Jib sheet at 50% of luff or 50% of girth for fractional?

[bcardarella]

I'm watching the Sail Trim Masterclass: 





and at 8m30s the presenter says the jib car should be set such that the jib sheet angle for a good neutral position should be pointed to the 50% of the luff height. The sail plan he shows is a masthead rig and a large overlap. I'm wondering if the intent was really 50% of the luff or should it really be 50% of the girth for the true neutral position?

 

[longy]

It's a basic trim guide, 50% of the Luff, and it works for any triangular sail, regardless of the size of the foretriangle

 

[SloopJonB]

I was taught that the jib sheet should be a line 90 degrees to the luff and running through the clew - the LP line.

From there you tune it fore or aft until the tell tales stream evenly.

 

[bcardarella]

@SloopJonB I assume you're doing that tuning in medium breeze?

 

[SloopJonB]

In whatever breeze I'm in and whatever sail I have up - I trim by the tell tales. The "LP" setting is simply the base line car position.

 

[bcardarella]

Oh I see, you set to that "base" along LP then tune afterwards.

 

[Steam Flyer]

If the boat is fully powered-up, it should be so that the upper and lower tell-tales break or flicker at the same time.

If overpowered, the lead should brought aft, to take some power out of the upper segment of the sail.

I don't understand why anybody would care if the sheet points toward 50% of the luff, other than as a rough-guide starting point.

FB- Doug

 

[El Borracho]

On a proper sailboat the distance from the block to the clew is so short that the angle is a pointless observation. The knot is in the block. The LP or 50% luff rules-of-thumb are for positioning the midpoint of the track. The position for proper trim is going to vary greatly with sail characteristics. Roach-y jibs in high tech materials need a great amount of leech tension vs. the foot. So the block may go forward. Reach-y jib tops and cruiser cut sails might have the sheet angle around the 50% luff. That's my feeling. Never measured it. As implied above, the block is moved until the boat sails fast, the luff is right, period.

LP is a bit odd for a guide as tall rigs with short I will have the LP very low on the luff.

 

[12 metre]

It's a basic trim guide, 50% of the Luff, and it works for any triangular sail, regardless of the size of the foretriangle

Yup.  Old school ball park approximation.  A good place to start. May have been in some North Sails literature, but I recall reading it many many years ago.

Come to think of it, I think some sailmaker, or maybe a few used to have a black stripe attached to the clew to make it even easier to sight.  You just made sure the jib sheet was in line with the stripe.

 

[OCS]

50% is an approximation on most genoas, from there work on telltale flying.  some high aspect jibs need to even higher up the luff (sometimes up top 70%). the LP line would generally be a heavy air setting, allowing to twist off at top and lessen main backwinding.

 

[LionessRacing]

Geez, you guys; you just set the sheet to be an extension of the miter, how hard can it be... ?

 

[SailRacer]

Maybe start at 50% -

If AWA is constant,  adjust car (for and aft)  in order to make telltales stall - fly evenly (if minimal shear is present).

Just my $.02

Sail safe!

 

[TUBBY]

It ain't where you start from that really matters.

It's that you can read what the sail is telling you and adjust accordingly!

 

[Grande Mastere Dreade]

on my fractional rig, I have the sheet from the jib car to the clew set on the 50% luff line as others have stated.  at that point on my sail the foot and leech are not streched into a different shape. then upon wind conditions I move the car backward to   flatten the foot and open the leech in heavier air or in lighter air move the jib car forward to give the sail for depth and close the leech for more power

here's another good video

 

[Mr. Squirrel]

Yup.  Old school ball park approximation.  A good place to start. May have been in some North Sails literature, but I recall reading it many many years ago.

Come to think of it, I think some sailmaker, or maybe a few used to have a black stripe attached to the clew to make it even easier to sight.  You just made sure the jib sheet was in line with the stripe.

I think all Lightning jibs still come with a trim line to align the car position/ sheet angle.

MS

 

[El Borracho]

I took a look at my jib sheet and deck leads yesterday. It is a reasonably young non-overlap jib. The sailmaker's clew reinforcing strop and the jib sheet do indeed almost align. Both point very high on the luff. Much higher than 50%. May 65%. So wayyy higher than LP. It is for luff tension and twist control. And more wind pressure up high.

 

[12 metre]

The reason I use the 50% of luff rule of thumb is because I usually work the main and the knowledge of the headsail trimmers sometimes doesn't go much beyond "grind in the headsail until it touches the spreaders".

So, from the cockpit I can't see much of the genoa luff, but I can usually see the clew and I can roughly site the sheet angle and suggest to the trimmers that they might want to consider moving the car forward or aft.  It is a good way of seeing if things are completely out of whack on the headsail and at least gets the trimmers to pay attention to such things.

 

[Fiji Bitter]

The reason I use the 50% of luff rule of thumb is because I usually work the main and the knowledge of the headsail trimmers sometimes doesn't go much beyond "grind in the headsail until it touches the spreaders".

So, from the cockpit I can't see much of the genoa luff, but I can usually see the clew and I can roughly site the sheet angle and suggest to the trimmers that they might want to consider moving the car forward or aft.  It is a good way of seeing if things are completely out of whack on the headsail and at least gets the trimmers to pay attention to such things.

12, I find it hard to believe you sailed all your life like that!

Sorry, I've seen better posts from you, if I may say so...

 

[Bump-n-Grind]

I'm watching the Sail Trim Masterclass: 

and at 8m30s the presenter says the jib car should be set such that the jib sheet angle for a good neutral position should be pointed to the 50% of the luff height. The sail plan he shows is a masthead rig and a large overlap. I'm wondering if the intent was really 50% of the luff or should it really be 50% of the girth for the true neutral position?

in almost 40 years of sailing, I have, not once, ever, thought about this. One of the first things I learned how to do as crew on a boat, was trim jib/genoa.  I'm akshully pretty not bad it, if I do say so myself. The jib fairleads on my J35 are infinitely adjustable along the track via a purchase system. I can put them anywhere I want them. I know about where they need to be for each headsail. In fact I've got two leads on each track: aft for genoa, forward for the #3. They are connected. Once the sail is up the car is constantly being adjusted in conjuction with the sheets to keep the tell tails flowing evenly along the length of the luff.

But never have I ever pondered about the angle of the sheet from the car to the clew.