Editable DC examples

12 V boat wiring diagrams

Explore a boat’s 12 V system: engine, starter and house batteries, DC-DC charging, a SmartShunt, bilge pump and navigation lights. Start with the core circuits or open the full demo with solar charging, cabin appliances and stern lighting.

mm² / metresAWG / feet

Follow the circuits

How to read the boat diagram

Start with the engine and battery drawing. Follow each positive supply and its negative return before moving to the full boat demo.

Find the starter circuit
The starter battery positive connects to the Volvo Penta engine’s starter terminal. The engine ground returns to starter battery negative. Keep this starting circuit distinct from the house battery’s accessory circuits.
Trace the DC-DC charging branch
The engine’s alternator-positive terminal feeds the Orion-Tr Smart 12/12-18 input. Its output connects to house battery positive. Follow the charger’s negative connections too: the saved demo’s return junction is unfinished, as explained below.
Follow house power to the loads
House battery positive feeds the engine-area positive bus. The bilge pump branches from this bus before the main switch; the switch feeds the distribution panel and navigation-light branch. The full demo adds solar charging, cabin appliances and stern circuits. Pump and navigation-light controls still need their own design.
Read the return through the SmartShunt
House battery negative connects to the SmartShunt’s battery side. The system side connects to the negative distribution bus and starter battery negative. Trace a load’s return back through those connections, then match both conductor runs to the cable table.

Unfinished charging return: the Orion’s negative terminals meet at a junction with no cable back to the battery or system negative. The full demo also connects the solar controller’s battery negative to that junction. Resolve this path and the engine findings shown with each drawing before adapting the charging design.

Boat engine, starter and house banks

14 components · 20 conductors · 12 V boat system

Open this example in Crimp →

Live Crimp simulation. Try equipment states and battery charge, or choose Wiring to inspect the circuit. Cable IDs match the table below.

View full screen

Red = positive · dark = return. Crossings are not junctions. Read the assumptions before adapting a circuit.

Protection is unfinished. The demo retains its battery-post fuses and cable fuse choices. These do not verify the complete protection or charging design; review the engine findings below and the actual installation. All charging and load currents below are design allowances, not measured operating currents.

Current engine findings

The fuse interrupt check uses the engine’s chemistry-based fault-current assumption. This is not measured fault current. Resolve the bank and protection design before installation.

Check the exact fuse, holder and battery evidence →

warning: Return path missing: Orion 18A (system)
warning: Conflicting fuse ratings: LiFePO4 100Ah (C15, C18)
warning: Check fuse suitability: Start 80 (C12)
warning: Check fuse suitability: LiFePO4 100Ah (C15, C18, C6, C11, C14, C17)
warning: Check monitor power: SmartShunt 500 (C10, C13, C14, C16)

Cable table — every displayed connection

Each length is one way. Drop is the engine’s run estimate including return, not a measured end-to-end system result; shared legs can have different conservative design-current bounds. “Pinned” marks a saved demo choice to review after edits. AWG is approximate; retain the stated conductor area when selecting actual wire.

