Practical Stability Test: Owner’s Guide

by | Jul 6, 2020

1.0 Introduction

The stability test is a scientific experiment, designed to achieve accuracy by controlling everything on the vessel during the test.  Unfortunately, a working vessel is a terrible place for a scientific experiment.  Which is why the stability test is so inconvenient.  The Test Coordinator needs trying to extrapolate critical numbers, based on very small measurements, while excluding all the normal complications of a working vessel.  That level of control requires extensive preparation and coordination between the vessel Owner and Test Coordinator.  This provides a practical guide to prepare you for a stability test.

1.1 The Test Coordinator

The Test Coordinator acts as your single point of contact and adviser throughout the test.  This will be the naval architect firm you hired.  They will coordinate times and resources for all the various parties involved.  You decide on your limits, and the Test Coordinator handles everything else.  Given all the steps necessary to execute a stability test, the Test Coordinator becomes a welcome ally.

During the preparations for the test, it may seem that the Test Coordinator transforms from ally to enemy, imposing dozens of requirements.  But just like an accountant at a tax audit, the Test Coordinator is there to guide you through the process and guard you against mistakes with government regulations.  That is why the Test Coordinator has so many requirements; to ensure USCG will easily accept the stability test on the first pass.

2.0 Practical Timeline for Stability Test

Use the following guide as a practical timeline for a stability test.  It is fairly conservative and will allow plenty of time for unexpected surprises.

2.1 Two Months Out

Contract with a naval architecture firm to conduct the test.  They will need ample lead time to prepare.  Ask the firm about the current lead time for USCG approvals.  Provide the firm with all required documentation. 

2.2 One Month Out

Naval architecture firm must submit the test procedure to United States Coast Guard (USCG).  USCG will require extensive time to review the procedure and approve it.  Officially, USCG requires one month for any review, but they can normally review procedures in two weeks.  An approved procedure is required before the stability test.

2.3 Three Weeks Out

Confirm that you are on schedule to complete all vessel modifications by the planned test date.  Plan alternative accommodations for any crew during the stability test.  They will be removed from the vessel for 12 – 24 hours.  Secure contracts for all test equipment, especially the following:

  • Crane
  • Test weights
  • Dynamometer (also called a load cell)
  • Harbor tug
  • Marine environmental inspector to certify tanks gas free
  • Secure pier-side storage for vessel equipment

If you are working with a shipyard, the yard will most likely handle all the logistics for the stability test.

2.4 One Week Out

Meet with Test Coordinator on the vessel.  Have them survey the vessel and provide guidance on vessel readiness.  Offload any fuel that needs to be removed for the stability test.  Offload any deadweight that needs to be removed for the stability test.  All items can be stored securely on the pier-side, or anywhere that is convenient.  But they can not be on the vessel. 

Any tanks listed as empty during the test should be emptied at this point and gas freed.

2.5 Two Days Before Incline Experiment

Confirm that all shipyard work will be completed by the next day.  Check the weather and confirm there will be fair conditions for a stability test.  Discuss any concerns about weather delays with the Test Coordinator.  Check that the vessel will be prepared and ready. 

2.6 One Day Before Incline Experiment

Test Coordinator and staff conduct the deadweight survey.  Depending on size of vessel, this may require more than one day.  Chief Engineer should configure any tanks that still have liquid to their final state for the stability test.  Reconfirm that all empty tanks are still gas free, and still have no pooled liquid.  (Sometimes the tank valves leak.) 

2.7 Day of Incline Experiment

Absolutely no construction work on the vessel.  Non-essential crew shall be off the vessel.  Shipyard workers shall be off the vessel.  The vessel will be shutdown to critical systems only and will be non-functional.  Crane and Incline weights should arrive very early in the morning, or the night before.

Master and Chief Engineer should be onboard for the stability test.  All crew present should prepare for a very long workday.  Vessel owner may attend incline experiment, if desired.  Ideally, vessel owner should observe test from the pier-side.

2.8 One Week After Incline Experiment

Vessel may depart port, under temporary authorization from USCG.  Test Coordinator will begin work to provide a new stability booklet or stability letter, subject to review of results from the Stability Test and a new stability analysis. 

3.0 Documentation

3.1 Required Documentation

The following plans are critical to the stability test and must be provided.  If the plans do not exist, they must be created new.

  1. Lines plan
  2. Hydrostatics computer model (GHS model), or sufficient data to create model
  3. General arrangement plan
  4. Tank capacity plan: showing tank names, location of manholes, vents, and sounding tubes
  5. Scantling structural drawings, showing plating thickness of decks

3.2 Supplemental Documentation

The following supplemental documentation is useful, but not required.

