The Truth About Anchoring Huge Ships - YouTube

do you remember the film battleship where the  uss missouri drops an anchor and appears to  

perform a handbrake return well there's boatload  of artistic license in use there and the reality  

of anchoring large ships is somewhat different  let's use this modern anchor as an example  

it's a stockless or patent anchor and  comprises the shank and the flukes it  

gets its name because it doesn't have the  stock that you would find on earlier anchors  

this part here is the stock which was used to keep  the flukes pointing straight down into the seabed  

the stopless anchor just uses the spread at the  end of the flukes to stop it laying the wrong way  

it lays flat and when force is applied the  flukes bury themselves into the seabed the seabed  

itself is critical to any anchoring procedure  specifically we're concerned about the nature  

of the seabed solid rock is pretty much useless  apply force on an anchor resting on solid rock and  

it's just going to slide along seaweed can have  the same effect creating a mat that the anchor  

just glides over swap the weed out for pebbles  or sand however and the anchor has a much easier  

time digging in for the very best holding power  what you really want is something like soft mud  

anything that makes the bottom nice and sticky not  only is the anchor itself going to dig in nicely  

but the chain leading towards the anchor is going  to get a good grip as well that part is critical  

because surprisingly with massive ships it's  not actually the anchor that holds them in place  

is the weight of the chain the anchor is simply  there to hold the end of the chain in position  

it allows the chain to lay flat along  the seabed before rising up to the ship  

in this diagram there's no force on the ship at  all and the anchor chain is just going straight  

down running along the seabed to the anchor we  actually call it up and down and it tells us that  

the ship is quite happy not applying any weight to  the anchor chain if the wind or current starts to  

tug the ship backwards the chain stretches out  as it starts to move we get light weight which  

increases through medium weight to heavy weight  these are all terms that the crew use to describe  

how the anchor chain looks so the bridge team know  how much force the ship is applying to the cable  

so with the chain under heavy weight you can  see that it's stretched out at quite an angle  

the anchor itself is just keeping the end of the  chain in position and the sheer weight of the  

chain is what's keeping the ship in position the  curve that the chain makes is called a catenary  

it's a physics term that describes the curve made  when a chain or a cable is suspended by its ends  

as you apply more force pulling the ends apart  the catinary becomes straighter it's absorbing  

the energy that you're putting into it as soon as  you stop applying the force the chain falls back  

to its natural resting position so when the wind  and the current ease the ship stops applying force  

to the chain and it falls back to its natural  resting position laying straight along the seabed  

and vertically up to the ship if there's a sudden  sharp tug on the ship it doesn't snatch tight  

on the anchor chain the chain gently lifts a bit  straighter absorbing the energy of that sharp tug  

if the catenary wasn't there and all the weight  was on the anchor alone a sharp tug would likely  

break it free from the seabed this is where the  length of anchor chain becomes so important if  

you let out a relatively short length the anchor  will bed down but there'll be barely any scope  

left for absorbing any energy before the ship's  applying force directly to the anchor itself  

if instead you let out lots of chain it's going to  take a huge force to pull it tight before breaking  

the anchor free but if it takes so much force to  pull the anchor free how can the ship ever get  

its anchor back well when the ship isn't applying  force to the chain the windlass on the forecastle  

can quite easily start to heave the ship uses its  main engines to drive towards the anchor as she  

heaves eventually she'll be in position directly  above the anchor continuing to heave on the chain  

the end of the shank lifts levering the flukes out  of the seabed the anchor is aweigh now it's just a  

case of continuing to heave until the anchor  returns home with the shanks safely inside  

the hawse pipe within the hawse pipe there are  powerful jets of water to wash the anchor chain  

as it's brought home when you see water running  out of a ship near the anchor that's all it is  

just the anchor washer running following  the anchor chain into the ship we can see  

the machinery at work the chain leads up the  hawse pipe over the windlass down the spurling  

pipe and into the chain locker within the chain  locker it's attached to the ship at the bitter end  

now did you notice these markings along the chain  itself those are used to indicate the length of  

the anchor chain anchor chains are produced in  lengths of 90 feet or 27.4 meters the lengths are  

joined together by joining shackles each joining  shackle is painted red indicating the joint  

then white links are painted on either side of  the joining shackle indicating how many shackles  

it is from the anchor the first will have one  white link either side then two white links  

three white links and so on it's an easy way for  officers to know how many shackles are out in this  

diagram there are five shackles at the waterline  so there's 137 meters of anchor chain in the water  

as we saw earlier the more chain you have out  the better the holding power you can expect  

so going back to the film we saw at the beginning  hopefully you can now imagine what would happen in  

reality you can pay out the anchor chain and maybe  at some point it will get a grip on the seabed the  

chain will pull tight absorbing more and more  energy the whole time then one of two things  

will happen either it's going to absorb enough  energy that the ship will come to a gentle stop  

or more likely it will absorb some energy then  the chain will pull too tight and the anchor will  

jump out to the seabed and start bouncing along  the ship would literally be dragging her anchor  

and that brings us to the end of today's  video apologies for the delay since  

the last one i'm hoping to be better this  coming year and aiming to publish monthly now  

on the last friday of the month either way to  stay up to date whenever i post new content  

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