Boat engine, starter and house banks cable schedule in metric with AWG
Circuit / endpoints	One-way length	Conductor	Design current	Fuse	Drop / allowance
C1 · Negative Bus Bar 1 − ↔ Lanterns (LED) −	One-way length5 m16.4 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0.5 A		Drop / allowance0.23% / 3%
C2 · Main Battery Switch B ↔ Positive Bus Bar +	One-way length2 m6.6 ft	Conductor4 mm²AWG 11 · 45 A table	Design current6 A	FuseNo cable fuse set	Drop / allowance0.41% / 3%
C3 · Victron Orion-Tr Smart 12/12-18 IN − ↔ Junction	One-way length50 cm1.6 ft	Conductor2.5 mm²AWG 13 · 35 A table	Design current20.7 A		Drop / allowance0.60% / 3%
C4 · Victron Orion-Tr Smart 12/12-18 OUT − ↔ Junction	One-way length50 cm1.6 ft	Conductor2.5 mm²AWG 13 · 35 A table	Design current18 A		Drop / allowance0.53% / 3%
C5 · Positive Bus Bar 2 + ↔ Main Battery Switch A	One-way length50 cm1.6 ft	Conductor4 mm²AWG 11 · 45 A table	Design current6 A	FuseNo cable fuse set	Drop / allowance0.10% / 3%
C6 · Bilge Pump 1100 GPH + ↔ Positive Bus Bar 1 +	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current3.5 A	Fuse7.5 A	Drop / allowance0.32% / 3%
C7 · Negative Bus Bar 1 − ↔ Bilge Pump 1100 GPH −	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current3.5 A		Drop / allowance0.32% / 3%
C8 · Negative Bus Bar 2 − ↔ Negative Bus Bar −	One-way length2 m6.6 ft	Conductor2.5 mm²AWG 13 · 35 A table	Design current6 A		Drop / allowance0.66% / 3%
C9 · Engine 36HP — Volvo Penta MD17C Block GND − ↔ 80 Ah Start Battery −	One-way length1.5 m4.9 ft	Conductor70 mm²AWG 2/0 · 330 A table	Design current150 A		Drop / allowance0.47% / 3%
C10 · 80 Ah Start Battery − ↔ Victron SmartShunt 500A LOAD −	One-way length50 cm1.6 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current9.5 A		Drop / allowance0.43% / 3%
C11 · USB-C PD Outlet (60W) + ↔ Positive Bus Bar 2 +	One-way length50 cm1.6 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current5.5 A	Fuse7.5 A	Drop / allowance0.25% / 3%
C12 · 80 Ah Start Battery + ↔ Engine 36HP — Volvo Penta MD17C Starter +	One-way length1.5 m4.9 ft	Conductor70 mm²AWG 2/0 · 330 A table	Design current150 A	FuseNo cable fuse set	Drop / allowance0.47% / 3%
C13 · Victron SmartShunt 500A LOAD − ↔ Negative Bus Bar −	One-way length50 cm1.6 ft	Conductor2.5 mm²AWG 13 · 35 A table	Design current9.5 A		Drop / allowance0.26% / 3%
C14 · Victron SmartShunt 500A B+ sense ↔ Positive Bus Bar +	One-way length50 cm1.6 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current0 A	Fuse2 A	Drop / allowance0.00% / 3%
C15 · Victron Orion-Tr Smart 12/12-18 OUT + ↔ 100 Ah LiFePO4 +	One-way length50 cm1.6 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current18 A	Fuse25 A	Drop / allowance0.88% / 3%
C16 · 100 Ah LiFePO4 − ↔ Victron SmartShunt 500A BATT −	One-way length50 cm1.6 ft	Conductor2.5 mm²AWG 13 · 35 A table	Design current9.5 A		Drop / allowance0.26% / 3%
C17 · Lanterns (LED) + ↔ Positive Bus Bar 1 +	One-way length5.5 m18 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current0.5 A	Fuse1 A	Drop / allowance0.25% / 3%
C18 · Positive Bus Bar + ↔ 100 Ah LiFePO4 +	One-way length1 m3.3 ft	Conductor10 mm²AWG 8 · 80 A table	Design current9.5 A	FuseNo cable fuse set	Drop / allowance0.13% / 3%
C19 · Engine 36HP — Volvo Penta MD17C Alt B+ ↔ Victron Orion-Tr Smart 12/12-18 IN +	One-way length1 m3.3 ft	Conductor6 mm²AWG 10 · 60 A tablePinned choice	Design current20.7 A	Fuse50 A	Drop / allowance0.50% / 3%
C20 · USB-C PD Outlet (60W) − ↔ Negative Bus Bar 2 −	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current5.5 A		Drop / allowance0.50% / 3%

