A boat is shown to be safe by calculation before it touches the water. Structural, stability and weight calculations are the design's evidence; approval is that evidence checked by an independent eye.
Main calculations
- Structure
- Scantlings and stiffening; ISO 12215 or class rules.
- Stability
- Stability appropriate to the design category; ISO 12217.
- Weight and centre of gravity
- A weight estimate updated through design; the basis for stability and waterline.
- Propulsion and power
- Speed prediction, propeller and engine selection.
- Rig loads
- On a sailing yacht, mast, rigging and attachments.
How approval happens
- When building to class, plan approval is by the classification society.
- For CE conformity, depending on size and category, assessment by a notified body where required.
- On the owner's side, review by an independent engineer; conformity with the specification and brief.
After launch
Calculated weight and stability are verified by an inclining test and waterline measurement after launch. The difference between calculation and reality is recorded in the design file.
Whose approval?
Design and calculations are assessed by different parties depending on the boat's conformity route. In the CE route, a notified body reviews the documents according to the boat's category and route; when building to class, the classification society approves drawings and calculations to its rules. What matters for the owner is that approval is complete before the build starts, and that approved drawings are used in the build.
What is reviewed
- Structural calculation: plate or laminate thickness, structural members and connections.
- Stability: the boat's balance in different loading conditions.
- Watertightness: height and closing arrangements of hatches and openings.
- Systems: fuel, electrical, gas and fire systems against the relevant standards.
Revisions and changes
A change after approval, especially one affecting structure or stability, may need reassessment. So change requests are tracked against the approved drawings and every revision numbered. The build is checked to be using the latest approved revision at all times.
Independent review
Approval shows a standard is met; it does not confirm the specification's quality expectations or the owner's particular wishes. The owner's inspector also reviews drawings with that eye: maintenance access, ease of use and consistency with the specification.
Documents
Approval letters and approved drawings go into the build file; they underpin the boat's conformity documents and any later modifications.
Timing
Approval takes time; building it into the programme from the start keeps the yard from starting on unapproved drawings under schedule pressure.
Later modifications
Years later, when an owner wants to add a generator or change the layout, the approved drawings are what the next designer needs first.
For that reason approved drawings are kept as part of the boat's permanent papers and passed to each new owner at sale, together with the approval letters and any later revision notes.
Conditions of approval
Conditions stated in approval letters, such as the use of a particular material or an extra test, are tracked during the build and their fulfilment documented. An approval with open conditions is not yet a complete approval, and the handover file should show each one closed.
Keeping correspondence with the notified body or society in order makes that tracking easy.
An orderly correspondence file speeds approval and keeps answers ready for any later question from an insurer, a buyer or a future designer.
Log each revision with its date and a one-line summary of what changed.