Innage/Ullage Equipment An innage tape shall only be used
with an appropriate innage bob. An ullage tape shall only be
used with an ullage bob. The measurement units on the
innage/ullage equipment used should be consistent with the measurement
units in the vessel's capacity tables; that is, the equipment should be
graduated in 1-mm, 1/8th-in, or 0.01-ft
Gauge Bars A water gauge bar may be used to
assist in determining the height of free water in a tank. Typically a
water gauge bar is a 12-in. (30-cm) or 18-in. (45-cm) round
bar. The longer length of these bars can reduce the incidence
of water cuts occurring on clasps and areas not scaled between the tape
and bob. A square bob is not recommended because the corners
on the bar may cause dips and slants to occur on the paste, resulting
in false readings.
Indicating pastes can be used to determine the levels of water in a
tank or assist in the reading of product levels. The pastes
should be applied and used according to the manufacture's
specifications and the shelf life should be noted before each use.
of Innage/Ullage Equipment
Before a tape is used, it should be checked for breaks, kinks, and
illegible markings. The tape hook should be inspected for
and distortion. Innage bobs should be inspected for wear and
damage of the tip and eye hole. The bob/tape interface should
measured to determine accuracy. If these inspections indicate
inaccuracies, the equipments should not be used. (API MPMS Chapter 3.1A
has more information for tape and bob accuracy requirements.)
capacity tables show the volume corresponding to each measured innage
or ullage. Measurements should be taken in the same units
the capacity tables. If measurements must be taken in other
units, the conversion factors should be used.
When tank capacity tables are
not calculated to the minimum prescribed graduations (1/8th
in., 1 mm, or 0.01 ft), and when gauge readings fall between the values
in the tables, interpolation will be necessary.
The observed reference height
should be compared with the reference height given in the tables and
Procedures for Open Manual
Gauging Manual gauging consists of either innage or ullage gauging of
the liquid level with appropriate gauging equipment.
Considerations in determining whether innages or ullages are to be
taken are whether the capacity tables are presented in inn age or
ullage format, the amount of liquid in the tanks and the nature of the
material. Measurements should be taken in the units in which
the tank capacity tables are presented.
When taking custody transfer
measurements, all cargo tanks, ballast tanks, bunker tanks, void spaces
and cofferdams should be inspected and/or gauged as
appropriate. Measurements should always be taken at the
reference points noted in the capacity tables. The reference height
should be stenciled or otherwise permanently marked near the gauge
point. The observed reference height should equal the reference height
of the tank. If it does not, the procedures described in Appendix B.3,
should be followed. An accurate permanent record of the gauge
measurements should be made when the readings are taken.
be noted that some tanks and void spaces on the vessel may not have
reference heights. Also, in some instances, it may be
to take gauges of water, ROB, OBQ, etc. at points other than those
designated as official gauge points. In those cases, full
of such gauging must be noted in the gauger's log and on the
appropriate cargo measurement documents. If foam is present
the surface of the liquid, no gauge should be taken until the foam has
subsided or been cleared from the surface of the liquid beneath the
gauging hatch. Before a tank is gauged, time should be
permit the oil to free itself of entrained air, gas, and
When the surface of the oil is at rest, at least two identical readings
should be obtained before a measurement is recorded. Best
accuracy is usually obtained when oil is motionless in the tanks.
Measurement procedures when the liquid in the tank is in motion, as
occurs when a vessel is pitching and rolling, as described in MPMS 9.3
should be followed.
Measurement procedures to be
followed when the vessel is out of trim are described in MPMS 9.7. In
all cases, trim and list should be recorded to determine the necessary
corrections to be applied.
Ullage measurement is the
determination of the distance from the gauge point to the surface of
the material being measured. This may be accomplished by
using ullage or innage tape and bob combination.
an Ullage Tape and Bob
Ullage measurement using ullage
equipment should be conducted as follows:
Obtain approximate tank ullage
using vessel ATG or other method.
After safely grounding the tape
and opening the gauge hatch, slowly lower the tape and bob into the
tank until the bob just touches the surface of the liquid (see Figure
After the bob bas stopped
swinging, lower the tape slowly until a small portion of the bob is in
the liquid and an even inch, centimeter, or hundredth of a foot
graduation on the tape is at the reference gauge point.
Record the tape reading at the
Withdraw the tape from the tank
and read the ullage bob scale at the liquid cut and record the-reading.
Care should be exercised during the withdrawal procedure to ensure that
the tape and bob are not allowed to re-enter the liquid and thereby
give a false reading.
The sum of the tape readings at
the reference gauge point and the ullage bob reading at the cut is the
ullage gauge (see Table 1).
Innage Tape and Bob
When innage equipment is used
to take an ullage, the procedure in the previous section should be
followed except the bob reading must be subtracted from the tape
reading. See the example in Table 1.
An innage gauge may be
converted to an ullage gauge by subtracting the innage from the
reference height shown on the capacity table.
Innage measurement is the
determination of the height of the liquid in the tank. This may be
accomplished by using ullage or innage tape and bob combination and may
be a direct reading or calculated value.
Sections of text taken from API - MPMS Chapter 17 Marine Measurement