - even if class legal.

But I don't see why you need a waypoint. VMG is velocity made good to windward, not made good to the top mark.

BUT, it's an interesting idea. If you could enter the top mark as a waypoint a phone with a GPS could give a reading of velocity made good towards that, without needing wind direction. That could be interesting?



Exactly; I can work out the average wind direction before the start ... type that in to the app and then get a VMG figure ... 

Back to Top
PeterG View Drop Down
Really should get out more
Really should get out more


Joined: 12 Jan 08
Location: United Kingdom
Online Status: Online
Posts: 808
Post Options Post Options   Quote PeterG Quote  Post ReplyReply Direct Link To This Post Posted: 09 Aug 21 at 11:18am
I think you need a waypoint to get a VMG readout

Is that true? I agree about rapid changes in wind making it unlikely to be useful as a method of calculating VMG. Realistically you need a wind direction transducer, which is likely to be tricky, and expensive on a dinghy - even if class legal.

But I don't see why you need a waypoint. VMG is velocity made good to windward, not made good to the top mark.

BUT, it's an interesting idea. If you could enter the top mark as a waypoint a phone with a GPS could give a reading of velocity made good towards that, without needing wind direction. That could be interesting?
Peter
Ex Cont 707
Ex Laser 189635
DY 59
Back to Top
Sam.Spoons View Drop Down
Really should get out more
Really should get out more


Joined: 07 Mar 12
Location: Manchester UK
Online Status: Offline
Posts: 3321
Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 09 Aug 21 at 9:21am
I think you need a waypoint to get a VMG readout, the wind direction alone wonít work (and will vary from minute to minute)
Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"
Back to Top
2547 View Drop Down
Really should get out more
Really should get out more


Joined: 11 Aug 11
Online Status: Offline
Posts: 1142
Post Options Post Options   Quote 2547 Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug 21 at 6:32pm
Iím after getting speed and vmg display. 

Loads of apps that will display speed, are there any I can enter the wind bearing into to display VMG upwind?
Back to Top
 Post Reply Post Reply Page  <123

Forum Jump Forum Permissions View Drop Down

Bulletin Board Software by Web Wiz Forums® version 9.665y
Copyright ©2001-2010 Web Wiz
Change your personal settings, or read our privacy policy