The essentials in 30 seconds
- Pure sine is mandatory in marine. Modified square-wave (quasi-sine) inverters damage laptop charger transformers and poorly power compressor fridges. Pure sine = 99% of sailboat use in 2026.
- Sizing = continuous power AND surge. A 1,200 W coffee machine draws 2,000 W at startup (3-5 sec). A "smooth" 1,200 W inverter will overload and shut down. Always size the inverter at 150% of continuous consumption.
- 2026 standards: Victron Phoenix 12/1600 Smart (~ $540 ex VAT) for occasional use. MultiPlus 12/3000-120 for continuous use with shore charger integrated.
- Idle draw matters. Inverter in standby draws 0.3-0.8 A continuously. 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 ex VAT (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 battery bank and the 230 V world. It converts the battery’s DC voltage into a clean sine wave, enabling household appliances (coffee machine, computer, absorption fridge, electronic chargers) to run. But without correct sizing, it’s the most temperamental piece of gear on board.
This article explains the difference between pure sine and quasi-sine, provides a sizing method, presents the Victron and Mastervolt ranges stocked at Skysat, and outlines installation rules. For the battery bank that powers the inverter, see our lithium battery sizing article.
Why pure sine, not quasi-sine
Two inverter technologies coexist: quasi-sine (modified square wave, stepped waveform) and pure sine (sine wave close to the EDF grid).
- Quasi-sine: cheaper, slightly higher efficiency, but high harmonic noise. Damages: transformers (laptop chargers, camera chargers), induction motors (fridge compressor, fan), medical equipment.
- Pure sine: voltage identical to the grid, powers everything without issues. 20-30% surcharge vs quasi-sine, but a worthwhile investment as soon as you go beyond basic smartphone chargers.
In modern 2026 sailboats, pure sine is the de facto standard. Unless you have a very specific use case (incandescent lighting only), go pure sine.
Sizing — workshop method
4-step calculation:
- List all 230 V equipment used simultaneously. Coffee machine (1,000–1,500 W) + laptop (90 W) + absorption fridge (300 W at startup). Continuous total: ~1,400 W.
- Identify startup surge. For coffee machines and fridges, multiply continuous power by 1.5–2.0. Estimated surge: ~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: 2,000–2,500 W inverter.
- Check surge compatibility: a 2,000 W Victron inverter handles a ~4,000 W surge for 1–2 seconds (datasheet). Compatible with coffee machine/fridge startup.
For light occasional use (laptop + USB chargers only): Phoenix 12/1600 Smart (~ $540 ex VAT) is more than enough.
Victron Phoenix range
Entry to mid-market Victron range, pure sine, 12 V and 24 V.
- Phoenix 12/500 Smart: ~ $270 ex VAT. Small uses: laptop, USB chargers, 230 V lighting.
- Phoenix 12/1200 Smart: ~ $470 ex VAT. Light coffee machine, drill, small tools.
- Phoenix 12/1600 Smart: ~ $540 ex VAT. Skysat’s workshop reference for 35–45 ft sailboats. 3,000 W surge (2–5 sec).
- Phoenix 24/1600 Smart: ~ $580 ex VAT. 24 V version for sailboats with 24 V architecture.
- Phoenix 12/2000 Smart: ~ $850 ex VAT. Fridge compressor + coffee machine + tools.
- Phoenix 12/3000 Smart: ~ $1,250 ex VAT. Intensive continuous use.
Mastervolt Mass Sine range
Direct competitor to Victron with MasterBus / CZone integration for yachts with configured systems.
- Mass Sine 12/1500: ~ $720 ex VAT. More expensive than Victron at equivalent power, but native MasterBus integration.
- Mass Sine 12/2000: ~ $980 ex VAT.
- Mass Sine 12/2500: ~ $1,250 ex VAT.
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 a single-unit inverter + shore charger (Victron MultiPlus).
- MultiPlus 12/3000-120: 3,000 W inverter + 120 A shore charger in one box. ~ $1,850 ex VAT. 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 ex VAT. 48 V version for large hybrid + solar setups.
If you plan to replace your shore charger and add an inverter, the MultiPlus saves on wiring and space.
Model comparison table
| Model | Continuous power | Surge | Efficiency | Ex VAT price |
|---|---|---|---|---|
| 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 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 draws 0.3–0.8 A. Physical button at the helm = 5 min of installation = 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 ground bonding. The inverter’s 230 V output must be bonded 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 cruising 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 surges: on small banks (< 200 Ah), voltage dips briefly and the alternator may overcompensate. Prefer starting the inverter with the engine running.
What is the idle draw of a modern inverter?
Victron Phoenix 12/1600 Smart: 0.4 A at idle (4.8 W). 24 h unused = 9.6 Ah. 1 year at anchor if never turned off = 3,500 Ah lost. Hence the need for 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 harbor stays.
Inverter-charger combo or separate units?
Combo (MultiPlus) if you plan to use both heavily (long anchorages + port calls). Separate units if the shore charger is already in place and you only need to add an inverter. The 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 ex VAT) + accessible ON/OFF switch in cabin + 200 A class T fuse. Typical use: coffee machine (1,200 W surge) in the morning at anchor, USB chargers while sailing. Average 24 h consumption: 30–40 Ah (including idle draw). The owner confirms: "Coffee at anchor changes the quality of the cruise."
Case 2 — Lagoon 42 catamaran for offshore sailing
Victron MultiPlus 12/3000-120 inverter-charger combo (~ $1,850 ex VAT) installed to replace the existing shore charger. Benefits: automatic transfer shore↔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 installation. Total install $2,200 ex VAT.
Case 3 — 8 m coastal sailboat for solo sailing
Small need: laptop charging + phone chargers. Phoenix 12/500 Smart (~ $270 ex VAT). 2 h installation, 80 A class T fuse + switch. Total install ~ $380 ex VAT. The owner confirms: "For my usage, it’s exactly the right power — not oversized, not frustrating."
Excluded alternatives — inverters not selected
- Chinese quasi-sine inverters (250–350 $ ex VAT for 2,000 W): avoid in marine. Waveform degrades laptop chargers and fridge compressors within months. Attractive price, but reduced lifespan and risk of damaging powered equipment.
- "All-in-one" combined 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 integrated ON/OFF switch: some entry-level models lack a physical power button. Idle draw (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 without shore power
An absorption fridge (Dometic, Vitrifrigo) draws 90–300 W in cycle, with a startup surge 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 surge).
- Battery bank: 400–500 Ah lithium minimum for 2–3 days of autonomy without recharge.
For this specific use case, the MultiPlus 12/3000-120 combo (~ $1,850 ex VAT) is our standard: integrated 120 A shore charger + automatic transfer. The owner gets their AC 230 V coffee even on long anchorages.
Skysat distributes Victron Energy and Mastervolt. 2026 ex VAT prices are indicative of authorized distributor rates.
