New Posts New Posts RSS Feed: VMG
  FAQ FAQ  Forum Search   Register Register  Login Login

VMG

 Post Reply Post Reply Page  <1 2345>
Author
transient View Drop Down
Really should get out more
Really should get out more


Joined: 21 Aug 12
Online Status: Offline
Posts: 715
Post Options Post Options   Quote transient Quote  Post ReplyReply Direct Link To This Post Topic: VMG
    Posted: 06 Sep 13 at 9:50am
Polars are available for a few boats. Few and far between though. How applicable are they in a real race?

http://100races.blogspot.co.uk/p/polars.html

Quote:
"Bear in mind these are numbers are essentially theory, having been collected in ideal flat water conditions. In practice, laser performances are affected by kinetics, waves upwind,  surfing waves down wind and sailing  by the lee."
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: 1151
Post Options Post Options   Quote 2547 Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 13 at 9:50am
Originally posted by iGRF

I assumed that compass thing with the electronic read out that some folk use did all that, why would it restrict itself to just compass angle degrees? Anyone can wear a wrist mounted GPS device, I must have done at one time or other.

So, no, don't tell me, it's not permitted because of 'the class' they will not 'allow' a polar thing to be constructed for their craft?

Oh and does this mean it's also illegal to take an iPhone out according to some classes? Given it's GPS and various tracking apps?


You are quite right; if you sail with your phone & a GPS watch you risk disqualification. These items are not permitted by almost every class.

Same applies to GoPros etc ... all effectively banned.

Some classes however are quite progressive on these matters such as the Musto Skiff who's class rule I have posted below. But I know your are not very keen on the Musto.

C.5 PORTABLE EQUIPMENT 
C.5.1 FOR USE 
 (a) OPTIONAL 
(1) Electronic or mechanical timing devices. 
(2) One magnetic or electronic compass showing only information relating to heading speed, VMG, bearing, current or elapsed time. 
(3) Maps charts and means of recording courses and compass headings. 
(4) Items on deck which functions are storage of food, drink, clothing, safety or relevant tools. 
(5) Mobile phone, solely for emergency communications. 
(6) Video and / or still cameras. 
(7) GPS device showing only information relating to heading, speed, VMG, bearing, current or elapsed time. 


Edited by 2547 - 06 Sep 13 at 9:51am
Back to Top
Fearful View Drop Down
Newbie
Newbie


Joined: 30 Jul 12
Location: Kent
Online Status: Offline
Posts: 19
Post Options Post Options   Quote Fearful Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 13 at 9:56am
To create proper polars you are also going to need to know what wind the boat is experiencing at that time.

Edited by Fearful - 06 Sep 13 at 9:57am
Back to Top
transient View Drop Down
Really should get out more
Really should get out more


Joined: 21 Aug 12
Online Status: Offline
Posts: 715
Post Options Post Options   Quote transient Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 13 at 10:08am
Originally posted by iGRF

So, are these 'polars' available for different boats, when was that one issued for the RS100? Where can I order one for the Alto and the EPS?

Then the next question (blindingly obvious even to an idiot) if there are such things, that are calculated on fact rather than anarchic fiction like club returns, why is it so difficult to have a given boat a permanent handicap calculated for it?


Too many variables.

A possible scenario for the future though could be a simulator. Maybe (fantasy) the designer could submit a bang on accurate 3d model to a PY com who then run the model on a sophisticated simulator that uses all the known variables to calculate a number......effectively a same helm same conditions comparison with other boats  
Back to Top
alstorer View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 02 Aug 07
Location: Cambridge
Online Status: Offline
Posts: 2899
Post Options Post Options   Quote alstorer Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 13 at 10:12am
Originally posted by Fearful

To create proper polars you are also going to need to know what wind the boat is experiencing at that time.
This is a good point- need masthead instrumentation
-_
Al
Back to Top
iGRF View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 07 Mar 11
Location: Hythe
Online Status: Offline
Posts: 6499
Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 13 at 10:20am
None of which would be beyond the wit of man, should he wish to correctly assess a mean boat speed in given controlled circumstances to be applied to all craft as the basis point within which to construct a fair handicap system devoid of the 'anarchy' of bumbling buffers and egregious event number driven organisers.
Back to Top
Fearful View Drop Down
Newbie
Newbie


