Martin Ludgate wrote:
> It's true that you're unlikely to damage a gate by pushing
> gently. But I'm surprised that you can push a gate open
> against a head as great as 6 to 8 inches. A
> back-of-fag-packet (except that I don't smoke) calculation
> suggests that on a typical narrow lock this would take
> between a ton and a ton and a third of force.
By my reckoning, the force on a typical single narrow gate with 8 inches
level difference is about a ton. Since the boat bow will be pushing in
the middle of the width of the gate it has to develop the full 1 ton
force to open the gate. However for double gates on a narrow lock, the
force from the water is applied over the full width of each gate, but
the force from the boat is applied at the mitre post, so a 2:1 advantage
is gained, halving the force required. And if the bows are actually
pushing only on one gate (as is sometimes the case at the bottom of a
lock with a short entrance and the boat not lined up) then the force is
halved again - to a quarter of a ton with an 8 inch level difference.
David Mack
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