How much Backstay? - SailNet Community
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post #1 of 20 Old 04-19-2008 Thread Starter
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How much Backstay?

Hi,

I race on an Elan 37 equipped with a good set of tape drive sails. Although we do well at lower winds, as the wind gets above 15knots we get control problems, with the boat constantly broaching into the wind with full main and even jib no 3.

We are trying all sorts to flatten the main including maxing out the outhaul, cunningham and the backstay but although matters have improved it appears not to be sufficient.

Now I am wondering if we are pulling up on the backstay hard enough. When i do still at the mooring and look up the mast I note that the very top is curving significantly but the middle part of the mast is hardly changing shape. Therefore we may not be flattening the main enough to maintain control.

How does one gauge the maximum amount that the backstay can be tensioned before risking trouble?

I get the impression that the inner stays may be set too hard and therefore they are stopping the mast from curving forward when tensioning the backstay. Is there any advice out there on how hard to set these what is the limit before one can cause damage?

thanks.

xuraax
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post #2 of 20 Old 04-19-2008
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I suggest that you talk to your sailmaker. A good sailmaker will design their sails for a specific range of mast bend and headstay sag. The old rule of thumb was that the aft lowers should just begin to go slack in heavy air with max backstay applied but this varies with rig and sail design.

As a mainsail trimmer on a Beneteau 40.7 with a similar rig, there is one other point here, as the wind comes up into winds over 15 or so knots, its not hard to end up being overpowered with a #1 genoa. As you approach those windspeeds it is not all that hard to be overpowered, and end up using too much helm.

It becomes incumbent upon the mainsail trimmer to aggressively pay attention to the position of the helm, (the mainsail trimmer often needs to mark the centered spoke of the wheel so you can monitor it. I carry blue masking tape in my seabag which works well as a temporary marker), heel angle, pointing angle, and boat speed. If the traveller is too high and the mainsail too powered up, it makes it very hard to for the helmsperson to bear down and keep the boat moving. If it the traveller is too low and the mainsail is too depowered its hard to point.

In winds approaching the limit of the genoa the key is that the jib needs to be set properly, (its head slightly open with the sheet lead slight aft so the upper teletales break slightly ahead of the lowers) and the boat needs to be sailed off the jib teletales without using too much helm. It is perfectly alright to carry as big a bubble in the main as it takes to keep allow the boat to sail off the jib and still be able to point. This takes time to learn out on the water watching the knotmeter and wind angles (or the windex which is actually a very precise instrument if you read the box that a windex comes in). It is important that you can very quickly shift gears because on gusty days at the upper end of the windrange the boat is ideally steered as much with mainsail as it is with the rudder and quick reactions and constant adjustments (as much as 3 to 6 times a minute) can result in huge gains upwind. (There is a reason that I need to work out att the gym during the winter)

One more point, there is a windspeed where using a #2 or #3 genoa can result in real gains in speed and points. (winds that are consistently over 15 knots on the 40.7 but I don't know what it would be on the Elan) and so it becomes critical to watch true windspeeds before the start and during downwind legs so that a change down can be made if it is needed.

Good luck out there,
Jeff

Last edited by Jeff_H; 04-19-2008 at 10:06 AM.
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post #3 of 20 Old 04-19-2008
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Great post jeff there is nothing I can add to that.

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post #4 of 20 Old 04-19-2008
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Xura...sorry but I have some bad news....

in a way, you guys are victims of the boat you sail...itīs not you or the sails or the crew, is the boat..these boats are designed, as many so called cruiser/racers in the proiduction series, (and I am assuming the boat in question still has original keel, rudder and has not gone thru a "weight loss program" to race), to be sailed as coastal cruisers with friendly multiple rating races schedules against other same type boats, and not One design or box rule type races......this to say that the type of mast adjustments, keels, sail, CofG, CofE etc. are all designed to be sort of neutral to provide confort to a regular coastal sailor, as that boat is a fast cruiser, that can be raced...
Therefore, mast trim, shroud tension, mast bend, sail plan, keel weight, draft and shape etc. are all designed for a lower band wind speed, and somewhat limited in the range of adjustment...and to the assumption that the "average" sailor will reef, douse, furl etc. as the wind increases.

However, and in your case, if you feel you need more bend, there are several things you can do, even with the present sails, these include,

1) adjusting mast tension with a loos gauge, based on the winds before departure to the race, this is a thing where the more you do it and the more you become expereinced, the better you become at it..select only one person in the crew and only him should do it to avoid arguments..I do it myself, but I have a hydraulic jack under my mast, to do it on the go. The advantage is I adjust shroud tension based on the winds.

