# Cotre Carantec 62 — design and project roadmap

## Purpose and design status

Cotre Carantec 62 is a preliminary concept for a small decked plywood-and-epoxy cutter inspired by traditional boats from northern Finistère. It is a modern interpretation, not a historical replica and not yet a construction-ready design.

Principal dimensions and design figures:

- Length overall: 6.20 m
- Waterline length: 5.55 m
- Maximum beam: 2.28 m
- Total draft: 1.15 m
- Light displacement: 1,490 kg
- Maximum displacement: 1,970 kg
- Ballast: 520 kg
- Intended use: 3–4 people for day sailing; 2 people for short overnight trips

The preliminary maximum-load model gives KG = 0.324 m, initial GM = 1.34 m and maximum GZ about 0.63 m near 70°. These values must be revalidated after modelling the cockpit, openings, downflooding, final structure, equipment and realistic load cases.

## Scale, geometry and sail plan

The CAD design is full-size at **1:1 scale**. Main model coordinates are in metres. The developed-panel DXF is expressed in millimetres. PNG and SVG exports are presentation drawings and must not be used directly as cutting templates.

Preliminary cutter sail plan:

- Gaff mainsail: 15.5 m²
- Staysail: 4.5 m²
- Jib: 5.5 m²
- Total upwind sail area: 25.5 m²
- Combined centre of effort: x = +0.402 m, z = 3.931 m
- Estimated centre of lateral resistance: x = −0.150 m
- CE/CLR lead: 0.552 m, approximately 9.94% of LWL

This balance is an initial geometric estimate. The sailmaker and naval architect must refine sail shape, reefing arrangements, mast and rig loads, weather helm, keel and rudder geometry.

## Available design package

- [Project overview](https://projects.alkemata.com/documents/3)
- [Calculation methodology](https://projects.alkemata.com/documents/2)
- [Stability calculations](https://projects.alkemata.com/documents/4)
- [FreeCAD hull model](https://projects.alkemata.com/documents/5)
- [Stage 2 design report](https://projects.alkemata.com/documents/11)
- [Stage 2 calculations](https://projects.alkemata.com/documents/12)
- [Stage 2 FreeCAD assembly](https://projects.alkemata.com/documents/13)
- [Deck plan](https://projects.alkemata.com/documents/15)
- [Sail plan](https://projects.alkemata.com/documents/17)
- [Developable panel DXF](https://projects.alkemata.com/documents/19)
- [FreeCAD perspective rendering](https://projects.alkemata.com/documents/23)

## Initial planning

| Phase | Target period | Main outcome |
|---|---:|---|
| WP1 — Design basis | Weeks 1–2 | Requirements and assumptions frozen |
| WP2 — Stability and flooding | Weeks 2–5 | Validated hydrostatics, openings and downflooding model |
| WP3 — Rig, appendages and mass | Weeks 4–7 | Refined sail balance, appendages and weight model |
| WP4 — Structure and drawings | Weeks 7–12 | Preliminary scantlings and coordinated construction package |
| WP5 — Review and release | Weeks 12–16 | External technical review and controlled design release |

## Useful references

- [World Sailing — Equipment Rules of Sailing 2025–2028](https://www.sailing.org/inside/technical/equipment-rules-of-sailing/) for standard sail terminology and measurement practice.
- [ISO 12217-2:2022](https://www.iso.org/standard/79073.html) for stability and buoyancy assessment of sailing boats of 6 m and above.
- [ISO 12215-5:2019](https://www.iso.org/standard/69552.html) for monohull design pressures, stresses and structural scantlings; relevant companion parts cover rudders, appendages and rig loads.

## Design explanation and open decisions

Added 28 October 2026. The figures above remain preliminary. This review covered the project wiki and work packages, not the linked calculation reports, CAD assemblies or DXF files. A task marked New is not proof that no work has occurred; it means completion evidence has not been recorded here. The explanations below interpret the recorded concept and identify what must be demonstrated.

### Hull, construction concept and structural logic

The documented concept combines a small decked hull, plywood/epoxy construction and a traditional cutter appearance. The deck/cockpit arrangement, panel shapes, ballast and rig must be developed together: moving a bulkhead or opening can alter structural support, access, weight and flooding behaviour.

Developed plywood panels are intended to translate the three-dimensional hull into cuttable flat shapes. A DXF export alone does not demonstrate that the panels will form the intended hull without unacceptable distortion. Fairness, developability, grain direction, joint positions, assembly tolerances and a representative fit check remain part of #52. The final drawings must state whether and where glass reinforcement is structural, protective or both.

