chainplate calculations for a jordan drogue

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Glen,

You are doing it backwards. The first question is what load does the drogue apply, then everything is sized to this. 800lbs may be perfectly sufficient, it may be highly conservative, or it may be incredibly low. Until you know the expected loads nothing else can be worked out.

In this case the peak load is 8,000lbs. The working load for the drogue is ignored, and everything needs to be sized to handle the 8,000lbs worst case scenario. Because of the way Jordan has engineered this however it is reasonable to step down the safety margin however. Where normally a life saving piece of gear should be 10:1 here it looks like in their worst case they have already assumed a substantial safety margin, and something more like 1.5 or 2:1 may be reasonable.

And keep in mind you can't just cut the expected load in half for each chainplate. First because they will be offset which even in a steady state will result in different loads, but for something like a drogue because there is a real likelyhood that one side may bear the brunt of a shock load substantially higher than half. I would like to design around each plate carrying the full load if I could. Giving complete redundancy, but I might be ok with each assuming 75% of worst case value.

So my ideal would be two chainplates each sized for 24,000lbs. If that was considered unreasonable then I would be willing to accept something down to a minimum of around 9,000lbs. Then size the rest of the gear to this. The fact that drogue plates are usually installed outboard and at deck level means that it isn't normal to have a problem with installing them. So oversizing is a pretty easy step to take, and no one has ever complained their gear was too strong.

Of course I am at best an amature, and would be happy to accept correction.