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Old 08-04-2011, 04:24   #1
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Unstable Mast/Genoa Combination

Here’s the situation: on broad reach or on a run, my genoa produces too much head luff, such that the mast vibrates uncomfortably and the boat appears to move forward in a somewhat unstable fashion, a bit like a car with a misfiring engine. This problem only occurs when going downwind, things are fine upwind.

I have tried sheeting in, sheeting out, trying different positions of the side travelers to no avail. The only action that seems to fix the problem is to furl-in the genoa- just to the first marker. I lose all vibrations this way, and the boat speed is not really affected.

The context: it is a recently acquired 3rd hand sailboat.

1) The Genoa is evidently a retrofit, not the same brand as the main sail. I cannot tell if it has been cut to spec or not.
2) The standing mast head rig appears “fine” – in as much as I can tell, in the absence of a tension-meter. That said, these are 18mm shrouds, and I cannot feel any looseness in the stays.


Anyone out there can provide an opinion or suggestions on whether this is a Genoa problem or a standing rigging problem (for eg, insufficient mast bend)



Thanks a bunch,
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Old 08-04-2011, 04:52   #2
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Re: Unstable mast/genoa combination

Can you explain " too much head luff " ?

I'm guessing either :

1. too much luffing in the upper 1/3 of the sail
2. too much luffing in the forward 3 ft of the sail
3. neither of the above.

Which is it ?
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Old 08-04-2011, 05:42   #3
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Re: Unstable mast/genoa combination

Savoir
thx for the post. It is indeed 1. too much luffing in the upper 1/3 of the sail
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Old 08-04-2011, 05:43   #4
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Re: Unstable mast/genoa combination

One further clarification: it is too much luffing in the upper 1/3 of the genoa... The main is fine
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Old 08-04-2011, 06:19   #5
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Re: Unstable mast/genoa combination

There are two solutions, easy one first.

1. When you bear away run your jib car forward heaps and plenty, 1 meter minimum and maybe 1 1/2m.

2. Lead an outside sheet from a forward position and haul it on when you bear away. In case you don't know what that means I will carry on. You want a pair of solid clunky snatch blocks for your boat to be used in sheeting either the spinnaker or jib. I can recommend the Ronstan ones which will easily give 10 years good service.

Snatch Blocks*Stainless Sheave, Roller Bearing | Ronstan Sailboat Hardware AUS

Clip one snatch block on to the toe rail each side of the boat beside the shrouds. That might not be the best place but it is the best place to start testing. Tie an extra sheet to the clew of the jib and lead it outside the lifelines, through the snatch block and across to the winch. Don't be afraid to move the blocks 1 meter or so forward of the shrouds. The idea is to keep moving them forward until the upper 1/3 of the jib sets. The further you bear away the further forward they must go. If you are only sailing at 60 apparent or so then you might get away with the blocks only 1/2 meter forward of the windward sheeting position whether you sheet from the track or the rail. If you are sailing 120 apparent then 2 meters forward of the windward position might be the place.

Sheeting outside can be a great move but if you are only on a Sunday picnic sail don't bother, just haul your car forward until the fluttering stops.

That'll do for now. Go try it.
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Old 08-04-2011, 06:28   #6
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Re: Unstable mast/genoa combination

Thanks savoir- the aptly named

Very helpful, will try this weekend. Cheers
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Old 08-04-2011, 06:30   #7
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Re: Unstable mast/genoa combination

Phoenician, have you played with your sheeting angles? Unless the sail is blown out (in which case, if the dacron is still in good shape, you could have it recut) then it strikes me that the easiest possible fix is the sheeting angle - try moving the lead forward a bit.

If you have roller reefing, is there a foam or rope luff? If not, your sail shape when reefed will tend to put too much tension on the head and tack of the sail and this will not only cause too much belly in the sail when reefed, but after use in heavy air it can lead to stretching of the sail at the head so that it tends to luff when not reefed.

Having said that, some rigs tend to 'pump' in the circumstances that you describe. It could be something as simple as too much tension on the forestay/backstay and cap shrouds versus the lowers. A tension gauge would help.

If none of that works, then the problem is with the design of the rig and not the sails (either a mast of insufficient strength, or insufficient standing rigging). I know of one person who received advice from a rigger that he needed to install a baby stay - a hugely complex undertaking because of the 'surgery' required to install the chainplate. At least in the end it eliminated the 'pumping' and allowed him to convert to a 'solent' rig with runners.

Good luck!


Brad
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Old 08-04-2011, 06:35   #8
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Re: Unstable mast/genoa combination

Here's a pic of outside sheeting.