  1. Inboard profile
  2. Midship section drawing
  3. Draft mark drawing: showing location and offset of draft marks.

4.0 Owner Supplied Equipment

We call the following equipment owner-supplied, meaning that the naval architect doesn’t own these assets.  In reality, most of the equipment will be rented.  This is an excellent opportunity to work with your Test Coordinator.  They can arrange the rental equipment, review the options, and then handle all the coordination.

  1. Incline weights
  2. Pier-side storage for any items which must be removed from the vessel
  3. Crane with sufficient capacity to lift the weights. Vessel cranes may be acceptable under certain circumstances.
  4. Load cell to measure the incline weights.
  5. One of the following:
    1. Camels / Yokahama fenders
    2. Small tug to help pull the vessel off the pier (NOT the ship’s rescue boat)
  6. Mooring lines
  7. Handheld VHF radios

5.0 Owner Supplied Personnel

The Vessel Master and Chief Engineer must be accessible during the deadweight survey to answer any questions.  The following personnel should be ready and available during the incline experiment.

  1. Vessel Master
  2. Chief Engineer
  3. Line Handlers
  4. Crane Operator
  5. Crane Ground Crew

Personnel on the vessel must be kept to a minimum during the incline experiment.  If desired, the Vessel Master and Chief Engineer can double as line handlers during the incline experiment.  This is left to the discretion of the vessel owner and operators.

6.0 Vessel Tanks

The stability test procedure lists a tank configuration.  This should be carefully reviewed and confirmed acceptable with the vessel before submittal to USCG. Any tanks listed as empty must be truly empty, stripped, and certified gas free.  Any tanks listed as full will need to be pressed full, with liquid overflowing out the tank vent.  The Test Coordinator can provide solutions to tank configurations, but any submitted configurations must be followed.

6.1 Gas Free and Strip All Empty Tanks

Any tanks listed as empty in the procedure must be gas free and stripped completely dry.  There can be moisture on the walls, but no pools of liquid.

7.0 Vessel Deadweight

Vessel deadweight can not exceed 2% of the lightship weight.  This is critical.  Stability tests have been in danger of rejection by USCG because deadweight exceeded 2%.  Roughly speaking, deadweight is anything not bolted down or necessary for fire protection and lifesaving.  Any items that regularly leave the vessel or change position are considered deadweight.  The best idea is to remove these items from the ship and temporarily store them in a secure facility.

8.0 Conclusion

The key to a successful stability test is preparation and communication between Owner, Crew, and Test Coordinator.  Remember that the Test Coordinator is there to help ensure a successful test.  Do not disregard their advice, and bring up any concerns you have, or any difficulties with the Test Procedure.  Any issues can be overcome with sufficient planning and preparation.

9.0 References

[1] Code of Federal Regulations, “Determination of Lightweight Displacement and Centers of Gravity,” in Code of Federal Regulations, Washington, D.C., U.S. Government, 2020, pp. 46 CFR 170, Subpart F.
[2] United States Coast Guard, “MSC Guidelines for the Submission of Stability Test Procedures,” Procedure Number: GEN-05, Washington D.C., Sep 27, 2012.
[3] ASTM, “Standard Guide for Conducting a Stability Test (Lightweight Survey and Inclining Experiment) to Determine the Light Ship Displacement and Centers of Gravity of a Vessel,” ASTM F1321-92, West Conshohocken, PA, 2004.
[4] United States Coast Guard, “Stability Tests (46 CFR 170, Subpart F),” Marine Safety Manual, vol. VI, pp. 6-18 to 6-27, Sep 29, 2004.
[5] US Coast Guard, “Line Handler,” Wikimedia Commons, 03 Sep 2016. [Online]. Available: [Accessed 13 Feb 2020].
[6] Marine Chemist Service, “Certified Marine Chemist,” Marine Chemist Service, 01 Jan 2020. [Online]. Available: [Accessed 13 Feb 2020].
[7] A. Kumar, “Ship Stability: Stiff and Tender Ship, Angle of Loll & Inclining Experiment,” Mariner Desk, 11 Dec 2017. [Online]. Available: [Accessed 13 Feb 2020].
[8] Wikipedia Authors, “San Francisco Harbor Tug Delta Deanna in Suisun Bay, CA,” Wikimedia Commons, 27 Aug 2005. [Online]. Available:,_CA.jpg. [Accessed 28 Feb 2020].
[9] Wikipedia Authors, “Harbor Tug Assists USN Ship Depar Port Naval Station Rota in January 2009,” Wikimedia Commons, 28 Jan 2009. [Online]. Available:,_Spain_2009.jpg. [Accessed 28 Feb 2020].


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