How do anchors on yachts work and how can they hold a whole boat when they lay on flat sea ground?



How do anchors on yachts work and how can they hold a whole boat when they lay on flat sea ground?

In: Technology

That’s not how anchors work. They act to hold one end of a heavy chain so that the ship can lay it out on the bottom. The chain applies the forces that keep the ship in the right area.

Most anchors have “wings” that dig into the bottom and that is how boats are held. On some anchors, the wings are movable so that instead of a flat piece, it becomes a piece with a 90 degree angle.

Unless you have a very small boat, it is not dependent on the weight of an anchor (or its chains) to hold it. It is dependent on the anchor digging into the bottom. That’s why they call it “good holding ground”. You don’t want to anchor over really soft mud or rocks, for instance.

The theory about “chains” and “heat” is just a mystery to me, a person who has owned boats and worked on and around boats for many years.

Firstly, the horizontal forces acting on a boat aren’t as big as you might think. Certainly less than the weight of the vessel.

Then consider the shape of an anchor. In all cases they are designed so that if you pull them horizontally they dig into the ground. The further you pull the deeper they dig. So suddenly you aren’t just trying to pull the anchor, you are trying to pull all of the ground that it is under. You can imagine that an anchor doesn’t have to be buried very deep before the amount of ground you have to pull far exceeds any force you can apply.

There seems to be a lot of misinformation/misunderstanding about anchors. First of all, if it was up to the chain to hold the ship, we wouldn’t even have anchors. Secondly, the anchor on my boat doesn’t even have chain, it has nylon line and it works quite well. The way anchors actually work is that the blades, tines, wings, whichever, dig into the sea/lake bed and prevent the anchor from sliding horizontally across the sea/lake floor. The “trick” to making anchors work is to pay out enough line/chain so that when the line is taught, it makes about a 30 degree angle with the water. The lateral force of the boat trying to drift tends to drive the anchor deeper, so if the force pulling the boat is greater, the holding power increases in kind. When it is time to lift anchor, the line is pulled until the boat is almost directly over it, the anchor has almost no holding power against vertical force and breaks free quite easily.