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Posts: 29 		Post Options Post Options   Quote Big-C Quote  Post ReplyReply Direct Link To This Post Topic: Dart 18 with spinnaker py
    Posted: 01 Sep 11 at 5:01pm
Does anyone know the py for a Dart 18 with the gennaker, mate of mine is taking his to sheppey on sat and reckons the schrs conversion gives him a py of 801 - published py for standard 18 is 798
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Posts: 1402 		Post Options Post Options   Quote Contender 541 Quote  Post ReplyReply Direct Link To This Post Posted: 01 Sep 11 at 6:09pm
I would take 798 and think myself lucky to be penalised 3 points only for carrying a spinnaker
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Posts: 2899 		Post Options Post Options   Quote alstorer Quote  Post ReplyReply Direct Link To This Post Posted: 01 Sep 11 at 7:24pm
I think he's saying that the SCHRS rough converter is giving the "with spinnaker" configuration a higher (ie slower!) handicap than the "no spinnaker" actual PY.
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Posts: 29 		Post Options Post Options   Quote Big-C Quote  Post ReplyReply Direct Link To This Post Posted: 01 Sep 11 at 7:38pm
Al that's exactly what I.m getting at and seeing as it's a southerly forecast for sheppey ie 75% of the course is a reach and darts always do well there anyway I think he has just found himself a bandit !
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Posts: 1810 		Post Options Post Options   Quote craiggo Quote  Post ReplyReply Direct Link To This Post Posted: 01 Sep 11 at 9:18pm
We used to have about 5 or 6 Dart 18s with spinnakers at our club back in late 90s. I've tried to look back through my sailwave archives to see if I could find the PY but alas my archive runs out in 2002! From memory it took a pretty big hit on PY for the kite, 740 rings a bell but of course how many clubs would have made a return! Most of the guys at our clubs realised that they only ever had a chance in long distance races with the kites on, so took them off for the round the cans stuff.
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Posts: 739 		Post Options Post Options   Quote ASok Quote  Post ReplyReply Direct Link To This Post Posted: 01 Sep 11 at 10:01pm
I believe that those in the know within the D18 class have always said that the Dart with a spinnaker is actually slower due to the windage effect upwind. Not sure whether thats true or not. I've only every seen them cruising rather than racing against them
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Posts: 314 		Post Options Post Options   Quote Sprint Bob Quote  Post ReplyReply Direct Link To This Post Posted: 02 Sep 11 at 4:41pm
Originally posted by Big-C

Does anyone know the py for a Dart 18 with the gennaker, mate of mine is taking his to sheppey on sat and reckons the schrs conversion gives him a py of 801 - published py for standard 18 is 798
Yes this is a problem if you use the conversion of estimated PY = SCHRS rating x 692.7 for any boat which has an actual RYA PY of one configuration which lies off the line PY= SCHRS rating x 692.7.
 
It is just an error introduced by using this method. If the same 2 boats sail under SCHRS ratings a standard Dart 18 has a rating of 1.181 and if you add a spinnaker it changes the rating to 1.157 (i.e significantly faster).
 
The 2011 RYA PY for a Dart 18 has moved to 800.
 
The methodology we use at Grafham to derive a PY for a Dart 18 with a spinnaker is
Estimated PY = 800 x the SCHRS ratio of the 2 configurations
i.e = 800 x 1.157/1.181 = 784.
 
You have the same problem with the Dart 18 if you use the SCHRS panel methodology to derive a PY for a single handed Dart 18.
 
We have pointed out this problem to the SCHRS panel a number of times but thus far they have not acted on it.
 
Cheers
 
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Posts: 62 		Post Options Post Options   Quote stewart smith Quote  Post ReplyReply Direct Link To This Post Posted: 12 Sep 11 at 6:01pm

I feel that the problem is not the handicap rating of the spinnaker equipped Dart 18, but the 800 PY number given to the standard Dart 18.  Talking to some of top Dart 18 sailors, they agree that this handicap number is totally unrealistic when sailing against half-boats.  The chart below is derived from putting different Dart 18 measurements into the SCHRS calculator.  As you can see, there is a difference if you use a spinnaker.  Looking at the results, they appear proportional and about right in the real world.  The last column on the right is the result of multiplying the SCHRS numbers by 692.7 to get the PY number.  You note, line 5, the standard Dart 18 two up with Main and Jib a PY of 818 and not the 800 given to the class by the Monohull  Mafia of the RYA.

