Installation manual

Simrad SH80

Dead Reckoning

The Dead Reckoning parameter dialogue opens when you click

the

Dead Reckoning button in the Setup menu.

The Dead Reckoning function is used to improve the position of

the historical track line from the vessel, relative to the actual

position of the drifting ﬁshing gear. In order to get correct dead

reckoning, a doppler speed log must be connected to the sonar.

When switched off, the vessel movement and track line will be

calculated from the GPS data, which then will be relative to the

bottom.

When switched on, the gyro and speed log are used to positioning

the vessel relative t o the water.

About Dead Reckoning

Dead reckoning is the process of estimating one’s current

position based upon a previously determined position, or ﬁx,

and advancing that position based upon measured velocity,

time, heading, as well as the effect of currents or wind. While

this method of navigation is no longer considered primary in

ships, it is still often used as a backup in case of failure of the

electronic navigation systems. Dead reckoning begins with a

known position, or ﬁx. This ﬁx is then advanced, mathematically,

by means of recorded heading, velocity, and time. The velocity is

determined by means of the doppler log.