T-Pain Is On A Boat: Re: [Electric Boats] Re: Water movement around a hull

Monday, August 16, 2010

Re: [Electric Boats] Re: Water movement around a hull

Good day all

In 1971 as a cadet on a fast cargo ship I remember going up the ship canal which runs ENE out of New Orleans, early on a Saturday morning. There were a couple of fisherman minding their business well out of the way in the shallows and in amongst the dead tree stumps probably looking for bass.

The pilot on board was in a great hurry to get where he was going and well exceeded the maximum allowed speed .

The result was that some of these poor fishing felllows found themselves pushed even further in amongst the sticks by the huge bow wave which the ship was pushing well ahead of us.

As the ship passed them the water was sucked away completely and they were left high and dry on the mud.

Then the "tidal wave" of broken brown water following the ship came along swamping them and rolled them over.

The old man had a huge shouting match on the bridge with the pilot but as I remember nothing ever came of the very dangerous incident.

rgds

Alan

----- Original Message -----

From: Capt. Mike

To: ELECTRIC BOAT GROUP

Sent: Monday, August 16, 2010 5:16 PM

Subject: Re: [Electric Boats] Re: Water movement around a hull

Bud

Yep training makes the difference. I remember about five years ago coming into the Houston ship channel on a freighter where I was a passenger. We passed another ship coming out in a narrow channel. I remember thinking that the sterns of the boats were very close as we passed each other. Probably the result of the effect described.
I think there is also a term used by tugboaters called "bank suction" which happens if a moving barge gets too close to the shallow side of a channel and it pulls the barge closer to the shore.
Those big boats have a lot of things we "lightweight" boaters don't have to worry about. But, it also means we should not get too close to them either.

Capt. Mike
Sent from on board BIANKA
http://biankablog.blogspot.com

From: "Bud" <geomarlogistics@gmail.com>

Sender: electricboats@yahoogroups.com

Date: Mon, 16 Aug 2010 08:57:35 +0000

To: <electricboats@yahoogroups.com>

ReplyTo: electricboats@yahoogroups.com

Subject: [Electric Boats] Re: Water movement around a hull

I believe that this is a common occurrence when two large vessels are travelling parallel to each other. There is a physics principle which applies, but the name escapes me. Marine Safety Internatiional in Rhode Island, which has computerized ship's bridges in simulation, does refueling practice runs while vessels are underway for the US Navy. It takes a steady hand and good eyes to maintain a safe distance from the other vessel. If you wanted to know more, I'm sure someone on staff could explain the principles at work here and how to deal with it. Tha or find an old Navy tankerman with lots of experience.

--- 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
>