# Admiralty Coefficient - Ship Construction

It sometimes necessary to obtain an approximation to the power of the ship without restoring to model experiments, and several methods are available. One system which has been in use for several years is the admiralty coefficient method. This is based on the assumption that for small variations in speed the total resistance may be expressed in the form:

### It was seen earlier that

### Hence with constant density

### But

### or

The coefficient is known as the Admiralty Coefficient.

Originally this method was used to determine the power supplied by the engine. Since size of machinery vary considerably, it is now considered as the relation between displacement, speed and shaft power(sp) is of more practical value.

Most merchant ships may be classed as slow or medium speed, and for such vessels the index 'n' may be taken as 2.

Thus,

The Admiralty Coefficient may be regarded as constant for similar ships at their corresponding speeds. Values of C vary between about 350 and 600 for different ships, the higher values indicating more efficient ships.

For small changes in speed, the value of C may be regarded as constant for any ship at constant displacement.

Thus if shaft power of one ship is known, the shaft power for a similar ship may obtained at the corresponding speed.

**References**

"**Reed's Naval Architecture for Marine Engineers**" By E.A. Stokoe

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