Most industry professionals know that inclining tests are performed to confirm a design’s longitudinal and transverse centers of gravity. Or, put simply, to assess whether a ship’s theoretical calculations match its actual performance.
What they may not know is that a successful test depends on the collaboration of multiple stakeholders and on numerous external factors, such as weather and sea conditions.
Having the test conducted by naval architects with wide test experience ensures a smooth process with accurate results.
The how and why of the tests
There are two scenarios in which an inclining test is mandatory. The first is just before the delivery of a new build, to confirm compliance with classification society requirements. The second is after a retrofit, to assess whether any of the modifications have affected the ship’s weight and center of gravity.
The test itself involves a lightweight check and a shifting of weights from one side of the vessel to the other, to measure its angles of heel. And accuracy — ask any naval architect — is the be-all and end-all of inclining tests. The weights are strategically placed and shifted with millimeter precision and must be of an exact weight to produce a measurable change in the vessel’s inclination.
Robin Berendschot, Naval Architect at C-Job, gives an example: “We inclined the 62,75 m new build dredger by moving four steel and concrete blocks, each of five to ten tons, from starboard to port. We then took measurements with a pendulum consisting of a bob and five-meter cord and consulted a digital inclinometer for added insights.”
Inclining tests are not all created equal
The results of an inclining test form the foundation of all stability calculations. Accurate data helps ship owners and operators to make informed decisions about loading limits, weight distribution, and ballast adjustments. This helps in maintaining a vessel’s stability and safety, protecting its crew and cargo.
But not all inclining tests are created equal. The best tests are tightly choreographed, with everyone on the vessel instructed to perform a specific task at precisely the right moment. And the benefits of an expert test extend beyond ensuring compliance. “A well-executed test results in the most accurate Lightship Weight particulars and unlocks the full potential of a vessel,” confirms Sjoerd Bouma, Lead Naval Architect at C-Job.
The devil is in the details
Achieving the best possible results is not easy, and this is where naval architects’ experience in inclining procedures and team management prove invaluable.
Jennifer Ryan, Director of Engineering at C-Job Houston, highlights a few of the difficulties. “There’s the weather. The wind can pick up or change direction or push sideways on the vessel. Then there are all the preparations that must be done—not just by us but by the yard, the classification society, and the vessel’s captain and crew.”
This presents a conundrum, since vessels are tested at the end of the build, when everyone involved is under pressure to meet deadlines.
“That’s why effective communication from our side is essential — both during the inclining procedure and in the weeks leading up to it — to ensure everyone is aligned and expectations are clear,” says Bouma. It makes sense. The better the preparation, the quicker the test can be completed—and the earlier everyone can return to their to-do lists.
A balance between science and that certain something
There is another aspect of the test where wide experience can be invaluable. Naval architects who have inclined the whole gamut of vessels, from tugs to cruise liners, can take accurate measurements even when awkward external factors (such as the wake of a passing ship or sudden gusts of wind) make it difficult to do so.
Bouma defines it precisely: “There are moments when the science of pendulums ends and a naval architect’s experience and instinct comes in.”