Component table and exact example assumptions

Components in Boat engine, starter and house banks
Component	Ratings, role and assumptions
80 Ah Start BatteryPlanning placeholder	12 V · 80 Ah Cranking battery for diesel/petrol engine.
Main Battery SwitchPlanning placeholder	Single-pole disconnect on positive bus.
JunctionPlanning placeholder	A wire splice — any number of cables can meet here. Born from a cable dropped into empty space; promotes to a real junction once a second cable lands on it.
Bilge Pump 1100 GPHPlanning placeholder	3.5 A load allowance Auto float-switch bilge pump, ~3.5A while running.
Positive Bus BarPlanning placeholder	Positive bus bar — common feed with multiple output studs.
Lanterns (LED)Planning placeholder	0.5 A load allowance · 6 W Modern LED navigation lights — port, starboard, stern and masthead. Low draw, suitable for night passages.
Negative Bus BarPlanning placeholder	Negative bus bar — common return with multiple output studs.
Engine 36HP — Volvo Penta MD17CMD17C	150 A load allowance · 35 A rated / planning output Volvo Penta MD17C with original 12 V / 1.5 kW starter and 35 A alternator. Modeled 150 A cranking and 300 A surge are estimates; replace the stock charging value if a different alternator is fitted. Retain panel and excitation wiring.
Victron Orion-Tr Smart 12/12-18Orion-Tr Smart 12/12-18	18 A rated / planning output Isolated 18A DC-DC charger from start to house battery. Detects engine run from the input voltage and charges with a three-stage algorithm, set up over Bluetooth.
Negative Bus BarPlanning placeholder	Negative bus bar — common return with multiple output studs.
Positive Bus BarPlanning placeholder	Positive bus bar — common feed with multiple output studs.
Victron SmartShunt 500ASmartShunt 500A/50mV (IP21)	500 A/50 mV battery shunt with Bluetooth and a VE.Direct port, no display. Reads out through the VictronConnect app or a GX device; the aux input can monitor a second battery, midpoint or temperature.
USB-C PD Outlet (60W)Planning placeholder	5.5 A load allowance · 60 W
100 Ah LiFePO4Planning placeholder	12.8 V · 100 Ah Generic 12V 100Ah lithium iron phosphate house battery.

Full boat demo — solar, cabin and stern

33 components · 53 conductors · 12 V boat system

Open this example in Crimp →

Live Crimp simulation. Try equipment states and battery charge, or choose Wiring to inspect the circuit. Cable IDs match the table below.

View full screen

Red = positive · dark = return. Crossings are not junctions. Read the assumptions before adapting a circuit.

Current engine findings

The fuse interrupt check uses the engine’s chemistry-based fault-current assumption. This is not measured fault current. Resolve the bank and protection design before installation.

Check the exact fuse, holder and battery evidence →

critical: SmartShunt 500: B+ sense is a sense lead, not a bus (C31, C50)
warning: Solar disconnection is missing (C1, C2)
warning: Return path missing: MPPT 100/30 (system)
warning: Return path missing: Orion 18A (system)
warning: Conflicting fuse ratings: LiFePO4 100Ah (C32, C49)
warning: Check fuse suitability: Start 80 (C29)
warning: Check fuse suitability: LiFePO4 100Ah (C32, C49, C8, C9, C16, C17, C26, C31, C34, C35, C36, C37, C39, C43, C45, C48, C50)
warning: Cable sizing needs checking (C48, C20, C8, C33, C26, C4, C23, C29, C3, C28, C38, C11, C41, C25, C36, C5, C51, C14, C12, C37, C6, C18, C7, C21, C19, C24, C9, C35, C52, C34, C49, C45, C44, C16, C43, C40, C32, C46, C42, C10, C39, C17, C53, C2, C13, C27, C15, C47, C30, C22, C1)
warning: CRX-65: verify manufacturer wiring (C27, C45, C7, C15, C49, C28, C18, C23, C30, C33)
warning: CRX-65: fuse below manufacturer requirement (C45)
warning: Check monitor power: SmartShunt 500 (C25, C30, C31, C33, C50)

