Too much vang

Moderator: GreenLake

Re: Too much vang

Postby GreenLake » Wed Oct 21, 2015 4:31 pm

Rake should move the center of effort backwards. One would think it should not have an effect on sail shape, because the boom would angle down until the geometry is the same. (There might be a second order effect based on the wind flowing along a slightly different line and the sheet pulling at a slightly different angle, but I would really like to see a coherent argument why sail shape should be affected by rake).

In contrast, vang changes the geometry by tensioning the leech, reducing twist.

Camber should be influenced by what?
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Re: Too much vang

Postby Salty Dog » Wed Oct 21, 2015 6:37 pm

When I am sailing in stronger wind and having more heeling than I like, and The boat is trying to round up.and my helm starts getting heavey trying to correct it. I can tighten my back stay and it will bend the mast back above the forstay. ( I have a 3/4 rig ). This dumps wind up top and helps to right my heel. I am able to sail in stronger wind with better control without taking a reef. I can feel it in my helm when I do it. I only tighten enough to trim out. When sailing to weather and I cant get the top tattle tale to fly I can give it a little tweak and get it to fly for me. My backstay adjuster is a 4:1 purchase it does not take much on my boat. Any time your helm is not centered up it slows you down. and if you are trimming with your helm you are producing too much drag.

SD
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Re: Too much vang

Postby Interim » Thu Oct 22, 2015 8:54 am

Keeping in mind that we're talking about two different types of rigs (with backstay and without)...

With a backstay on a fractional rig, I think rake bends the mast a bit (it is not simply changing the angle). That might change leech tension, but it might also pull the middle of the luff forward (relatively).

On a DS, bending the mast would assume the turnbuckle or partners provide some resistance. This isn't true on my boat; I don't know about others. But it does change the angle of the sail, along with moving the CE.

--john
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Re: Too much vang

Postby GreenLake » Thu Oct 22, 2015 9:46 am

Mast bend and mast rake are two different things in my book. Rake you get by moving the mast step, or making the forestay longer. Bend is what you get with a back stray, or also with leech tension. I fully agree that bending the mast will flatten the sail (less camber). Will it also move the location of max camber forward?
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Re: Too much vang

Postby Salty Dog » Thu Oct 22, 2015 6:10 pm

I agree, mast rake is what you do when you tune your standing rigging usually on dry ground.
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Re: Too much vang

Postby GreenLake » Fri Oct 23, 2015 2:01 pm

In rig trim many things have multiple effects, so for example, mast rake is not the only thing that has an effect on the location of the center of effort.
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Re: Too much vang

Postby K.C. Walker » Fri Oct 23, 2015 11:23 pm

Some people use an adjustable mast step with a one-piece mast. That is, the mast step is adjustable fore and aft on the keelson. They are not really adjusting the rake of the mast but adjusting the prebend of the mast. Moving the mast base back without changing the shrouds introduces bend. Also, the swept back spreaders, under rig tension, introduce some prebend.

Once the rig has prebend and is under a fair amount of rig tension it becomes more flexible and responsive. It becomes more responsive to vang tension and also responds more readily to gusts by opening up the leech and allowing it to twist. The tapered masts are desirable for their flexibility up top. It is somewhat the same effect as pulling on the back stay, only it's automatic with wind pressure.

I run pretty high rig tension and use a 20:1 vang. If I pull the vang on tight to bend the mast, with a tight outhaul and cunningham pulled on, I can pull out an awful lot of camber. This greatly reduces the need for reefing. As pointed out earlier this reduces the heeling moment and weather helm.

When close hauled, one benefit of using the vang to control leech tension rather than the main sheet is when a gust hits and you release the sheet, the leech tension does not release. Therefore the jib stay does not sag and power up the jib (just what you don't want at that point).

Another interesting thing about using the vang to control leech tension, instead of sheeting, is it makes the boom more flexible
because of its foreword attachment point. This makes the boom more gust responsive, as well.
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Re: Too much vang

Postby Salty Dog » Sat Oct 24, 2015 3:05 pm

I have yet to put a vang on my DS. I have not worked on it at all. I have just retired , so that should change, hopefully.
I like your vang K C I think I will try to copy it unless you have it patented. :D

SD
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Re: Too much vang

Postby K.C. Walker » Sat Oct 24, 2015 5:46 pm

Salty Dog wrote:I have yet to put a vang on my DS. I have not worked on it at all. I have just retired , so that should change, hopefully.
I like your vang K C I think I will try to copy it unless you have it patented. :D

SD

Go for it! It's all borrowed information, and mostly from this forum...
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Re: Too much vang

Postby lemsteraak » Sun Oct 25, 2015 3:06 pm

SaltyDog,

I would highly recommend rigging a simple vang. I view them primarily as a safety control. Going downwind, the sail will lift your boom, in high winds, your boom can really lift. The problem is that this changes the sail's center of effort and can "control" and turn your boat resulting in an accidental jibe. On a DS it isn't such a big problem because the boat planes and your speed can match the windspeed pretty well. Still, I like to have a vang.

