Why Do Ships Have Two Balls?

All Ships have one of these strange shaped boxes with one ball on each side of a central tower but have you ever wondered what they're actually for obviously when the balls are painted red and green it's an indication of port and starboard but they also play a critical role in helping ships stay on course this is a ship's binacle which houses her magnetic compass traditionally they were found on the ship's bridge but nowadays you're more likely to find them up on the Monkey Island with a series of mirrors leading to the bridge so that you can still read it a magnetic compass is basically just a tiny Magna floating in a low friction fluid so that it's sensitive enough to align with the Earth's magnetic field with no other influences it will point to the Magnetic North Pole which was fantastic back when ships were made of wood today however the iron used in ship construction gives another unwanted magnetic influence which throws the magnetic compass off course the problem comes from the fact that the hull itself sits within the Earth's magnetic field so it takes on some of that magnetism essentially the Earth's magnetic field forces the mag magnetic domains within the iron of the hull to align iron that experiences this induction relatively easily is called soft diet and its magnetism will constantly update as it moves within the Earth's magnetic field hard iron is a bit different its domains will only align if you excite the atoms a bit by heating them up or applying a percussive shock it's effectively a permanent magnet as it will then hold its magnetism even when you move it around within a magnetic field but what's this got to do with ships well ships actually contain both hard and soft iron the soft iron components fairly obviously will continuously update their magnetism as the ship moves around and the hard iron will only update when it's subjected to heat or percussive shots like welding or hammering during construction maintenance or dry docking this means that the ship's magnetic compass is under the influence of not only the Earth's magnetic field but also the ship's permanent magnetic field and the ship's induced magnetic field to get any sort of reliable reading from it we need to compensate for all the it feels let's start with the permanent ones say for example our ship was constructed in a dry dock in the northern hemisphere oriented on a northeasterly heading the Earth's magnetic field runs across the dock in this direction I'm going to use blue for the Earth's north pole and red for the South Pole for consistency because I want to use red on the ship's compass needle in a minute the Earth's field is effectively going to turn the ship's hard iron into a permanent magnet running diagonally across the vessel obviously that's needlessly complicated so let's instead treat it as an a thwartship's magnet and a four and aft magnet when we remove the ship from the dry dock it's going to retain that magnetism no matter what heading it happens to be on let's take the four and aft component first and see what it does to the ship's Compass when the ship is heading north the ship's magnetic field is competing against the Earth's magnetic field meaning that the compass needle will still Point North but it's going to be a little sluggish as the pull isn't as strong as it would be if the ship wasn't magnetized when the ship is heading east the ship's magnetic field is going to deflect the compass needle making it Point West of where it should when it's heading south the fields are again aligned causing a strong pull with no deviation and finally when the ship is heading west the compass needle will again be deflected giving us an easterly deviation the thing is as the four and a half component of the ship's magnetic field is constant It's relatively easy to correct we just need to add a permanent magnet near the ship's Compass to compensate we want it to be such that when the ship is heading east or west the corrector is strong enough to compensate for the deviation caused by the ship's magnetic field within the Pinnacle there are a series of holes to hold four and aft correctors allowing you to move them closer to the compass to increase their strength or move them further away to decrease it the exact same process applies for the throat ships component as well it's going to have the greatest effect when the ship is heading north or south and is going to cause no deviation when steaming East or West again you just add permanent to throat ships characters to compensate slotting them into to their thwart ship slots on the binnacle brilliant but there's still another permanent component that we haven't yet considered vertical at the poles the Earth's magnetic field lines are completely vertical and only become horizontal exactly on the Equator this means that our ship constructed in the northern hemisphere will have a permanent vertical component with red at the bottom and blue at the top of course as the compass operates perpendicular to the vertical it's not actually going to have an impact most of the time but when the ship heals over it will this is why it's known as the healing error and is corrected by the healing bucket just like the horizontal correctors you need a magnet to counter the ship's vertical hard iron magnetic field so we just place them in a bucket hanging below the compass brilliant so we've now corrected for all the permanent magnetism but what about that soft iron induced magnetism we mentioned before this one is a little trickier to imagine as it's not so much about the polarity but more about the strength you see when a ship is heading north or south the soft iron component will only be induced for and after it's not going to deflect the compass needle but it is going to reduce its strength as the ship's magnetism is going to work against the Earth's magnetism when heading east or west likewise the needle isn't going to be deflected but its strength is going to be reduced even more so than it was when heading north or south because they are thought ship's poles are closer to the compass deflection is going to happen on the intercardinal headings however when heading Northeast for example their thwart ship's poles are much closer to the compass than the four and a half poles so they're going to be the dominant deflective Force this time as we're dealing with induced magnetism we can't correct it with permanent magnets instead we correct it with two soft iron spheres placed on either side of the compass these are kelvin's balls or Navigators balls if you're of an American disposition they work by weakening the earthworldship's magnetism so that it no longer dominates when heading Northeast kelvin's port ball takes on polarity such that its net effect is to weaken the force from the red pole of their thwartship's soft iron magnetism the port Falls North and South polarity have the same magnitude of force but as the blue one is closer to the compass it acts to oppose the red force from the ship's of thwartship's magnetism heading north or south kelvin's balls will have zero effect while heading east or west will give the maximum effect placed correctly not only will they remove the intercardinal deflection due to that soft iron magnetism but there will also even out the force felt by the compass needle allowing it to rotate smoothly around its full 360 Degrees perfect but what about the final component the soft iron vertical magnetic field well this is what our final character is for the Flinders bar this is a soft iron bar placed on the front of the binnacle to counter the vertical induced magnetism the idea is that the biggest culprit towards the vertical soft arm field will be the funnel and masts placing the Flinders bar on the opposite side of the binacle below the Compass should induce the same pole at the top of the Flinders bar as you would find at the top of the funnel when the ship heals the induced magnetism in the hull and the induced magnetism in the Flinders bar should cancel out again resulting in zero deflection in the ship's Compass combining all of the characters that we talked about today does do a reasonable job of correcting the magnetic compass but over time of course things will inevitably change you're going to carry different potentially magnetic cargos and you're going to be undertaking ongoing maintenance which will involve welding and hammering slowly changing the magnetic profile of the ship Compass adjusters will occasionally visit and swing the compass to reposition all the correctors but other than that all you can do is keep a log of the errors at least once per watch and simply be aware of what your error is at every point in time

Channel: Casual Navigation

Views: 802,400

Keywords: casual navigator, marine, shipping, casual navigation, maritime explaination, merchant navy, sailing, marine animation, kelvins balls, navigators balls, flinders bar, magnetic compass, magnetic compass correction

Id: ckhPRie1iKk

Length: 7min 48sec (468 seconds)

Published: Fri Sep 01 2023