24-Foot Trailerable Aluminum Fishing Boat

1. Mission profile and design drivers

A 24-foot trailerable fishing boat for the San Juan Islands in winter is fundamentally a cold, wet, high-current platform. Northern Inland Waters around the islands regularly see advisory-level wind and steep chop, and currents are a dominant operational factor when transiting passes and setting up to fish.¹²

Design priorities that follow from the mission

• All-weather habitability: fully enclosed cabin, windshield wipers/defogging strategy, and reliable cabin heat.¹⁶⁸
• Fishability: unobstructed cockpit sized for a dedicated cleaning table, coolers, and safe movement in foul-weather gear.
• Self-sufficiency: safe sanitation and pumpout plan (Puget Sound is a no-discharge zone), plus simple galley basics.³⁴⁵
• Reliability and redundancy: one main outboard plus an auxiliary “kicker” outboard for get-home and trolling capability.
• Trailerability: keep road-legal width and manage overall towing weight early (weight creep is the main risk on cabin aluminum boats).¹²

2. Key constraints and early “numbers”

2.1 Trailer envelope and launch profile

Treat road limits as a hard boundary: Washington’s legal outside width limit is 8.5 feet (8’6”).¹² For a “no-permits, no-drama” trailer boat, target a beam at or under 8’6” and design the cabin roof height, bow rail, and antennas for practical overall tow height on a trailer.

• Beam: ≤ 8’6” (legal width baseline).¹²
• Launching: assume cold, wet ramps; specify non-skid, handholds, and trailer-access steps that work with gloves.
• Trailer interface: define keel/bunk support and tie-down points during the structure phase so the hull is not an afterthought.

2.2 Payload and endurance assumptions

Build your first Excel “weight and balance” model in week one and keep it live through the build. The goal is not precision; it is early detection of CG drift (cabins and hardtops move weight upward and forward; outboard brackets move weight aft). Use conservative payload cases:

• People: 2–4 adults in winter gear
• Fuel: sized for winter range with margin (include auxiliary outboard consumption)
• Fish load + ice: coolers and a “wet weight” scenario for a full day’s catch
• Water/gear: fresh water for sink; safety kit; spare parts; anchor/rode

2.3 Safety and compliance “guardrails”

Use the most conservative safety baseline available to you, then validate against Washington’s minimum equipment rules and federal requirements: state equipment checklists, navigation lights, and general federal equipment regulations.⁶⁷¹⁰¹¹ For enclosed-cabin winter boats, carbon monoxide risk management is not optional—design it in with exhaust routing, ventilation, and CO detection.⁸⁹

3. General arrangement for a fishing-first cabin boat

3.1 Cabin

A practical 24-foot cabin arrangement is “short cabin, long cockpit.” Your cabin needs to deliver: weather protection, helm ergonomics, heat, and basic sanitary/galley features—without consuming the cockpit.

• Helm: stand/sit option, good sightlines, wiper coverage, and a dedicated dry electronics console.
• Heat + condensation control: ducted heat with a defog outlet to windshield; insulation where feasible; controlled ventilation.¹⁶¹⁵
• Porta potty: secure mounting, privacy curtain/door, and a shore disposal plan consistent with Puget Sound NDZ rules.³⁴
• Sink: small freshwater tank with foot pump or 12V pump; overboard discharge only if compliant, otherwise capture/shore disposal.
• Single-burner cooking: treat any open-flame appliance as a CO/ventilation design problem; provide ventilation and CO alarm strategy.⁸⁹

3.2 Cockpit

Design cockpit “work triangles” the way you would in a commercial skiff: where fish come aboard, where they get cleaned, and where they get stored. Provide clear deck area for:

• Fish cleaning table: dedicated mount points, drainage management, and a washdown hose.
• Coolers/fish boxes: tie-downs, under-gunnel storage, and the ability to load/unload without climbing over seats.
• Safety movement: high coamings, toe-kick space, and handholds for moving fore/aft in chop.

3.3 Deck drainage

A winter fishing cockpit should be self-bailing (scuppers sized for real water, not just rain). The drainage design is part of safety, not comfort. Document your target “drain-down time” and ensure it remains valid after adding fish boxes, deck fittings, and plumbing runs.

4. Hull form and hydrodynamics

4.1 Start with an aluminum-friendly hull geometry

For welded aluminum, prioritize hull shapes that can be fabricated from developable (single-curvature) plating: hard-chine, moderate-deadrise planing hulls with panels that can be rolled or “pulled” into shape without compound forming. This reduces cost, distortion, and fairness problems when you weld.

4.2 Planing performance: a practical calculation stack

For a 24-foot outboard fishing boat, you will likely target a planing regime at cruise. A practical approach is: (1) an early Excel speed/power model using a validated planing resistance method, (2) a weight/CG iteration loop, and (3) later refinement using sea trial data. Savitsky-style planing analysis is widely used as an engineering baseline.¹⁴

• Inputs: displacement by loading case, LCG/VCG, deadrise, beam at chine, appendages, and target cruise speed.
• Outputs: required shaft power (proxy for outboard rating), running trim, wetted length, and sensitivity to LCG drift.
• Design action: use sensitivity results to place tanks, batteries, and fish boxes so you avoid “trim surprises.”

