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.
Does anyone could help me, about that formula, please?
Best regards,
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.
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.
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=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.
In order to (possibly) get the right answers to your questions you have to ask your questions correctly.
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.
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.
Weel, in my opinion, there is a lot of factor to consider to do it. like bottom, anchors 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 Im suggest this procedure beloww
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.
While overtaking the pontoon, the cargo vessel’s main engine suddenly failed. Since the electrical systems on board the vessel were linked to the main engine via the shaft generator, the electricity failed as well and for a short period of time the vessel suffered a blackout. During the blackout, the rudder unexpectedly turned to port, causing the vessel to deviate sharply from its course and toward the tug and tow. In order to prevent a collision, the captain, on VHF radio, ordered the anchor let go. As there were crew on deck at the time, the anchor was let go very quickly after the order – within 15 seconds. At the time the anchor was let go the cargo vessel still had a speed over ground (SOG) of 7.5 knots.
Despite the attempts by the AB to secure the winch brake, the anchor chain continued to run out. The last length of chain had broken loose from the chain locker, and the AB was hit and fatally injured by the bitter end.
The cargo vessel collided with the pontoon almost simultaneously with the breaking free of the anchor chain. Both vessels sustained limited damage as a result of the collision.
Lessons learned
The use of the anchor to slow down the ship in an emergency:
IACS stipulates that an anchor must be constructed in such a way that it is suitable to anchor a ship temporarily in ‘moderate’ ambient conditions. The anchor gear is not designed to stop a ship. Anchoring at high speed is an extremely risky operation that may result in fatal injuries to crew members and serious damage to the ship. Such a manoeuvre should only be considered in an extreme emergency.
