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Today I went sailing and observed a Hunter 260 with his topping lift very tight so that it lifted the boom to the point that his mainsail never was anything but a flapping piece of fabric on any point of sail. I wanted to pull along side and to suggest to him to slack off so that the sail could take a proper shape, but he was with his girl/wife, so I was afraid that I would embarrass him. Later he put up his bimini and it became obvious that he had shortened the topping lift so that the boom would clear the bimini (but he was attempting to sail this way even before the bimini was raised). With the rig that he had, he will never get satisfactory sailing performance. And, probably in time, he will abandon sailing as being frustrating and unfulfilling.

If you happen to have a similar situation on your boat, take the sail to a sailmaker and get it recut so that the boom will clear your bimini without using the topping lift to hold the boom clear of the bimini. If you sometimes sail without the bimini and want the full size of the sail, then have the sailmaker to put in a flatting reef cringle/reef points on the sail....this is a relatively shallow cringle at the boom/leech end of the sail used normally to flatten the sail, but if done properly for this application, it will lift the boom also.

I'm sure that someone will disagree, but don't sail with your topping lift tight...if you do, you distort the shape of the main sail. Slack the topping lift off so that it does not distort the sail shape....the boat will sail better. Also, never sail with with boom attached to the pig tail wire on the back stay if you have one...the pig tail is to support the boom when sails are down. And if you don't have a topping lift, put one on your boat, but don't sail with it tightened....use it to keep the boom from dropping down into the cockpit when putting up sails.
 

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Ditto. The topping lift is there to hold the boom when the sail is NOT raised. Of course, if you are sailing with the bimini up you probably don't have any idea what your sail shape is anyway, so....
 

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The only time you might want to sail with the topping lift tight is if you're in very, very light winds... and that only in very rare circumstances. :) Other than that, it should really be slackened enough to allow the boom's weight to load the leech properly.... :)
 

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NCC320, you are SO right on. I removed the topping lift from my boat as soon as I bought it. It's just another line to get in the way. It's not a sail control and if you have a solid vang (which I highly recommend) there is just no need for the topping lift.

I have to disagree with sailingdog on one issue however. In very very light conditions the main needs to be made as flat as possible to try and squeeze as much power out of the breeze as possible. In these conditions air flow has a very hard time staying attached to the sail. Detached air flow means loss of efficiency and power. A flat sail allows the breeze to maintain nearly complete flow attachment for best sailing performance.
 

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I have to disagree with sailingdog on one issue however. In very very light conditions the main needs to be made as flat as possible to try and squeeze as much power out of the breeze as possible. In these conditions air flow has a very hard time staying attached to the sail. Detached air flow means loss of efficiency and power. A flat sail allows the breeze to maintain nearly complete flow attachment for best sailing performance.
... the problem is, though, that the weight of the boom will close the leech of the sail off and you'll lose that attached flow because, essentially 'the flaps are on'. The topping lift's support will allow the leech to maintain its proper shape without the force of a reasonable breeze.

Today's rigid vangs can often provide the same function.
 

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Faster, I hear you and have a suggestion. Next time you're out in ultra light conditions try flattening the sail and give the boat time to establish a steady speed. Then without changing anything else apply your topping lift as you suggest and watch the boat speed. I guarantee it will drop as the boom lifts.
 

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In very light conditions, a flat main won't generate any lift...and you won't move... also, not supporting the boom will close the leech of the sail, as Faster pointed out, which was my reasoning for supporting the boom with the topping lift...to allow the sail to have a fuller shape to help generate lift and to keep the leech open. Yes, flat sails help with attached flow, but you have to balance keeping the flow attached with sail shape to maximize lift. A flat sail generates almost no lift.

I have to disagree with sailingdog on one issue however. In very very light conditions the main needs to be made as flat as possible to try and squeeze as much power out of the breeze as possible. In these conditions air flow has a very hard time staying attached to the sail. Detached air flow means loss of efficiency and power. A flat sail allows the breeze to maintain nearly complete flow attachment for best sailing performance.
 