The structure must provide continuous load paths: mast compression and rig tension into suitable foundations and hull structure; ballast/keel loads into floors and adjacent structure; rudder loads through stock/bearings and attachments; deck fitting loads through backing and supports. Plywood thickness alone cannot define these load paths. Member sizes, spans, joints, laminates, fastening and local reinforcement remain design outputs of #51.

### Displacement, loading and ballast

Displacement is the mass of water displaced by the floating boat, equal to total boat mass in equilibrium. The proposed light and maximum displacements differ by **480 kg** (1,970 − 1,490 kg). This is a provisional loading allowance, not a demonstrated passenger capacity. The definition of light condition must first establish what fixed equipment, rig, ballast, propulsion and fluids are already included. People, stores and loose equipment must then be added without double counting.

The 520 kg ballast figure is a target. Its final mass, vertical/longitudinal position and attachment influence stability, trim, structural loads and handling. The mass model must include resin, glass, coatings, hardware, rig, sails, systems and realistic uncertainty as well as plywood and timber. Added equipment high in the boat can raise the centre of gravity; component weights must be reconciled with the material take-off.

### How to interpret the stability figures

KG is the height of the centre of gravity above the model's vertical reference. Its reported 0.324 m is only interpretable once that datum is documented. GM describes initial stability near upright. A preliminary GM of 1.34 m does not establish safety at larger heel angles or in waves.

GZ is the horizontal righting lever at a given heel angle. The reported maximum of about 0.63 m near 70° is one point on a preliminary curve; assessment requires the complete curve, load condition and flooding limits. A positive calculated lever is useful only while the assumed watertight boundary remains valid. Openings, cockpit water, crew movement and actual equipment/ballast positions can change the result.

The remaining stability study must therefore model openings and downflooding, cockpit drainage, relevant load cases and sensitivities, and the applicable buoyancy/recovery criteria. Intended design category and operating limits remain unvalidated until the reviewer accepts the relevant evidence. Nominal overall length is not automatically the hull-length measurement used to choose a standard.

### Sail plan and steering balance

A cutter divides the headsail area between the staysail and jib; together with the gaff mainsail this gives several possible sail combinations. The proposed areas total 25.5 m², but the final reefing and sail-handling arrangements remain to be designed.

The centre of effort (CE) is an estimated resultant location for sail forces; the centre of lateral resistance (CLR) is an estimate for the underwater lateral plane. The recorded longitudinal separation is 0.552 m, or about 9.94% of the 5.55 m waterline length. Its meaning depends on the CAD axis and sign convention, which must be stated before calling it forward or aft.

Geometric separation alone cannot establish helm balance. Sail shape, heel, reefed combinations, hull form and keel/rudder behaviour affect the actual forces. The sailmaker/reviewer must coordinate mast position, sail geometry, appendages, steering and rig attachment loads, then define what commissioning trials will verify.

### Layout, systems and buildability still to decide

The day-sailing and two-person overnight intentions need dimensioned cockpit, accommodation, ventilation, stowage, movement and maintenance-access checks. Auxiliary propulsion and its energy/fuel system, electrics, pumping/drainage and navigation equipment are not specified in this wiki. Decisions are required before freezing weights, openings, reinforcement and the BOM.

The documented rationale is still incomplete: record why the selected hull dimensions, draft, ballast, rig and layout best meet the agreed use, along with alternatives considered and their cost, transport, handling and sailing tradeoffs. Do not present a plausible rationale as an established design decision without owner/designer confirmation.

## Remaining design work and acceptance evidence

All entries below remain open in project tracking at this review. Existing task descriptions have been expanded rather than duplicated.

