The essentials in 30 seconds
- Pure sine is mandatory in marine. Quasi-sine inverter (modified square wave) damages laptop charger transformers and poorly powers compressor fridges. Pure sine = 99% of sailboat use in 2026.
- Sizing = continuous power AND peak load. A 1,200 W coffee maker draws 2,000 W at startup (3-5 sec). A 1,200 W "smooth" inverter will overload and shut down. Always size the inverter at 150% of continuous consumption.
- 2026 standards: Victron Phoenix 12/1600 Smart (~ $540 VAT excluded) for occasional use. MultiPlus 12/3000-120 for continuous use with shore power charger integrated.
- Idle loss matters. Inverter in standby consumes 0.3-0.8 A continuously. Over 24 h unused = 7-20 Ah loss. Always install an accessible ON/OFF switch.
- Installed workshop budget for 35-45 ft sailboat: ~ $700-$1,200 VAT excluded (inverter + wiring + protection + switch), excluding battery bank which depends on lithium sizing (see our sizing article).
The DC/AC inverter is the bridge between your 12/24 V bank and the 230 V world. It converts the battery’s DC voltage into a sinusoidal AC output, allowing household appliances (coffee maker, computer, absorption fridge, electronic chargers) to run. But without proper sizing, it’s the most temperamental piece of equipment on board.
This article explains the difference between pure sine and quasi-sine, provides a sizing method, presents the Victron and Mastervolt ranges stocked by Skysat, and outlines installation rules. For the battery bank powering the inverter, see our lithium bank sizing article.
Why pure sine, not quasi-sine
Two inverter technologies coexist: quasi-sine (modified square wave, stepped waveform) and pure sine (waveform close to the EDF grid).
- Quasi-sine: cheaper, slightly higher efficiency, but high harmonic noise. Damages: transformers (laptop chargers, camera chargers), induction motors (fridge compressors, fans), medical equipment.
- Pure sine: identical to grid power, runs everything without issues. 20-30% surcharge vs quasi-sine, but worthwhile investment as soon as you go beyond basic smartphone chargers.
In modern sailboats in 2026, pure sine is the de facto standard. Unless you have a very specific use case (incandescent lighting only), go for pure sine.
Sizing — workshop method
Calculation in 4 steps:
- List the 230 V equipment used simultaneously. Coffee maker (1,000-1,500 W) + laptop (90 W) + absorption fridge (300 W at startup). Total continuous: ~1,400 W.
- Identify startup peak load. For coffee makers and fridges, multiply continuous power by 1.5-2.0. Estimated peak: ~2,100 W.
- Choose an inverter at 150% of continuous consumption. Continuous consumption 1,400 W × 1.5 = inverter 2,100 W minimum. Round up to the next range: inverter 2,000-2,500 W.
- Check the peak load: a 2,000 W Victron inverter handles a ~4,000 W peak for 1-2 seconds (datasheet). Compatible with coffee maker/fridge startup.
For light occasional use (just laptop + USB chargers): Phoenix 12/1600 Smart (~ $540 VAT excluded) is more than enough.
Victron Phoenix range
Entry and mid-range Victron range, pure sine, in 12 V and 24 V.
- Phoenix 12/500 Smart: ~ $270 VAT excluded. Small uses: laptop, USB chargers, 230 V lighting.
- Phoenix 12/1200 Smart: ~ $470 VAT excluded. Light coffee makers, drills, small tools.
- Phoenix 12/1600 Smart: ~ $540 VAT excluded. Skysat’s workshop reference for 35-45 ft sailboats. 3,000 W peak (2-5 sec).
- Phoenix 24/1600 Smart: ~ $580 VAT excluded. 24 V version for sailboats with 24 V architecture.
- Phoenix 12/2000 Smart: ~ $850 VAT excluded. Fridge compressor + coffee maker + tools.
- Phoenix 12/3000 Smart: ~ $1,250 VAT excluded. Intensive continuous use.
Mastervolt Mass Sine range
Direct competitor to Victron with MasterBus / CZone integration for configured yachts.
- Mass Sine 12/1500: ~ $720 VAT excluded. More expensive than Victron at equivalent power, but native MasterBus integration.
- Mass Sine 12/2000: ~ $980 VAT excluded.
- Mass Sine 12/2500: ~ $1,250 VAT excluded.
Mastervolt is preferred on new Bénéteau/Jeanneau/Bavaria yachts equipped with CZone (native dashboard integration).
Inverter-charger combo
For intensive use and regular harbor stays, consider the inverter + shore charger combo in a single unit (Victron MultiPlus).
- MultiPlus 12/3000-120: 3,000 W inverter + 120 A shore charger in one box. ~ $1,850 VAT excluded. At the dock, it functions as a charger; at anchor, as an inverter. Automatic transfer in under 20 ms.
- MultiPlus II 48/3000: ~ $1,950 VAT excluded. 48 V version for large hybrid + solar banks.
If you plan to replace your shore charger and install an inverter, the MultiPlus saves on wiring and space.
