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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