Ron,
Here is how I look at the effect you describe. I think if you take into account the "displacement" of a vessel, the movement of water around a hull and interactions with nearby vessels in a narrow channel may be more easily understood. That is, a ship rated at several thousand tons displaces that much water to all sides as it passes. In the ocean there is less resistance to the movement so the bow wave and wake are the major effects. In a narrower waterway there are forces from the displaced water meeting the confinement at the river banks that results in a height increase from the heavier displacement vessel. That, and possibly a reflecting bow wave, plus the water's habit of seeking a normal level help to move the two vessels together.
I'm a design engineer, no naval architect, so my analysis may be flawed.
--- In electricboats@yahoogroups.com, "Ron" <rlgravel@...> wrote:
>
> 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
>
No comments:
Post a Comment