Still never saw anyone standing the anchor comming into port, going up river, or in a chanel.
On a square-rigged sailing ship, the footrope hangs a few feet below the yard. You walk out along that rope, braced against the yard, to furl and unfurl the sails.
I don’t think that’s a good example. The body has ‘hinges’ or flex points at the leg, it’s not like a rope or chain. And even if it were, I cannot exert as much force as a huge ship pulling on an anchor chain.
With enough force to pull on the chain to make the anchor dig in to the ground and do its job holding the ship, there would be a catenary curve on the chain beginning at the anchor and ending at the ship. As such I’ll concede due to that maybe, depending on the length of the chain, a very small portion of it near the anchor may be touching the seabed even with an infinite amount of force.
It’s EXACTLY like a tugboat low to the water (say the line is tied off exactly at water level for this example even though it would be several feet above it on the tugboat) with a tow line going up to the bow of a huge ship, say 70’ above the water line.
Anyway, think of the tug boat as analogous to the anchor… in fact it’s doing a very similar job. As it pulls on the line going up to the ship, the shape of the long tug line (some can be quite long) is a catenary curve, not a straight line, and NONE of the tow line is going to be laying on the water. Remember, in this example the line is tied to the tug low, at water level (the water level being analogous to the seabed where the anchor is tied off).
Obviously in this example I am assuming the ship is actually pulling on the anchor with more than a trivial force. I’m assuming it’s pulling with sufficient force to make the anchor dig in to the seabed and do its job. In that case, none of the anchor line would be touching the seabed - but some of it would be very close to it at an angle (due to the catenary curve) more than sufficient to pull the anchor parallel to the seabed and dig it in.
I’ll concede that if you had a floating chain/rope/etc then you’d have a problem because it would end up being an upside down catenary curve and would make it pretty hard if not impossible to get the anchor to dig in. The weight helps a little bit by causing the catenary curve, if the line were neutrally buoyant it would be a literally straight line between the ship and the anchor and you’d have to let out more line to get the anchor to dig in than you would with a line that sinks. So in that sense, it’s just necessary to have a line that’s heavier than water. But that’s it.
When American super carriers visit the U.K. they are too big to go alongside in the major Naval Base so anchor offshore in the Solent.
Why would you think that they weight of the chain has nothing to do with forming a suitable catenary curve? For a given amount of tension in a line/cable/chain, the weight per unit length determines the amount of sag. It’s a critically important factor.
I’ve seen a couple of episodes of Deadliest Catch in which the crabbing boats anchored on the leeward side of an island during particularly bad weather. They drop the anchor, to which a substantial length of heavy chain is attached - but that length of chain is connected to the boat by a length of much lighter wire rope. No doubt a crab boat doesn’t weigh as much as a supercarrier, but tell me, why would they use a length of chain AND a length of wire rope, instead of just straight wire rope? Clearly the wire rope is strong enough to bear the required tensile loads, so why do you suppose they don’t discard the chain and simply run that wire rope all the way to the anchor?
Why do you suppose even very small vessels use anchor chain?
small anchor chain vendor (with diagram explaining how chain helps
yet another small anchor chain vendor
Yes, this would work, but you don’t want two miles of line between your ship and your anchor; that means your ship could drift anywhere within a circle four miles in diameter. You’d like your anchor line to be as short as possible without uprooting your anchor. How to do that? Put a length of deliberately-heavy chain on the anchor so that the portion of it nearest the anchor will lay on the bottom, even if your total amount of line/chain paid out from the ship is relatively short (compared to depth of water).
Again, can you explain why smaller boats use a length of chain AND a length of cable/rope, instead of running cable/rope all the way from the boat to the anchor?
According to the previously cited Wikipedia entry on anchors, it’s called a “rode” not a rope. And surely there’s a lot of rope on ships (some more than others).
Machine Elf: see my recent post responding to Princhester. I agree about the catenary curve but only insofar as the boat-anchor connection (the “rode” as it’s apparently called) is not buoyant. A foating “rode” would make it hard (but not necessarily impossible) to get the anchor to dig in. So in that sense a heavier-than-water connection is important. But that’s all. See my comparison to the tugboat and tug-line.
Also, I never questioned why small vessels like fishing boats needed anchors, just the super-huge ones like giant container ships, mega-size oil tankers, and aircraft carriers. I couldn’t think of any reason they’d ever need to use them, but my question has been answered and now I know the reasons.
Yes I agree with this 100%. I think you just need a chain/rope that weighs more than the water it displaces so it sinks. A buoyant anchor-ship connection would pose problems, it would form an upside-down catenary curve when being pulled and that wouldn’t pull the anchor practically parallel to the seafloor, it would pull it at an angle regardless of the length.
