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Old 14-07-2020, 10:36   #1
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Car position for jib sheet aft/forward

Relative newbie flying a 130 this year and trying to learn about the proper positioning of the car for the jib sheet. (Camber and twist are new terms to me as I read about it.) The "simple" explanation seems to be big wind = car aft, less wind = car forward. With so many position options along the track I'm sure there are nuances to be considered. Anyone care to weigh in with a relatively basic description of what I should be looking for?
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Old 14-07-2020, 10:55   #2
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Re: Car position for jib sheet aft/forward

Assuming you have telltales on the jib luff - sail upwind with the jib sheeted in and all telltales streaming aft. Slowly turn upwind until the telltales start to flutter. If the top windward or bottom leeward telltale flutters first, move the car forward a little. If the top leeward or bottom windward goes first, car goes back a little. Goal is for all windward telltales to flutter at the same time.

Once you get that, you have a base position and you can make minor (couple of inches) adjustments for wind speed like you were talking about.
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Old 14-07-2020, 11:07   #3
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Re: Car position for jib sheet aft/forward

There are many good books on sail trim. While I'm sure you will get lots of good feedback, even the basics require a far more comprehensive explanation, with greater continuity, than is possible in a forum.


35 years into it, I'm still learning boat- and sail-specific nuances.



https://www.amazon.com/Manual-Sail-T...4749861&sr=8-2
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Old 17-07-2020, 11:39   #4
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Re: Car position for jib sheet aft/forward

I was taught to imagine a line perpendicular to the luff of the sail, passing through the clew and down the jibsheet. That would be the initial position for the car to maintain that perpendicular line, with adjustments plus or minus for uniform wind as sandy stone described.
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Old 17-07-2020, 12:53   #5
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Re: Car position for jib sheet aft/forward

Quote:
Originally Posted by sandy stone View Post
Assuming you have telltales on the jib luff - sail upwind with the jib sheeted in and all telltales streaming aft. Slowly turn upwind until the telltales start to flutter. If the top windward or bottom leeward telltale flutters first, move the car forward a little. If the top leeward or bottom windward goes first, car goes back a little. Goal is for all windward telltales to flutter at the same time.

Once you get that, you have a base position and you can make minor (couple of inches) adjustments for wind speed like you were talking about.

The point being to have the shape of the foot about the same as the shape of the leech.


You can also do that by eye, or by the method Gansett mentions.


All my headsails have lines drawn from the clew which lets you set it at a glance.


Headsail trim is much less interesting than mainsail trim. I adjust the clews of both my jib and staysail with barber haulers, inboard and outboard, to have some modicum of control over the angle of attack, but it's a very meagre effort compared to what you can do with the mainsail on a boom, where you can make the sail fatter or flatter, and feather it, or bite it into the wind. Headsails, unlike mainsails, are basically "on", or "off".
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Old 22-11-2020, 00:38   #6
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Re: Car position for jib sheet aft/forward

Sail “twist” refers to the different angle to the wind that the sail has at its foot and its head. Typically, the head twists out to leward more than the foot because the wind velocity is more up there than down on the water. You can control twist by moving the sheeting position fore or aft. More aft, makes the foot tighter and the head twist out more, more forward losens the foot giving more camber (belly) to the lower part of the sail and pulling the head of the sail more toward the centerline of the boat (less twist). You are correct, generally you want more twist in heavier air...
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Old 22-11-2020, 15:18   #7
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Re: Car position for jib sheet aft/forward

This article will give you a good head start:

https://www.rya.org.uk/knowledge-adv...ly-genoas.aspx
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Old 22-11-2020, 18:34   #8
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Re: Car position for jib sheet aft/forward

Gansett and Dockhead have both touched on the essentials, and Thinwater states correctly that there's a heckuvalot more to it than can be communicated by e-mail.

BUT: You gotta start somewhere :-).

So start by promising yourself to do things in such way that they can be REPLICATED precisely each time you do them. The basic trick is to slide the sheet car fore or aft as required to get equal tension on the leech and on the foot of the sail, i.e. so there is no twist in the leech and no sag in the foot. That's where the imagined line perpendicular to the luff and passing through the clew comes in. That's your basic position for THAT sail. Mark the car position on the track so you never have to guess at it again. You want to use THAT sail? Put the car at the mark, then trim up the sheet. You want to use another sail? Well, THAT will have the appropriate car position marked already, so there is no guesswork involved.

