We all know what happened to the Titanic, (and if somehow you don’t know, well, have
we got some videos for you!)
Anyway, when I was a lot younger, maybe in my 20’s ha, I was wondering every time I
heard the story – why hadn’t they just hit the brakes as you would do with the car?
Well, of course, because ships don’t have brakes!
But… why?
The first thing that comes to mind is that ships move in water – duh! – how do you
even brake in water?
But then you need to remember that even airplanes have something similar to brakes, and they
work to slow down a plane in the air!
It seems like it’s not that simple, after all.
Every kind of brakes out there works because of friction.
When you hit brakes in a car, it stops because brake pads tightly grip wheels’ rotors and
cause a lot of friction, basically restricting them from moving at all.
And if wheels stop, they cause friction with the road, and more friction means less speed
until the car eventually stops.
As you can tell, something like this won’t possibly work in water.
Motorized ships are mostly driven either by the motion of propellers or by a jet stream
of water shot from the nozzle.
Simply stopping those won’t produce nearly enough friction with water to effectively
stop the ship.
Ships still have brakes, though, they just need a lot more to properly work.
To produce more friction, the first thing a ship needs to do is to reverse her thrust.
This is much more efficient with jet engines with controlled nozzles and less so with propellers.
And if we’re talking about a big modern ship, you can be almost certain she uses propellers.
Reversing the rotation of propellers will start to slow the ship down, but the heavier
the ship, the harder it is to stop.
They are slow to muster speed, but inertia doesn’t let them decelerate fast enough.
It seems the water itself is the main reason why it’s impossible to use brakes on a ship,
but in reality, the clever use of water’s properties is the key to stopping it.
The friction with water depends on three main factors: the surface of the ship, her velocity,
and viscosity of the water.
Velocity, viscosity?
– oh boy!
You can’t do much with water viscosity, obviously – sort of the thickness of it
-- it will stay the same no matter what.
The ship’s velocity, though, is another matter.
Imagine a ship with a velocity so huge it almost reaches infinity!
Funny thing – she won’t go anywhere fast, because there is a paradox at play.
(A paradox is where two ships offload their passengers – no not really).
The conflict here is that the bigger the velocity, the more the power with which water will drag
this ship back because the friction and the water resistance will also almost reach infinity.
Meaning, it’s not really useful in stopping the ship.
But one thing you still can control – the wetted area of the ship.
Some ships have so-called stabilizer fins.
Submerging those underwater will help the ship to slow down.
These are actually the closest ships get to having brakes because there is one kind of
brakes that operates similarly – air-brakes.
Most jet airplanes have a special kind of spoilers that allow them to slow the plane
down significantly by increasing the drag of air around.
Stabilizer fins don’t stand against the mass of water coming into them, but they expand
the wetted surface and slow ship down this way.
If you would decide to put brakes like that on a ship, once again the water won’t have
it and will show its anger.
Ha ha angry ship.
Imagine a spoiler coming from the bottom of the ship – it will meet an incredible pressure
from the water.
A mass of water pressing on the brake would be so huge there is simply no way it won’t
break off eventually.
Even if we’re able to make an unbendable and unbreakable water-brake spoiler, we’ll
meet another problem.
Water pressing on the spoiler will simply force a ship down, maybe even submerging her
nose underwater!
More fantasy than anything, but anyways, you can be sure that maintenance of these things
would be too expensive.
And you would need to have a whole team of scuba-divers for that at all times during
the trip, imagine how inconvenient that might be.
A much better decision is to start turning the ship.
While propellers provide a reverse thrust, the ship’s inertia is still moving it forward.
All ships are made so that they basically cut water in front of them, and their streamlined
design lowers the friction.
When the ship is turning, she reduces this advantage and the speed goes down.
In general, ships don’t even need emergency brakes.
There is usually enough space to make a maneuver even without reversing thrust, and to stay
on the spot ships deploy anchors.
I know what you’re thinking – an anchor is the brake stop we’re looking for!
But this strategy is best left for action movies.
Should an anchor get a grip on the seabed, it won’t move an inch, and this will result
in a huge dunk for a ship.
This can quickly turn into a full-blown disaster.
The only way to implement that strategy is to combine it with all the previous steps
– reverse engines, start a sharp turn, and when the speed goes down, the anchor is released
on the side of the ship’s turning.
It will only work if the cable of the anchor or the chain is not stressed too much, and
is more suitable for smaller vessels in general.
If everything’s done right, the ship will spin around the point of the anchor drop,
but won’t go any further.
Still, this way of stopping a ship is awfully -- extreme, and if a mistake were made, it
can do more harm than good.
Most of the time lesser ships will use a cycling method to lose all the speed.
Just laying rudder as far as you can sounds better than risking your ship sinking because
of an anchor.
You may think things are much better for small yachts and motorboats as they are much more
maneuverable, but they also go faster.
And the bigger the speed, the more the distance you go before you can stop.
An average time one would need to react and slow down the boat is more than 5 seconds.
Let’s imagine an average 30 ft long boat that goes on 50 mph.
5 seconds will be enough for this boat to go for another 12 times its own lengths.
That’s a recipe for a disaster.
If two boats head towards each other at a similar speed, the distance until the crash
will cut in half, and the collision will be almost inevitable.
Fortunately, an occasion like that is improbable.
No one leaves rudder without attention while going at full speed, and most of the time
other vessels are clearly visible in the sea.
But another thing does pose a great danger– ships come in different sizes.
That means it’s much harder to tell how far from you is another vessel.
It may be a big yacht really far away, or a small boat and already too close.
It’s hard to tell in the sea, especially if bad weather comes into play.
The lack of an effective way to stop is also the reason why ships have good signaling systems.
Few airhorns can be louder than the one of a ship – it’s hard not to get startled
by one, let alone ignore it.
Another way a ship can let everyone around know that it’s here is signaling with projector
lights.
These can shoot right through the darkest night and the thickest fog.
So overall ships can’t stop in place, because water won’t let them do that.
But seamen learned how to avoid trouble related to that.
Being warned is much better than doing risky moves to prevent trouble.
And no, the TV anchor people you see on the news, did not get their starts working on
ships, just so you know.
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