Sunday, February 21, 2021

Drogue Chainplate Design

 Don Jordan, the father of the series drogues, suggested a chainplate of conservative dimensions, but did not detail the design. He wanted to keep it simple so that people would use them. Most commonly, these plates are installed horizontally, because that looks right. But what if the pull is not horizontal?

In my limited experience, and based on what I think is common sense, the strongest pulls are from a downwards angle. From basic engineering statics, the largest bending forces are near the transom end, and the largest shear loads on the bolts will be when the load is off-axis. That suggests either more or larger bolts near the transom, but more will better distribute the shear stress load to the laminate.

Hardly a detailed analysis, just thinking. In practice, it would be simpler just to build it oversize, though internal reinforcement of the laminate might be avoided by this sort of design.

Wednesday, February 17, 2021

The Jawbone and Other Mysteries

 There we were, sailing across the Chesapeake in moderate winds when, something small and hard clattered into the cockpit from the masthead. For a moment were were terrified that i must be some critical pin, and that any moment the mast would go over the side. But upon closer inspection, it was a jawbone.

A brief Google search confirmed it was most probably from a raccoon.
But how did that get up there? I can only assume an owl was responsible, since I clean owl pellets off the deck now and them. Seems more likely than an osprey. 
But then what explains this chunk of asphalt, neatly lodged on my aft starboard aka? I doubt a bird carried it. Why would a racoon, and besides, there were no sings of attempted forced entry, which I would  expect if raccoons were about.

It's a puzzlement.