Worst Case Scenario: Hitting A Sunken Container - What To Do!??

[transmitterdan]

Originally Posted by hellosailor

"If it is just beneath the surface, it will keep descending until it has found its final resting place."
Oliver, you are obviously not a SCUBA diver. Divers are trained to trim to a neutral buoyancy and "hover" at any depth they please in the water. Not all do this well, but the training is standard practice and you can ask at any dive shop. "Hovering" is indeed simple, and the same physical conditions and principles apply to a cargo cube as they do to a diver. The only difference is that the diver is actively adjusting his buoyancy, while the cargo cube is "set" randomly.

Divers have to add air to stop sinking. There is nothing like that in a container. Once a container gets awash it will keep going down barring some peculiar automatic inflating device inside. Even then it would rise to the surface. No way it will hover in the water column like a diver can.

[roverhi]

A container or anything floating in the ocean can reach a level of equilibrium where they will float indefinitely. Might be with signficant freeboard or just barely awash. Eventually they will sink if it's just an air pocket keeping them afloat when corrosion or motion releases the air. If it's floating because the cargo is buoyant enough to keep the container afloat, even barely, it could float around for a very very very long time. Refrigerated containers are the ones most likely to float as they are lined with buoyant insulation, sealed to keep the cold in and the contents will be a gas generator as they rot. Once the containers buoyancy allows it to slip below the surface, it will probably continue on to the bottom. Too many things that would/could happen that would destroy perfect neutral buoyancy

In any case, if a container floats, it will probably just barely float with only a few inches above the surface. Fortunately, very very very few of the containers will float after being swept off a ship. Yes there probably are some containers floating around out there but there is probably just as many or more logs and other lesser sized detritus out than containers that happen to float.

[noelex 77]

I would expect the distribution of container buoyancy to roughly follow a normal distribution pattern.
It follows that if a high percentage of containers sink most of those that do float will do so with little freeboard.

[Oliver L.]

Two comments to references on my post: I have two tanks of 300 l each for fresh water. Therefore I am not compromising safety if I drain the side that is affected. That's what I like about catamarans.

Second, I just finished my free water diving course, and I stand absolutely by my comment. A scuba diver "floats"in an unstable equilibrium - you move up an inch, you will start rising and won't stop until you hit the surface, you move down one, you will keep going down. A container does not have lungs to do the fine trimming. It's physics, guys - that's what is so nice about it...

Oliver

[Panaseaya]

Op asked "what would you do? "
Let us now reflect on our basic seamanship training :
"When in danger, when in doubt,
Run in circles, screen and shout"

[Group9]

It's not just containers. I used to run on the beach every morning and one of my shocking discoveries was a huge rusted cylindrical float that had come ashore one night, and had obviously been floating in my area of boating operations for some time.

The main thing I do is slow down at night. I had a friend on an Aegis Cruiser that was doing high speed night runs (this was in the 80's during the Cold War and their top speed was classified so they would only do it at night when Russian spy satellites were less able to track them) during final construction at Ingalls boatbuilding yard, that hit an unknown object out in the Gulf of Mexico and barely made it back to dry dock because it was taking on so much water.

I know the Aegis cruisers carry better radar and sonar, and have a lot thicker hull, than I do.

[noelex 77]

Originally Posted by Group9

The main thing I do is slow down at night.

With the typical look out maintained by a cruising sailboat offshore I think the chances of seeing a sleeping whale, container, or other large debris during the day is not very high. Unlike military, or large commercial ships the lookout on a cruising sailboat offshore is not typically continuous.

[goboatingnow]

slowing down at night !, huh, I mean going from 7 kn to 5 kn isn't going to make any difference anyway, given the momentum

dave

[Ocean Girl]

Originally Posted by MarkJ

I think you should stay at home. Really, I dont think it will be fun for you if you worry about all this stuff.

Uh, I don't think you read his post, or are you just being a curmudgeon? He has been there don't that, and gave very good advice. I realize you sailed around the world and didn't see one container, my parents also didn't see a container on their RTW trip, but they did see one crossing the gulf. Enough miles under your belt, you just may see one too. hopefully not.

Being prepared for too water inside the boat is good idea.
Peace out

[Capt Rottnest]

Originally Posted by goboatingnow

slowing down at night !, huh, I mean going from 7 kn to 5 kn isn't going to make any difference anyway, given the momentum

dave

Momentum? Ha!
I think its energy that counts when there's damage and 7kn has double that of 5kn.

