Freighter on Columbia River causing shoreline water level to drop - why???
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- čas přidán 10. 09. 2024
- Loaded cargo ship moving upstream (south) on the Columbia River headed to Vancouver and Portland. Why does the water pull away from the shore as it passes?
Visualize this: As the ship moves through the water it forms a temporary trough because it is displacing the water as it moves. This temporary trough then fills with water. The action of the water filling the temporary trough is what causes the water to recede from the shore.
Imagine a semi truck going by... it pushes a very large blast of air.... the pressure wave... ahead of it. Behind it is a low pressure area... you might notice if you pull up very close behind the trailer you get pulled along and use much less throttle to keep your speed up.
This ship is in a very narrow, shallow channel, so it pushes a huge pressure wave in front of it. That is what draws the water off the beach. The rush of water after it goes by is the river refilling behind it. THEN the actual ship wake reaches the beach. Two completely different wake effects from one ship going by.
As someone who kayaks, the faster you try to go, the more resistance you face and the harder you have to paddle. Think of it being equal to the surface area of Depth x Width let’s say 80 feet wide x 20 feet deep for 1600 square feet of resistance. The prop is sucking water under the boat equal to that resistance. Low pressure under the boat that gets lower the closer you get to the propeller and high pressure behind the propeller. There is no point trying to argue with the “it’s only displacement” and “water doesn’t compress” people. Low water lower pressure, high water higher pressure. Just like a cruise ship sucking all the water out of port when it starts moving, an equal and opposite reaction where the propeller moves water equivalent to Mass x Acceleration. Except here that is equivalent to resistance (square feet of water it has to push through x speed).
When I was young we'd hang out on a sandy beach call Reeder Beach on Sauvie Island. The river is fairly narrow. As a large freighter would pass we'd have a two or three foot wave racing up the beach. I'd drink to that. :)
The Propeller is causing this, it pushes water behind the ship. If the ship stopped and stayed the water would rise just as it does when you get in a bathtub.
I fish for bass way up river on the Columbia. Below Mcnary dam a big barge or freighter will make HUGE swells.
I think its like this but i am not sure lol. When the ship moves it displaces the water with itself. When the ship's tail passes by, a big hole kinda thing is formed behind it so the water just falls into it to fill it but it falls with force so it sucks water around it too but soon the water starts rushing back after the hole is filled. I dont know if i am correct. You can correct it if i am not.
It due to the ship displacement of water
the displacement would raise the level. a prop pushing large volumes would venturi effect the river... prop not displacement
@@darrylstein187 you're relying on a logical fallacy it's the displacement of the ship as it moves through the water.
The props aren't actually moving water the props are moving the boat because you can't compress water
Imagine a piece of wood and a wood screw when you turn the screw it moves through the wood the wood doesn't move through it.
It's called the Venturi Effect
ok thx .. now what is that??
google it
Its from the props pushing water backwards and away from the shore.
Now that's a reason that makes sense, thanks!
id have to agree. all thought experiments lead to this conclusion.
Nope. It’s the ship creating a trough as it passes that fills with water. When the ship is gone by, no trough exists and it returns. My father was a naval commander on an aircraft carrier.
@@judyscheiber3661 Sorry JLS. It's the props. Action -Reaction. Props push a column of water the rear, pushing the ship forward. The water that makes up the column has to come from somewhere. It comes from the water in front of the ship, and is pushed to the rear of the ship.
@@dl9799 The water is pulled out to fill in the void left behind after the ship passes. Once the void is filled, you get a rebound effect at the center point of the void where all the incoming water met. The energy is release back outward in all directions. In deep water it is hardly noticeable, but when the energy wave reaches shallow water it slows down and begins to stack. The front of the wave slows but the back is still traveling at higher velocity. The tide direction, amount of water displaced, and the makeup of the shoreline has a big affect on how this all plays out.
The props really don’t have much affect on the wave action.
Squat effect
Displacement
Yep. That’s water displacement. Big deal.
Venturi effect