Joined: 30 Jul 12
Location: Kent
Online Status: Offline
Posts: 19
Post Options Post Options   Quote Fearful Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 13 at 10:38am
Originally posted by iGRF

None of which would be beyond the wit of man, should he wish to correctly assess a mean boat speed in given controlled circumstances to be applied to all craft as the basis point within which to construct a fair handicap system devoid of the 'anarchy' of bumbling buffers and egregious event number driven organisers.


BOOM! Knowingly (or unknowingly) you have just stumbled upon the biggest can of worms in the none one design sailing world.


Back to Top
JimC View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 17 May 04
Location: United Kingdom
Online Status: Offline
Posts: 6662
Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 13 at 11:36am
I'm not aware of reliable polars for any dinghy class in the UK. The problem with that sort of thing is that it needs a small team of people and a huge amount of time and boring effort to setup, and most people would rather go sailing. Also, as mentioned above, you need the instrumentation to be able to establish true wind speed and direction (lets not even get into tides).

The only people who have really done much of it to my knowledge are the Bethwaites, and that seems to be because father, son and daughter comprised their own team of sailing 'anoraks' who lived near each other and were prepared to put the effort in.

For example I've tried to set up tow testing in a development class and failed, because no-one else near enough to me for it to be practical was really interested enough...

And even I am not so interested in this stuff that, for example, I'd be prepared to drive 50 or 60 miles for umpteen weekends in a row to go and spend days sitting in a motor boat reading off measurements on a spring balance.

Edited by JimC - 06 Sep 13 at 11:38am
Back to Top
Daniel Holman View Drop Down
Really should get out more
Really should get out more


Joined: 17 Nov 08
Online Status: Offline
Posts: 997
Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 13 at 1:37pm
Physical testing of dinghies "in the field" would be impossible to do in a scientific and meaningful manner whereby you could quantify every aspect of the aero and hydro characteristics accurately enough.
Big boat IMS (and I believe subsequently IRC) handicapping sought to handicap the boats based on their VPPs - i.e velocity prediction programmes - maths models of the aerodynamic and hydrodynamic components of the yacht which can resolve the equilibriums for any speed / heading / sail set to effectively produce polar charts from which theoretical times around theoretical (perfect triangle or ww/lw or point to point) courses. Most polars that you get on leadmines to steer and trim to are derived from the VPPs that have been created rather than physical testing (far, far more expensive given that you'd have to do extensive wind tunnel and towtank / CFD analyses to populate all the physical models).

There is no reason why you couldn't run every dinghy class through a vpp, apart from effort and expense. Trouble is then, what windspeed would you decide to take the relative handicaps at? Thats a can of worms to start with. Also, the VPP number will have to be given for whatever course config (i.e. ww/lw; specific point to point etc) that has been fed into the computer. I don't need to overstate the disparity in performance between most classes depending on time spent on which leg of the course or wind strength.

Then the aspect that could never be simulated in a computational environment, except by means of a massive subjective fudge, is that an empirical scheme like the PY is the only way to capture the differences between how a boat should perform on paper compared to how it performs in practice - how easy it is for the performance to be realised by the crew etc.
An RS 100 may be a rocket at VMG running in moderate breezes, easily captured in a maths model for steady state, but how do you quanitify and account for the ballache of raising and hoisting the kite singlehanded on a 70 yard run on a pond?

Believe me, as one who has thought about this more than most, PY especially of late with all the effort going into it, is by far the least imperfect way of divining some comparisons between disparate craft in disparate circumstances competing in the sport with the largest set of variables.
Back to Top
Daniel Holman View Drop Down
Really should get out more
Really should get out more


Joined: 17 Nov 08
Online Status: Offline
Posts: 997
Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 13 at 1:45pm
Sorry meant that last one for the handicap final solution mein kampf by adolf fuller thread! fair bit of crossover between these threads though
Back to Top
 Post Reply Post Reply Page  <1 2345>

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