1. Single handed with Main Jib and Spinnaker        1.063 = 736PY

2. Single handed with Main and Jib                           1.081 = 749PY

3. Single handed with Main and Spinnaker              1.145 = 793PY

4. Two-up with Main Jib and Spinnaker                    1.157 = 801PY

5. Two-up with Main and Jib                                       1.181 = 818PY

6. Single Handed Main only                                         1.186 = 822PY

7. Two-up Main and Spinnaker                                   1.241 = 860PY

8. Two-up Main only                                                     1.285 = 890PY

If you would like to check these numbers on the SCHRS calculator please note that I used the sail weight of 142.5Kg for all boats fitted with a spinnaker and the water line length of 5.09m for the Single-handed.

I feel that the 800 PY number given to the Dart 18 is not right or fair to Dart 18 sailors.  I am surprised that U.K.I.D.A. dose not protests more vigorously.  I do not sail a Dart, but I do want more people to sail and race at my club, Grafham Water.  I feel they are put off because the bias against cats on handicap is so bad and it makes them give up.

I understand Sprint Bobs methodology, but I feel that he misses the main point, the 800PY for the Dart 18 is WRONG!  The same methodology gives my fellow club sailors who sail their Dart 18 single handed with Main only, a 801 PY and not the 822PY.(Line 6)  They have to sail against me on a Topaz 14 Xteme with its 858 PY.  On the race course we find that it is almost boat for boat sailing, with some days suiting my spinnaker and tight power reaches good for the Darts.

This could suggest that I have a “Bandit” handicap, but I find I am about the same speed as RS 600 when I sail in the mixed racing on Wednesday evenings.  Their handicap is 920PY !
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Posts: 314 		Post Options Post Options   Quote Sprint Bob Quote  Post ReplyReply Direct Link To This Post Posted: 14 Sep 11 at 6:36pm
Originally posted by stewart smith

I feel that the 800 PY number given to the Dart 18 is not right or fair to Dart 18 sailors.  I am surprised that U.K.I.D.A. dose not protests more vigorously.  I do not sail a Dart, but I do want more people to sail and race at my club, Grafham Water.  I feel they are put off because the bias against cats on handicap is so bad and it makes them give up.

I understand Sprint Bobs methodology, but I feel that he misses the main point, the 800PY for the Dart 18 is WRONG!  The same methodology gives my fellow club sailors who sail their Dart 18 single handed with Main only, a 801 PY and not the 822PY.(Line 6)  They have to sail against me on a Topaz 14 Xteme with its 858 PY.  On the race course we find that it is almost boat for boat sailing, with some days suiting my spinnaker and tight power reaches good for the Darts.

This could suggest that I have a “Bandit” handicap, but I find I am about the same speed as RS 600 when I sail in the mixed racing on Wednesday evenings.  Their handicap is 920PY !

 Hi Stewart,
I think that you miss the point. PY numbers are not changed by complaining that they are not fair. They are changed as a result of Clubs returning their race results to the RYA. It is true that there are some handicaps that seem unfair and also that they take too long to change. The RYA have taken action to speed up the rate of change of PYs by taking race data direct from the sailing clubs by Sailwave data. The RYA also recommend that clubs are more proactive in changing handicaps to suit their own local conditions and provide guidance on how clubs should analyse their own race results to develop their own handicaps. The RYA handicaps represent just an average for clubs around the Country. The data they average includes returns from clubs on lakes, rivers and coastal tidal locations. The effect of tides makes a huge difference - just look at the Hayling Island algorithm for allowing for tides. So there is a strong argument that Grafham should adjust it's handicaps based on club results on Grafham and to exclude variables such as tides and rogue PYs from our handicaps. As you probably know that the Club is well on with this work and the Racing Committee will be reviewing the last 4 years worth of race data and determining how we can make our handicaps more fair. I see this as the way forward rather than bad mouthing the PY of the Dart 18 without any data and which, as you say, you do not even sail.
The SCHRS system is a formula based system and the fit of this model to actual performance data is not perfect (or even documented). The 692.7 conversion factor is based on the F18 conversion and assumes a straight line fit between PY & SCHRS. It is well known that some designs get SCHRS ratings that are not reflected in performance but basically it is all we have got for many catamarans which seem to specialise in a multitude of configurations. The Dart 18 has been around for many years (34ish), has the biggest UK fleet of any catamarans and is one of the few catamarans that has had many many returns to the RYA. It's PY is better established than almost all catamarans so to disregard it without any data "because you think it is unfair" is highly dubious. It is better to put your faith in the Club initiative to apply local fair handicaps in Club racing.
Cheers
Bob


