An ullage gauge may be
converted to an innage gauge by subtracting the ullage from the
reference height shown on the capacity tables.
The use of water-indicating
paste in conjunction with innage or ullage procedures provides a
measurement of the free water in a vessel's tanks. The recommended
procedure for free-water gauging is by the innage method. If the level
of the water being measured is high enough to show a cut on or above
the tape clip, a larger gauge bar should be used. How- ever, if
measurement conditions dictate, it may be necessary to utilize the
ullage method or other methods as agreed upon by all the parties. For
measurement under adverse conditions.
Vessel tanks should be gauged
for free water using water- indicating paste or other equipment agreed upon by
the par- ties involved. Measurements should be taken independently of
any other innage or ullage measurements and should be properly
recorded. Free water should be measured at both the loading and the
Innage Tape and Bob To Measure Free Water
Apply the water-finding paste
on the bob or bar sufficiently high to measure the anticipated level of
water (see note 2).
After grounding, .the innage
tape and bob should be lowered into the tank until the bob is a short
distance from the bottom, as determined by the tape reading at the
The tape should then be unwound
slowly until the tip of the bob just touches the bottom or datum plate.
If the tape is lowered too far, the bob will tilt and an incorrect
gauge will be obtained.
Once the bob touches bottom,
keep it there long enough for the paste to react to the water (see note
Withdraw the tape and read and
record the highest, clearly defined water cut (see notes 4 and 6).
Repeat steps a through e until
two identical readings are obtained.
Record the cut as "clearly
defined," "speckled," or "slightly discolored." Measurement of free
water on vessels that are out of trim is addressed in MPMS section 9.7.
Note 1: There are many
brands of water-indicating pastes available that change color on
contact with free water. It should be noted, however, that all brands
may not react the same in the presence of water. Accordingly, the
following qualities should be known before selecting a water paste:
Clarity of color change.
Ability to "shed" oil.
Ease of application to the bar
and ability to "grip" the bar.
Dense enough not to wash off
when passing through the oil.
It is recommended that two different pastes be applied on the bar for
each free water innage gauge at the beginning of gauging. After it has
been established which paste yields the highest, continuous clear water
cut, the other can be discontinued. 'When applying the two
pastes to the bar, cover a little less than one-half of the entire
surface of the round bar with each paste. Make sure that the
measurement scale remains free of paste. The coating of paste on the
bar should be thin but opaque.
Allow the paste-coated bar to remain in the gauging position for a
minimum of ten seconds for gasoline, kerosene, and similar light
products, and one-to-five minutes for heavy, viscous products (or as
otherwise specified by the manufacturer). This amount of time
is required to shed the petroleum that adheres to the paste. in heavy
viscous petroleum, apply an even film of light lubricating oil over the
paste to facilitate the shedding of the petroleum from the paste (see
When the bob or bar is removed to read the water cut, do not blow or
wipe the petroleum off the paste as this may distort the clarity of the
water cut. If the water cut is obscured by the petroleum (black oils),
wash the surface of the paste with a suitable solvent. The solvent
should be poured or lightly sprayed on the paste-covered bar well above
the anticipated cut and allowed to rinse down over the cut area.
Pouring directly on the paste may distort the clarity of the water cut.
Note 5: Wipe the bar
clean after gauging each tank and re-apply paste before gauging
If the paste on one side is spotted or lower than the other, record the
highest level reading as the official measurement of free water
level. Oil adhesion may cause low readings, but will not
cause high readings. Spotting may indicate a layer of
emulsified oil and water or that the product did not completely shed
off the paste.
If water cuts indicate that an
emulsion layer may be present, read and record both the clear cut and
the height of the spotting measurement.
Sections of text taken from API - MPMS Chapter 17 Marine Measurement