#1

Dear Sirs,

I’m a Captain of Merchant Navy, and I’m doing a MsC about Emergency Anchoring.
In order to give a better contribute to our area, I’d like to present some calculations, deploying how many knots can a ship loose after has dropped her anchor (per metres or per seconds) in an emergency.
I suppose it will depends on her speed (maximum 5 knots, according Capt. Jeff Pierce, on his Statement Regarding Cook Inlet Risk Assesment Seven) and displacement, but I can’t find out any formula concerned about.

Best regards,

Antonio Canas

#2

Too many variables, the most significant being the type of ground, but also type of anchor. I would say that if you are in a situation where the only thing that might stop you hitting something is emergency anchoring, no formula is going to be relevant,just do it.

#3

You’d have to have someone at the bow ready to release it anyway.

A good example I could think of would be you’re approaching an anchorage and you loose power and/or steering for some reason. In that situation though you have men at the bow ready to do exactly that.

#4

Sure, no doubt at all! But my main question remains: in theory, is there any formula that could give us how many knots a ship can loose, after has dropping her anchor in an emergency?
In so many years of navigation, probably someone had studied that; the question is: who? What’s the name of the book where it’s stated? Where can I get an evidence of that (book’s name, author, chapter, page, ISBN)?

#5

[QUOTE=Antonio Canas;165834]Sure, no doubt at all! But my main question remains: in theory, is there any formula that could give us how many knots a ship can loose, after has dropping her anchor in an emergency?
In so many years of navigation, probably someone had studied that; the question is: who? What’s the name of the book where it’s stated? Where can I get an evidence of that (book’s name, author, chapter, page, ISBN)?[/QUOTE]

Don’t know where to find a formula. However I would think if you can find the number of tons force a dragging anchor can develop under various conditions (type and weight of anchor, bottom characteristics, amout of scope etc) and you know how fast a ship decelerates under various backing bells expresed in tons it could be estimated.

In my limited experience the best use of a dragging anchor is turning the ship rather then trying to stop it if that’s a practical option. A ship with an anchor down will turn in a surprisingly tight space.

#6

Here are two options:
If the anchor digs in the ship will lose 100 percent of its forward motion.
If only a couple of fathoms of cable are let out in deep water its not going to make any difference to ship speed.
That is all you need to know. If you are actually a Captain you could have worked this out for yourself.
Get a rowing boat and try it - you will see what I mean.

#7

My questions were asked perfectly; the evidence of that is I have two previous answers, gave by professionals, who at least understand what an a MsC work can implies. And by that, I’m meaning, my sources (books and internet sites) must have references - books with authors, titles and ISBN, sites with links -, in order that can be checked.
Your suggestion of a rowing boat can’t be applied, of course (have I done this before and published it? No! Even supposed I had did it, could it be applied into a normal ship No!), but if you are a Captain, you were supposed to know that.
But perhaps you don’t what Msc means - it means Master of Science; I suggest you check about it, just to know how hard it is.

#8

Antonio, it has been a while with your quest for emergency anchoring. Are you still working on it? Is there amything enlighting?

#9

Hi Bruce,

Yes, I’m still working on it, thanks.

Best regards,

António Canas

#10

Good…
What did you found about emergency anchoring? Have you come up with certain

#11

The Hong Kong Authorities will know all about it…

#12

Well, one good thing I found out was the maximum speed of 5 knots for
letting go the anchor; more than that and the anchor will drag!

#13

Weel, in my opinion, there is a lot of factor to consider to do it. like bottom, anchor`s model, speed, deep, space to maneuvering in basin etc..... Otherwise to stop a ship the more important factor is how do it and not how many phantom let go. if you have space, the best technique is let go just 1,5 x depp of cable just to drag while move rudder hard to port or starboard. You ship lost 50% of speed every 90 grades of turn and change your bow to back. If you let go anchor which more than 4 kt (in some kinds of ship) certainly you will lost your anchor which no one affect in stop the ship. Like rule of thumbs to use anchor in emergency case I`m suggest this procedure beloww

#14

Your anchor is likely going to drag with any headway. If to little chain is used your dredging it, if to much is out you run the risk of parting the chain or damaging the brake. In an emergency anchoring situation I would try to get five or six shots in the water then tighten up the brake then I would engage the windlass. Five/Six in the water (depending on depth) should stop you in good order with out parting the chain and if more needs to paid out you can do it on the windlass in an orderly fashion with out worries that you chain will run. If needed then you can drop the second one. My own experience so YMMV depending on the situation.

#15

Hi, Fernando,
Can you elaborate more on how those 8, 6 and 2 knots speed limits on varies size of ship worked out?

#16

Antonio,
Why the 5 knots became so critical? Is it generic? What are the contributing factors? I am interested.

#17

This paper is about VLCC but it is of interest. It includes force calculations.

The Nautical Institute

ANCHORING LARGE VESSELS
A new approach

#18

Those guys LOVE having tons of letters after their names.

#19

Perhaps the ratio lenght/breadth would be the maximum at that speed,
concerning the ship’s inertia. But I’m still working on it.
As far as what I could found out, I would say it is generic, yes.

#20

There are no generics - the range of anchor types, vessel types, seabed characteristics and depths all make a difference.

The CSCL Indian Ocean lost an anchor prior to berthing,

http://www.oceanships.de/?tag=cscl

There are papers ot suggesting the anchor arrangement for ULCCs are inadequate due to windage and mass.

The P & I Clubs all have papers:

http://www.nauticalplatform.org/docs/files/Standard%20Club%20Anchoring%20procedures.pdf