Facebook

Login

Support Sailonline

If you haven't already - join the SAILONLINE YACHT CLUB!

Please also consider making a donation - all amounts are greatly appreciated!

Board » Technical Discussion » Performance loss

Page: Previous 1 2 3 4 5 6 7 Next Last

I just did two gybes in a row in the start of the Kergulen timed race. In the first I forgot about the 93% and my perf dropped below 85%. I started the second gybe with a perf of 89% and stepped around in about 4 or 5 steps, completing my gybe at a perf of 90% increasing my perf at each step.
I contend this is vital information that should be known to all, that it cannot be derived by direct observation, or by prior knowledge of how a sailboat performs in reality!
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
These discussions have occurred in the past but it tends to run in cycles so that when it re-emerges often what was once public knowledge can subside into a quasi state of urban lengend.

Finding these nuggets in this Forum can be a challenge even if you are looking for something that you yourself have posted.

=========================
Wrong Speed VMG

Posted by
Jakob Kuttenkeuler
2009-02-09

(discussing performance loss model)

"Well, the current model determines
if the maneouver is a tack or a gybe
or just a minor change in twa
(dTWA is the twa change).
If (tack or gybe)
{e = 1.0-self.bs/200.0}
else
{e = 1-abs(dTWA)/25.0}.
perf = perf*e.
However if perf<0.93
no further maneouver loss is done. something like that."

--- Last Edited by A2R at 2013-10-11 13:48:19 ---
None so blind
Many thanks, A2R!!!!
That is the information that we should have had right at the beginning of this whole discussion. I hope that it will be incorporated in the Manual in a prominent position.
I have inquired about the perf loss problem several times over the last three four years and, until now, never received even a hint of an answer
P.S. I will attempt to generate a diagrammatic representation of this situation for the benefit of those among us who are more comfortable with diagrams than equations.
P.P.S. Now all we need to find out is the rate at which the Performance returns to 100% after a Tack, Gybe, or Course Change.
I do hope someone will post the info---in the meantime I will experiment in the Kergulen screen (there are no good windows in the time remaining.)

--- Last Edited by Rod at 2013-10-11 14:33:17 ---

--- Last Edited by Rod at 2013-10-11 14:41:56 ---
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Well depending on your Point of View it was either hiding in plain sight or it was a needle in the haystack, so to speak.

I found it because I went looking for it, plain & simple, as anyone could have done.


None so blind
You can only look for things that you suspect do exist. My point is that there is nothing in the performance of a sailboat during a change in course that would lead anyone to suspect that the loss of speed would be reduced by dividing the course change into two steps.
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
I neither knew that it existed or that it did not exist. Looking is a choice as is not looking. I found more than I expected to, so let's move forward from here.
None so blind
"You can only look for things that you suspect do exist."
No accounting for Serendipity, eh Rod?
;-)
Relying on Serendipity makes you a "Prince of Serendip". I am no 'prince'...science does not rely on just good luck. It needs observation, reasoning, and experimentation. Good luck may happen---then you win the lottery and don't have to worry about anything except greedy relatives.......
If it breaks, it's not strong enough--if it doesn't, it's too heavy.
Initiative often succeeds where rationalization cannot.
None so blind
ciao ALL my friends ;)

just a little contribution from me on this subject :

I remember a few years ago a french soler discovered that jybing in several steps was reducing the perf loss, so I tried to see how it worked ......I did it once only and never again .

two main reasons for that :

1) by so doing the boat runs a longer course , and some of your perf loss saving is gone already, and the time at lower speed below VMG during the maneuver eats away another portion of the saving

2) ( and this is the main reason ) ....after the jybe your angle towards the next mark will no longer be the same and could be worst .......for longtime.

It is very true that also the contrary of item 2) may occur , but item 1) still stands .

IRL an offshore jybe is " smoothed" not so much for performance , but maily for smoothing the maneuver by the crew and keep the spi flying ......whilst , in-shore jybing around a mark smoothing the jybe could cost a number of positions .

Hope you all accept it as an opinion and contribution ..

ciaooooooooooooo ;) ;) ;)

Piero

PS : I did win quite a number of races in SOL , but never because I smoothed jybing or tacking to reduce perf loss..;)

Page: Previous 1 2 3 4 5 6 7 Next Last

Please login to post a reply.

Races

Next Race: 00d 00h 00m


Current Races:

Melbourne to Hong Kong
After celebrating Christmas and New Year it is time for the second run in this year's Ocean Race Championship. After leaving Melbourne on this (about) 5.500 NM course, we will leave the Solomon Islands, Papua New Guinea and the Philippines, all to port. And remember, once again we'll have to choose the best way to cross the Doldrums
PRIZE: SMPF
Race #1658
INFOfrom brainaid.de
OD65v3 Particulars
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
OCQ1-OCCH-SUPSOL-SYC
Race starts: Feb 04th 05:00 Registration Open!

▶ Flash
GO TO RACE

China Sea Dash 2023
The waters of the China Sea beckon for this short race around the cans. We'll be racing 128nm in our TP 52s as the local racers warm down as their sailing season closes.
Race #1551
INFO by brainaid.de
TP 52 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Feb 04th 02:15 Registration Open!

▶ Flash
GO TO RACE

Buenos Aires to Rio 2023

This year's second ARCH series race will run from Buenos Aires, Argentina to Rio de Janeiro, Brazil on a route designed by SOLer Vida_Maldita (under his former alias of zero) in 2013. This is a replica of a classic triennial race of 1200nm, first run in 1947. More information about this IRL race can be found here.
So, Bemvindo/Bienvenidos in this coastal classic and prepare your 90ft Monohulls well.
Race #1662
INFO by brainaid.de
90ft Monohull PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
ARQ1 - ARCH - SUPSOL - SYC
Race starts: Feb 01st 18:00 Registration Open!

▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

  1. Sailonline Yacht Club Member WRmirekd
  2. Sailonline Yacht Club Member Pit8008
  3. Sailonline Yacht Club Member FreyjaUSA
  4. Sailonline Yacht Club Member Vida_Maldita
  5. Sailonline Yacht Club Member Kipper1258
  6. Sailonline Yacht Club Member bonknhoot
  7. Sailonline Yacht Club Member Sax747
  8. Sailonline Yacht Club Member rafa
  9. Sailonline Yacht Club Member SlideRule
  10. Sailonline Yacht Club Member TarassBoulba

View full list

Series

Mobile Client

SYC members have the benefit of access to our mobile/lightweight web client!

The mobile client