Nope. Wouldn’t make a difference. Think of the huge thick cables that hold up suspension bridges. Same idea, except those cables weigh far more than 50 pounds every few feet and can be up to 3’ thick. Go look at the Golden Gate Bridge, for example, particularly the extremely long portion of the cable than anchors into the ground on either side of the bridge.
For what should be the absolute last word on this try here, for a very solid mathematical treatment. (Follow the tiny arrow in the lower right hand corner.) For a one page summary try this. (although the latter conclusions are mostly directed at smaller boats.)
Spoilsport.
Oh my lord.
Aye, but that Black Dog was using special lead zeppelin anchors.
…
I don’t understand kaltkalt’s objections. Yes, at some measure of force you can pick up a length of cable/chain and tie it to the top of the Golden Gate. But the job of the anchor-putter-downer is to put out enough chain to be stronger than that force. Weighing the anchor when your right on top means pulling straight up. Doing it from a distance means you need to pick up all that heavy chain before pulling on the anchor itself. Put down more heavy chain and you need more force than wind/water/imagination can exert on the chain.
I am terrified of open water (kraken, you know), so I don’t know much about big boats and whatnot. But after a couple posts this seems pretty straightforward. Am I missing something about the question?
A couple of questions that I did not see either asked or answered.
The anchor on a supercarrier gets hauled in by a motor of some sort, from one of the replies. Is it geared in such a way that if needed a ships party could haul the anchor in by hand. Old school sort of way turning a capstan ?
And the second, is the anchor chain constructed in such a way that it could be simply let go and dropped. As in for what ever the reason, the captain orders the ship out to deep sea yesterday, if not sooner.
Declan
On a large freighter, there is no such provision for a manually operated capstan. (Of course, with crews ranging from 22 to 35 men, no crew would have the manpower to haul up the chain, regardless.)
I suspect that the same is true of large Navy ships, these days. Even with a crew numbering into the thousands, it would take the entire crew to weigh the anchors on those ships–and even having a capstan that extended through several successive decks, (as they did in old ships of the line), there would not be enough room to put all the men to the handle the bars. One could probably set up some sort of complex gearing that would permit multiple capstans to be employed, but I suspect that the complexity, (and weight), of such a device would be prohibitive. Ships stopped carrying sails after steam became reliable for much the same reasons.
On the ships I worked, dropping the hook was simply a matter of putting the anchor’s winch motor into neutral. (Of course, one needs to know that the water depth is rather less than the length of the anchor chain when doing this.) I would guess that the Navy anchors are dropped in the same way. One can pay out an anchor using the winch motor if one does not want the anchor to run out too fast, but I don’t know how often either method is used, relative to the other. When we would simply drop the hook, it was in very shallow water where the anchor and chain would not build up enough speed in the drop to become dangerous, using the winch for deeper water. One would really not wish to be in the foc’s’le with an anchor chain snapping about out of control.
Here is a short video clip of a carrier paying out the anchor.
I think your geometry may be in error. The actual “shape” of the anchor chain is a long curve from the anchor to the ship called a catenary. In its most simple form it is the shallow curve you see on telephone wires between poles, caused by the weight of the cable/wire itself versus the tension applied at the ends. If you’ve ever seen a loaded barge pulled by a tug, you’ll observe that the tow cable leaves the barge at a fairly steep angle, disappears into the water and only emerges at the tug’s stern. Even though the cable has a large “sag” in it, it still transmits the pulling force. Same with the long anchor chain- the long scope allows the ship to move considerably by pulling/lifting some of the sag out of the cable without a lot of force applied directly to the anchor. Them physics be some cool stuff.
Wait, so what’s the shape of a rope between two fixed points, again?
Does this have anything to do with tugboats?
Instead of dropped, I probably should have said jetisoned, I figured deploying the anchor would have been a mixture of gravity and braking mechanism to slow it down.
Declan
That was probably me. Just a bit of old-fashioned bragging about a trip I took a few years ago.
Here’s the windlass on my ship (the large mechanism with the red spools on either end; the capstan is in the foreground). That black part in the center has a bit on top that rocks back and forth. There are handles that go in each side and then it works like the old hand-operated rail carts in old westerns.
We had six people on each handle. I don’t remember how much the anchor and chain weighed, but we had about 150 feet of chain out in 25 feet of water. Each back-and-forth of the handles brought in about 6 or 8 inches of chain.
I would not want to perform a similar job on a supertanker.
(Always preview posts. I almost included a link to a picture of my shoes.)
That’s because the ship can’t be directly OVER the anchor…that’s what you do when you want to leave, you position the ship directly over the anchor by slowly reeling it in on the capstan until it’s “up-and-down”, or the rope is vertical. In this position, the anchor can be relatively easily pulled from the seafloor. No, in order for the anchor to hold, the ship needs to be some distance away from the anchor, pulling on the chain to make the anchor dig into the seafloor…it has to be pulling SIDEWAYS, in the general direction the flukes have dug in, to have any holding force. It stands to reason that a length of chain equal to the depth of the water will leave you exactly “up-and-down” (and you won’t be able to set the anchor in the first place that way). A ratio of 5 times the depth of the water gives you a good 5:1 ratio slope angle, allowing you to set the anchor, the flukes to hold, yet limiting the amount of swing you are subject too: when the wind or tide changes, the ship travels in an arc with the anchor as the pivot point. You COULD anchor with a chain ten times the depth, but you’d be moving about in an arc twice as big then, taking up much more sea room and risking running into any object that strays into your anchorage. That’s the reason for the 5:1 ratio; it has little if anything to do with the chain.