The larger question, how you use a vang to shape your sail, is a lot more complex. Going downwind or on a reach, it does keep the boom down so you spill less air, pretty simple. Going upwind on a DS, I don't use it much. If my mainsheet was connected only mid-boom, it would be another story. In this configuration, you set the vang tight when beating and the mainsheet controls the placement of the boom. In gusts the sail will cause the end of the boom to bend and lift the end allowing the sail's leach to twist off and spill air. This can be a really handy self regulating feature in big waves and winds. The skipper can concentrate more on the course and how best to steer through waves while the main is on auto pilot. In big gusts, you just drop the traveller a tad to spill more air but you never have to touch to mainsheet.
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Re: Too much vang

Postby Salty Dog » Mon Oct 26, 2015 4:12 pm

lemsteraak

Thanks for the advice. I do have a vang on my boat it is a small line about a 4:1 purchase with a small V jam cleat. I use it for running like you described. It has a hook on the boom end. so it can serve dual purpose. close hauled I can take it off the boom and hook it in my Cunningham grommet and use it as cunningham. It is not a very good set up for playing it like it is set up right now. I have been reading about the 20:1 vang and was curious about what it could do for sail shape and was going to try it out. The only thing I'm not sure of is , I have mid boom sheeting and no traveler, so I was considering going to end of boom sheeting so I would have the option you talked about as far as a traveler. All of this would require some sailing time for experimenting which I have not had much time for until now that I have just retired. I am excited about getting to sail and work on my boat and getting it set up.

Any advice is appreciated. speaking of that how is the best way to attach the barber hauler lines to the sheets. If I use a bowline it will prob. be too much friction. If I use a block , it may beat my deck up when the jib is flogging in a tack.

Thanks SD
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Re: Too much vang

Postby GreenLake » Mon Oct 26, 2015 5:54 pm

On barber haulers I did a jury rig with loops just to prove to myself that I could tell a difference in how the sail sets. I then replaced these with the smallest blocks I could find, and initially wrapped them in rigging tape for deck protection. The tape has worn off, but I don't recall the blocks banging the deck very much. My tendency is to not release the jib sheet until the turn into the tack is well started, pretty much until the jib would backwind otherwise. At which point it is ready to come over and can be sheeted home directly.

Occasionally I'll let the jib be backwinded for a bit, if it helps push the bow through the wind.

As a result I don't see a lot of "flogging" in the jib.
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Re: Too much vang

Postby K.C. Walker » Mon Oct 26, 2015 8:39 pm

I, like Greenlake, use the smallest blocks I could find. In my case it was racelite. I also have not noticed any banging of blocks on the deck. I remember worrying about it before hand, though.

I use about a 10 inch long 1/8 inch Amsteel line attached to my jib clew from my jib sheets. If there is any flogging of the jib it seems to get mostly absorbed before it is transmitted to the jib sheets. I've spliced this through a straight sheet that is continuous. I also use a soft shackle to attach this to the jib (another metal object eliminated from the flogging). The setup eliminates a lot of fouling and hangups when tacking. Greenlake uses a similar set up, so I suspect that this cuts down on the blocks of the barber hauler flogging, as well.
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Re: Too much vang

Postby Interim » Tue Oct 27, 2015 2:57 pm

I get jib sheets flying around quite a bit. The one and only cause is that the new leeward sheet will catch on the mast tabernackle during a tack, and we won't be able to trim it.

Our solution is to put a wrap around the base of the mast where the tabernackle and halyards pose lots of traps. I'm currently using a cut-open 1 gallon jug with a small shock cord to hold it closed. This presents a better (smoother) surface for the sheets to come across, but it is still fallible.

I imagine a barber hauler would reduce our problem, but I'm not there yet.

--john
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Re: Too much vang

Postby TIM WEBB » Tue Oct 27, 2015 7:42 pm

I'm using barberhaulers and a pigtail/soft shackle as well, and have pretty much eliminated jib sheet/mast hinge hangups by not letting the jib over until well into the tack as described, but also by, after the tack, tossing the new lazy sheet well forward onto the cuddy roof, with lots of slack. This way, on the next tack, it's not being tugged past the hinge.
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