Cable table — every displayed connection

Full boat demo — solar, cabin and stern cable schedule in metric with AWG
Circuit / endpoints	One-way length	Conductor	Design current	Fuse	Drop / allowance
C1 · Flexible 100 W Panel + ↔ Junction	One-way length50 cm1.6 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0 A	FuseNo cable fuse set	Drop / allowance0.00% / 3%
C2 · Junction ↔ Victron MPPT 100/30 PV +	One-way length4 m13.1 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0 A	FuseNo cable fuse set	Drop / allowance0.00% / 3%
C3 · Victron MPPT 100/30 BATT − ↔ Junction	One-way length30 cm1.0 ft	Conductor4 mm²AWG 11 · 45 A table	Design current30 A		Drop / allowance0.33% / 3%
C4 · Junction ↔ Victron MPPT 100/30 PV −	One-way length4 m13.1 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0 A		Drop / allowance0.00% / 3%
C5 · 200 W Solar Panel − ↔ Junction	One-way length50 cm1.6 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0 A		Drop / allowance0.00% / 3%
C6 · Negative Bus Bar 1 − ↔ Lanterns (LED) −	One-way length5 m16.4 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0.5 A		Drop / allowance0.23% / 3%
C7 · Main Battery Switch B ↔ Positive Bus Bar +	One-way length2 m6.6 ft	Conductor16 mm²AWG 6 · 120 A table	Design current23.5 A	FuseNo cable fuse set	Drop / allowance0.40% / 3%
C8 · Whale Universal Pump + ↔ Positive Bus Bar 3 +	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current6 A	Fuse7.5 A	Drop / allowance0.55% / 3%
C9 · USB-C PD Outlet (60W) + ↔ Positive Bus Bar 5 +	One-way length2 m6.6 ft	Conductor2.5 mm²AWG 13 · 35 A tablePinned choice	Design current5.5 A	Fuse7.5 A	Drop / allowance0.60% / 3%
C10 · Victron Orion-Tr Smart 12/12-18 IN − ↔ Junction	One-way length50 cm1.6 ft	Conductor2.5 mm²AWG 13 · 35 A table	Design current20.7 A		Drop / allowance0.60% / 3%
C11 · Flexible 100 W Panel − ↔ Junction	One-way length90 cm3 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0 A		Drop / allowance0.00% / 3%
C12 · Victron Orion-Tr Smart 12/12-18 OUT − ↔ Junction	One-way length50 cm1.6 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current18 A		Drop / allowance0.88% / 3%
C13 · 12V LED Downlight + ↔ Positive Bus Bar 1 +	One-way length30 cm1.0 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0.3 A	FuseNo cable fuse set	Drop / allowance0.01% / 10%
C14 · 12V LED Downlight + ↔ Positive Bus Bar 2 +	One-way length50 cm1.6 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0.3 A	FuseNo cable fuse set	Drop / allowance0.01% / 10%
C15 · Positive Bus Bar 2 + ↔ Main Battery Switch A	One-way length50 cm1.6 ft	Conductor16 mm²AWG 6 · 120 A table	Design current23.5 A	FuseNo cable fuse set	Drop / allowance0.10% / 3%
C16 · Positive Bus Bar 1 + ↔ Eberspächer Airtronic D2 +	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current3 A	Fuse20 A	Drop / allowance0.27% / 3%
C17 · Bilge Pump 1100 GPH + ↔ Positive Bus Bar 3 +	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current3.5 A	Fuse7.5 A	Drop / allowance0.32% / 3%
