if an anchor is heavy enough to hold a ship in place, how does the ship not sink when hauling it?
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the anchor is heavy, but it also digs into the sand when tugged on by the motion of the boat.
The anchor does not hold the ship in place simply by weight. It is friction from the anchor and its chain resting on the bottom that keep the ship in place,
It’s not about the weight per se; the anchor does need to be heavy but it’s not purely its inertia that’s holding it in place. Rather, it creates friction through contact with the ocean floor.
There’s a concept called static friction; you know how, if you’re pushing a heavy box or something else, you need to push really hard to get it moving, but once it’s in motion keeping it moving is a lot easier? It’s the same idea. Once the anchor’s on the ground, the ship can’t pull it along without producing enough force to overcome the static friction it’s generating with the ocean floor. It doesn’t need to weigh as much as the rest of the ship, it just needs to weigh enough that the forces generated by the ship drifting around can’t overcome its static friction.
Or, to put it another way: if the ship itself was in contact with the ground, it would also be unable to move because of friction, even though the ship has no problem floating.
The anchor needs to resist the force of the waves/current, which is does by digging into the seabed and by being relatively heavy. It *doesn’t* support the full weight of the boat itself – water/buoyancy does that. So the anchor is really only experiencing a fraction of the weight of the boat compared to say…the boat hanging off a cliff and the anchor holding it from falling down into a canyon.
Edit: Spelling
For an easy comparison, small boats also have anchors. They are big hunks of metal but not so big a healthy adult couldn’t toss it in the water when they want to stay put. It works by getting lodged in the seabed.
Anchors don’t work by putting the bottom of the boat on the ground. They work by making it so that the sideways motion of the boat doesn’t have enough force to drag the anchor across the ground. Some anchors are quite light, and do this by digging into the bottom. Most anchors use some sort of combination of weight and digging action.
actually the anchor doesn’t work by itself. it’s also the weight of the chains that kinda pull the ship towards the anchor (it always want to lie flat).
The anchor does not hold the ship. The anchor holds the anchor cable in place while the ship pays it out.
The heavy anchor cable lying on the sea floor holds the ship. More accurately, it dampens the ship’s movements to the point that below certain limits of wind and sea current, the ship stays within a defined geographic area centred on the anchor.
To securely hold a ship in most conditions, the length of anchor payed out is usually at least 4 to 5 times the water depth.
In high seas and heavy weather an anchor is never used to hold a ship in place it simply is not enough.
All the anchor has to do is be heavy enough to resist the “drag” from the tide or the “blow” by the wind. When a boat is placed head on into a tide/wind the cross section available for it to act on is very small so the weight/drag from the anchor needs to be way less than the weight of the ship.
If a ship gets “side on” to the wind/tide an anchor will easily be dragged and is a very dangerous situation but because a ship is naturally dart shaped this situation is rare as it’s normally stays head on. If it’s unable to stay head on then they will draw the anchor and use the engines to out of the danger zone.
If not shaped as it is, a whole ship can sink. By distributing the weight properly, buoyancy can be maintained.
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