Tuesday, May 30, 2017

Solving the wobbly dock spur problem

Our marina has put in docks like this, with a main runner, and spurs for boat access.  Trouble is that these spurs are connected with hinges, so that they can take the big waves.  These hinges have a give which translates into a wobble at the end of about 2 cm either way.  There is no damping, so the velocity is about 10 cm/s.  So a displacement of 2 cm with 10 cm/s is a good earthquake.  People are going nuts!

This ground motion, just like an earthquake, makes people think they are going to dump into the lake.  But you really need a displacement of 20 cm to lose your balance, and probably 50 cm/s.  That's a damaging earthquake!

Nevertheless, these dock earthquakes are a bad feeling.  You need to dampen the torsion of the spurs.  Basically, I am thinking about rubber at the inside corners.  I was looking at an inside corner docking bumper, but they don't have those.  Probably just heavy dock bumper strips bent at a 50 cm radius on the inside corner will do.

ps.  I really like recycled rubber crumble stuff.  The damping coefficient must be huge.

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