C18 · Negative Bus Bar − ↔ Negative Bus Bar 3 −	One-way length1 m3.3 ft	Conductor10 mm²AWG 8 · 80 A table	Design current17.5 A		Drop / allowance0.24% / 3%
C19 · Whale Universal Pump − ↔ Negative Bus Bar 3 −	One-way length50 cm1.6 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current6 A		Drop / allowance0.27% / 3%
C20 · USB-C PD Outlet (60W) − ↔ Negative Bus Bar 4 −	One-way length50 cm1.6 ft	Conductor2.5 mm²AWG 13 · 35 A table	Design current5.5 A		Drop / allowance0.15% / 3%
C21 · Negative Bus Bar 1 − ↔ Eberspächer Airtronic D2 −	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current3 A		Drop / allowance0.27% / 3%
C22 · Negative Bus Bar 3 − ↔ Bilge Pump 1100 GPH −	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current3.5 A		Drop / allowance0.32% / 3%
C23 · Negative Bus Bar 2 − ↔ Negative Bus Bar −	One-way length2 m6.6 ft	Conductor16 mm²AWG 6 · 120 A table	Design current23.5 A		Drop / allowance0.40% / 3%
C24 · Engine 36HP — Volvo Penta MD17C Block GND − ↔ 80 Ah Start Battery −	One-way length1.5 m4.9 ft	Conductor70 mm²AWG 2/0 · 330 A table	Design current150 A		Drop / allowance0.47% / 3%
C25 · 80 Ah Start Battery − ↔ Victron SmartShunt 500A LOAD −	One-way length50 cm1.6 ft	Conductor6 mm²AWG 10 · 60 A table	Design current41.5 A		Drop / allowance0.47% / 3%
C26 · USB-C PD Outlet (60W) + ↔ Positive Bus Bar 4 +	One-way length50 cm1.6 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current5.5 A	Fuse7.5 A	Drop / allowance0.25% / 3%
C27 · Dometic CRX-65 Fridge + ↔ Positive Bus Bar 3 +	One-way length3 m9.8 ft	Conductor4 mm²AWG 11 · 45 A table	Design current5.5 A	FuseNo cable fuse set	Drop / allowance0.56% / 3%
C28 · Dometic CRX-65 Fridge − ↔ Negative Bus Bar 5 −	One-way length3 m9.8 ft	Conductor4 mm²AWG 11 · 45 A table	Design current5.5 A		Drop / allowance0.56% / 3%
C29 · 80 Ah Start Battery + ↔ Engine 36HP — Volvo Penta MD17C Starter +	One-way length1.5 m4.9 ft	Conductor70 mm²AWG 2/0 · 330 A table	Design current150 A	FuseNo cable fuse set	Drop / allowance0.47% / 3%
C30 · Victron SmartShunt 500A LOAD − ↔ Negative Bus Bar −	One-way length50 cm1.6 ft	Conductor16 mm²AWG 6 · 120 A table	Design current41.5 A		Drop / allowance0.18% / 3%
C31 · Victron SmartShunt 500A B+ sense ↔ Positive Bus Bar +	One-way length50 cm1.6 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current0 A	Fuse2 A	Drop / allowance0.00% / 3%
C32 · Victron Orion-Tr Smart 12/12-18 OUT + ↔ 100 Ah LiFePO4 +	One-way length50 cm1.6 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current18 A	Fuse25 A	Drop / allowance0.88% / 3%
C33 · 100 Ah LiFePO4 − ↔ Victron SmartShunt 500A BATT −	One-way length50 cm1.6 ft	Conductor16 mm²AWG 6 · 120 A table	Design current41.5 A		Drop / allowance0.18% / 3%
C34 · Victron MPPT 100/30 BATT + ↔ Positive Bus Bar +	One-way length50 cm1.6 ft	Conductor4 mm²AWG 11 · 45 A tablePinned choice	Design current30 A	Fuse40 A	Drop / allowance0.55% / 3%
C35 · 12V Reading/Wall Lamp + ↔ Positive Bus Bar 4 +	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current0.3 A	Fuse1 A	Drop / allowance0.02% / 10%
