chainplate calculations for a jordan drogue

[Brion Toss]

Hello,
Let's start with that shackle. The 9,000lb working load is, I believe, one-fifth of the rated break strength. So right away there's a bit of a strength discontinuity with the chainplate numbers you have.
Next, while the yield strength is an important detail, and needs to be considered when determining scantlings for a given material and application, ultimate tensile strength is of primary importance. Imagine a material with an extremely high yield strength. This will break very shortly after it reaches yield, so there is basically no reserve of strength before failure. by contrast a material with a low yield strength (like 316) has a huge reserve, and can be scaled such that the design load never approaches yield.
In your case, the strength of the proposed chainplates would approach 19,000lbs. This is still way short of your shackle strength, so the we need to ask, is the shackle correct, the chainplate correct, or neither? Which of course brings us tot the question we really need to start with: what is the load? This is followed by: What is the appropriate factor of safety? So far we only have vessel displacement and weight, which are related, but not nearly definitive.
Fair leads,
Brion Toss