CALCULATORS / MARINE AND UNDERWATER DEVICES

Initial floating-body stability screening calculator

Small-angle metacentric roll restoring moment with supplied GM; no hull hydrostatics.

marine-stability.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	momentN*m
	17.1
	13.68

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

positive initial stability0.20 m✓ passes

BASELINE INPUTS

mass100 kgmetacentricHeight0.2 mheel5 deggravity9.81 m/s^2

CALCULATED

moment17.1 N*m

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Initial floating-body stability screening
# Scope: Small-angle metacentric roll restoring moment with supplied GM; no hull hydrostatics.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

mass = 100 kg
metacentricHeight = 0.2 m
heel = 5 deg
gravity = 9.81 m/s^2

moment := mass*gravity*metacentricHeight*sin(heel) [N*m]

check positive initial stability: metacentricHeight > 0 m

scenario alternative: mass = 80 kg

Calculated from your source · not saved

Baseline · Baseline

positive initial stability0.20 m ✓ passes

alternative · alternative

positive initial stability0.20 m ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

moment: moment = mass*gravity*metacentricHeight*sin(heel) [N*m]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

mass: 100 kg
metacentric height: 0.2 m
heel: 5 deg
gravity: 9.81 m/s^2

Calculated

moment: 17.1 N*m

Assumptions and limits

Small-angle metacentric roll restoring moment with supplied GM; no hull hydrostatics.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Initial floating-body stability screening. Inputs: waterplane properties; displacement; centers of mass/buoyancy. Outputs: metacentric-height estimate; small-angle restoring moment. Model scope: Hydrostatics and calibrated hydrodynamic coefficients. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: waterplane properties, displacement, centers of mass/buoyancy
Outputs: metacentric-height estimate, small-angle restoring moment
Modes: calculate, compare, sweep
Drawing: Hull and underwater load diagram

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS