This is interaction. Caused by the pressure drop or increase between two
vessels when they are close. Also called bank effect, canal effect or
shallow water squat when the interaction is between the ship and shore.
Nautical colleges teach how it works and you can read about it in seamanship
texts.
-----Original Message-----
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
On Behalf Of Ron
Sent: Monday, 16 August 2010 5:06 a.m.
To: electricboats@yahoogroups.com
Subject: [Electric Boats] Water movement around a hull
Wow!! so many different things and people that need a response. I have a
question about something that happened years ago, knowing what happened and
the outcome, I still am not sure what the really correct action should have
been. The answer might be a help to anyone active in boating today.
The situation took place on the Mississippi river just below New Orleans, I
was at the wheel (rudder stick) of a 65' pushboat going downstream pushing
two barges (end to end) the river bank on my right, the engines were set at
3/4 throttle. From behind, a freighter (running lite) is moving downstream
at a much faster speed, his location seemed to be near the center of the
river and as everyone should know it is pretty wide. Signals were made for
the passing and as far as I knew everything was fine.
As the ship gets closer I notice the space between us starts to narrow, but
still no need for worry (so I thought), I give a little right rudder
thinking of moving closer to the bank, in a very short time it is obvious
the gap is closing (more right rudder). The bow of the ship now about even
with me, things are changing fast, so I go to full throttle and hard right
rudder, at just a few moments we are at mid ship and I know this is kicking
my boat harder towards the ship, but I'm trying to get enough space to allow
hard left rudder and not swing the barges into the side of the ship. At what
I thought was the right moment (and maybe was) I go to full left rudder, at
which point my boat is under the stern of the ship and 10 to 15 feet away
from the ships propeller, which is chopping water at about 1/3 above
surface. the last image I had of the ship pilot, was him leaning over the
bridge rail as far as he could and a real look of concern was easy to see.
It was a very close call and I survived as is obvious....the point in
relating this event is to draw attention to the massive amount of water that
moves, as Chris and a few others have commented, in relation to a hull of
any size.
The surface in some cases seems to move forward with the vessel while a
large amount under water and not visible is being pushed away, which in my
mind forms something like a vortice or contrail behind the wing of an
airplane. As it seems in my mind, my boat and barges started riding the top
of that swirling cone shaped body of water and at some point started being
floated or sucked toward the ship.
Even in a river as large as the Mississippi, if you are close to the bank
you can see water fall and rise as a ship approaches and passes.
Other than more space, does anyone have anything to suggest or make comment
on that would help someone else keep from falling into a possible similar
situation ?
Ron
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