Shipwright principals are versed in the requirements to create stability booklets, lightship surveys, and inclinings
Every loading condition in your stability booklet starts from the same numbers: the weight and center of gravity of the empty ship. We measure them on the vessel, witnessed by class or flag where required, and deliver the report and updated stability data that keep you compliant.
Lightweight survey
An item-by-item audit of everything aboard that is not part of the empty ship (stores, spares, tank contents, tools, the inclining weights themselves) and of anything missing or not yet in its final position. Each item’s weight and location are recorded so it can be deducted, added or relocated on paper.
Gives you: lightship displacement and its longitudinal center of gravity (LCG).
Inclining test
With the vessel afloat in calm water and moored on slack lines, known weights are shifted across the deck in a planned series of moves. Pendulums or electronic inclinometers record the heel after each one. The heeling moment and the angle give the metacentric height (GM) and, from it, the vertical center of gravity.
Gives you: the lightship VCG (KG), the figure every stability calculation depends on.
Lightweight survey: items aboard that aren’t part of the empty ship are deducted, missing items added, and misplaced items moved to their final positions on paper.
Why it matters
SOLAS requires the master to determine the ship’s trim and stability after loading and before departure, and to record that the ship meets the applicable stability criteria (Chapter II-1, Regulation 20). That check is only as good as the lightship data behind it.
Owners must also supply the stability information the master needs to operate safely (Regulation 5-1), including:
minimum GM, or maximum KG, curves against draught
cross-flooding arrangements and how to operate them
the data needed to maintain intact and damage stability
damage control information: watertight boundaries, openings and the means of correcting list
As the ship heels, buoyancy moves to the low side. The righting lever GZ is roughly GM · sin θ at small angles, so an error in KG becomes an error in every righting arm.
When you need one
New vessels
Shortly after completion, a lightship survey and inclining test establish the lightship weight, centers of gravity and GM recorded in the stability booklet.
Passenger vessels
A lightweight survey at intervals of no more than five years, to confirm the ship hasn’t quietly gained weight.
After a change
A reincline if lightship displacement has changed by more than 2%, or the LCG by more than 1% of the ship’s length, or if planned alterations are expected to exceed either limit.
Conversions and retrofits
Scrubbers, ballast water treatment, ducktails, bulbous bows and fuel conversions all add or move weight. Plan the stability work with the design, not after it.
SOLAS limits for passenger vessels. Requirements vary by flag, class and vessel type (for U.S.-flag vessels, see 46 CFR Part 170, Subpart F); we confirm what applies before the survey.
How a survey day runs
Plan. We review the stability booklet, the last inclining report and drawings, then agree the test plan, weights and witnesses with class or flag.
Prepare. Tanks emptied or pressed full to limit free surface, loose gear secured, mooring lines slackened, and everyone not involved ashore.
Survey. We tally items to add, deduct or relocate, read drafts and freeboards at several stations, and measure the density of the water.
Incline. Weights are shifted in a planned series of moves, port to starboard and back, with the heel recorded and plotted after each.
Report. We calculate lightship displacement, LCG, TCG and VCG, submit the inclining report for approval, and update the stability booklet.
What to have ready
Current stability booklet and the last inclining report
General arrangement and tank capacity plans, with sounding tables
Hydrostatic data or a lines plan
A list of modifications since the last incline
Access to every tank and space for the survey team
Missing drawings? Our 3D scanning service can capture as-built geometry.
Why Shipwright
Shipwright’s principals have prepared stability booklets, lightship surveys and inclining tests for passenger vessels, workboats and cargo ships. We have three offices and fly our team to the vessel, wherever it lies.
Surveys follow the IMO 2008 Intact Stability Code (Part B, Annex 1) and ASTM F1321, as your flag and class require.
