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What are the form coefficients?
Form coefficients are ratios that numerically compare the ship’s underwater form to that of regular shapes having the same majority dimension as the ship.
Where are the form coefficients used?
The form coefficients are used at the designed stage, prior to the construction of a ship.
Why are the coefficients important?
The coefficients are important because you can predict the resistance to forward motion that the ship will experience during the operation.
The value of the form coefficients is then used to estimate the ship’s power requirements for the desired service speed.
The most important ratio that is used to assign the ship freeboard is the block coefficient.
Now we will see the essential form coefficients.
COEFFICIENT OF FINENESS OF THE WATERPLANE AREA
The coefficient of fineness of waterplane area is defined as the ratio of the ship’s water-plane-area (WPA) to the area of a rectangle having the same length and breadth of the ship at the waterline in question.
The formula of the form coefficient fineness of waterplane area is
BLOCK COEFFICIENT
block coefficient is the ration of the underwater volume of a ship to the volume of the circumscribing block.
The formula to calculate the block coefficient is:
Midships area coefficient
midships coefficient at any draught is the ratio of the underwater transverse area of the midships section to the product of the bread and draught.
LONGITUDINAL PRISMATIC COEFFICIENT
longitudinal prismatic coefficient at any draught is the ratio of the underwater volume of the ship to the volume of the prism formed by the product of the transverse area of the midships section and the waterline length.
The formula to calculate the prismatic coefficient of a ship is :
EXERCISE WITH SOLUTION OF THE FORM COEFFICIENTS
EXAMPLE FOR THE COEFFICIENT OF FINESESEN OF THE WATERPLANE AREA
A ship has a length and breadth at the waterline of 40.1m and 8.6m respectively if the waterplane area is 280mq calculate the coefficient of fineness of the waterplane area.
Solution example of COEFFICIENT OF FINESESEN OF THE WATERPLANE AREA
If we use the formula of the COEFFICIENT OF FINESESEN OF THE WATERPLANE AREA
The result will be like this :
EXAMPLE FOR the block coefficient
A ship floats at a draught of 3.20m and has a waterline length and breadth of 46.3m and 15.5m respectively.
Calculate the block coefficient if its volume of displacement is 1800m3
Solution for block coefficient example
Example midships area coefficient
A ships float at a draught of 4.40m and have the waterline breadth of 12.70m.
Calculate the underwater transverse area of the midships section if Cm is 0.922
Solution for the midships area coefficient example
Example prismatic coefficient
A ship has the following details:
Draught 3.63m
Waterline length 48.38m
Waterline breadth 9.42m
Cm 0.946
Cp 0.778
Calculate the volume of displacement
Solution for the midship coefficient
Read: How anchor a boat
