Trimaran Bonito 12 V Electrical System

Complete redesign of the boat's 12 V electrical system around modern Victron components, four independent solar MPPTs, dual AGM battery banks, a Cerbo GX for monitoring, and the DJI Power 2000 acting as the on-board 230 V AC source.

Project layout

.
├── README.md                ← this file
├── docs/
│   ├── architecture.md      ← block diagram, charging logic, Cerbo/network
│   ├── BOM.csv              ← bill of materials with part numbers
│   ├── wiring.md            ← per-circuit wire gauges, fuses, terminals
│   └── open-items.md        ← decisions still needed before ordering
├── KiCad/
│   ├── boat_electrical.kicad_pro
│   └── boat_electrical.kicad_sch
├── Fritzing/
│   ├── README.md
│   └── boat_overview.svg    ← printable one-page visual overview
└── Fusion/
    ├── README.md
    ├── analysis.md          ← marine electrical CAD best practices
    ├── component-dimensions.md
    ├── panel-layout.svg     ← 1:1 fabrication drawing of the two panels
    └── build_layout.py      ← Fusion 360 Python script (creates 3D model)

System at a glance

• Solar: 4 × 50 Wp panels → 4 × Victron SmartSolar 75/15 (one MPPT per panel, so partial shading on one panel does not drag the rest down).
• Batteries: 2 × 100 Ah AGM house bank, 1 × 35 Ah AGM starter bank (same chemistry → no DC-DC charger required; a Cyrix-ct 120 battery combiner handles starter top-up from solar).
• Engine: Yamaha 9.9 outboard alternator wired directly to starter battery (never disconnected by main switch).
• Monitoring: SmartShunt 500 A on house negative, four MPPTs and the shunt all report via VE.Direct to a Cerbo GX, which sits on the RUT901 LAN.
• AC power: DJI Power 2000 charged from the 12 V house bus via its DC input, and its 230 V AC output feeds the boat's AC outlets.
• Network: Cerbo GX ↔ RUT901 (Ethernet); RUT901 + PoE injector → mast camera.

Loads

On the 8-circuit distribution panel:

#	Circuit	Fuse
1	Cabin lights + reading + floor	15 A
2	ST60 wind + depth	3 A
3	Fridge	15 A
4	Autopilot	25 A
5	Powerrigger	50 A
6	Wallas Diesel cooker	15 A
7	12 V outlets / USB	10 A
8	Always-on (Cerbo / RUT / PoE)	5 A

Direct from a battery bank (too high-current for the panel):

Circuit	Bank	Fuse
Yamaha starter motor	Starter	150 A Class-T
Bow thruster (Bugstrahlruder)	House	250 A Class-T
Anchor windlass (Ankerwinsch)	House	150 A MEGA

Bow thruster and windlass negatives go through the SmartShunt with the rest of the house loads so the state-of-charge stays accurate. Only the starter motor (which draws from the starter bank) bypasses the shunt.

How to open the deliverables

• KiCad schematic: open KiCad/boat_electrical.kicad_pro with KiCad 7 or 8 (free, kicad.org).
• Visual overview: open Fritzing/boat_overview.svg in any browser, or import into Fritzing for further editing.
• 3D layout in Fusion 360: run Fusion/build_layout.py via Utilities ▸ Add-Ins ▸ Scripts and Add-Ins ▸ My Scripts. See Fusion/README.md for the full walk-through.
• Front-panel fabrication drawing: open Fusion/panel-layout.svg in a browser and print at 100 % scale.
• Wiring tables / BOM: plain Markdown / CSV — open with any editor or spreadsheet.

Safety notes

• The Yamaha starter run is the highest-current circuit on the boat. Keep its cable short (< 1 m if possible), use 35 mm² minimum, and protect with a 150 A MEGA or Class-T fuse at the starter battery + terminal.
• The SmartShunt MUST be in the house bank negative ONLY. The starter battery negative goes directly to the common negative bus.
• Every positive cable leaving a battery is fused within 18 cm of the battery terminal (ABYC E-11 best practice).