Physics Issue

[HunterSeeker]

Lets imagine you are on a ship proppeled by a propeller. Suddenly the engine dies and the propeller stops. The ship is head towards a reef, now would turning the rodder allow you to avoid the reef or would it just change which part of the ship takes the initial inpact?

 

[Pesmerga]

If the engine stops... you've got no propulsion, and no way to change course. I don't even know what a rodder is, but I doubt it would change anything. You'd crash head first.

 

[kirovman]

Think about a glider, which is similar to this, an unpropelled vehicle. A glider can manuver with it's rudder and ailerons, so I would say the same goes for the ship.

 

[Pesmerga]

But the rudder is beneath the water, it's not like airflow. You'd just be adding resistance... so you might change course, but very insignificantly, and not enough to really make a difference, especially at the distance given.

 

[Parrot of doom]

The rudder will steer the ship.

Engines are a relatively new concept. Think about a sailship with its sails up. The current will push the boat in whatever direction it likes.

 

[kirovman]

Hmm, actually, I suppose it's the aircraft's lift that's redirected in the case of glider, whereas the ship does not have that additional consideration.

But actually, if the rudder turned the ship to be perpendicular to it's original direction of travel, the friction would be so great that it might slow it down before it hit the reef anyway.

The rudder would act in the same way as directional thrusters on spacecraft, to some extent (i.e. re-alligning the ship, but not changing it's direction of motion).

I think:
a)it wouldn't change direction very much
b) and it would slow down before it hit the reef when it had become perpendicular (depends on the ship though - an oil tanker would be difficult to stop/steer)

 

[Pesmerga]

But a sailship uses teh wind! Again, airflow!

 

[kirovman]

What about the aircraft on the conveyor belt?!?

 

[Pesmerga]

That was a topic I was saddest to be banned from.

 

[Parrot of doom]

The answer relies on:

1) Momentum of ship
2) Direction of current
3) Direction of airflow

And thats about it. So given still waters and no breeze, it will turn until it runs out of forward velocity.

 

[HunterSeeker]

Lets say the ship has no sails or oars or anything like that, and the current takes the ship towards the reef. I am trying to convince a friend here that the ship would not change direction just becouse the rudder makes the front point another way.

 

[dream431ca]

Unlike a glider a ship needs propulsion of some kind to change course, so no propeller, means the rudder is useless. A glider is different because it's propulsion comes from gravity and the airflow over the rudder can move the aircraft, while gravity is pulling it in that direction.

Lets say the ship has no sails or oars or anything like that, and the current takes the ship towards the reef. I am trying to convince a friend here that the ship would not change direction just becouse the rudder makes the front point another way.

Your right. As soon as the prop stops working, the only thing pushing the ship is the current. Regardless of what the rudder is doing, the ship will always follow the current because there is no force counteracting the current of the water. You need a prop to do that.

 

[spookymooky]

The ship takes the past of least resistance. It will go wherever the prow is pointed. If you changed the direction of the ship, it will still head as straight as possible towards the prow.

 

[dream431ca]

The ship takes the past of least resistance. It will go wherever the prow is pointed. If you changed the direction of the ship, it will still head as straight as possible towards the prow.

ummm....hmmm. What do you mean least resistance. That makes no sense. If the prop is not working, the ship will follow the current of the water. It doesn't matter where the prow is pointed.

 

[xcellerate]

listen, all you need to know is f=ma and you can't push with a rope.

I'm gonna say no, because if the current is moving the boat, then the boat is moving with the current. If they are both at the same speed then there is no water flowing around the rudder making it useless. For a rudder to function it needs water constantly flowing around it.

However, if either the boat the water is moving at different speeds then you can use the rudder to steer the ship, however unsuccessfully.

 

[Ikerous]

Internet forums are a terrible place for physics questions...
Everyone has an answer but almost no one knows wtf they're talking about

 

[Pesmerga]

The waterflow around the ship forces the bow of the ship into random directions, causing a vortex of unadulterated sex.

 

[spookymooky]

ummm....hmmm. What do you mean least resistance. That makes no sense. If the prop is not working, the ship will follow the current of the water. It doesn't matter where the prow is pointed.

Hmmm, I was assuming the ship had forward momentum. If not, that changes things.

I think it is possible to change the angle its travelling at. For example, pointing the prow about 45 degrees from the direction of the current should make it travel a few degrees off course. I know you steer rafts with nothing but a steering oar, so somehow it can be done.

 

[short recoil]

Definitive awnser:

The boat can be steered with the rudder without engine power, however it is unlikely to be very effective (depending on the size of course).

A rudder behind a prop directs the current of water created and allows much more effective turning of the ship, on a lot of modern ships the prop actually turns itself in the form of an azepod (i think they are called that?)

 

[AH_Viper]

I put together a wee MSN paint job

 

[Raziaar]

Put your hand in the water and start paddling like an oar on one side only so you don't hit that reef!

 

[MiccyNarc]

If the water is COMPLETELY STILL, then the ship will turn.

 

[bbson john]

The direction of the ship turns, Viper explained it*. The vector (path) of the ship changes as well. When you consider the net force acting on the ship when there is a change of direction of ship occured*, you will find that there is a lateral force, by water (still or moving), acting on the ship. The lateral force pushes the ship (path of the ship) to right or left (depend on which direction the head of the ship has turned to). This force continuously acts on one side of the ship and eventually turns the vector (path) of the ship. Of course it is not as efficient as that when there is engine propelling.

 

[Pesmerga]

My fingers smell like peanut butter, which probably accounts for the ship's mass over density problem, causing the ship to inexplicably explode when someone says the words "neener".

 

[bbson john]

My fingers smell like peanut butter, which probably accounts for the ship's mass over density problem, causing the ship to inexplicably explode when someone says the words "neener".

I am not making a joke. It is true
My theory is negligible only if the distance between the ship and the reef is very small, or the velocity of the ship and the velocity of water is very close or equal.

 

[Dan]

As long as it has both a rudder and a keel it can maneuver. The keel keeps the boat from drifting sideways, so it can only travel straight forward in the direction it's facing. The rudder turns the ship so that it's not facing the reef.

 

[Parrot of doom]

^^ The truth.

The keel is the big bit of curved wood on the bottom of the hull.