A weight of 250 tons is loaded on your vessel 95 feet forward of the tipping center. The vessel's MT1 is 1000 ft-tons. What is the total change of trim?
A. 11.90 inches
B. 18.75 inches
C. 23.75 inches
D. 38.01 inches
A. 11.90 inches
B. 18.75 inches
C. 23.75 inches
D. 38.01 inches
Change of Trim = Trimming Moment / MT1 or MTC depending on the units.
ReplyDeleteWhere:
Trimming Moment is in ft-tons and is the product of multiplying the weight by its distance from the Tipping Center or LCF, Longitudinal Center of Flotation.
MT1 = Moment to Trim One Inch
or
MTC = Moment to Trim One Centimeter.
In this case the question uses Imperial Units of Long Tons and Feet.
Change of Trim = 250 LT x 95 ft / 1,000 ft-LT/inch = 23.75 inches.
So the best answer is C.
What is so hard about this question? You need to know Tipping Center is the same as LCF. You also need to know that the answer will be in inches!
Something to consider: A Trimming Moment of 1,000 ft-tons can be produced with 1,000 tons loaded one foot from the LCF or 10 tons 100 feet from the LCF or 100 tons loaded 10 feet from the LCF!
Which way will the vessel's Trim change? If we are loading a weight the draft will normally increase at the nearest end to where the weight is loaded. If the weight is discharged it will be the opposite.
Where can you load a weight so that the draft will change at one end only?
Set parallel sinkage = 1/2 change in trim to find the distance
W/TPI = 1/2 W x Dist from LCF / MT1
Dist from LCF = 2 MT1 / TPI
So for the draft you are floating at look up MT1 and TPI and solve for the distance in feet from the LCF. Then use the Capacity plan to locate both points. There is one forward and aft of the LCF.
To learn more about this you can find it in my book, STABILITY AND TRIM FOR THE SHIP'S OFFICER, 4th Edition, Chapter 9 TRIM, page 195.
Thanks for working this one out, tough one.
ReplyDeleteCharley
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