NVIC 03-69: Z nomograph method for calculating available GM

Last reviewed: October 14, 2026

This circular publishes the Z nomograph short form as an acceptable method of calculating available GM. The Coast Guard says the method may be used in Trim and Stability Booklets. Using it is not mandatory, because other simplified forms that effectively comply with current regulations are also acceptable.

Applies toThe text says the short form concerns trim and stability booklets for general dry cargo vessels, and it discusses container ships as vessels needing a more accurate method.

What it says

  1. The purpose of this circular is to publish an acceptable short form method of calculating available GM.

    “The purpose of this circular is to publish an acceptable short form method of calculating”

  2. The regulation cited in the circular requires a suitable short form for calculating a vessel's stability and freeboard in the trim and stability booklets for general dry cargo vessels.

    “This regulation requires the inclusion of a suitable short form for the”

  3. The Z nomograph short form eliminates the need for multiplication and division, so it is a simple, rapid and accurate method for calculating available GM.

    “The Z nomograph short form eliminates the need for multiplication and division, thus”

  4. The Z nomograph method requires additional preparation before it is approved and issued to the Master of the vessel.

    “The Z nomograph short form method requires additional preparation prior to its approval and”

  5. The Coast Guard describes the method as an acceptable short form method for calculating stability that may be used in Trim and Stability Booklets.

    “This method is an acceptable short form method for calculating stability, and may”

  6. Use of the enclosed method is not mandatory, because presenting stability information in any other simplified form that effectively complies with current regulations is also acceptable.

    “The use of the enclosed method is not mandatory since the presentation of stability information”

Common questions

Is the Z nomograph method mandatory?

No. The circular says use of the enclosed method is not mandatory, because other simplified forms that effectively comply with current regulations are also acceptable.

“The use of the enclosed method is not mandatory since the presentation of stability information”

What is the Z nomograph method used for?

It is an acceptable short form method for calculating stability that may be used in Trim and Stability Booklets.

“This method is an acceptable short form method for calculating stability, and may”

What equipment does the Z nomograph method need to read?

The circular says the end product is easy to use and requires only a straight edge to read the nomographs.

“the end product is easy to use (requires only a”

The text of NVIC 03-69

U.S. Coast Guard, NVIC 03-69 (main body; enclosures not shown)

Z Nomograph Method of Calculating Available GM

DEPARTMENT OF TRANSPORTATION COAST GUARD COMMANDANT (MMT-5) U.S. Coast Guard WASHINGTON, DC 20591 NVIC 3-69 22 May 1969 NAVIGATION AND VESSEL INSPECTION CIRCULAR NO.3-69 Subject:Z Nomograph Method of Calculating Available CM

Z Nomograph Method of Calculating Available GM — Purpose. The purpose of this circular is to publish an acceptable short form method of calculating

available CM.

Z Nomograph Method of Calculating Available GM — Background. Section 93.10-1 of the Coast Guard Rules and Regulations for Cargo and

Miscellaneous Vessels states, in part, * * * information shall be prepared. * * * and furnished to the Master. * * * This information shall be such that the Master can, for any condition of loading, by rapid and simple process, obtain accurate guidance as to the stability of the vessel * * * This regulation requires the inclusion of a suitable short form for the calculation of a vessel's stability and freeboard in trim and stability booklets for general dry cargo vessels.

Z Nomograph Method of Calculating Available GM — Discussion. The Z nomograph short form eliminates the need for multiplication and division, thus

providing a simple, rapid, and accurate method for calculating available CM. Many of the present short forms require tedious arithmetical operations as well as considerable averaging to place the cargo in arbitrary layers. Container ships with many cargo layers in addition to sizable deck loads often operate near their required CM in the fully loaded condition, thus a more accurate method is needed to determine the available CM. The Z nomograph short form method requires additional preparation prior to its approval and issuance to the Master of said vessel. Nonetheless, the end product is easy to use (requires only a straight edge to read the nomographs) and provides a more accurate stability evaluation.

Z Nomograph Method of Calculating Available GM — Action. Enclosure (1) contains instructions on how to prepare the nomographs for calculating

available CM. This method is an acceptable short form method for calculating stability, and may be used in Trim and Stability Book-lets. Enclosure (2) is an acceptable format for the short form part of such a booklet. The use of the enclosed method is not mandatory since the presentation of stability information in any other simplified form which effectively complies with current regulations is also acceptable. End: (1) Instructions for the Preparation of the Z Nomograph Method for Calculating Available GM. (2) Example Short Form Dist: (SDL No.88) A: None B: n(45); c(l0); eg(3); q(6); bdp(l) C: m(4); 0(2) D: i(2); k(l) E: o(2) F: None List 112-155

The plain-English explanation on this page was written with AI from the regulation text above and checked automatically before publishing: every quote appears in the text, every number comes from it, and a second model confirmed each statement adds nothing the text doesn't say. The regulation text governs. RegKnot is not affiliated with the U.S. Coast Guard.