if an anchor is heavy enough to hold a ship in place, how does the ship not sink when hauling it?
In: 12
Here’s a way to think about it:
**A boat on the water simultaneously weighs 10,000 lbs (or whatever the boats dry weight is) and 0lbs**, which is what I tell everyone when I describe what it’s like to pilot a big boat. At rest, a single person can easily push even a pretty large yacht around when it’s floating on the water. This is why you see really tiny tugboats capable of towing really huge ships. This is important to understand why the anchor works.
If the water is calm enough, a moderately strong swimmer could move a large-ish boat. A large *breeze* can move the boat around.
So when a boat is *at rest*, the boat really only moves because of the current / wind. The boat itself, being buoyant, doesn’t really weigh much, while at the same time the weight of the boat is also resisting moving at all.
The anchor and chain weight only need to overcome ***the current***. It doesn’t actually need to hold the **weight of the boat** – it just needs to resist the forces that would normally just float the boat away.
This is why a 30lb anchor can hold a 10K lb boat in place. The weight of the anchor (and digging into the sea floor), plus the weight of the chain resting on the sea floor, is providing enough resistance to keep the boat from floating away.
Note also – a boat doesn’t stay *stationary* at Anchor. The anchor stays stationary, and the anchor chain has enough slack that the boat pivots around the anchor as the current and wind move the boat around. So when you anchor, you need to account for a the circular movement of the boat around the anchor pivot to make sure you don’t hit other boats.
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