Upwind Light Air-Mainsheet/Mastbend/Sailshape Relationship. Was: ISO Article by Ron R

C

Colinkites2000

Member
I wanted to get a new thread going on this because it no longer relates to the article by Ron I was looking for. What I am looking for is information on the mainsheet tension/mastbend/sailshape relationship (upwind) moving from sheeted out 6-8" (super light conditions) to 2 blocked. Continued below from the other thread.


Thanks for the info here. I am pretty clear on the effects of the vang/cunningham as you start to use them more in mediun/strong winds. The part that I was/am unsure about is in lighter conditions going from sheeted out to ensure flow, to sheeting in to increase return - as the breeze picks up a little. I got the impression from the laser tuning guide that when you sheet in to two blocked, the mast bends and therefore opens the leech-- (comments from the guide below)

"As a result, as the Laser mainsheet is pulled tighter, bending the mast and flattening the sail, it reduces leech/batten hook or "return" and opens the leach."

and

"Conversely, easing the Laser mainsheet makes the sail fuller, causing more return in the leech and adding power."

George says that when the sheet is pulled tighter, it closes the leech and therefore this would offer more return if you could ensure flow... but the tuning guide implies that if you want maximum return, you would ease the sheet so that mast is straight and pulling the sheet in further will only reduce return and open the leech.


Other advice states that as soon as you can ensure flow, it is ideal to be two blocked for maximum return- as George implies. Maybe once there is a little power in the sail when the mast is straight, you need to pull it in further just to keep the boom in towards the middle of the boat due to the load pushing sideways on the mast.... but to me with the information in the guide, it seems like sheeting in further would only reduce power when you are still not at hiking max.... thus hurting pointing ability.

Cheers
Colin

181255 said:
181255 -> Good comments George, I think it is also important to note that in that last picture they are probably sheeted out a litte. For sure tons of vang and cuningham, and totally working the boat in every single wave they see in front of them. The Locks is good for this type of sailing.
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Re: Upwind Light Air-Mainsheet/Mastbend/Sailshape Relationship. Was: ISO Article by R

Also one other line from the guide below;

A result of this situation is that we often find sailors "two-blocked", thinking that gives max power (tightest leech), when they should be eased one to two feet on the sheet to straighten the mast and make the sail fuller.

So if this is true, when and why would I want to be two blocked?
 
Re: Upwind Light Air-Mainsheet/Mastbend/Sailshape Relationship. Was: ISO Article by R

Colinkites2000 said:
Also one other line from the guide below;

A result of this situation is that we often find sailors "two-blocked", thinking that gives max power (tightest leech), when they should be eased one to two feet on the sheet to straighten the mast and make the sail fuller.

So if this is true, when and why would I want to be two blocked?
Click to expand...

You don't want to 2-block until you are hiking. 2-blocking opens/flattens the leech and thus depowers. The following article in the Laser Sailor may be of use. It is by Ryan Minth for Radial sailors, but the principals are the same.

http://216.119.101.65/c/cnt/down/Winter2005.pdf

Merrily
 
Are we discussing Radial or Full rig mainsheet tension ?

If it's full rig, then I disagree with Merrily (even Ryan in his article talks about two blocking in 8 knts in a Rad) - you can start two blocking well before you are hiking, especially in flat water. I find most people two blocking more or less as soon as they get their rear ends out near the edge of the side deck.

The tradeoff between more mainsheet tension is that you loose forward drive (power) because the sail is getting flatter (because the mast is bending more). However the leech is getting tighter which increases your pointing ability (as does the flatter sail from the mast bending) .

Two blocking does not open the leech (lots of cunningham does that, as does easing the mainsheet out beyond the point where the vang loads up, as does tightening the vang so that it's bending the mast beyond what the mainsheet bends it ie supervanging.)

I find it pretty simple on the water when racing to tell how much mainsheet tension to use in medium air (8-12). If I'm not going fast - ease a couple inches. If I'm not pointing high enough, trim harder by a couple of inches. If I'm slow and low, I need to review all settings or go in ;-)

Only in wind below 5 with the mainsheet well eased do I sometimes find it pays to carry the boom closer to centerline by easing the trav (I'm talking about 2-4" inboard of the trav fairlead for the bottom block) . Otherwise the trav is tight or really tight to make sure the bottom block is out against the trav fairlead in all other conditions.