C36 · 12V Reading/Wall Lamp + ↔ Positive Bus Bar 3 +	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current0.3 A	Fuse1 A	Drop / allowance0.02% / 10%
C37 · Positive Bus Bar + ↔ Positive Bus Bar 4 +	One-way length1 m3.3 ft	Conductor4 mm²AWG 11 · 45 A tablePinned choice	Design current11.5 A	Fuse15 A	Drop / allowance0.39% / 3%
C38 · USB-C PD Outlet (60W) − ↔ Negative Bus Bar 2 −	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current5.5 A		Drop / allowance0.50% / 3%
C39 · USB-C PD Outlet (60W) + ↔ Positive Bus Bar 2 +	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current5.5 A	Fuse7.5 A	Drop / allowance0.50% / 3%
C40 · 12V Reading/Wall Lamp − ↔ Negative Bus Bar 4 −	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0.3 A		Drop / allowance0.02% / 10%
C41 · 12V Reading/Wall Lamp − ↔ Negative Bus Bar 3 −	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0.3 A		Drop / allowance0.02% / 10%
C42 · USB-C PD Outlet (60W) − ↔ Negative Bus Bar 1 −	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current5.5 A		Drop / allowance0.50% / 3%
C43 · USB-C PD Outlet (60W) + ↔ Positive Bus Bar 1 +	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current5.5 A	Fuse7.5 A	Drop / allowance0.50% / 3%
C44 · Negative Bus Bar − ↔ Negative Bus Bar 4 −	One-way length1 m3.3 ft	Conductor2.5 mm²AWG 13 · 35 A table	Design current11.5 A		Drop / allowance0.63% / 3%
C45 · Positive Bus Bar + ↔ Positive Bus Bar 2 +	One-way length1 m3.3 ft	Conductor10 mm²AWG 8 · 80 A tablePinned choice	Design current6 A	Fuse10 A	Drop / allowance0.08% / 3%
C46 · 12V LED Downlight − ↔ Negative Bus Bar 2 −	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0.3 A		Drop / allowance0.02% / 10%
C47 · 12V LED Downlight − ↔ Negative Bus Bar 1 −	One-way length80 cm2.6 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0.3 A		Drop / allowance0.02% / 10%
C48 · Lanterns (LED) + ↔ Positive Bus Bar 1 +	One-way length5.5 m18 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current0.5 A	Fuse1 A	Drop / allowance0.25% / 3%
C49 · Positive Bus Bar + ↔ 100 Ah LiFePO4 +	One-way length1 m3.3 ft	Conductor35 mm²AWG 2 · 210 A table	Design current71.5 A	FuseNo cable fuse set	Drop / allowance0.28% / 3%
C50 · Victron MPPT 100/30 BATT + ↔ Victron SmartShunt 500A B+ sense	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A tablePinned choice	Design current0 A	Fuse2 A	Drop / allowance0.00% / 3%
C51 · Engine 36HP — Volvo Penta MD17C Alt B+ ↔ Victron Orion-Tr Smart 12/12-18 IN +	One-way length1 m3.3 ft	Conductor6 mm²AWG 10 · 60 A tablePinned choice	Design current20.7 A	Fuse50 A	Drop / allowance0.50% / 3%
C52 · 200 W Solar Panel + ↔ Junction	One-way length50 cm1.6 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current0 A	FuseNo cable fuse set	Drop / allowance0.00% / 3%
C53 · USB-C PD Outlet (60W) − ↔ Negative Bus Bar 2 −	One-way length1 m3.3 ft	Conductor1.5 mm²AWG 16 · 25 A table	Design current5.5 A		Drop / allowance0.50% / 3%