At the start of this thread you knew so little about large ships you thought they wouldn’t use their anchors and that the anchors on carriers were for decoration. Now you are telling people who have worked in the industry for decades that they are wrong about how an anchor and chain lies in operation.
You know how tugs pull on ships even with a deep catenary in the towline? And you know how most of the first half of the length of a heavy towline slants down, even when under heavy strain? Now consider that an anchor chain is orders of magnitude heavier than a heavy towline. Now think what happens when the theoretical catenary that would be formed in the anchor chain intersects the seabed.
There are few if any “ropes”. There are sheets and guys (the ropes that control the sails) halyards (the rope that hoists a sail) braces, shrouds, stays, lines, hawsers, up-hauls, down hauls, out-hauls, and more. But although they are often made of rope, they are not called ropes. On any sailing craft (which is where all the terminology began, power vessels being a rather modern innovation) everything has a very specific name. On any sailing vessel of serious size getting the bit of rope wrong could be reasonably expected to kill or seriously injure another sailor. There is never just “a rope” for any purpose. Its a bit like the old saw of Eskimo’s having a zillion words for snow.
You seem to be missing the fact that the weight of the chain lying on the bottom acts as a considerable shock absorber. Before motions of the ship can exert significant force on the anchor, the chain must be under tension, and it takes very significant horizontal force to lift & tension a heavy chain - much more than the weight of the chain.
So the ship can be surging strongly in response to strong wind and waves, but the chain means the forces at the anchor will be moderate. A lightweight rode will transmit higher forces to the anchor.
Well, in addition to the above-mentioned footropes, there are boltropes and manropes.
One could probably plead that even these are not “ropes” but proper names that include the word “rope” in their spelling. Being a bit over the top here, but it does illustrate the core point - everything has a proper and unambiguous name. The critical running and standing rigging components have very specific names.
Exactly.
When I was a kid we went sea fishing a lot, usually in water between 100 and 300 feet. Our anchors held much better when the chain was longer rather than shorter. We basically had as much chain was we could stand to lift.
I’m not asking you to explain why smaller vessels need anchors. I’m asking you to explain why you think they bother to use a length of pain-in-the-ass heavy chain at the anchor, instead of running much lighter cable/rope all the way from the boat to the anchor.
Anchors are pretty much “standard equipment” on ships and most boats.
Even if a Carrier’s operational schedule is such that it doesn’t get to use it much (but I can see from other respondants that I would be wrong), I would no more do away with carrier anchors than I would with the spare tire (with jack and tire iron), warning triangles, and first aid kit in the trunk of my car.
You just do not go to sea without certain things: food and water, lifeboats, radio, anchor(s), etc.
Just. NOT. Done.
I’m not a sailor, I haven’t commanded anything bigger than a canoe, and even I know that.
The way you keep circling back to “how much it costs,” and keep going on-and-on about cost of all the necessary equipment to outfit a carrier with an anchor system, gives me to wonder if perhaps you have something else on your mind?
Did the meany-weany Bosun make you scrape some harbor sludge off of an anchor chain once?
What you’d want in a storm at sea is not an anchor attaching you to the seabed (except in an extreme emergency to prevent running aground), but a so-called “sea anchor”:
a) I thought it was a rope until it was performing a function and then it became a line/sheet/whatever.
b) What do you suppose the breaking strength is of one of those carrier anchor chains?
c) How much drag or tension on the anchor line would a carrier or other big ship sitting bow into a 100 kt wind create?
He doesn’t linger on it, he addresses directly in the very next sentence.
This is wrong. Surely you can imagine a situation where the force required to drag the chain is less than the force required to lift the chain off the bottom.
If you toss a chain on the ground and drag it, does the entire chain lift off the ground and only drag the tip? Of course not.
Imagine this. A ship is anchored in still water. The chain drops straight down from the ship to the bottom, with a length of chain on the bottom. If you apply a force to the ship, it moves slightly and the chain becomes less vertical. In order for the chain to be less vertical, it (the unsupported section) needs to be longer. It gets longer by lifting another link off the bottom. Apply more force and another link lifts off the bottom. In this way, the force being applied to the ship is being used to lift chain off the bottom. The chain acts as a shock absorber, rather the the rigid, unforgiving hold you would get if the chain were merely a connection between the ship and the anchor.
Not all do, in fact the few boats I’ve been on either had 100% chain or 100% rope. But if there are some small/midsize boats that have an anchor with a chain and rope connection (the chain being closer to the anchor, obviously) I can see how it would be to lower the catenary curve a bit at that end, but I’d think a more likely reason would be to allow for a firmer attachment to the anchor. Like the thick lead on the end of (some) fishing line that attaches to the lure.