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News f2s
 
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Default Rope/Chain Rode calculations


"Wayne.B" wrote in message
...
On Sun, 18 Dec 2005 18:03:41 -0000, "News f2s"
wrote:

The
common mooring there is bows or stern to, when the rode is
usually
stretched off the ground already. I've had many a quayside
discussion (complete with bits of string and jugs of beer)
explaining why the surge from a ferry caused an anchor to snatch
out.


When you are bow (or stern) to the quay you really don't want a
lot of
stretch in the system however. Better to use more scope if
needed to
get the required holding power, or a better anchor.


I assumed that adequate scope and anchor have been used. The
stretch you want will depend on the surge you face. Without
stretch to match the surge you're (as you rightly pointed out
earlier) either risking your fittings or going to snatch out the
anchor. So far I've seen more anchor snatches. But also fittings -
torque failure on a winch drum shaft, tilted anchor winch.

Suitable stretch depends on the cruising area and the harbours. I
don't know your cruising area, but fast ferries entering some
Greek harbours cause a surge giving up to 3 metre fore and aft
movement relative to the quay with about an 8 to 12 second period.
Poros west quay, outside berths in Paros harbour and Ermoupolis
town quay in Syros immediately come to mind. Other quays facing
east to the fast ferry routes in Ithaca are also affected. And
quite a few south Spain marinas suffer similar surges in winter
storms.

It means, of course, that you have to tie off at least 2m from the
quay (3m is my preferred distance) pulling the boat in against the
stretch for that brief period when you dance ashore (or back
afloat) along a bouncing passarelle. Not my wife's favourite trip!
Or use the dinghy.

JimB