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Survey Documentation 

Open Measurement

Closed / Restricted Measurement

Data Collection

Special Considerations

Precautionary Notes

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Survey Documentation - Precautionary Notes.


Personnel involved in the handling of petroleum-related substances (and other chemical materials) should be familiar with their physical and chemical characteristics, including potential for fire, explosion, and reactivity, and appropriate emergency procedures.  These procedures should comply with the individual company's safe operating practices and local, state, and federal regulations, including those covering the use of proper protective clothing and equipment.  Personnel should be alert to avoid potential sources of ignition and should keep the materials' containers closed when not in use. 

API Publication 2217 and Publication 2026 and any applicable regulations should be consulted when sampling requires entry into confined spaces.  Information regarding particular materials and conditions should be obtained from the employer, the manufacturer or supplier of that material, or the material safety data sheet.

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Different Types of Ships and Barges

There are various types of ships and barges used to carry oil.  Each presents its own challenges to the performance of accurate measurement.  This section discusses most of the basic types and the potential problems each may cause in obtaining proper cargo measurements.  When going on board a ship for the first time, the ship's general arrangement plans should be reviewed to see where all the tanks are and whether the ship is single- or double-hulled.  Barges usually do not carry such plans and the bargeman should provide the required information.


The most common type of ship and barge currently is the single hull or single skin vessel.  These generally cause the least problems for measurement because their single skin design usually allows easy access to all compartments.  Even on these, however, obstructions may prevent gauge tapes from getting all the way to the bottom of the tank.  In addition, it is not uncommon to have some leakage of cargo between tanks due to small cracks in internal bulk- heads.  Therefore, it is important that all tanks be gauged and the reference heights of each tank carefully noted and recorded


Double hull ships are becoming more and more common due to increased environmental and industry regulations.  These ships differ from the single hull vessels in that the cargo tanks are surrounded by another hull or series of tanks.  Because of the "clean" tank design of the ships cargo tanks, there usually are no obstructions in the cargo tanks to hinder the taking of good innages.  However, because the main cargo tanks are located above a series of other tanks, it may be difficult to measure any material, cargo, water, bunkers, etc. in those tanks.  Double hull ships also usually have fewer tanks to gauge than does a conventional, single hull ship.  Some of the problems with double hulls are similar to those of OBOs/OROs


One of the detriments to the double hull design is that ships can lose as much as 33% of their potential cargo-carrying capacity to the empty spaces comprising the double hull.  In order to help remedy this problem, alternate hull designs have been proposed by ship owners.  The mid-deck tanker is one of several designs that provide protection of the cargo in case of a hull rupture without significantly reducing the vessel's carrying capacity.  The existence of a two-deck cargo tank system, however, can cause various potential measurement problems, many of which may not be fully realized until ships of this type come into full service.  Some of the problems would be similar to those noted in OBOs or OROs


Combination carriers, such as ore/bulk-oil carriers (known as OBOs) and ore-or-oil carriers (known as OROs), are specialty vessels designed to carry either dry or liquid bulk car- goes.  The basic procedures described in this publication apply to combination carriers.  In addition, because of the unique design of combination carriers, extra care should be taken when liquid cargoes are measured on board these vessels.  The following points should be noted:

  1. Combination vessels usually have double bottoms and side and wing tanks in addition to normal cargo tanks.

  2. Bottom lines on combination vessels may not be calibrated and often run beneath the cargo tanks.

  3. Because of the large width of each ore/bulk-oil tank, trim and list corrections are critical, and error scan be magnified if the corrections are not correctly applied.

  4. Some combination vessels have cargo ducts instead of piping systems.

  5. Because the bottoms of combination vessels' tanks may sustain random deformities resulting from dry bulk handling procedures, OBQ/ROB determinations may be affected, especially in regard to the establishment of the liquid plane.

  6. Such deformities may affect the validity, development, and application of the vessel's VEF.


Many aspects of measurement on board vessels require thorough knowledge and experience so that an accurate survey can be produced.  Without adequate and recurrent training of personnel, many errors may be introduced during the measurement and sampling process.

Inaccuracies in the survey obviously have an economic impact on the seller and buyer, and periodic training and review is required to maintain measurement skills.  Training and review are essential in maintaining awareness of improved techniques and equipment that allow better measurement and sampling of cargoes on marine tank vessels.

Although this describes parties for proper measurement and sampling of liquid cargoes on board vessels, it is not intended to be a training manual.  Additional training should be provided to those involved in measurement activities and should be based on current API material.  Appropriate training in shipboard operations and safety practices should be provided to all personnel working on board any vessel.

Sections of text taken from API - MPMS Chapter 17 Marine Measurement

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