# chain plates

Discussion in 'Sailboats' started by Scofield, Mar 31, 2008.

1. Joined: Dec 2007
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### ScofieldJunior Member

I need assistance to locate chain plates. I located them on 3d model and also I marked them on the boat. But I need some resources or help because I am not sure about how can I strengthen them under the deck, how can I calculate strength of this system. If you have some resources about this subject, please inform me.
(35 m sailboat.)

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### LandlubberSenior Member

You are kidding right!

A 35m boat without a designer speced layup?

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### alan whiteSenior Member

It is simple to calculate cross-sectional tensile strength. Usually the chainplates will be a 300 series stainless. If the rigging (shrouds and stays) has been specified already, making the chainplates twice as strong is adaquate.
You may see specified a 1/4" (or 8mm) turnbuckle (for a single shroud) and 8mm round is a certain portion of a square centimeter.
Using this cross-section, you size your chainplate to have twice that value.
The next step is to find out the tensile strength of the stainless you are using. This for you will be kilo per square centimeter, for me pounds per square inch.
If, for example, I see that my stainless is 125k psi tensile strength, and I need 12,500 lbs to safely anchor my shroud, then my cross-sectional area required is .1 of a square inch This applies to the smallest cross-section of the chainplate in tension, in other words, where a hole has been drilled for attachment (both sides of the hole are added), which is the weakest section along the length of the chainplate.
Locating chainplates is a matter of comprimise if you have no backstay and the shrouds are backswept. This is a distance aft of the mast. Too little and you have too much mast compression. Too much and the boom can't run forward enough. The wider the staying base, the further back they must go too. The lower the rig, or whether spreaders are used also matters. You do need a real pro to assist you in locating backswept shrouds.

Alan

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4. Joined: Dec 2007
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### ScofieldJunior Member

thanks so much Alan...

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