| Task | Remaining output / completion evidence |
|---|---|
| [WP1.1 — Requirements](https://projects.alkemata.com/work_packages/47) | Approved use/load assumptions, coordinate/unit conventions, standards route and versioned baseline |
| [WP1.2 — Layout and access](https://projects.alkemata.com/work_packages/54) | Dimensioned general arrangement and ergonomics/maintenance-access checks |
| [WP2.1 — Stability](https://projects.alkemata.com/work_packages/48) | Reproducible hydrostatics/GZ, openings/drainage/downflooding assessment and accepted load limits |
| [WP3.1 — Rig and appendages](https://projects.alkemata.com/work_packages/49) | Coordinated rig/sail/reefing, keel/rudder and load/interface drawings |
| [WP3.2 — Mass and trim](https://projects.alkemata.com/work_packages/50) | Traceable mass/CG register, load cases, uncertainty and BOM reconciliation |
| [WP4.1 — Structure](https://projects.alkemata.com/work_packages/51) | Reviewed scantlings, load paths and joint/laminate/fastener details |
| [WP4.2 — Panels and drawings](https://projects.alkemata.com/work_packages/52) | Checked CAD/DXF revisions, developed panels, nesting, datums/tolerances and coordinated assembly package |
| [WP4.3 — Systems](https://projects.alkemata.com/work_packages/55) | Equipment decisions, schematics, routing, penetrations and installation/test criteria |
| [WP5.2 — Mock-ups and joints](https://projects.alkemata.com/work_packages/56) | Representative fit/access/joint evidence with findings resolved in drawings |
| [WP5.1 — Technical review](https://projects.alkemata.com/work_packages/53) | Closed review findings and controlled construction release |
| [M2 — Reviewed construction package](https://projects.alkemata.com/work_packages/46) | Accepted design evidence and consistent released calculations, drawings, specifications and build/inspection instructions |

Suggested progression: requirements/layout → stability/mass/rig iterations → structure/systems → coordinated drawings and mock-ups → review → M2. Revisit earlier calculations whenever an interface or mass changes.

## Construction phase after design release

The [construction preparation and build plan](https://projects.alkemata.com/projects/cotre-carantec/wiki/cotre-carantec-62-construction-preparation-and-build-plan) now contains:
- A 20-category preliminary BOM with units, quantity basis and required specifications.
- A method for obtaining quantities from reviewed nesting, parts and equipment schedules.
- A proposed C0–C11 procedure with inspection points before closure, turning, launch and trials.
- Tool/facility requirements and buy/hire/outsource decisions.
- Workshop, storage, people, heavy handling, procurement, transport and launch logistics.
- Quality records, mass reconciliation and commissioning/handover criteria.

Trackable preparation and construction work:
- [WP6 — Construction phase overview](https://projects.alkemata.com/work_packages/57)
- [WP6.1 — BOM, quotes and procurement](https://projects.alkemata.com/work_packages/58)
- [WP6.2 — Workshop, tools and handling](https://projects.alkemata.com/work_packages/59)
- [WP6.3 — Procedures and inspection](https://projects.alkemata.com/work_packages/60)
- [M3 — Construction readiness](https://projects.alkemata.com/work_packages/61)
- [WP7.1 — Hull and primary structure](https://projects.alkemata.com/work_packages/62)
- [WP7.2 — Deck, appendages, fit-out and rig](https://projects.alkemata.com/work_packages/63)
- [WP7.3 — As-built checks, launch and trials](https://projects.alkemata.com/work_packages/64)
- [M4 — Commissioning and handover](https://projects.alkemata.com/work_packages/65)

Quotations and workshop planning can be prepared during design. Production cutting and permanent construction require accepted M2 and construction readiness. Quantities, prices, labour estimates and calendar dates remain TBD, pending released design, supplier quotations and owner resource decisions. Dependencies are described in the tasks; formal predecessor links, hierarchy, assignees and dates could not be set through this connector.

## Reference edition check

On 28 October 2026, ISO's catalogue lists ISO 12217-2:2022 as published with a revision under development, and ISO 12215-5:2019 with a March 2024 corrected version. Reconfirm applicable editions with the reviewer at release. Catalogue summaries establish scope, not compliance or a substitute for the full standards.

## Safety and validation boundary

The current files are suitable for concept development and technical review. Panel patterns, plywood thicknesses, structural details and stability results must be checked against the applicable standards and approved by a qualified naval architect before material is cut or construction begins.


## Reproducible hull design notebook — 31 October 2026

The [parametric hull design notebook](https://projects.alkemata.com/projects/cotre-carantec/wiki/cotre-carantec-62-parametric-hull-design-notebook) is now available with an attached, executed `.ipynb` file. It explains input selection and hypotheses, generates an editable educational hard-chine candidate, calculates upright flotation/initial stability, compares load cases and shape variants, and includes optional online data imports with provenance. Numerical checks passed. Live imports remain untested and disabled by default. The model is independent of the existing FreeCAD hull and does not validate its GM/GZ figures, develop panels or release construction. See the notebook page for reconciliation steps against #47, #48, #50 and #52.