I recently did the procedure Alan describes on my 35-3, using the main halyard and a six-pack for weight. With the boom slightly off to starboard, I used tape as markers on the boom for each of my ‘soundings’. I started with no tension on the hydraulic backstay, and progressed to 500 kpsi, 1000, and 1500 kpsi. Each of those increments moved the masthead aft 2 to 3 inches. From the no-tension position to 1500 kpsi, my beer-bob weight moved aft a total of 10 inches. I didn’t notice a difference in the beer-bob with the babystay tensioned or not (which makes sense because the babystay won’t affect the masthead), but it was easy to see the bend in the mast. If you stand at the mast with any amount of tension on the backstay, and you flex the babystay by hand, you’ll see how the mast flexes. Not hard to see how this is an important control in sail trim.
Jason Ainslie, Spirit C&C 35 Mk III Port of Bayfield Ontario _____ From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of ALAN BERGEN via CnC-List Sent: June-04-16 2:35 PM To: cnc-list-requ...@cnc-list.com Cc: ALAN BERGEN Subject: Re: Stus-List Adjustable backstay? The babystay doesn't go slack. The whole mast moves back, but more at the top than at the middle. If you want to see the effect of tightening the backstay, look at the forestay, and sight up the mast from the side while the backstay is not tensioned too tight. Then run a weighted line (or even your main halyard if the main is down) from the top of the mast to the boom. When you tension the backstay, the top of the mast moves back; the middle of the mast moves back (less than at the top); the weighted line will move aft along the boom; the forestay will be straighter and you'll see the bend of the mast when sighting from the side from the boom to the top of the mast. Alan Bergen 35 Mk III Thirsty Rose City YC Portland, OR On Sat, Jun 4, 2016 at 10:14 AM, Ronald B. Frerker via CnC-List <cnc-list@cnc-list.com> wrote: Sam, like you said, the mast is more or less fixed, but not completely. As you decrease backstay length the mast has two motions, bending and rotating from the deck pivot point. As it rotates (pivots) backward it tightens the forestay. That's about all I get with my tree trunk of a mast; no bending, but more than an inch back and down. The thinner sections with multiple spreaders and/or babystays will get more bending. Both motions move the tip of the mast back and down since the forestay is mostly fixed (it does lengthen slightly since it's a bit of a catenary and more tension takes some droop out). Since systems seek an equilibrium which reduces overall tension, the babystay will loosen slightly with the bending, but will assist the bending motion until equilibrium. Frac rigs get a lot more bending of course by geometry alone. And tuning them starts with lighting a candle by the hollow stump at midnight! Those with multiple spreaders are the devils own design. Ron Wild Cheri C&C 30-1 STL _____ From: Sam Salter via CnC-List <cnc-list@cnc-list.com> To: CNC-LIST <cnc-list@cnc-list.com> Cc: Sam Salter <sam.c.sal...@gmail.com> Sent: Friday, June 3, 2016 9:50 PM Subject: Re: Stus-List Adjustable backstay? Looking at this as an engineering problem (I don't have a 30-2) - explain what I'm missing: Top of the mast is more or less fixed (fore and aft) by the forestay. Sure, it will move back an inch or two when it takes up slack in the forestay, but mostly it's going to stay put. Baby stay puts pre bend into centre of mast or at least fixes it in space, fore and aft. When backstay is tensioned won't the top move mostly down and push the middle of the mast forward, slackening the baby stay? Tensioning the forestay and taking draft out of the main. Do you guys see the baby stay go slack or am I full of it??? sam :-) C&C 26 Liquorice Ghost Lake Alberta _______________________________________________ This list is supported by the generous donations of our members. If you like what we do, please help us pay for our costs by donating. All Contributions are greatly appreciated!
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