Roller FURLING is not the same as roller REEFING. It's hard to get a decent REEF in a roller FURLING sail, but you do the best you can. It CAN be done. Conceptualize a "rolled in" sail as a separate sail of a different size. With "hank on"s, you'd typically have three sails: Genoa (say 130% of foretriangle), Working Jib (90% or 100%) and Storm Jib (35% or 40%)". If you "roll in" from 130% to 100% the car will need to be moved forward to the position that is marked for 100%, but of course, that will only be the right position IF you have rolled in to 100% - not 105% or 95%. If you need to "roll in" to a "storm jib", say 35%, this is even more of a problem.

Depending on how your main is cut, and how good you are at trimming it, the headsail may require a bit of twist, or it may not. If it does, you'll need to shift the sheet car forward a tad. These are things that experience will give you a feel for, but if you mark your tracks as I suggest, then at least you'll have a known datum from which you can work consistently, and one that you can find again without fail.

Have a go at it. Perfection is NOT required - particularly not with "roller reefing" ;-)

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Old 30-11-2020, 23:56   #9
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Re: Car position for jib sheet aft/forward

All good advice above but if you know any good dinghy sailor from local yacht club that wants to try a bigger boat he/she might be able to show you what you are striving for.
But sandystone gave you the btm line.
IMO starting in dinghys gives you an instant feel for what works, not so easy in a keelboat
Reading is good too
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Old 01-12-2020, 04:57   #10
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Re: Car position for jib sheet aft/forward

J105s race with furlers. There are lots of photos that show lead positions. Imo, the best thing for headsail trim is an inhaul.
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Old 01-12-2020, 07:00   #11
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Re: Car position for jib sheet aft/forward

Quote:
Originally Posted by TrentePieds View Post
So start by promising yourself to do things in such way that they can be REPLICATED precisely each time you do them.

Mark the car position on the track so you never have to guess at it again.

You want to use THAT sail? Put the car at the mark, then trim up the sheet. You want to use another sail? Well, THAT will have the appropriate car position marked already, so there is no guesswork involved.

+1; marking the track is an excellent practice so everyone knows what position to move the car for best performance.
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Old 01-12-2020, 23:56   #12
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Re: Car position for jib sheet aft/forward

We only just touched on this in my ASA 103 class and I haven't wrapped my head around this yet. I realize that the twist is trying to compensate for the situation in which the wind aloft is faster (and therefore at a different apparent wind angle) than the slower wind at the foot of the sail. However, is the change in apparent wind angle aloft always in the direction of the twist? Can you ever have a situation where you need to twist the head of the sail in the opposite direction to windward (which I'm assuming is impossible to achieve)?
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Old 02-12-2020, 10:28   #13
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Re: Car position for jib sheet aft/forward

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Originally Posted by nuku34 View Post
More aft, makes the foot tighter and the head twist out more, more forward losens the foot giving more camber (belly) to the lower part of the sail and pulling the head of the sail more toward the centerline of the boat (less twist).
Quote:
Originally Posted by TrentePieds View Post
Depending on how your main is cut, and how good you are at trimming it, the headsail may require a bit of twist, or it may not. If it does, you'll need to shift the sheet car forward a tad.
Not back a tad?
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Old 02-12-2020, 10:59   #14
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Re: Car position for jib sheet aft/forward

Quote:
Originally Posted by djousset View Post
Relative newbie flying a 130 this year and trying to learn about the proper positioning of the car for the jib sheet. (Camber and twist are new terms to me as I read about it.) The "simple" explanation seems to be big wind = car aft, less wind = car forward. With so many position options along the track I'm sure there are nuances to be considered. Anyone care to weigh in with a relatively basic description of what I should be looking for?

I've read all the sail trim books. This one's a winner:


https://shop.sailboatowners.com/prod.php?55534
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Old 02-12-2020, 11:00   #15
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Re: Car position for jib sheet aft/forward

Quote: "Not back a tad?"

Yes, of course!! Slack-botted proof reading :-) Nuku34 is absolutely right. I'll go stand in the corner now :-).

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