Component table and exact example assumptions

Components in Full boat demo — solar, cabin and stern
Component	Ratings, role and assumptions
80 Ah Start BatteryPlanning placeholder	12 V · 80 Ah Cranking battery for diesel/petrol engine.
Main Battery SwitchPlanning placeholder	Single-pole disconnect on positive bus.
Flexible 100 W PanelPlanning placeholder	18 V · 5.6 A rated / planning output · 100 W · 21.6 V STC Voc
Victron MPPT 100/30SmartSolar 100/30	30 A rated / planning output MPPT solar charge controller. 30A output, max 440W @ 12V / 880W @ 24V, 100V PV. Bluetooth built in; 12/24V battery auto-detect.
JunctionPlanning placeholder	A wire splice — any number of cables can meet here. Born from a cable dropped into empty space; promotes to a real junction once a second cable lands on it.
JunctionPlanning placeholder	A wire splice — any number of cables can meet here. Born from a cable dropped into empty space; promotes to a real junction once a second cable lands on it.
Bilge Pump 1100 GPHPlanning placeholder	3.5 A load allowance Auto float-switch bilge pump, ~3.5A while running.
200 W Solar PanelPlanning placeholder	24 V · 8.5 A rated / planning output · 200 W Generic 200W mono panel (≈5.6A Imp).
JunctionPlanning placeholder	A wire splice — any number of cables can meet here. Born from a cable dropped into empty space; promotes to a real junction once a second cable lands on it.
Positive Bus BarPlanning placeholder	Positive bus bar — common feed with multiple output studs.
Lanterns (LED)Planning placeholder	0.5 A load allowance · 6 W Modern LED navigation lights — port, starboard, stern and masthead. Low draw, suitable for night passages.
Negative Bus BarPlanning placeholder	Negative bus bar — common return with multiple output studs.
Eberspächer Airtronic D2Airtronic D2	3 A load allowance · 34 W 2.2 kW diesel air heater. Runs on roughly 8–34 W (under 3 A at 12 V) depending on heat level; the glow pin draws about 100 W (~8 A) for the first minutes of each start.
Engine 36HP — Volvo Penta MD17CMD17C	150 A load allowance · 35 A rated / planning output Volvo Penta MD17C with original 12 V / 1.5 kW starter and 35 A alternator. Modeled 150 A cranking and 300 A surge are estimates; replace the stock charging value if a different alternator is fitted. Retain panel and excitation wiring.
12V LED DownlightPlanning placeholder	0.25 A load allowance · 3 W 3W warm-white downlight.
Whale Universal PumpUniversal	6 A load allowance Whale Universal pressure-pump family; exact UF model is unspecified. The manual requires the motor-label fuse, positive isolation switch and inlet strainer. Modeled current and daily runtime are estimates until the installed pump is identified.
USB-C PD Outlet (60W)Planning placeholder	5.5 A load allowance · 60 W
12V LED DownlightPlanning placeholder	0.25 A load allowance · 3 W 3W warm-white downlight.
Victron Orion-Tr Smart 12/12-18Orion-Tr Smart 12/12-18	18 A rated / planning output Isolated 18A DC-DC charger from start to house battery. Detects engine run from the input voltage and charges with a three-stage algorithm, set up over Bluetooth.
Positive Bus BarPlanning placeholder	Positive bus bar — common feed with multiple output studs.
Negative Bus BarPlanning placeholder	Negative bus bar — common return with multiple output studs.
Positive Bus BarPlanning placeholder	Positive bus bar — common feed with multiple output studs.
Negative Bus BarPlanning placeholder	Negative bus bar — common return with multiple output studs.
Victron SmartShunt 500ASmartShunt 500A/50mV (IP21)	500 A/50 mV battery shunt with Bluetooth and a VE.Direct port, no display. Reads out through the VictronConnect app or a GX device; the aux input can monitor a second battery, midpoint or temperature.
USB-C PD Outlet (60W)Planning placeholder	5.5 A load allowance · 60 W
Dometic CRX-65 FridgeCRX-65	5.5 A load allowance · 66 W CoolMatic CRX65 compressor refrigerator, rated 5.5 A at 12 V or 2.8 A at 24 V. Manufacturer DC supply protection is 15 A at 12 V or 7.5 A at 24 V; compressor duty and daily energy depend on installation and use.
100 Ah LiFePO4Planning placeholder	12.8 V · 100 Ah Generic 12V 100Ah lithium iron phosphate house battery.
USB-C PD Outlet (60W)Planning placeholder	5.5 A load allowance · 60 W
USB-C PD Outlet (60W)Planning placeholder	5.5 A load allowance · 60 W
12V Reading/Wall LampPlanning placeholder	0.25 A load allowance · 3 W Adjustable LED reading/wall lamp, typical bunk or saloon fixture.
12V Reading/Wall LampPlanning placeholder	0.25 A load allowance · 3 W Adjustable LED reading/wall lamp, typical bunk or saloon fixture.
Positive Bus BarPlanning placeholder	Positive bus bar — common feed with multiple output studs.
Negative Bus BarPlanning placeholder	Negative bus bar — common return with multiple output studs.

