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Old 02-09-2019, 11:59   #1
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Longtitudinal Centre of Gravity for Ship Cargo

Hoping someone here can advise me on the correct way for calculating the following and is there enough data given to work this out.?

This is from a textbook that I have from a Civil Engineering course I did some years ago.

A ship displaces 10,000 metric tons and area of its plane of flotation is 1,480 m^2. The centre of mass is 49 m and centre of area of the plane of flotation is 55 m from the stern. The metacentric height for pitching motion about transverse principal axis is 91.5 m.
The ship is loaded in sea water with 300 metric tons of extra cargo.

Find minimum allowable distance of mass centre of this extra load from stern if, when ship passes from sea water into a freshwater canal, the stern draft must not increase by more than 0.3 m?

Assume metacentric height and area of plane of flotation are not altered by change in draft and that density of sea water is 1025 kg/m^3 and density of fresh water is 1,ooo kg/m^3.

Answer from textbook is given as 46.2m.
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Old 04-09-2019, 04:16   #2
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Re: Longtitudinal Centre of Gravity for Ship Cargo

I don't know what your problem is (It seems to be pretty straight-forward to me)


Maybe this article will help?
Ship Stability – Understanding Intact Stability of Ships


https://www.marineinsight.com/naval-...surface-ships/


https://www.google.com/search?ei=_Zp...Z5MDKkQ4dUDCAs
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Old 04-09-2019, 04:20   #3
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Re: Longtitudinal Centre of Gravity for Ship Cargo

Greetings and welcome aboard the CF, Rob.
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Old 04-09-2019, 06:31   #4
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Re: Longtitudinal Centre of Gravity for Ship Cargo

Better question for Quora methinks
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Old 05-09-2019, 19:28   #5
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Re: Longtitudinal Centre of Gravity for Ship Cargo

Maybe it would be easier in feet and inches?
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Old 06-09-2019, 23:07   #6
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Re: Longtitudinal Centre of Gravity for Ship Cargo

Sorry Rob. None of us can answer your question.


Maybe you should test some other forum?


Good-bye
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Old 07-09-2019, 01:23   #7
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Re: Longtitudinal Centre of Gravity for Ship Cargo

Quote:
Originally Posted by RobWilk View Post
Hoping someone here can advise me on the correct way for calculating the following and is there enough data given to work this out.?

This is from a textbook that I have from a Civil Engineering course I did some years ago.

A ship displaces 10,000 metric tons and area of its plane of flotation is 1,480 m^2. The centre of mass is 49 m and centre of area of the plane of flotation is 55 m from the stern. The metacentric height for pitching motion about transverse principal axis is 91.5 m.
The ship is loaded in sea water with 300 metric tons of extra cargo.

Find minimum allowable distance of mass centre of this extra load from stern if, when ship passes from sea water into a freshwater canal, the stern draft must not increase by more than 0.3 m?

Assume metacentric height and area of plane of flotation are not altered by change in draft and that density of sea water is 1025 kg/m^3 and density of fresh water is 1,ooo kg/m^3.

Answer from textbook is given as 46.2m.
Hi Rob and welcome to CF
Sorry you got some snarky answers as it is a challenging question

Started to work it out the way I was taught via drawing to first calculate TPCI , then apply after the Trim calculation
, but realised it might be a trick question, since they ask you to ignore floatation yet introduce a salinity factor.

Maybe I'm just rusty at doing these, so I'll get out the old books to refresh
Cheers
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Old 07-09-2019, 19:16   #8
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Re: Longtitudinal Centre of Gravity for Ship Cargo

I have balanced 747 freighters pre-flight, to make sure the tails didn’t hit on take-off because we loaded the horses up front and the machine parts in the back, or put too much fuel in the wrong tank. There are pragmatic work-arounds to solve this shipping problem. In the OP’s case, simply load the extra cargo forward.
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Old 07-09-2019, 20:52   #9
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Re: Longtitudinal Centre of Gravity for Ship Cargo

Robert

I note you've put the same question to a number of different people/forums but I really don't think this forum is appropriate as it is more a forum for amateurs.

Surely the advice (SEE BELOW) by Peter Edmonds (Naval Architect Perth) is on the ball?

https://engineering.stackexchange.co...for-ship-cargo

https://projectboard.engineering.com...tre-of-gravity

https://www.boatdesign.net/threads/c...m-stern.59800/

Placement of cargo from stern – DELFTship Forum

Longtitudinal Centre of Gravity for Ship Cargo

Merchant Ship Stability - Stability, Trim and Strength for Merchant Ships and.
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Old 07-09-2019, 22:29   #10
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Re: Longtitudinal Centre of Gravity for Ship Cargo

Maybe your problem and solution (or principles anyway) can be found here?

