Information for containers

F or containers we also need to know the information for the list mentioned in Tanks.

In the stability booklet there is a special page with all that info on it (Appendix C). The weight and position of the container you get from the stow plan. You must know the position of the container in order to get the right information for this container.

The plan is made for 20 feet containers only. This means that you must calculate what the values are for a 40 feet container. This has to be done only for the LCG.

Eg: a 40 feet container in bay 14 on deck will have the next LCG

Bay 13 has LCG: 81.49

Bay 15 has LCG: 75.37

This means that bay 14 will have a LCG of: (81.49+75.37)/2, giving 78.43 for LCG

VCG is depending in what tier the containers is and,

TCG is depending in what row the container is.

Now that we have the necessary information, we can go to Step 1 of the manual calculation.

Step 1: Recalculating all the values to one easy value

W e have to bring back all the values to on easy to use value. In order to this we need to make use of the following calculation method:

Weight	LCG	Mlcg	VCG	Mvcg	TCG	Mtcg	IT (FSM)
X	A1	X*A1	B1	X*B1	C1	X*C1	D1
Y	A2	Y*A2	B2	Y*B2	C2	Y*C2	D2
(X+Y)	Mlcg/weight	(X*A1)+(Y*A2)	Mvcg/weight	(X*B1)+(Y*B2)	Mtcg/weight	(X*C1)+(Y*C2)	(D1+D2)

Info: remember to correct the weight for the right density. To do so use the next formula:

» Correct weight = sounded volume * actual density

We have to make this correction because the actual density is not always 1.025t/mі.

You see that we have now just one value to work with which makes it easier.

Step 2: GM calculation

I n the Hydrostatic Particulars table (Appendix A) we search for our weight and look for the corresponding value for KM (KMT in table), appendix A.

The formula to get the GM is: KM – KG = GM.

We know our KG because KG is the same as VCG.

We now know our GM, but we have to apply a GM correction in order to get the right GM or GM final.

For the GM correction we need the following information: total FSM from the all the tanks.

The formula for calculating the GM correction is:

» GM correction = FSM tanks / weight

So to continue the calculation for GM:

» GM – GM correction = GM final

Info: remember to always subtract the GM correction from GM to get GM final.

Step 3: Draughts

F or the draught calculations we need more information from the Hydrostatic Particulars (appendix A).

We need to know the following:

• LCF draught (= Mean draught or Md)
• LCB
• LCF
• MTcm
• LCG (step 1)

We use the next formulas to calculate the trim and draughts. (Remember, with weight in 1.025t/mі)

A) The trim

» Trim = (LCG – LCB) * weight / MTcm * 100 (*100 is to get the value in mtrs)

B) Δt

» Δt = LCF * trim / Lpp Lpp Sirrah is 125.5mtr

C) Aft draught (Aft d) and Fore draught (Fore d)

» Aft d = LCF draught + Δt Fore d = Aft d - trim

D) Double check Mean draught (Md)

» Md = (Aft d + Fore d) / 2

Step 4: List and Wind Surface moments

A) List

I n order to know what our list is we need a GZ value. We get the GZ value using the next formula:

» GZ = Mtcg / weight

We also apply a correction for the FSM on our GZ value. Herewith we use the next formula:

» GZ correction = GM correction * sinφ

So our final GZ value will be:

» GZ final = GZ – GZ correction

Now we need to know how many degrees our GZ will be. Therefore we need to have the information from the Cross-Curves values table (appendix E).

We will put the information in a table and later with the calculated values we’ll make a Cross Curve chart (Image 39).

Image 39: Example of table and Cross Curve chart

For list calculation the chart will be the same for Portside and Starboard side. Normally the chart is only made for the Starboard side. This is because for most ships the Portside is the same as the Starboard side.

Info: If GZ is negative the list is to Portside, if GZ is positive the list is to Starboard side.

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