How Do Ships Stop Without Brakes?

in a car when you want to stop you put your foot on the brake pedal the force you apply gets amplified by a vacuum system which moves a piston inside the brake master cylinder in turn sending a hydraulic force to the brake pads which apply pressure directly to the disc rotor slowing the wheels the system relies on friction friction between the brake pads and the disc rotor and friction between the tyres and the road surface that friction turns the kinetic energy from the moving car into heat energy so what happens on a ship where there's effectively no friction between the ship and the water you've got drag but there's no way of pressing a brake pedal and dramatically increasing drag in the same way you can with friction in a car instead we have a number of different techniques that we use to slow down ships first you can cycle the rudder moving the rudder between hard to board and hard to starboard increases drag the technique relies on moving the rudder without inducing a turn when you move a rudder it does take some time for a vessel to begin turning so you can keep it hard over for a little while as soon as the turn begins though you turn the rudder hard the other way these relatively rapid rudder movements lead to the term high frequency rudder cycling it slows the ship using only the additional drag created by the rudder itself developing that idea further we move on to low frequency rudder cycling the idea is you do induce a turn you want the vessel's drift angle to increase your drag you'll get a vessel swinging 30 40 degrees one way before returning to your original heading reducing the engine power the whole time as the vessel's momentum is in this direction the increase in angle leads to a huge increase in drag rapidly slowing the ship low frequency rudder cycling can get a ship to stop within five or six ships lengths so on a 300 meter ship you could stop within a mile or so of course if there are no restrictions with regards to sea room the next development in stopping with a rudder is to simply go hard over and let it turn this is known as turning under full helm and is a recognized emergency stopping maneuver it also relies on the increase in drag caused by the angle between the vessel's heading and the direction of momentum when turning under full helm it's possible to stop within a couple of ships lengths albeit you will be either to portal starboard of your original track depending on which way you turned of course if you've spotted a last minute hazard up ahead it can be a very effective way of keeping yourself safe so we've looked at using the rudder but what about the engine we've all seen it in the movies where a ship immediately orders fuller stern to try and stop again this is a recognised maneuver it's called a crash stop a crash stop would probably be my last choice if i had to undertake an emergency maneuver though simply because it leads to a complete loss of control of the vessel putting the engine's fuller stern stops the water flow over the rudder so you've got no way of steering or correcting a shear not only that but the propeller will have much less of an effect than you would expect turning a propeller in the opposite direction to the flow of water kind of creates a vacuum there's a lot of water coming from this direction hitting the blades the blades are trying to push it back creating a flow in this direction but in doing so where can the water now come from all the water on this side of the prop is moving away so there's no water for the propeller to propel so what else could we do with the engines instead we could just stop them again this isn't recognized maneuver two it's called an inertia stop you literally stop the engines and let the ship drift until it stops moving as there is still water flow over the rudder you do maintain some control the faster the ship the more control you have but you're gonna lose control as she slows down the other consideration is that you might need miles and miles of sea room you're literally only using the drag from the hull to slow the ship it's really not very efficient so on a day-to-day basis what do ships actually do when they want to stop we've talked about emergency maneuvers but we don't do those every day instead what we normally do is known as a controlled speed reduction it involves a lot more planning ahead but the idea is you maintain full control of the vessel the whole time crossing an ocean you would be traveling at full sea speed a good few miles before maneuvering you would start to reduce speed initially dropping the engine to full ahead this would be marked on your passage plan and is part of the voyage planning process that navigators go through before every passage as you get closer to your destination you'll have planned points for speed reduction the whole way in the idea is that each time you only need to reduce the power a small amount you keep the propeller running ahead maintaining the flow of water over the rudder giving you full control over the vessel the whole time each time you reduce power the drag force applied by the hull through the water becomes greater than the force delivered by the propeller the overall effect is that the vessel slows down until the force applied by the propeller matches the resistance force due to the speed through the water a controlled speed reduction takes the overall momentum of the ship and slowly dissipates it using the resistance of the water our car which we talked about at the beginning can very quickly use friction to transform its kinetic energy into heat a ship has to slowly use the water resistance instead gradually slowing down over a number of miles but what about our anchor well we actually covered that recently so check out that video and you'll see why they can't be used to stop your ship and that brings us to the end of today's video i now publish content like this on the last friday of every month to stay up to date every time i upload be sure to subscribe and turn on notifications until next time thank you for watching and goodbye

Channel: Casual Navigation

Views: 1,375,723

Keywords: casual navigator, marine, shipping, casual navigation, maritime explaination, merchant navy, sailing, marine animation

Id: 1vHPx4bKjIQ

Length: 6min 1sec (361 seconds)

Published: Fri Apr 30 2021