Model comparison chart
| Model | Continuous power | Peak | Efficiency | Price VAT excluded |
|---|---|---|---|---|
| Victron Phoenix 12/500 | 500 W | 900 W | 89% | ~ $270 |
| Victron Phoenix 12/1200 | 1,200 W | 2,200 W | 91% | ~ $470 |
| Victron Phoenix 12/1600 | 1,600 W | 3,000 W | 92% | ~ $540 |
| Victron Phoenix 12/2000 | 2,000 W | 4,000 W | 92% | ~ $850 |
| Victron MultiPlus 12/3000-120 | 3,000 W + 120 A charger | 6,000 W | 93% | ~ $1,850 |
| Mastervolt Mass Sine 12/2000 | 2,000 W | 4,000 W | 93% | ~ $980 |
Workshop installation — technical rules
Skysat workshop rules
- DC side cable sized for max current. 12/1600 W inverter → 130 A continuous → 35 mm² cable minimum, length ≤ 1 m if possible. Too thin = voltage drop → inverter shuts down on undervoltage.
- Class T or MEGA fuse in series with battery. Rated at 1.5× nominal current. 1,600 W inverter = 200 A class T fuse.
- Accessible ON/OFF switch. Inverter in standby consumes 0.3-0.8 A. Physical button at the helm = 5 min install = 100-300 Ah saved per year at anchor.
- Mandatory ventilation. 1,600 W inverter produces 100-150 W of heat at full load. Ventilated compartment required, never in a closed locker.
- AC earth bonding. The inverter’s 230 V output must be connected to the boat’s ground for safety. ISO 13297 standard.
FAQ — Inverter in practice
12 V or 24 V inverter?
12 V if your bank is 12 V (95% of pleasure sailboats). 24 V if bank is 24 V (yachts ≥45 ft). Converting 12→24 V to power the inverter is inefficient; better to use a direct inverter on the bank voltage.
Can the inverter be used while sailing (engine running)?
Yes, it’s even optimal — the alternator recharges the bank while compensating for inverter consumption. Watch for startup peaks: on small banks (<200 Ah), voltage briefly drops and the alternator may overcompensate. Prefer starting the inverter with the engine running.
What is the idle loss of a modern inverter?
Victron Phoenix 12/1600 Smart: 0.4 A at idle (4.8 W). Over 24 h unused: 9.6 Ah. Over 1 year at anchor: 3,500 Ah lost if never turned off. Hence the benefit of an ON/OFF switch.
Can the inverter power an air conditioner?
Theoretically yes, but not recommended. Marine AC consumes 500-1,500 W continuously. On batteries, autonomy is limited to a few hours max. Prefer a generator or shore power for extended anchor stays.
Inverter-charger combo or separate units?
Combo (MultiPlus) if you plan to use both intensively (long anchor stays + dockside stays). Separate units if shore charger is already in place and you only want to add an inverter. Combo wins on space and wiring, loses on maintenance flexibility.
3 real-world workshop cases — inverter install
Case 1 — Bavaria 41 cruising with family crew
Inverter installed in 2024: Victron Phoenix 12/1600 Smart (~ $540 VAT excluded) + accessible ON/OFF switch in cabin + 200 A class T fuse. Typical use: coffee maker (1,200 W at startup) in the morning at anchor, USB chargers while sailing. Average 24 h consumption: 30-40 Ah (including idle loss). Customer feedback: "Coffee at anchor changes the quality of the cruise."
Case 2 — Lagoon 42 catamaran offshore
Inverter-charger combo Victron MultiPlus 12/3000-120 (~ $1,850 VAT excluded) replacing the existing shore charger. Benefits: automatic transfer dock↔battery in <20 ms, continuous 230 V power at anchor (1,200 W AC possible for 2-3 h), space saved in the technical locker. 6 h workshop install. Total install $2,200 VAT excluded.
Case 3 — 8 m coastal sailboat solo
Small need: recharge laptop + phone chargers. Phoenix 12/500 Smart (~ $270 VAT excluded). 2 h install, 80 A class T fuse + switch. Total install ~ $380 VAT excluded. Customer feedback: "For my use, it’s exactly the right power — not oversized, not frustrating."
Excluded alternatives — inverters not selected
- Chinese quasi-sine inverters (250-350 $ VAT excluded in 2,000 W): avoid in marine. Waveform degrades laptop chargers and fridge compressors in months. Attractive price promise, but reduced lifespan and risk of damaging powered equipment.
- Combined "all-in-one" inverters (generator + inverter integrated): practical for very large units (yacht ≥60 ft), but expensive and complex to maintain. Prefer separate components under 50 ft.
- Inverters without built-in ON/OFF switch: some entry-level models lack a physical power button. Idle loss (0.5-1 A continuous) consumes 4-8 kWh per month. Always choose a model with ON/OFF or add an external switch.
Specific case — powering an absorption fridge when off-grid
An absorption fridge (Dometic, Vitrifrigo) draws 90-300 W in cycle, with startup peaks 2-3× continuous consumption. For a 200 W fridge on average:
- 24 h consumption: 200 W × 12 h cycle = 2.4 kWh = 200 Ah at 12 V.
- Inverter sizing: Phoenix 12/1200 minimum (for ~600 W startup peak).
- Battery bank: 400-500 Ah lithium minimum for 2-3 days of autonomy without recharge.
For this specific use, the MultiPlus 12/3000-120 combo (~ $1,850 VAT excluded) is our standard: integrated 120 A shore charger + auto transfer. The customer gets their AC230 V coffee even on extended anchor stays.
Skysat distributes Victron Energy and Mastervolt. 2026 VAT-excluded prices are indicative distributor rates.