Click image for larger version

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You won't get it right first go. Just keep playing with the settings. The basic idea is to haul the upper jib leach inwards until the whole sail sets. When you sheet from a position forward of the windward position the upper leach will move in.
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Old 08-04-2011, 06:36   #9
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Re: Unstable mast/genoa combination

When you crack the leech opens, you must change lead positions or the sail will beat itself to death. It's best to keep the luff breaking evenly by moving the lead outboard and forward. A Jeaneau 54 will not have an outboard track, they have a teak cap so all you can do is run your genny track forward so the luff breaks evenly. Don't forget to move the car back as you trim the genny back in or you will stretch the leech.

Most new boats have no outboard tracks and no way to adjust lead positions when off the wind. Pet peave of mine, that is crap to have to bolt on a track when buying a new boat.
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Old 08-04-2011, 06:39   #10
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Re: Unstable mast/genoa combination

I don't think the rig on the 54 will pump, it has swept spreaders so it should be nailed down pretty good. My guess it is just the top of the sail luffing since the the lead is wrong. Maybe get a sailmaker to go out with him since he is a new sailor.

Quote:
Originally Posted by Southern Star View Post
Phoenician, have you played with your sheeting angles? Unless the sail is blown out (in which case, if the dacron is still in good shape, you could have it recut) then it strikes me that the easiest possible fix is the sheeting angle - try moving the lead forward a bit.

If you have roller reefing, is there a foam or rope luff? If not, your sail shape when reefed will tend to put too much tension on the head and tack of the sail and this will not only cause too much belly in the sail when reefed, but after use in heavy air it can lead to stretching of the sail at the head so that it tends to luff when not reefed.

Having said that, some rigs tend to 'pump' in the circumstances that you describe. It could be something as simple as too much tension on the forestay/backstay and cap shrouds versus the lowers. A tension gauge would help.

If none of that works, then the problem is with the design of the rig and not the sails (either a mast of insufficient strength, or insufficient standing rigging). I know of one person who received advice from a rigger that he needed to install a baby stay - a hugely complex undertaking because of the 'surgery' required to install the chainplate. At least in the end it eliminated the 'pumping' and allowed him to convert to a 'solent' rig with runners.

Good luck!


Brad
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Old 08-04-2011, 06:47   #11
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Re: Unstable mast/genoa combination

No metal toe rail on a Jeanneau 54 ? Gosh ! That buggers up half my post.

If that's right Phoenician, then all you can do is play the jib car forward and aft.
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Old 08-04-2011, 06:48   #12
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Re: Unstable mast/genoa combination

Brad, Joli and Savoir: thanks for all the comments:

1) yes, I did play with the sheeting angle, but did not move the side car all the way forward yet. Will try this weekend see what happens
2) Joli, you're right, the 54 does not have an outboard track, it is covered in teak, so not a good option - at this time - to latch a block on for an extra outside sheet. And it is indeed a pain not to have the track... like for fixing a safety net (i have 2 small kids) on the thing
3) i hope changing the sheeting angle will work. It is near impossible to find a qualified rigger in these parts!


One last question: to the extent that the sails will need replacing at some point in the future, is there any specific design recommendations to make the genoa...
more "user friendly" (let's say)
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Old 08-04-2011, 07:10   #13
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Re: Unstable mast/genoa combination

You don't need a rigger, you want a sailmaker or a knowlable sailor to go out with you and review lead positions. Unfortunatly your trim positions will be limited without adding track to the cap rail.

If you can't get the car far enough forward to stop the leech from shaking when you are deep then you'll have to raise the clew (ie recut the sail).

Get a sailmaker to come out with you, they are happy to help and will freely give their time.
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Old 08-04-2011, 07:12   #14
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Re: Unstable mast/genoa combination

Savoir and Jolie your comments about the lack of an outside track are of course correct. Its funny, over the years my boats have all had the shrouds mounted well outboard (Folkboat, Alberg 30, Bayfield 32, Cartwright 36 Pilothouse and my current cat) and hence, the tracks were also mounted well outboard. The issue for me has always been the opposite: while I could get decent sheeting angles on runs/reaches, upwind I had a need to move the sheeting angles inboard (and indeed, this year I am installing a coachroof mounted fiddle blodk to run a cummingham to a snatchblock on my staysail/storm jib for precisely that reason).

Brad
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Old 08-04-2011, 07:22   #15
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Re: Unstable mast/genoa combination

I just took a look at some Jeanneau 54 pics. Those toe rails are too skinny to mount anything. If you like the idea of outside sheeting you could always mount two or three padeyes near the gunwhale just inside the teak. The boat has three shroud mounts so try tying any old block to each with some 3/16 string and see what works. I'm a big believer in it at any angle from 60 to 120.

Back in the day I would fit a padeye to the gunwhale of a race boat every 3 feet.

As for the children, get yourself some of that tennis net stuff.
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