Car Carrier overturns in Brunswick River, Ga.

[AA3JY]

Ahhh Ohhh..

https://thebrunswicknews.com/news/local_news/freighter-overturns-in-st-simons-sound/article_552ce395-3c75-5e45-94b4-8badce1fda9c.html

[tkeithlu]

Do you get the feeling that maybe someone unloaded the cars on the lower decks before the cars on the upper decks?

[Dockhead]

This looks like the Hoegh Osaka incident which took place a few years ago in the Solent. Also a car carrier. That incident was caused by sloppy maintenance and sloppy work of the crew -- no stability calculations were done although a dangerous load situation existed (low bunkers and full upper car deck); inoperative ballast tank level gauges; no additional ballast loaded; bla bla bla -- usual litany of carelessness.



See: https://assets.publishing.service.go...port6_2016.pdf

[Dockhead]

Originally Posted by tkeithlu

Do you get the feeling that maybe someone unloaded the cars on the lower decks before the cars on the upper decks?

Unloading the lower car decks with the upper decks full will INCREASE, not reduce stability, so long as the lower decks are above the ship's VCG, as they normally would be.

[Snore]

Originally Posted by Dockhead

Unloading the lower car decks with the upper decks full will INCREASE, not reduce stability, so long as the lower decks are above the ship's VCG, as they normally would be.

Having a hard time with that physics. The further mass is from the VCG, the more of an impact it will have. Even if lower cars were below VCG, unloading them would place more mass above the VCG.

Am I missing something? Curious where next port was- assuming close by.

NTSB report should be interesting.

[a64pilot]

It’s how some define stability, maybe.
I define it the way it’s done in aviation, the force required to upset from a stabilized condition.
For example, remove the mast on a mono sailboat and stability the way I define it will increase, however the ride quality will suffer and the thing will be very uncomfortable in any amount of seas, some say it makes it unstable.

Cruise ships are intentionally top heavy for instance, to slow down the roll rate and make them more comfortable. Some I guess would define them as being more stable, but they are more likely to turtle than a vessel that has a lower CG.

What is VCG? Vertical?

[foggysail]

Originally Posted by a64pilot

It’s how some define stability, maybe.
I define it the way it’s done in aviation, the force required to upset from a stabilized condition.
For example, remove the mast on a mono sailboat and stability the way I define it will increase, however the ride quality will suffer and the thing will be very uncomfortable in any amount of seas, some say it makes it unstable.

Cruise ships are intentionally top heavy for instance, to slow down the roll rate and make them more comfortable. Some I guess would define them as being more stable, but they are more likely to turtle than a vessel that has a lower CG.

What is VCG? Vertical?

Are you sure cruise ships are top heavy? That is not what I read.

https://www.beyondships2.com/faq-top...ise-ships.html

[Dockhead]

It's very simple, actually.

If you remove weight from the vessel, it will lower the VCG and improve stability, if the weight you remove is above the VCG of the vessel. Or make it worse, and raise it, if the weight you remove is below the VCG of the vessel. It doesn't matter what's on the upper decks.

Got it now?

Originally Posted by Snore

Having a hard time with that physics. The further mass is from the VCG, the more of an impact it will have. Even if lower cars were below VCG, unloading them would place more mass above the VCG.

Am I missing something? Curious where next port was- assuming close by.

NTSB report should be interesting.

[john61ct]

Phew, read that as "aircraft carrier" [emoji2962]

[a64pilot]

Originally Posted by foggysail

Are you sure cruise ships are top heavy? That is not what I read.



https://www.beyondships2.com/faq-top...ise-ships.html

Yes I am sure.
Read the first paragraph and then the one on high GM and rolling period
https://en.m.wikipedia.org/wiki/Metacentric_height

I guess to be more accurate I should have said that by design, cruise ships are more top heavy than tanker or cargo vessels, this slows the rolling moment, which of course slows the rate the ship recovers from an upset and is more comfortable for the passengers.

A very stable power boat is very uncomfortable in a rolling sea state because it’s so stable that it recovers from an upset very quickly.
To a great extent a mono sail boat is more comfortable in a rolling sea state because of the mass of the mast being so high from the roll center of the boat slows down the rolling period, and the boat recovers from an upset slower than it would if it didn’t have the mast installed.

[foggysail]

Originally Posted by a64pilot

Yes I am sure.
Read the first paragraph and then the one on high GM and rolling period
https://en.m.wikipedia.org/wiki/Metacentric_height

Stick to cruise ships being top heavy. Their center of gravity is at the bottom of the ships

https://www.beyondships2.com/faq-top...ise-ships.html

[Q Xopa]

Originally Posted by Dockhead

It's very simple, actually.

If you remove weight from the vessel, it will lower the VCG and improve stability, if the weight you remove is above the VCG of the vessel. Or make it worse, and raise it, if the weight you remove is below the VCG of the vessel. It doesn't matter what's on the upper decks.

Got it now?

Im not sure what you are saying either.

My understanding of Weight and Balance is-
Removing weight from below the CoG (centre of gravity) and/ or adding it above the CoG will Raise the CoG. The further from the CoG, ie the 'Arm', the greater this effect. Its a simple Force (weight) x Distance calculation. A raised CoG is less stable by my understanding.

In sailboat terms its the equivalent of less low weight ie ballast in the keel and more weight aloft. This sounds less stable to me.

But I am obviously misunderstanding some terminology or something here.
If you could try and re explain please.

[a64pilot]

You guys need to dig a little deeper than published articles to soothe the public on why cruise ships don’t topple over

[foggysail]

Originally Posted by a64pilot

You guys need to dig a little deeper than published articles to soothe the public on why cruise ships don’t topple over

Fair comment

[Q Xopa]

Originally Posted by a64pilot

Yes I am sure.
Read the first paragraph and then the one on high GM and rolling period
https://en.m.wikipedia.org/wiki/Metacentric_height

I guess to be more accurate I should have said that by design, cruise ships are more top heavy than tanker or cargo vessels, this slows the rolling moment, which of course slows the rate the ship recovers from an upset and is more comfortable for the passengers.

A very stable power boat is very uncomfortable in a rolling sea state because it’s so stable that it recovers from an upset very quickly.
To a great extent a mono sail boat is more comfortable in a rolling sea state because of the mass of the mast being so high from the roll center of the boat slows down the rolling period, and the boat recovers from an upset slower than it would if it didn’t have the mast installed.

This sounds like a 'terminology' discussion. I would term what I think you are talking about as 'inertia'. As in the skater spinning with arms out slowly, but arms in spins faster.