What is VNET in Terms of Bunker Survey?
Remembered that unanswered question about Bunker Survey VNET by Surveyor on this site. We have collected two similar information to solve it.
QUESTION: Recently, many Chinese built vessels using the VNET calibration table for calculation of the bunker received on board and many a time, ended with dispute. What is VNET?
FIRST
• Many Chinese ship builders are calibrating vessels tanks via the use of VNET.
• What is VNET?
• VNET: Net Volume of tanks taking structural reduction into consideration
• Calculated by the below formula:
VNET = VOLM x RED
• VOLM: Gross volume of tanks without structural reduction
• RED: Reduction coefficient due to structure in tanks, usually recognized as 0.98 in the shipbuilding industry.
VNET is an Auto calculator program being used by some Chinese shipyards for calculating the Net Volumes of the tank.
The API MPMS 2.8A is globally the most accepted method for determining tank capacities. It requires tank cross sectional measurements at frequent horizontally sliced intervals to account for:
• Tape rises during strapping (i.e. vertical welds, laps and other obstructions).
• Shell temperature and tape calibration temperature during strapping.
• Physical characteristics of the tank shell material.
• Paint and plate thickness.
• Effects of positive and negative deadwood on tank volumes.
• Tank tilt
SECOND
VNET Calibration uses an Auto calculator that does not require horizontal cross sectional measurements. Instead, it allows for the tank internals, curvatures, deadwood etc. by applying a factor for these variables.
Through our research on this subject we found that the VNET calibration process calculates the volume of the tank by taking the external dimensions and then arriving at the Net Volume by multiplying it by a structural factor for taking into account the internal structures of the tanks.
Hence if
V(N) = Volume determined by the VNET method.
V = Volume determined using the external dimensions of the tank
V(F) = V Net Factor (typically this factor can be anywhere between 0.95 to 0.98 and is also referred to as the “Structural Factor” by some shipyards).
then,
V(N) = V x V(F)
Sources: IBIA & Royal Marine