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  #1  
Old 10-03-2007, 08:06 PM
catd catd is offline
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Join Date: Oct 2007
Location: Old Saybrook, CT
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Default Backstay with sheave and 7x9 wire OK?

Hi all. Just wanted an opinion, or two. We recently replaced all our standing rigging excluding the backstay. Then we noticed a crack in one of the swage fittings on it and decided we should replace it too. Our current configuration is 1x19 wire at the mast head running about 2/3 the way down, it then attaches to an aluminum sheave which has 7x9 wire running through it to each side. Our rigger didn't like that set up with the sheave (too much pressure on it he said). He recommended all 1x19 starting at the masthead, spitting near the top of the mast and then running down to turnbuckles on each side.
Well, we actually like the way it's set up now with the backstay adjuster on the 7x9 because it's really easy to adjust. We don't really want to change the setup, however ,if it really is a weak point in the system (as our rigger said) then we'd switch.
Hope I gave enough info here. Thanks for any opinions, thoughts...
Catherine
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  #2  
Old 10-04-2007, 04:29 PM
Ian McColgin Ian McColgin is offline
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Join Date: Jun 2005
Location: Hyannis, MA
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I'm with your rigger. The back stay to a triangular plate that serves as the splitter would be far far better.

Better yet is one backstay. Why's it split? On some double-enders it's split to get the backstay around a tiller. But depending on the boat, it may be just a well to have but one, slightly off-set. On some yawls and more ketches it's split to get around the mizzen. Again, it's often perfectly possible to make a tie a bit off-center from the horn timber up to connect on deck or cockpit sole if the stay can be located back far enough and still pass the mast at or below the mizzen gooseneck.

A third option, rarer to say the least, was found on my Granuaile, an LFH Marco Polo. The fore and main backstays came to the main and mizzen respectivly at about the spreaders where the aft lowers could oppose. The stays went through a turning form to get down the foreward side of the mast to get the turnbuckle to a convenient height. This is best in rigs with raked masts and lots of follow to those lowers.

Whatever but I say get rid of the split by pulley.

G'luck

Ian
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  #3  
Old 10-04-2007, 07:14 PM
catd catd is offline
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Location: Old Saybrook, CT
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I would guess it is split because we have a tiller and an outboard hung rudder. Our boat is a heavy displacement steel cutter - I don't think we'll be converting to a single back stay. That said, if we use a plate to split the stay, does it matter where we spit it? As I mentioned, our rigger was going to split it high near the top of the mast. Since we will probably do this ourselves, just wondering if it matters (or how it matters) where the back stay is split? Thanks.

Catherine
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  #4  
Old 10-05-2007, 05:56 AM
Matthew Sebring Matthew Sebring is offline
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Join Date: Jun 2006
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Brion posted his thoughts on the evils of a double backstay elsewhere on the site - basically it boils down to there not being many, if any, pros and a whole bunch of cons (weight, windage, etc.) I'd put the plate as high up as can be comfortably reached from deck. This reduces the angles of the legs plenty but also allows for ease of inspection and adjustment. You also need to decide if you want a single turnbuckle above the plate or a pair at the chainplates. Either would be appropiate but if you go with the single you certainly want to reach it. You'd mentioned liking the existing setup because it's easy to adjust. If you are wanting a backstay you can adjust on the fly you can use a split backstay adjuster - the type that draws the legs together as you haul down on it. That would be another reason to not place the plate too high.
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  #5  
Old 10-05-2007, 06:36 AM
Andrew Craig-Bennett Andrew Craig-Bennett is offline
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"...the type that draws the legs together as you haul down on it."

Technically, as reader's of Patrick O'Brian's novels may care to note, a catharpin!
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  #6  
Old 10-05-2007, 07:55 AM
Brion Toss Brion Toss is offline
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Posts: 1,180
Default It depends

Hello,
Sounds like your backstay is split for two reasons: to accomodate the rudder and tiller; and to provide a 2:1 purchase on the pendant. I agree with Ian that a block can be a vulnerable item to hang a backstay on, particularly with a masthead rig, but will note that an adequately stout block can be utterly trustworthy. Still I'd likely only use one with a cascading purchase at the bottom, rather than a turnbuckle, because to me a block's big advantage is range of motion, and a turnbuckle doesn't readily provide that.
That's why we would, instead, install a linkplate down as low as possible, while retaining a suitably narrow angle between the legs. Then we'd tune the backstay such that, in light airs, the delta plate was off-center, putting most of the load on one leg, and that in heavy airs the delta was on-center, with the legs equally sharing the load. We'd put a long-throw adjuster on one leg, and a regular turnbuckle on the other. That way you could establish and adjust basic tune.
At least the turnbuckled leg would be heavier than usual, just in case a gust hit while the stay was in light-air mode, and a lot of load got onto that side.
In any event, I see no logic in splitting the backstay up near the masthead. Perhaps I am missing some piece of your rigger's logic here.
Fair leads,
Brion Toss
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  #7  
Old 10-06-2007, 11:57 AM
catd catd is offline
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Thanks for the comments Brion. I would definitely call it a stout block; a 6 inch aluminum sheave between to large stainless plates and two 1/2 in. clevis pins. As we are considering what to do about this piece of the backstay, we had another thought: what about using amsteel (or similar) line ? We happen to have some 3/8 amsteel (that we are using for running backs) and tried it out in the block. It runs through it smoothly(doesn't seem to slip) and fits in the sheave nicely. I seem to recall hearing (not sure where) that amsteel would require a different type of sheave. Could it work with the sheave we have? If not, does anyone know what type of sheave is required? Thanks again for any input.
Catherine
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