The parts quoted from the tuning guide are confusing at best and flat out wrong at worst.

I'm not sure I would put much faith in the tuning guide on the vanguard site, I don't think it's been updated in years.... You'd be much better off talking to the top guys in your area, some of the more current books/dvd's
 
Re: Upwind Light Air-Mainsheet/Mastbend/Sailshape Relationship. Was: ISO Article by R

Yes talking about full rig. Thanks for the explanation. This is what I was looking for. I think it would be cool for someone to revise the tuning guide to make things less confusing. Really helpful explanation. Cheers Colin
 
Colinkites2000 said:
George says that when the sheet is pulled tighter, it closes the leech and therefore this would offer more return if you could ensure flow... but the tuning guide implies that if you want maximum return, you would ease the sheet so that mast is straight and pulling the sheet in further will only reduce return and open the leech.
Click to expand...

Be careful with paraphrasing someone else's words. I am not even sure what you say that I said, but I do not think I said what I think you say I said.
In any case what I wrote earlier is that two-blocking will start somewhere between 10 and 12 knots. If air is lighter, you will indeed want to ease the sheet. Sheeting in (and thus closing the leech) will improve your pointing ability but you will also loose power as you flatten the sail.
My best advice: hit the water and see what happens!

GWF
 
Rick Rothenbuhler said:
You need to find a better tuning guide. The Ainslie book recommends two-blocking in 5 knots, I think.
Rick.
Click to expand...

Yes a better book is definitely required!
You are right, Ainslie indeed says 5 knots! I don't think I ever sail it that tight in 5 knots. Tillman suggests in the 8-12 knots range to go from 6 inches (distance between the blocks) to two-block. That sounds better to me, but what do I say: unless Ainslie made a typo he is "The King."

GWF
 
The tuning guide is correct, if confusing in its description of what happens. When to be two-blocked is a bit more subjective, and will vary based on variations in sail, mast stiffness and boat stiffness/traveler height and of course your hiking and weight.

The most confusing thing about sailing a Laser, is that the unstayed mast bends based on the mainsheet and or vang tension. In order to get enough tension on the vang to bend the mast (which makes the sail less deep/powerful), you have to tighten it so much that the leech is totally closed, to use terms from a stayed rig.

Where the tuning guide talks about opening the leech, at least on the upwind, it is really talking about making the draft shallower. The leech is always closed.

So, when sailing in light air, ease the mainsheet until it seems like you are going fast - this is probably less than 10" off the two blocked position, and it may be two-blocked. Big fat guys like me can sail with a pretty full sail pretty far into the wind range.
 
Drift conditions (ultra light airs <3kts before there is an actual 'breeze' due to turbulent mixing) seems to be a compromise upwind between pre-bend with vang to get the type of entry you need to point while trading off some reduced draft in the head where the air velocity is greatest. The instant you get 'breeze' (i.e. sufficient mixing to give same velocity at boom height as at the head) you need to switch to a more sheet acive and vang passive mode.

Some useful articles you may already have seen include:
The Un-stayed Rig, Rooster Sailing Coaching Tips, Steve Cockerill
Tuning the Radial, Ryan Minth
Sailing with the new laser Vang, Ed Adams in Sailing World, may 2003 P76

Also discussions in High Performance Sailing, Frank Bethwaite 1993, published by International marine a Division of McGraw Hill has some relevant information - although emphasis is wider than just Lasers and focuses more towards wind, weather and skiff development and techniques in apparent wind sailing.

GL
 
I think that everyone is looking for the magic formula.. what may work for some may may not work at all for others.
I say you guys should get on the water and try, and find out what suits you best.
The sail trim, vang tension, cunningham and outhaul setting depend a lot on the weight of the sailor, the sea state and many other factors.
On the same conditions and for tactical reasons you may want to go fast or point really high and so need to be able to shift gears.
The only way is to hit the water and sail preferably with other people to compare your evolution.
Don't bother looking for "in theory" answers.
Good luck to all!!!



POR - 183426
 
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