4.3 Seakeeping and “winter usability” checks

Winter usability is less about top speed and more about ride, dryness, and control at moderate speeds in steep chop. Use your operating area sources to define a conservative “go/no-go” envelope and build the boat to operate safely inside it.¹²

• Spray control: chine geometry and spray rails are not cosmetic; they reduce freezing spray exposure and windshield load.
• Directional stability: skeg/keel geometry, strakes, and proper LCG reduce broaching tendencies.
• Static stability: cabin weight raises VCG; validate “at-rest” heel behavior with passengers on one side and a loaded fish box.

5. Structure, alloys, and strength-to-weight

5.1 Material selection

Most welded aluminum fishing boats use a marine 5xxx-series plate (e.g., 5086) for hull plating and 6xxx-series extrusions (e.g., 6061-T6) for framing/extrusions; these choices balance corrosion resistance, weldability, and availability.¹⁸

5.2 Scantlings: use a recognized rule set, then engineer the exceptions

For a one-off build, pick a coherent scantling framework and stick to it. ISO 12215 provides an internationally recognized structure and loading framework for small craft scantlings; ABYC’s aluminum technical guidance is a complementary resource for practical construction details.¹³¹⁴

• Define load cases: bottom slamming, side pressure, deck loads, transom/outboard thrust, and trailer point loads.
• Build a grid: frames + longitudinal stringers sized so plating spans are reasonable (smaller spans reduce plate thickness and oil-canning).
• Transom and bracket: treat as a primary structure with its own load path; don’t “inherit” thickness from the rest of the hull.

5.3 Welding approach and distortion control

Aluminum boat success is largely weld discipline: joint prep, sequencing, fixturing, and thermal management. Select filler alloy based on your base materials, corrosion environment, and mechanical requirements; 5xxx-series structures commonly use 5356-class filler, with selection guided by welding/filler selection references.¹⁹²⁰

• Sequence: tack everything, verify fairness/diagonals, then weld in a balanced pattern (alternate sides, work from center outward).
• Fit-up: small gaps, consistent bevels, and clean oxide removal immediately before welding are non-negotiable.
• Isolation: plan your stainless fasteners, hardware backing, and bonding system to prevent crevice and galvanic issues.

6. Systems integration (outboards, heat, water, galley, sanitation)

6.1 Propulsion: main outboard + auxiliary outboard

From a design standpoint, the dual-outboard concept drives: (1) transom structure, (2) fuel plumbing redundancy, (3) steering integration, and (4) battery capacity for cold starts. Decide early whether the auxiliary outboard mounts on the transom or on a bracket, and ensure the kicker can be steered (tie bar or independent steering) and can charge a battery if needed.

6.2 Fuel system and ventilation

Treat fuel compartments and any enclosed machinery spaces as regulated safety systems, even on an outboard boat. Federal regulations provide baseline requirements for boats and associated equipment, including fuel and ventilation topics.¹⁰

6.3 Cabin heat

In a winter-use cabin, a sealed combustion heater (typical examples are diesel-fired forced-air units) is often preferred because combustion air and exhaust are routed outside. Regardless of technology, treat heater installation as a design-critical safety feature: correct exhaust routing, ventilation practice, and CO monitoring are essential.¹⁵¹⁶⁸⁹

6.4 Water, sink, and sanitation

Puget Sound is a no-discharge zone for vessel sewage, which affects how you handle portable toilets and any installed sanitation. Design your porta potty arrangement for secure retention and easy shore disposal at a dump station or pumpout facility.³⁴⁵

6.5 Galley (single-burner cooking)

If you choose an open-flame single burner (propane/butane/alcohol), document ventilation and CO controls and treat the appliance like a “system.” If you want simplicity, consider a non-flame alternative (e.g., electric via shore power / inverter) and reduce combustion risk. In all cases, include CO risk education and a pre-departure checklist.⁸⁹

6.6 Electrical

Winter fishing loads are real: cabin lighting, electronics, bilge pumps, washdown, wipers, heater fan, and charging. Your workflow should include a power budget spreadsheet, a wiring diagram set, and a bill of materials tied to your CAD assembly.

7. CAD and documentation workflow (Rhino + Fusion + Office)

7.0 Stage-gate workflow (recommended)

A stage-gate workflow reduces rework by forcing the key decisions (hull form, weight/CG, and fabrication approach) to stabilize before you release cut files. The table below is a practical “minimum set” of deliverables for a one-off aluminum build.

7.1 File strategy and “single source of truth”

Keep your geometry in Rhino as the hull-form master. Keep your structure and mechanical assemblies in Fusion where parametrics and assemblies help. Use Office 365 as the documentation and build-control layer: weights, BOMs, cut lists, bending schedules, and QA check sheets.