[MarkJ]

Originally Posted by Ocean Girl

Uh, I don't think you read his post, or are you just being a curmudgeon? He has been there don't that, and gave very good advice.

OK I re-read his post and must have misunderstood his point. Appologies to Mr B.



Yes its good to know what to do and to have a secure boat before a passage.
I met a guy (I better not say last night incase he reads this) and his anchor locker drains directly into his bilge. So if a wave comes over the deck some water from outside ends up inside in his bilge.

Thats bad in my thoughts, but worse if he does his something, a tree is a valid example, and the bow is stove in he is immediately taking on water! As much as everyone seems to hate Beneteaus at least they have a crash bulkhead sealed off from the rest of the boat. I can splinter the bow back 5 feet and still not take on water.


@ Momentum difference 7 knots to 5 knots....
Well the impact force on a 5 second impact of a 10 tonne boat at 7 knots is 14400 Newtons.
For the same boat at 5 knots = 10400 Newtons

Basically that means that the 10 tonne boat at 5 knots feels like a 14 tonne at 7 knots in the same collision.

So 2 knots does make a lot of difference.

But if you were doing a 6,500nms passage across the Pacific you would do an extra 400 hours sailing at 5 kts compared to 7 knots so you increase your chance to die in some other way.

All in all it means if someone is scared of every little thing sailing then you are better off at home in a cotton wool cocoon. Which is the statement I made in the first place!


Mark

[captain58sailin]

Certainly doesn't hurt to be prepared. I wouldn't spend much time worrying about it. We have big tides and in the spring of course they are sometimes much bigger and a lot of debris gets in the water. I had one summer where I took out an average of 1.5 props per month on a twin screw boat. The real puzzler is, I never saw the objects, I hit, and they never hit the hull, just the propellers. Trust me, I was paying attention. We get dead heads here that do float just barely submerged.

[Mr B]

Its quite easy to misread things, Its the written word, With out a face to look at, your words can mean any thing, Misconstrued, Opposites to what is being said,

I do have a boat that will sink if it gets a hole in it, Very fast, Proven Fact,

I am not worried about it in the least now, I have countered the sinking problem with the air bags,
I am resourcefull enough to counter any problems that I do encounter,

I am just lucky, That in my case the boat sank on the beach, Not at sea, It opened my eyes to just how vunerable my boat actually is,

At sea, Container, log, tree, Etc, If hit hard enough and poked a hole in my boat, I would have lost my boat entirely,

You will find that going slow, like on a sail boat, you will probably slide over the object in the water,

Unless you hit a protruding sharp edge, Which can slice you open,

But reading thru these posts, hitting a container is not your worry, a submerged uncharted reef is more the worry, Or run down by a Container ship, With thousands of containers on board,

But a good depth sounder covers that, And good eyeballs,

Being prepared for the worst, Makes your sailing easy, And I do sail in the three worst oceans on the Planet,
Southern ocean, Tasman and Bass Straight, and Port Phillip Bay as well,

Being prepared, is not being scared, It is to save my neck when the going gets rough,

If I was scared of every little thing, I would not ski the Black runs, I would not ride one of the fastest motor bikes of all time, I would not sail, or water ski,

I have been called a Tough Old Bastard, You want some thing done thats difficult, Call Brian, He will fix it,

Thats me, But I will wade in amongst the blood and gore to save you,

Me. I can save myself, With out any problems, Or help, I stand solidly on my own two feet, and dont expect it to change any time soon,

Cheers,
Brian,

[Mr B]

Originally Posted by Oliver L.

Two comments to references on my post: I have two tanks of 300 l each for fresh water. Therefore I am not compromising safety if I drain the side that is affected. That's what I like about catamarans.

Oliver

Thats a good idea on pumping the fresh water tanks, for bouyancy, Make sure your tanks are screwed down first,
I did that and the tanks floated up, Mine were not screwed down,

[Group9]

Originally Posted by noelex 77

With the typical look out maintained by a cruising sailboat offshore I think the chances of seeing a sleeping whale, container, or other large debris during the day is not very high. Unlike military, or large commercial ships the lookout on a cruising sailboat offshore is not typically continuous.

I don't slow down so I can see it. I slow down so the impact is not so great when I hit something I can't see.