As for the weight of the chain being what holds the ship in place, I think that’s generally bogus. I’m not an expert; at best, I’d say “the weight is usually sufficient to hold the ship stationary in calm waters with little tide”, but the anchor and flukes are what develop the real anchor point. If there is any heavy wind or tides, a real anchor is required; hell anchors themselves are prone to dragging in heavy storms, even in the modern day. If an anchor AND the weight of the chain can’t hold a ship against a gale, then I certainly wouldn’t want to rely on the chain alone. That’s why it’s generally much safer for a vessel to be far out at sea in heavy weather, contrary to the instincts of the typical landsman. Safest place to be is where there is nothing to run (or be blown) into!
As has been pointed out, they wouldn’t bother with the modern anchor design if the chain was heavy enough. And of course, the weight of the chain depends entirely on how deep the water is. If you’re moored in shallow water and only need to pay out 1/20th of your chain, it’s only going to weigh 1/20th of what it would in maximum depth water. And, it would rely on having enough chain on the seabed to actually provide enough drag to hold the boat, so the depth you could moor at would be less than the length of the chain…your maximum mooring depth would require that depth of chain, PLUS enough additional to lie on the seafloor, just to act as an anchor. That’s another good reason to just use an anchor instead.
As for the original question, as has been made clear, there are many good reasons to have an anchor on a carrier or tanker, but I’d like to add that it would be the height of foolishness to NOT give a vessel an anchor “because it probably won’t need it”. A supercarrier or tanker (hell any vessel) is a huge investment. Anything can and does happen at sea. What happens when you’re trying to make the Dardanelles, and suddenly you loose all propulsion, and find yourself drifting towards the shore, unable to steer or stop, because he designers figured you’d never probably need to anchor anywhere? To hell with that, you should ALWAYS have a good way of holding a vessel, even if you don’t expect to need it much. Most yachts never sail anywhere except in and out of the marina, but they still carry an anchor. A supercarrier is a warship, and has to be ready for any eventuality. You never know what might happen, if there is a war. Most of the fleet could be taken out with nuclear anti-ship missiles, all major ports gone, and then they find themselves without an anchor, because “they didn’t figure a carrier would need one”, so they can’t even moor at some secluded island to replenish or do repairs? No. Always best to have an anchor; it’s a cheap insurance for an expensive shit (even aside from the reasons they DO use the anchor).
There are anchors on both sides of the bow because sometimes, you want to drop both of them. It’s like this… you drop one anchor (let’s say the starboard one) as you’re heading into the current, pay out some chain, and cut engines or reverse engines to pull on the anchor enough to set the flukes into the bottom. Then you pull up moving to the port. Well, the goal is, if you can imagine the current as a line, you want a line between the two anchors set in the seabed to be perpendicular to the current. So you drop the port anchor, back off to set that, then take in enough chain as necessary to keep bow pointed into the current with enough slack on both sides to allow for tides.
That’s a nitpick…
On anchoring large ships… My brother served on supertankers for some years. Part of that was hauling iron ore from Australia to Germany. They would sometimes anchor in the Bay of Gibraltar, some thee miles offshore, waiting for the price of ore to go up. They stayed there because it was international waters so no mooring fees to pay and the bay is shallow enough and has a good enough floor to make it viable.
Looks like white/black, and then yellow, then red.
https://www.youtube.com/watch?v=Lg3wwhhJ1aM (2:45 for the yellow, and about 5:15 for the red)
It was always essential to secure the shipboard end of an anchor cable or chain to stop it from being lost. This point is known as the bitter end.
this leads naturally to the meaning of soldiering on right to the end of some task, even though *bitter *in this sense has no connection with a sour taste.
There are 4 deep basins in the Med, they are so deep they were thought to be literally the remains of an ocean, but now known not to represent anything so old, there’s some trenchs like the start of a new ocean, thats all.
Well anyway, there’s heaps of anchorage depth sea …
The east of Spain has heaps, way out to around the Ballaeric Islands (Majorca).
The east of Tunisia has two gulfs named, but they merge into a large area … this extends a long way out, 1/3 of the way to Italy…
Most of the Adriatic Sea is shallow enough to anchor in, all the way north from Montenegro up to Trieste.
There’s a large strip from Alexandria to Israel, and theres the sound (shallows between island and main land) formed by Cyprus … There’s numerous thin strips which are liable to be in the local nations control.
The heavy chain acts a shock absorber too…
The force to be avoided is due to the equation, force = mass * acceleration.
Because the chain moves, but resists movements and acts slowly to restore the regular position ,it reduces acceleration…
Imagine a big wave coming along and raising the water level around the boat…Well, F=ma , the boat is being pushed up two meters in a second, thats quite some force !. So what if the boat is pushed up at speed, and the chain pulls tight, and all the weight of the anchor suddenly applies to the ship ? Well its not just the weight of the anchor, its the acceleration force too … F=ma …if the anchor is suddenly accelerated up to the speed the boat is rising at, then its going to be causing quite some tension on that chain… The ship is either damaged or the anchor pulls the ship down into the water…
Also, if the force on the anchor is increased by the chain being pulled up by the yacht all at once, the anchor itself may pop up out of the sea bed, and thus cease to act as an anchor…
The weight of the chain used on the anchor ,as a minimum, is related to both the windage of the vessel (given the expected winds… this is the force the wind is going to put on the boat … pushing it off anchor… ) and the weight of the boat (to ensure the weight of chain can absorb the tugging of the waves )
However the guide “5 times as much line as depth” is just to ensure the angle is low… that guide assumed the ship only used chain… In general, the sum of the chain + rope is 5 times depth… The length of chain required really depends on the weight of each link…, since its the movement of the weight which gives the shock absorber effect… Even just 4 links or weights with half the weight of the anchor each would be effective as a shock absorber… But chain links are generally far less than the weight of the anchor, so you use many links…