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Full sail for light air.

Flatter sail for heavier air. I will flatten a sail prior to reefing.

Compare that to airplane wings. Short Take Off and Landing planes have deeper camber, while high speed fighters have much thinner wings.

 

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I agree with Skipper995!
Below 2 or 3 knots wind the sail needs to be flattened or you can't keep the flow attached.
 

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I agree with Skipper995!
Below 2 or 3 knots wind the sail needs to be flattened or you can't keep the flow attached.
I'm not arguing flat vs full...what I'm trying to say is that in real light air, the full weight of the boom alone will physically pull the clew down (gravity sucks...) and this will cause the leech to turn hard to 'windward', closing off the leech. This creates a very non uniform camber that cannot promote good attached flow - it is, as I said, like having full flaps on an airplane wing.

Whether you're of the 'flat' or 'full' mindset - you want a smooth uniform curve and a clean exit...

In light air do you crank on the leech line on the genny to induce a 'hook' in the leech??? Same thing.
 

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There's evidently some disagreement here among authorities, with at least two schools of thought. I'm still learning; my general understanding was similar to jackdale's, but perhaps things are not so simple...

Dedekam's Sailing & Rig Tuning says that in very light air (2-5 knots) your traveller should by high and pretty much everything else should be really loose, bagging out the sail and maintaining high twist to open the leech.

Mainsail Trimming by Marks disagrees, stating the sail should be (quoting) "flattish" by having the outhaul and backstay both half-on. This is for the same reason Skipper995 gave, to maintain air attachment, whatever that means. (Dedekam did not mention this effect at all; I'm guessing it hypothetically has something to do with formation of a boundary layer?) Marks agrees about the open leech, though.

So the advisibility or importance of flatness is not really clear to me. I think really what is needed here is experiment. SF Bay summer weather is still a ways off, so I think there may be some opportunity yet. :)
 

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Yes, but in either case, you want to keep the leech of teh sail open...without adjusting the topping lift to support the boom, you can't do that.
There's evidently some disagreement here among authorities, with at least two schools of thought. I'm still learning; my general understanding was similar to jackdale's, but perhaps things are not so simple...

Dedekam's Sailing & Rig Tuning says that in very light air (2-5 knots) your traveller should by high and pretty much everything else should be really loose, bagging out the sail and maintaining high twist to open the leech.

Mainsail Trimming by Marks disagrees, stating the sail should be (quoting) "flattish" by having the outhaul and backstay both half-on. This is for the same reason Skipper995 gave, to maintain air attachment, whatever that means. (Dedekam did not mention this effect at all; I'm guessing it hypothetically has something to do with formation of a boundary layer?) Marks agrees about the open leech, though.

So the advisibility or importance of flatness is not really clear to me. I think really what is needed here is experiment. SF Bay summer weather is still a ways off, so I think there may be some opportunity yet. :)
 

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jackdale, your diagrams for air foils for aircraft are very appropriate for aircraft but they do not cover ultra light air movement nor are they intended to. No aircraft designer is interested in the lift/drag qualities of a foil in 1 - 5 knots of wind for obvious reasons but as sailors we are sometimes required to deal with just such conditions.
My only suggestion is to go and try it out. Run an actual experiment to demonstrate it for yourself. The knotmeter is the final judge. Allow the boat to settle into a course and speed that is stable. Then simply adjust the boom height and give the boat some time to readjust and note the boat speed. Then do it again to verify your readings. You will see a speed decrease as the boom is raised and a speed increase as it is lowered.
 

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You will see a speed decrease as the boom is raised and a speed increase as it is lowered.
If the leech is being choked off, then the boom needs to be raised. This is actually easier with a rigid (spring loaded) boom vang. Hardening the topping lift may interfere with the roach.
 
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