7.2 Rhino: hull and arrangement definition

1. Set up reference planes: baseline, stations, buttocks, and waterlines.
2. Block the hull: sheer, chine, keel, and transom curves; create developable panel surfaces.
3. Check fairness: curvature graphs, section continuity, and symmetry.
4. Generate hydro inputs: export sections/offsets for displacement and LCG checks; iterate with the Excel weight model.
5. Prepare fabrication surfaces: ensure plating is unrollable (single curvature) where you intend to form from flat plate.

7.3 Excel: early performance and weight/CG loop

Implement a speed/power estimate (Savitsky-style or another validated method) and drive it from your weight cases. Use SNAME-style notes and references to keep your implementation grounded.¹⁴

7.4 Fusion: structure, fittings, and manufacturing outputs

1. Create a skeleton assembly: hull reference surfaces imported from Rhino (STEP/IGES) and a coordinate system shared with Rhino.
2. Parametric structure: frames, longitudinals, deck beams, cabin framing, transom reinforcements.
3. Simulation: focus on transom/bracket, cabin roof beams, deck openings, and trailer point loads.
4. Manufacturing drawings: shop-ready prints with weld symbols, cut lengths, hole callouts, and bend angles.

8. Panel development, nesting, and forming

8.1 Developable panels and “unroll” workflow

Aluminum hull plating is easiest when the geometry is developable and the fabrication is predictable. In Rhino, use surface analysis to verify single-curvature plating, then generate unrolled patterns for CNC cutting. Create a part naming scheme that matches your build sequence: e.g., HULL-BOT-P01, HULL-SIDE-S02, DECK-AFT-D03.

8.2 Nesting and cut files

• Output format: DXF for waterjet/laser/plasma shops; include bend allowance notes where relevant.
• Kerf and edge quality: specify whether edges will be welded as-cut or will be milled/cleaned.
• Identification: ask for etch marking or light scribe for part IDs and frame station numbers when possible.

8.3 Forming and rolling

Keep forming demands realistic for local capability: press brake for cabin panels and smaller components; rolling for mild curvature plates; avoid compound-curvature panels unless you have a clear forming plan and budget.

9. Build sequence, QA/QC, and commissioning

9.1 Suggested high-level build sequence

1. Strongback/jig: build and level; establish station marks.
2. Frame and longitudinal assembly: tack, measure, brace; verify symmetry.
3. Bottom plating: fit, tack, weld in balanced sequence; manage distortion.
4. Side plating and chine: maintain fairness; check diagonals each major tack stage.
5. Deck and cabin: install with planned cable/pipe chases; seal penetrations deliberately.
6. Systems: fuel, electrical, steering, heater, plumbing, pumps, electronics.
7. Finish: coatings (if any), non-skid, hardware, anodes, and final rigging.

9.2 QA/QC checkpoints

• Dimensional: station spacing, beam, transom angle, shaft/engine alignment (outboard mounting geometry).
• Watertight: pressure test sealed compartments; hose test deck penetrations.
• Electrical: insulation resistance checks, load test, charging verification in cold conditions.
• CO safety: confirm detector placement and test procedure; validate heater exhaust routing.⁸⁹

9.3 Sea trials

Sea trials should validate: trim and planing behavior, steering control, self-bailing function, fuel burn, and safe operation at realistic winter speeds. Document results and feed them back into your CAD and spreadsheets for the “as-built” package.

10. Washington State sources for aluminum supply, cutting, and forming

The following Washington-based sources are commonly used for supplying marine aluminum and/or processing (waterjet/laser/plasma cutting, press brake forming, and general fabrication). Confirm capability for your plate thickness and part size before committing.

11. Starter checklists and spreadsheet tabs

11.1 Office 365 workbook tabs (recommended)

• Requirements: mission, range, max crew, fishing load cases, trailer limits
• Weights: itemized weight estimate (structure, engines, fuel, systems, interior)
• CG/Trim: LCG/VCG by scenario; sensitivity to moving tanks/batteries
• Power & speed: planing resistance model; cruise targets; prop selection notes
• BOM: part numbers, vendor, lead times, cost, revision tracking
• Cut list: plate thickness, alloy/temper, sheet size, part IDs, nesting file name
• Bend schedule: part ID, material, thickness, inside radius, bend angles, notes
• Weld map: weld type/length by assembly; sequencing notes; inspection sign-off
• Electrical loads: duty-cycle loads; battery sizing; charging sources
• Sea trial log: speed/RPM/fuel burn, handling notes, trim, issues, fixes

11.2 Build-phase checklists

• Pre-cut: verify alloy/temper, thickness, and sheet sizes; lock revision of DXFs
• Jig setup: level strongback; station marks; diagonal checks
• Pre-weld: fit-up, bevels, cleanliness, tack pattern review
• Compartment test: pressure test sealed volumes; document results
• Systems safety: fuel line inspection; ventilation checks; CO detector test.⁸⁹
• Required gear: Washington checklist cross-check before first sea trial.⁷