Edited by Sprint Bob - 15 Sep 11 at 9:58am
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Posts: 2415 		Post Options Post Options   Quote Scooby_simon Quote  Post ReplyReply Direct Link To This Post Posted: 15 Sep 11 at 9:50pm
Originally posted by Sprint Bob

Originally posted by stewart smith

I feel that the 800 PY number given to the Dart 18 is not right or fair to Dart 18 sailors.  I am surprised that U.K.I.D.A. dose not protests more vigorously.  I do not sail a Dart, but I do want more people to sail and race at my club, Grafham Water.  I feel they are put off because the bias against cats on handicap is so bad and it makes them give up.

I understand Sprint Bobs methodology, but I feel that he misses the main point, the 800PY for the Dart 18 is WRONG!  The same methodology gives my fellow club sailors who sail their Dart 18 single handed with Main only, a 801 PY and not the 822PY.(Line 6)  They have to sail against me on a Topaz 14 Xteme with its 858 PY.  On the race course we find that it is almost boat for boat sailing, with some days suiting my spinnaker and tight power reaches good for the Darts.

This could suggest that I have a “Bandit” handicap, but I find I am about the same speed as RS 600 when I sail in the mixed racing on Wednesday evenings.  Their handicap is 920PY !

 Hi Stewart,
I think that you miss the point. PY numbers are not changed by complaining that they are not fair. They are changed as a result of Clubs returning their race results to the RYA. It is true that there are some handicaps that seem unfair and also that they take too long to change. The RYA have taken action to speed up the rate of change of PYs by taking race data direct from the sailing clubs by Sailwave data. The RYA also recommend that clubs are more proactive in changing handicaps to suit their own local conditions and provide guidance on how clubs should analyse their own race results to develop their own handicaps. The RYA handicaps represent just an average for clubs around the Country. The data they average includes returns from clubs on lakes, rivers and coastal tidal locations. The effect of tides makes a huge difference - just look at the Hayling Island algorithm for allowing for tides. So there is a strong argument that Grafham should adjust it's handicaps based on club results on Grafham and to exclude variables such as tides and rogue PYs from our handicaps. As you probably know that the Club is well on with this work and the Racing Committee will be reviewing the last 4 years worth of race data and determining how we can make our handicaps more fair. I see this as the way forward rather than bad mouthing the PY of the Dart 18 without any data and which, as you say, you do not even sail.
The SCHRS system is a formula based system and the fit of this model to actual performance data is not perfect (or even documented). The 692.7 conversion factor is based on the F18 conversion and assumes a straight line fit between PY & SCHRS. It is well known that some designs get SCHRS ratings that are not reflected in performance but basically it is all we have got for many catamarans which seem to specialise in a multitude of configurations. The Dart 18 has been around for many years (34ish), has the biggest UK fleet of any catamarans and is one of the few catamarans that has had many many returns to the RYA. It's PY is better established than almost all catamarans so to disregard it without any data "because you think it is unfair" is highly dubious. It is better to put your faith in the Club initiative to apply local fair handicaps in Club racing.
Cheers
Bob
 
You miss the point that the D18 number is skewed by the fact that the 18's do little handcap racing and when they do they are more interested in racing when there is wind "so we can have a chance" as D18's don't go until a good F4.
 
So; when D18's do race on PY; there is usually wind and thus the handicap gets skewed by the better performance (relative to the mono's they are racing) in more wind. 
 
Simple problem with the way PY works. 
 
It measures the performance of the boat; the performance of the sailors and the effect of the wind on the boat the races were sailed in. 
 
 
 
Thus because the D18 sailors do not bother in lighter wind; the effects the results; because the D18 is woefully underpowered and an inefficent hull shape for slower speeds.
 
 
How many actual returns were made last year for the D18 to PY? Not many I would guess.
 
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