Forestay breaks for second time in three years

[CaptVR]

On the M25 and lower... the back stay is slack unless running down wind. I don't really know why they were designed that way but I've owned three and sailed on more than that and they were all that way. It is also true that the shrouds were a little slack and instead of turn buckles they used the really cheap tension brackets like these
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The recommendation in post #9 about pumping as the culprit may be the correct answer. Macs were made to trailer and not to sit on a mooring ball. So the O.P. may need to work on the standing rig to tighten it up a bit if he keeps it on a ball.

CaptVR here: Just to give this member a quick lesson. These toggle stay adjusters are more expensive than turn buckles, they are stronger than turnbuckles for the same pin size. The reason Roger used them on Mac's is because there not prone to bending and failing the way turnbuckles are when used on a mast and rigging that has the mast layed down and put back up repeatedly. They are not to be beat, for a trailerable sail boats. I have sailed my Mac 26X all over the Northern Caribbean including Cuba and Haiti. I have changed and installed 5/32 on all my standing rigging and put on a substantial split back stay. As far as Nico press fittings, I'll swear by them. After surveying for 20+ years, never seen a Nico press failure, have seen swagged, Norseman, Staylock failures. The proper Nico press fitting is far superior to the cable it is fastened to, cable may fail, the swages never. Capt. Vince Rakstis, Ret. MS

 

[CaptVR]

The forestay is most likely breaking due to work hardening. The wire flexes, the metal gets brittle, a few wires break. Repeat until the last wire breaks and the forestay parts. That’s what’s happening to break two forestay sin a couple of years.

It's not breaking because i'ts too weak. The loads generated when it's just sitting at the mooring without any sails or heeling are comparatively light, Getting a bigger diameter forestay won't stop the work hardening. You've got to reduce severity of the bending of the wire rope.

You say the forestay broke both times at the gap between the thimble and the first nicopress compression sleeve, right? That's where the bending is occurring. You need to allow it to bend else where rather than between the thimble and the nico -ress compression sleeve. So you have to change something the geometry of the rigging.

Your boat has a rotating mast, with the "jesus shackle" at the mast hound, righ?
Here's a picture from the Mac 26M owner's manual. Is this how your forestay is rigged?
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When there is a lateral (non-axial) load on the forestay, the wire is flexing between the thimble and the sleeve, leading to work hardening. If you can rig it so that the lateral pressure is transferred to the top of the forestay, the cable won't flex repeatedly to the point of breaking individual wires.

I would recommend a couple of approaches to reduce wire bending

1. Figure out a way to limit the rotation of the mast when it's on the mooring. You could bolt a lever onto the mast near the foot, and attach lines to limit the rotation. Google "mast rotation control arm".
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2. *** Very Important: add an extension plate (or a rigging toggle) to the top of the forestay, similar to the two upper shrouds. This will permit one more axis of rotation that will greatly reduce the degree to which the wire rope is being bent. (you will need to shorten the forestay to compensate for the added hardware).
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CaptVR here: When on the ball. Main is down and covered or removed. With a slight tightening of the Cunningham, and no slack in the main sheet the mast will not rotated. At least with normal anchorage conditions. For the strands to break above the Nico fitting, the thimble has to be binding on the pin with a high amount of flex between crimp and thimble for strand breakage. As someone else said, put a 90 short pinned toggle on the hound and cable to the bottom of the pined toggle. Your set for any amount of mast rotation.
Happy sailing all, Capt. Vince Rakstis, Ret. MS

 

[DrJudyB]

These toggle stay adjusters are more expensive than turn buckles, they are stronger than turnbuckles for the same pin size.

@CaptVR, Can you give some examples where the strength of the shroud adjuster exceeds the strength of a bronze open body turnbuckle with the same pin size?

I found only one stay adjuster with a breaking strength greater than 400 pounds. CJ Johnson’s makes a single row adjuster with 1/4” pins with a SWL of 1000 pounds ( breaking strength of 2000-2500 max). Everything else I found from several manufacturers had a max safe working load of 400pounds.

Breaking strength of bronze body turnbuckles meets or exceeds the breaking strength of the relevant diameter wire. The breaking strength of 5/32 1x19 SS316 is approx 2800 pounds.

 

[CaptVR]

@CaptVR, Can you give some examples where the strength of the shroud adjuster exceeds the strength of a bronze open body turnbuckle with the same pin size?

I found only one stay adjuster with a breaking strength greater than 400 pounds. CJ Johnson’s makes a single row adjuster with 1/4” pins with a SWL of 1000 pounds ( breaking strength of 2000). Everything else I found from several manufacturers had a max safe working load of 400pounds.

Breaking strength of bronze body turnbuckles meets or exceeds the breaking strength of the relevant diameter wire. The breaking strength of 5/32 1x19 SS316 is approx 2800 pounds.

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Look at it again friend, the 400lb adjust is a 3/16 pin CaptVR