Calculating Slip

Slip is a very important calculation that goes into the noon report, official logbook, etc. Slip is the difference between engine speed and the actual speed of the vessel and it is calculated in percentage.

Slip are of two types 

• positive-due to hull fouling, wind and/or current running against the ship 
• negative slip wind and/or current running with the ship 

Step 1- Find engine distance

• avg rpm=revolutional counter /(running hour*60)

revolution counter can be found out by finding the difference between the present counter and previous counter and then calculate average rpm from the above formula

• Engine distance=(pitch *avg rpm*60*running hours)/(1000*1.8253)

or

• Engine distance=(pitch *revolution counters )/(1000*1.8253)

where the pitch is in meters

Step 2 -Find actual distance
This is normally provided by the bridge team.

Step 3 Calculate slip

Slip%={(engine distance-actual distance)/engine distance}*100