2) Preset intermediate inner shrouds to limit mast bend. You can ease some the inner shrouds to allow more belly in the mast. How to adjust..in a calm day hoist the main, so you can look at camber, tension the BS and release slightly the intermediate inner shrouds as you bend the mast backwards, with the BS..with this method the inners will be almost completely loose when mast is at rest..I have mine set like this..I provided maximal bend and the limit is set by the inners intermediate that tension at full BS tension..be carefull you need to know what youīre doing..

3) Check angle between genoa and main, and if needed open the gap between them, or close as needed, with the installation of barber haulers.

4) donīt be affraid to release some the main sheet until the portion of the sail along the mast actually cambers the other way, this will help even the boat, and it will actually accelerate. The cunningham plays an important role here..



I have a formula that allows you to measure maximal mast bend at the tip of the mast and how much belly you can induce, based on mast height, that I will provide to you by private pm, should you require so.

These will do for now, should you want to pursue this discussion further let me know..Jeffīs points are 100% right on..he knows main trim for sure.

Alex
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post #5 of 20 Old 04-19-2008
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Two excellent posts above from Jeff and Gui. I would just reinforce the idea of aggressively playing the traveller in the conditions you describe. Easing the traveller will keep the helm under control (watch the helm angle as Jeff pointed out) and be ready to power up in the lulls.

If the traveller is already all the way to leeward, then the vang should be on hard so that when the mainsheet is eased further the boom can't lift...and it has a similar effect to further easing the traveller if you could.

Ron

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post #6 of 20 Old 04-19-2008
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Actually Faster brings a good point...the vang...and itīs use.

In fact in some settings and with certain sails and configurations, releasing a little the vang can help open the roach and spill wind aloft..

Like I said, it really depends on ther boat, system and sail..

With mine, releasing some vang tension helps spill wind aloft, but If if I need with other vang tensionings I can also prevent that from happening...

Faster is right...the vang..

Experiment with your boat with tension and mild tension. Play with the vang and see.
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Thanks G..

Another thought, xuraax.. This boat looks very similar to the Bene 36.7 we sail on a bit. Often you can do well in heavier air by not fighting the roundup quite so hard, let the boat feather up into "pinch" mode (a bit - you don't want to backwind the jib).

You may find some heel coming off, and the helm easing at that point. In puffy conditions on our former 24' frac rigged racer we went into what we called "survival pinching" in puffs and often gained a length to weather each time.

The Elan may be too heavy for this to work, but it may be worth a try.

Ron

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Thanks one and all for your quick replies and sound advice.

Perhaps there is one point that I did not explain very well. When our boat rounds up, it does so quite violently to the point that we loose rudder control and we end up pointing almost straight into the wind. Picking up speed again is QUITE SLOW. Although I sail normally on multihulls I have sailed on other monos and although all monos tend to round up, it is only here that the rounding up is so damaging. I do not think the problem is the boat itself since, from what I here the Elan 37 does well in club racing. On this boat I am in general the main trimmer and I can assure you the traveller is continually on the move.

To keep the boat on its feet we find that many times the traveller is all the way down and the main reversing. This surely can only mean drag.

This is why I am asking the question of how much bend is allowable in a mast for this size of boat.

On another point, in all the advice I get, I wonder why nobody ever mentions reefing the main before reducing the jib. I believe theory tells us that the force on the jib is acting to push the boat away from the wind and the main the reverse. Therefore when, to reef, we reduce the jib before we actually reduce the main we are in fact increasing the possibility of rounding up into the wind.

I know that in practice this is not done but why?

Giuletta, I will try to send you a pm to get the formula you mentioned if you don't mind.

regards

xuraax
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post #9 of 20 Old 04-20-2008 Thread Starter
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Giulietta,

I have tried to send you a PM but was not allowed by the forum because I have to send 10 messages before I am allowed to PM.

This is my number 3.

xuraax
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Reefing is, of course, an option but on short course racing many boats will want to avoid the work of shaking out the reef for the off wind legs, and so will invert part of the main to try to get by.

Having the ability to fully flatten the main helps here, of course.

Carrying a bubble in the main does not really slow you down, the leech is still driving, and keeping the boat upright more than makes up the "bad" trim.

For longer legs a reef (or two) would clearly be a good idea.

btw - go to the song chain to build up your post count!

Ron

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Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
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