What are Errors of Dopller Log ?

In modern transducers the angle at which the beam is transmitted is controlled with the help of phase difference.

Error due to ship’s motion- 

During the interval between transmission and reception, the ship may marginally roll or pitch and thereby the angle of transmission and reception can change and for a two degree difference between the angle of transmission and reception, the net effect will be an error of 0.10% of the indicated speed which is marginal and can be neglected.

Error due to the effect of rolling and pitching-

The effect of pitching will cause an error in the forward speed but it has no effect on the athwartships speed.