ShipCalculators.com

Methodology

How ShipCalculators.com calculates and cites

Every calculator and reference page on this Site links the formula it implements to the exact published source: an IMO MEPC resolution, an EU regulation or directive article, an IACS Unified Requirement, a class-society circular, or a recognised industry standard (ISO, ASTM, IACS Rec). This page documents how we choose sources, how we maintain calculation accuracy, how we handle ambiguity in regulations, and how we update content when regulations change.

1. Source hierarchy

When a calculator or wiki article cites a regulation, we use the following hierarchy, highest authority first:

  1. The regulation itself. For IMO instruments, that means the consolidated text of the convention or code (MARPOL, SOLAS, COLREG, IMSBC, IMDG, IGC, IGF, MEPC resolutions). For EU law, the Official Journal text of the regulation or directive. For US law, the CFR or USC section. For class-society output, the published Rule, UR, or circular.
  2. Published guidelines and unified interpretations. IMO MEPC and MSC circulars (MSC.1/Circ., MEPC.1/Circ.), MEPC unified interpretations, IACS PR (Procedural Requirements), IACS UI (Unified Interpretations), flag-administration circulars where they materially affect interpretation.
  3. Standards bodies. ISO, ASTM, IEC, IEEE, IACS Rec where the regulation defers to a standard.
  4. Peer-reviewed academic literature and CIMAC / SNAME / RINA papers for technical-engineering content (engine theory, hull resistance, materials).
  5. Maker spec sheets and class-society type approval registers for product-specific data (engine bore, stroke, output ratings).

Wikipedia is used for orientation and biographical detail (history of the firm, career arcs of named engineers). It is never the sole citation for a regulatory or technical claim.

2. Formula derivation and verification

Every calculator's formula is checked through a four-step process before publication:

  1. Source extraction. The formula is transcribed verbatim from the regulation, with explicit symbol definitions, units, and validity range. The regulation's article or paragraph reference is recorded in the calculator's citation block.
  2. Symbolic rewrite. The formula is rewritten in the calculator's input variables. Where a regulation uses one symbol for two distinct quantities (a common pattern in IMO MEPC text), each is given an unambiguous name.
  3. Worked example. A worked example with a published reference value (a sea-trial figure, a class-society sample calculation, or an EU-published example) is computed against the implementation. The result must agree to within rounding tolerance.
  4. Edge-case check. Inputs at the boundary of validity (zero deadweight, zero speed, infinite-fuel-density, etc.) are tested for sensible behaviour: either a sensible limit or an explicit "outside the calculator's validity range" message.

Where a regulation has been amended, the calculator is dated to the regulation version it implements. EEDI, EEXI, CII, EU ETS, and FuelEU Maritime calculators all carry an explicit "implements regulation as of YYYY-MM-DD" line in their formula and assumptions section.

3. Handling ambiguity in regulations

IMO regulatory text is sometimes ambiguous on parameter scope, unit conventions, or rounding. We resolve ambiguity by referring to:

  • The MEPC unified interpretation for that paragraph, where one exists.
  • Class-society common interpretation. When DNV, ABS, ClassNK, LR, BV, RINA, KR, IRS, CCS, and PRS all interpret a clause the same way (often documented via IACS PR), we follow that interpretation.
  • Flag-administration guidance. Where a regulation requires an administration's discretion (for example, a flag's verifier-acceptance rule), we cite the most-restrictive published guidance among major flag states.
  • Explicit calculator notes. Where ambiguity remains, the calculator's "Formula and assumptions" section documents the choice and offers the alternative interpretation as a note.

4. Update cadence

Regulatory amendments are tracked via:

  • IMO MEPC and MSC sessions. Each session's outcome (resolutions adopted, circulars approved) is reviewed within four weeks of publication. Affected calculators are updated and re-verified.
  • EU Official Journal. Maritime regulations and directives are tracked via the EU's published amendment notifications; affected calculators are updated when the amending instrument enters force.
  • Class-society circulars. Each major society (DNV, ABS, ClassNK, LR, BV, RINA) publishes circulars on its website. We check quarterly.
  • IACS Unified Requirements and Procedural Requirements. Updated as IACS publishes them.

When a regulation is amended, the affected calculators are tagged with the new effective date and the "Formula and assumptions" section gains a "Change history" subsection that lists the prior version, the amendment, and the date of cutover.

5. What ShipCalculators.com is not

We are an unofficial reference. Nothing on this Site constitutes legal advice, classification advice, or a substitute for a recognised organisation's plan-approval review. Calculators and articles are educational tools. For a regulated outcome (a Statement of Compliance, an EIAPP certificate, a class notation, an EU MRV verification statement) the operator must engage the relevant flag administration or recognised organisation directly.

6. Reproducibility

The Site is fully static and client-side. No calculator's logic depends on a server. Anyone can verify a result independently by reading the formula and the cited regulation. Where a calculator implements an iterative algorithm or a numerical approximation (for example, a Newton-Raphson root-find on a hull-resistance curve), the algorithm is described in the formula section and the convergence tolerance is stated.