Author Topic: Boat tuning  (Read 29045 times)

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Offline Tom K

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Re: Boat tuning
« Reply #30 on: April 20, 2012, 04:33:15 PM »
Ok, If I have offended, I apologise. I in no way disrespect your experience or expertise. My only concern is that I have seen new cherubists join the the class before and tinker their way to the back of the fleet in the first few months, before taking years to work back forward.

Re the 18, I'm not sure what you mean by 'break point' but we do sail with varying amounts of twist depending on the conditions.


Offline Andrew Whapshott

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Re: Boat tuning
« Reply #31 on: April 20, 2012, 04:37:28 PM »
On a beat, Max draft (according to my magic tuning book) should roughly be:

<F3 = 45% Jib 50% Main     In chop = 40% Jib 45% Main  (Unless really really light+flat in which case.. flat as possible)  
F3-4 = 45% Jib 50% Main    In chop = 40% Jib 45% Main
F5-6 = (chop) 45% Jib, 50% Main

 Its a fairly standard value I would have thought, a lot of maths behind aerofoils is known, and this must work its way into our sails...  

Offline Torchy

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Re: Boat tuning
« Reply #32 on: April 20, 2012, 04:53:23 PM »

Re the 18, I'm not sure what you mean by 'break point' but we do sail with varying amounts of twist depending on the conditions.



I've seen an 18 with the big rig up when the small rig would have been better, still able to sail fast by letting the top sag...I think it was a round topped sail tho'

I'm experimenting with having Loco's sail just at the edge of freeing off upwind - it wouldn't sag, just some reverse bend appear in the top 2 battens and that's what I mean by 'break point'. I may put a little tension back to stop the reverse bend if it causes problems
Previously 2685 'Loco Perro' and 2345 'Tachyon'

Offline Torchy

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Re: Boat tuning
« Reply #33 on: April 20, 2012, 04:54:02 PM »
..and Tom and I chatted...still friends
Previously 2685 'Loco Perro' and 2345 'Tachyon'

Offline Torchy

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Re: Boat tuning
« Reply #34 on: April 20, 2012, 04:56:00 PM »
Good info Andrew...is that from Sail to Win or another?

Seems a good place to stat from  :)
Previously 2685 'Loco Perro' and 2345 'Tachyon'

Offline Torchy

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Re: Boat tuning
« Reply #35 on: April 20, 2012, 05:02:59 PM »
Its a fairly standard value I would have thought, a lot of maths behind aerofoils is known, and this must work its way into our sails...  

The difference for us is the slot and from my understanding this is why we let the draft go further aft, especially low down (I think)...and flatter low down...tho' this is built into the sail design.

Previously 2685 'Loco Perro' and 2345 'Tachyon'

Offline Stuberry

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Re: Boat tuning
« Reply #36 on: April 20, 2012, 05:05:29 PM »
This is a spade...


Offline Torchy

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Re: Boat tuning
« Reply #37 on: April 20, 2012, 05:10:25 PM »
Oh mighty guru...who is that aimed at?  :)

If at me...I am picking brains...and have gathered many nuggets...the secret is to keep talking even if people take one for a fool...in fact if taken for a fool all the better ;)
Previously 2685 'Loco Perro' and 2345 'Tachyon'

Offline Andrew Whapshott

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Re: Boat tuning
« Reply #38 on: April 20, 2012, 05:24:38 PM »
Good info Andrew...is that from Sail to Win or another?

Seems a good place to stat from  :)

It's a Fernhurst book called "Sail and RIg Tuning" Its mostly yacht related, but cetain things in it are translatable.   I have an even better book that was published by Sobstad,  Covers pretty much everything about sails, although I think you only get it when you buy a sail (Mine fell out of a bag from a new kite on the first hoist so I pocketed it..)

 

Offline Torchy

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Re: Boat tuning
« Reply #39 on: April 20, 2012, 05:26:47 PM »
Nice one Andrew, thank you
Previously 2685 'Loco Perro' and 2345 'Tachyon'

Offline Torchy

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Re: Boat tuning
« Reply #40 on: April 20, 2012, 06:38:38 PM »
On a beat, Max draft (according to my magic tuning book) should roughly be:  

Does the book give a rationale for pulling the draft forward in a chop? I guess one would be sailing deeper but why move the draft forward too?
Previously 2685 'Loco Perro' and 2345 'Tachyon'

Offline Stuberry

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Re: Boat tuning
« Reply #41 on: April 20, 2012, 07:00:23 PM »
Not aimed at anyone particular. More a cryptic commentary on Toms post, calling a spade a spade.

I can assure you know one in the class takes anyone for a fool. You are travelling down a well trodden path.

Offline Torchy

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Re: Boat tuning
« Reply #42 on: April 20, 2012, 07:33:32 PM »
Experienced people have pointed out the dangers of 'fiddling' and I would totally agree...

...if people want to discuss tuning, please do.
Previously 2685 'Loco Perro' and 2345 'Tachyon'

Offline Torchy

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Re: Boat tuning
« Reply #43 on: April 20, 2012, 07:39:32 PM »
btw On internet forums I have posted on previously the spade usually means 'dig yourself a hole as deep as you like' - sorry if I misunderstood your meaning Stuberry
Previously 2685 'Loco Perro' and 2345 'Tachyon'

Offline andy_paterson

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Re: Boat tuning
« Reply #44 on: April 20, 2012, 09:16:03 PM »
I seem to be a "one-setting " person - Shiny Beast had everything fixed regardless of conditions.
Maybe the 97 rig was simpler ( less need to depower )
After initial tuning ( on my own ) for mast rake, rig tension etc, I just used the same settings - fixed length jib/forestay, fixed shrouds.
Boatbreaker to fit the jib/forestay in the same place.
Enough rig tension so it never went loose downwind ( or upwind ), and meaning that the support to the mast was not changed by trapezing, and no nasty mast wobbling downwind
Fixed uppers - tight enough to prebend the mast for light winds, but giving sideways support in a breeze.
Fixed jib downhaul.
Even the kicker seemed mostly to be about the same place, except for light winds to allow twist.
Adjustable things - main downhaul was important, kicker and jib and main trim had to be right - sailing with the right heel also very important.
Jib sheeting - 4:1 on the sheet gives good leech tension/twist control.

The mast /sail combo was just perfect! enough power in light stuff, auto-opening leech. The top went inverted in a breeeze upwind.
The sails were quite flat, with smooth shape, maybe 40% back at the bottom, 30% at the top, unlike many of the full front sails of others.
Flat kite, but we were able to sail deeper than everyone else.

Two - boat tuning ?  no, maybe an open, then just see how it went at the Nationals   - and by luck or skill = fast  ;)  a few times, even with a new crew.

The best thing was being able to rig the boat in 10 mins, having a calm chill feeling before racing, knowing the settings were good for the conditions, and never having the psychological block of thinking the settings were wrong!

Batten tension?  Just enough to stop windward side wrinkles, and sometimes I even let the tension off in the winter when not sailing!

Maybe 30 years of Cherubbing helps - just get sailing and do more sailing, don't worry too much about the settings.

Cherub = too hard for the Olympics  ;D