Babystay and mast bend - SailNet Community
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post #1 of 6 Old 11-12-2015 Thread Starter
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Babystay and mast bend

I have a 1987 35MK3. It is a keel stepped mast with an adjustable babystay and a hydraulic backstay. How much can I bend the mast with this combo. I'm talking about bending not raking.
This winter I will step the mast and redo the top of the solid rod rigging. The adjustable backstay only pulls 2" of rod and the babystay doesn't pull until the last 2" of travel.
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post #2 of 6 Old 11-12-2015
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Re: Babystay and mast bend

Sounds like your hydraulic adjuster needs a rebuild, and the babystay tackle needs adjustment.

How much bend you get depends on the rigidity of the mast section and the amount of force you apply. On our last boat, a 40' masthead rig with a light section we could pull a good 8-10 inches of mast bend with the hydraulic backstay. We didn't need a babystay, in fact had checkstays to LIMIT the mast bend due to backstay tension. The bend is induced this way similar to holding a toothpick between your thumb and forefinger and compressing it. You need to limit that effect because you're actually shortening the height of the mast and your shroud tension backs off too as the masthead gets closer to the deck.

Also, if you don't limit the bend then you're not really tensioning the forestay either.

Sounds like your mast may be stiff enough to require the babystay, but it may also be that the babystay is there to discourage/stop mast pumping under certain conditions. However the main purpose of the babystay is to complicate your spinnaker pole jibes


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post #3 of 6 Old 11-12-2015
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Re: Babystay and mast bend

I have an 83 35 Mk III.

The babystay is really only to prevent the mast from pumping. You might want a shorter shackle on the bottom so you can tension it a little more.
The backstay should have a gauge on it. Don't go over 2,000 pounds or you will flex the hull, not the mast. I would guess that from slack to 2,000 pounds is about 4-5 inches of travel, but I've never measured it.

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post #4 of 6 Old 11-12-2015
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Are you pre loading the spar at the partners?
Are the spreaders in line or swept?
How loose is the rig when the hydraulics are eased?
How long is the truck, back of the spar to the backstay pin?

Given the boat I would think you could easily achieve two sections. Who built the spar?
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post #5 of 6 Old 11-12-2015
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Re: Babystay and mast bend

I would start getting nervous with anything more than 6" of bend. But, nothing handles like a loaner so I'd pump it up to 8" and see what happens.

Do you have aft lowers or single in line lowers?

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post #6 of 6 Old 12-08-2015
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I have an 84 MKIII. I use the baby stay upwind to stop mast pump as mentioned. The backstay is primarily going to tension the forestay while the baby stay induces mast bend to flatten main a little more. I never measures the effect of the this. I also never go over 2000 lbs tension, if that, and you can also watch how much the leach opens to gauge how much you're bending the mast. I'm also interested in opinions on how best to utilize this combo as I've heard varying opinions in the subject.
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