Backstay tension - SailNet Community

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  #1  
Old 08-26-2013
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Backstay tension

My current boat has a navtec hydraulic backstay on a mast head rig, along with with a baby stay that goes about 2/3 up the mast. This is a new thing to me as all my previous experience has been on boats with either split backs or no adjustable backstay at all. That said I've found it to be essential upwind on the race course to pull the baby stay on tight and crank in the back stay, and it's been a lot of fun to play with a new sail control.
However, I had a situation the other day that got me wondering what was too little and what was too much tension on the back stay; while heading downwind on a leisure sail, no spin or anything, I asked a non-sailor friend to ease off the back stay. It didn't occur me to mention that when you turn the knob to ease it, it continues easing until the knob is turned back. About five minutes later the rig was so lose that the forestay turn buckle was bouncing back and forth off the deck on either side of the chainplate. it was so lose that the five shims placed in the mast when it was stepped all fell to the floor inside. I cranked the stay back on until most the sag was gone and everything has been fine, although I can't get the shims back in the mast, I don't imagine that matters much. Basically, I was surprised to see that it can ever get this loose, IMHO, it was dangerously loose. If it's possible to ease to this degree, is it also possible to crank it on way too tight, even to breaking load (for example if I had been as undetailed in my instructions and asked a inexperienced crew member to put crank on the back stay and he just went all the way to the end of the rod.) There is a gauge on the pump that lists tells the load between 1 - 6 kpsi. I've found that half way between one and two the rig is pretty tight with minimal bend in mast, but how much can I go? Can I find some recommended min and max tensions somewhere on the web? Boat is C&C 35-3.
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Old 08-26-2013
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Re: Backstay tension

Hey,

In the C&C 34 I race on, we tension the backstay to take all the sag out of the headstay for upwind work. For downwind, we want it loose, not as loose as you had it, but almost that loose.

Barry
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Old 08-26-2013
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Re: Backstay tension

the backstay on a masthead rig is to control the headstay sag and the baby stay will give you some mast bend to flatten the mainsail.
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Old 08-26-2013
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Re: Backstay tension

It is possible to overtension the backstay. I've of race boats that were damaged by over zealous use of the backstay tensioner. Easy to do with a hydraulic unit. Mine has a pressure gauge, and the previous owner put a piece of tape on the piston rod at the maximum tension point.
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Old 08-27-2013
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Re: Backstay tension

An adjustable backstay doesn't make the boat sail any faster or point any higher to windward than it would be capable of sailing without a backstay adjuster. The ability of a boat to sail to windward is limited by it's design. If you didn't have an adjuster, you could get out your tools and adjust your rig more taut, and the boat would point as high as it's design permits. What a backstay adjuster does is, it enables you to change the tuning of the rig very quickly, on the fly, from taut to loose, without getting out your tools. The taut setting enables the boat to go as fast and point as high to windward as it's design permits. The loose setting enables it to sail as fast off the wind and in lighter winds as it's design permits.

If a backstay adjuster is over-tensioned, it can damage the boat structurally. As you have seen, in some cases it is also bad to adjust it too loose. The maximum tension recommended for a boat is generally based on the type and size of the boat's shrouds.
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Old 08-28-2013
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Re: Backstay tension

I have a Navtec hydraulic system as well. For racing purposes you should be able to ease it off so that the forestay is a bit floppy, but nothing like you describe. Last summer when we were out cruising the pump blew a seal and we had no hydraulics. I was able to tighten the backstay turnbuckle that attaches to the ram enough to allow us to sail comfortably in moderate breeze, albeit with more headstay sag than I would like. A couple of times it was breezy enough so that I REALLY wished I had more tension, and we became overpowered much sooner than I am used to. Now that I have rebuilt the pump I am going to keep the minimum tension a bit higher than I used to. I consider around 3000psi to be a pretty good Max, but you definitely want to make sure you don't forget to ease it off when you are done! When it is quiet at the dock and I crank it on I can hear the boat creak and groan a bit!

I never realized how much difference having that adjuster made until I was forced to live without it. I don't think I would ever own a boat without one!

BTW my boat is a masthead rig, and I get plenty of mast bend even without the baby stay on hard. It makes a huge difference to the main as well as the genoa. It certainly DOES make the boat faster because it allows me to make tuning adjustments that just aren't practical if I just had turnbuckles. Let's face it; not many people are going to go grab their wrenches and start cranking the turnbuckle every time the wind picks up! I'll wager most people never touch their backstay once the mast is up! While those people are contemplating putting in a reef, I just reach down, and with a few strokes of the handle and I am good for another 10kts of wind! It's a no-brainer to me!
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