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Old 13-01-2010, 14:22   #1
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Self-Tacking Jib...in 'Genoese Sauce'

A question for riggers (and non-riggers as well...)

Data
- 29’ sloop with 140% furling genoa
- The owner also has a furling self-tacking type jib

Problem
It would be nice to use a self-tacking jib, when single-handling, maybe in winter with some wind, but... fitting rails or other contraptions is out of question. Is there any easy alternative? (possibly a cheap one... this is the essence of the “genoese sauce”, we Genoa dwellers are well known for been quite keen about these details… )

Solution (see sketch)
Take a long sheet and lead it fwd of mast through both (P+S) genoa cars, located fwd enough. Pass it through a simple block in front of mast, tied to the jib’s clew. Fasten the bitter end of the sheet to, say, SB winch and its cleat. Loop the other end around PS winch.
Now, it’s just a matter of controlling the length of sheet between the cars (acting on PS winch). Check for chafe on shrouds, in case reposition the cars and/or sheath the shroud chafe area with a rubber hose or the like.
Let’s unfurl the jib on a broad reach. Just pull on the sheet and the jib automatically sets on the correct tack. Pull as needed and it’s done.
Now let’s tack. Keep everything tied up. Tiller to downwind as needed, the bow comes to wind and the jib tacks automatically, thanks to its clew running freely along the sheet through the block.
In case of strong wind, pull the sheet as much as possible prior to tacking, so as to take the clew closer to the centerline and minimize the travel of the block and relevant shock.

Question
Why did I never hear of such a procedure? Looks easy, but I’m not an expert and maybe there’s a huge bug I can’t see…
Of course, selftacking jibs have their clew running parallel to a curved rail, with proper upward/fwd convexity. In this case, the “virtual” rail is the sheet itself.
The only problem I see is a relative lack of control over the jib’s shape. Depending on how high is the clew, the tension of the sheet will result in control of either the foot tension (if the clew is low) or of the leech (if it’s high).
If the clew is low enough, the pull direction will be rather horizontal, which IMHO is good for stronger winds

Thanks in advance for any comments!
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Old 13-01-2010, 15:03   #2
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I don't see the sketch...

Wouldn't the major issue be the risk of the block smashing into the mast each time you go about?

Because the sheet between the cars won't be taut when you head up, unless you sheet it in tight every tack and let it out again - which kind of defeats the idea of "self-tacking"....

Unless I misunderstand your description (without a sketch).

Edit: OK, forget that... I did misunderstand now I re-read it... Sorry
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Old 13-01-2010, 15:11   #3
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Why bother with a jib? If there is no overlap there is minimal sheet to deal with. Just ease the lazy sheet as you tail the new sheet. The main is self tailing and the tiller is between your legs.
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Old 13-01-2010, 15:12   #4
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Oooops... I missed the sketch.... sorry, its past 11 pm here and am pretty tired after a working day.... wouldbe less tired if I'd been working on my boat!!!
No chance of hitting the mast (theorically), because the block is tied to the clew (which is quite clear of the mast)
Attached Files
File Type: pdf autov.pdf (30.8 KB, 272 views)
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Old 13-01-2010, 15:35   #5
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Lucio,
For close-hauled efficiency, it is necessary to adjust precisely the camber of the jib , so that the leading edge is correctly adapted to the inflow. IMO, the system that you propose will not be able to do this: the sail will be too hollow.

Usual self-tacking jibs have either a rail on the deck or a boom, precisely for the purpose of controlling the sail camber.

Alain
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Old 13-01-2010, 15:36   #6
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With that set-up, your sail trim will be horrendous for anything other than beating hard to windward (and horrible even then). If you look at the angle formed by the sheet between the cars, you're effectively sheeting the clew in toward the mast (you could actually achieve almost the same by just passing a single sheet from the clew through a block at the mast and back to a single winch - equally disastrous for sail shape).
Also for anything other than close hauled, you'll have a LOT of sheet out there (you'll need twice as much length of sheet out than a normal setup because of the block leverage) so when you go about from a broad reach, say, that's a lot of sheet flapping about, and the block has to sort itself out along it? Not sure about how that would work in practice.
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Old 13-01-2010, 15:46   #7
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Lucio

Have a look at this link for an easy self-tacking jib using a boom and single sheet run through a block at the mast. Still not perfect but much better and it might work for you?

Rigging for Self Tacking - Page 2 - SailNet Community
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Old 13-01-2010, 18:45   #8
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Many options, some worse than others, much depends on deck layout and jib size.

E.g.:

- sheet thru a block on stbd via clew grommet to a block on port, seen on a small boat somewhere,
or
- boom the jib, sheet midships,
or
use a length of line in place of the track, sheet to a block running along this line then up the mast, back down, then to the cockpit.

All such solutions are difficult to achieve good trim, but you might be lucky on your specific boat.

b.
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Old 14-01-2010, 14:24   #9
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Thank you all guys for your advice.
I'm not sure it will behave as poorly as most think, maybe the sketch I did is not really clear, I guess that if I ease the sheet enough, the block will run to leeward until it gets to a halt: where it will stop, will depend on the balance of forces on ropes and sail. As to the quantity of sheet needed, t's not an issue: you may fasten the bitter end to one shroud, the other end will go to the opposite genoa winch: not much longer than an ordinary genoa sheet.
Anyway, 'nuff of these theories, time to go for seatrials... be sure I'll do that at the first opportunity, I'll keep results posted!
FW
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Old 14-01-2010, 14:59   #10
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As you say Lucio, the only true test will be how it performs in real life. Let us know how it goes.

Remember though that if you are on a reach, although the wind is abeam, the force on the jib acts forward (since the jib is fixed at the forestay) so it will tend to force the clew FORWARD, not just leeward, if you ease the sheet. The counter force from your sheet through the block will tend to act along the bisection of the angle formed, which is roughly towards the mast - not leeward enough to give the sail a decent shape against the forward force.

In the event it somehow does work ok for your particular boat set-up, you might like to then try a single sheet from the clew run midships through a block forward of the mast - much simpler and same forces (and not usually successful without a boom).

I like barnie's idea of a line in place of a track, with the usual self-tacking sheeting. That sounds more likely to offer a good solution for you.
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Old 14-01-2010, 15:19   #11
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Here's a link to someone trying a set-up similar to your suggestion.

Note how the clew is drawn in towards the mast.

If that sail shape works for your boat, maybe you're ok.

You can see that if the sheet is eased, the clew will move forward and leeward - not just leeward - and continue to be drawn as if to the mast.

Alacrity sailboat: Self-tacking jib experiment
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Old 15-01-2010, 11:19   #12
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Paradix,
that video is almost exactly what I had in mind. I guess the theory here is quite complex, since the position of the block, the angle made by sheet at the block, the length of the sheet between cars, the force and direction of wind, the shape assumed by the sail and other parameters as well, are all inter-related. There will be for sure some set of very nice formulae, that my math & mechanics teachers of my old days at university would be more than happy to investigate.
But weather forecast are apparently not that bad for tomorrow... and I haven't been at sea for 5 weeks now (mind you, I'm in the northern emisphere....) so I'll definitely try this stuff and let you know.
FW
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