Fluid Mechanics Worked Examples for Engineers

https://www.scribd.com/doc/109900858...-for-Engineers

If you need a copy of J F Douglas's book it can be downloaded here:
solving problems in fluid mechanics volume 1 by J. F. Douglas

https://www.researchgate.net/publica...by_J_F_Douglas
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Old 09-09-2019, 10:34   #11
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Re: Longtitudinal Centre of Gravity for Ship Cargo

Quote:
Originally Posted by coopec43 View Post
Robert

I note you've put the same question to a number of different people/forums but I really don't think this forum is appropriate as it is more a forum for amateurs.

Surely the advice (SEE BELOW) by Peter Edmonds (Naval Architect Perth) is on the ball?

https://engineering.stackexchange.co...for-ship-cargo

https://projectboard.engineering.com...tre-of-gravity

https://www.boatdesign.net/threads/c...m-stern.59800/

Placement of cargo from stern – DELFTship Forum

Longtitudinal Centre of Gravity for Ship Cargo

Merchant Ship Stability - Stability, Trim and Strength for Merchant Ships and.
Hi Coopec43

Yes I have put several posts up to try and get this solve.

Check out my reply to Adhoc on this post
https://www.boatdesign.net/threads/c...n.59800/page-2.
He said there was an unknown in this question, so this is why this is still unsolved for me.

You reckon it is not that difficult.
Can you try calculating it and see if you can get the answer of 46.2m from the stern?

Once you have done that, can you please show me how you have calculated it.
I think if you do this, then that would help come to a conclusion on this.
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Old 09-09-2019, 19:13   #12
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Re: Longtitudinal Centre of Gravity for Ship Cargo

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Originally Posted by RobWilk View Post
Hi Coopec43

Yes I have put several posts up to try and get this solve.

Check out my reply to Adhoc on this post
https://www.boatdesign.net/threads/c...n.59800/page-2.
He said there was an unknown in this question, so this is why this is still unsolved for me.

You reckon it is not that difficult.
Can you try calculating it and see if you can get the answer of 46.2m from the stern?

Once you have done that, can you please show me how you have calculated it.
I think if you do this, then that would help come to a conclusion on this.

Robert

I wouldn't know where to start!

After reading about the cargo ship that capsized just yesterday I realize it is a very, very important aspect of loading a ship. (The cargo must have moved?)

Cheers

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Old 09-09-2019, 20:07   #13
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Re: Longtitudinal Centre of Gravity for Ship Cargo

These Car Carriers have massive ballast tanks and my guess is the engineer was running very light on ballast and bunkers when leaving port.

Being at or near Angle of Loll, when vessel heeled with wiind or a sharp turn, things went very bad
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Old 10-09-2019, 01:44   #14
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Re: Longtitudinal Centre of Gravity for Ship Cargo

Quote:
Originally Posted by RobWilk View Post
Hi Coopec43

Yes I have put several posts up to try and get this solve.

Check out my reply to Adhoc on this post
https://www.boatdesign.net/threads/c...n.59800/page-2.
He said there was an unknown in this question, so this is why this is still unsolved for me.

You reckon it is not that difficult.
Can you try calculating it and see if you can get the answer of 46.2m from the stern?

Once you have done that, can you please show me how you have calculated it.
I think if you do this, then that would help come to a conclusion on this.

I'm trying to find the solutions manual. I think I saw that the question was

QUESTION 26
CHAPTER 3
TITLE OF TEXT BOOK (I know I've seen the title but am now confused)

AUTHOR ?

PUBLISHER ?

Any chance of providing that information?

Clive
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Old 10-09-2019, 06:54   #15
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Re: Longtitudinal Centre of Gravity for Ship Cargo

Quote:
Originally Posted by coopec43 View Post
I'm trying to find the solutions manual. I think I saw that the question was

QUESTION 26
CHAPTER 3
TITLE OF TEXT BOOK (I know I've seen the title but am now confused)

AUTHOR ?

PUBLISHER ?

Any chance of providing that information?

Clive
Hi Clive

Textbook Title is Solving Problems in Fluid Mechanics volume 1,
Author is J F Douglas
and Published by Longman Scientific & Technical in 1986.

Yes you are right Question 26 from Chapter 3 Buoyancy and Stability of floating bodies.

If you can find the solutions manual and share the link with me, then that would be great help thanks.

If you can't, then I guess just calculate yourself and see what you come up with and then show me.

It was interesting that you mentioned about what happened in the real world with the car carrier Golden Ray.
An interesting response from Pelagic saying the tank maybe running light on ballast and bunkers. In that case maybe it was to do with the free surface moments.


Robert
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