Before adapting an example

What these drawings assume

Both drawings come from the same boat demo project. The first keeps its engine and battery area, load distribution panel and bow; the full demo also includes solar, cabin and stern circuits. Equipment, connections, cable lengths and protection choices are retained from the demo, with cable sizes recalculated by Crimp. The demo is a starting project with unresolved engine findings, not a verified installation. Switching controls, bonding, shore power and the actual installation environment need separate review.

Equipment and saved settings come from the boat demo. Battery acceptance, BMS controls, charging configuration, solar compatibility and runtime have not been verified for an actual installation.
Battery-post and cable fuse choices are retained from the demo. Check the actual device, holder, interrupt rating and placement, and resolve the engine findings before adapting the project.
Lengths are physical one-way conductor runs. Voltage drop includes a return; shared paths use the engine’s conservative current bounds, not a prediction of simultaneous power flow. The calculation does not verify unequal shared-return lengths as one complete circuit. AWG labels are approximate table counterparts to metric conductors, not identical cross-sectional areas.
Sizing uses Crimp’s ABYC-based tables for 105°C copper outside engine spaces, with no additional heat or bundling derating in these examples. Explicit 3% circuit targets and 10% cabin-light allowances are planning choices; terminals on placeholders carry generic planning limits, not verified connector ratings. US RV, UK campervan and Australian 4WD wording does not establish UK or AS/NZS installation compliance.

Adding monitoring or larger distribution changes the current paths. Read the SmartShunt return-path example and Lynx Distributor example, including their conservative series-current bounds and unresolved protection. The model pages keep those limitations visible.

Demo equipment

Component references

Read the catalog notes and linked documentation for the equipment used in the boat demo. Imported settings are example choices to review.

Crimp component libraryVolvo Penta MD17C engineEngine, starter and alternator terminals used in the boat demo.Crimp component libraryOrion-Tr Smart 12/12-18The demo’s DC-DC charger, with model notes and linked documentation.Crimp component librarySmartShunt 500 ABattery and system sides of the house-bank shunt.Crimp component librarySmartSolar MPPT 100/30Solar controller in the full boat demo.

Keep goingWire size calculatorEnter one-way length, current and installation conditions to compare ampacity and voltage drop.Keep goingDC-DC charger size calculatorCheck vehicle headroom and battery acceptance before choosing a charging current.Keep goingCampervan & RV 12 V wiring diagramsVictron-based DC diagrams with solar, house loads and optional Orion XS alternator charging.Keep going12 V dual battery wiring diagramsStarter-to-auxiliary charging with Orion XS or REDARC BCDC1240D, plus protected house loads.Keep goingLiFePO₄ fuse size calculatorCheck exact fuse/holder, voltage, whole-bank fault current and placement evidence.Keep goingLead-acid to LiFePO₄ conversion guideReview charging, protection and monitoring when changing battery chemistry.Keep goingSizing methodologyRead the engine’s ABYC assumptions and limits before adapting an example.

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12 V boat wiring diagrams

How to read the boat diagram

Find the starter circuit

Trace the DC-DC charging branch

Follow house power to the loads

Read the return through the SmartShunt

Boat engine, starter and house banks

Full boat demo — solar, cabin and stern

What these drawings assume

Component references

Ask your AI. Check the plan in Crimp.