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 startup 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 load.
- 2026 standards: Victron Phoenix 12/1600 Smart (~ $540 USD ex-VAT) for occasional use. MultiPlus 12/3000-120 for continuous use with shore power 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.
- Skysat workshop installed budget for 35–45 ft sailboat: ~ $700–1,200 USD 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 smooth AC sine wave, enabling household appliances (coffee machine, laptop, absorption fridge, electronic chargers) to run. But without correct sizing, it becomes the most temperamental piece of gear aboard.
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 gives 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 distortion. Damages: transformers (laptop chargers, camera chargers), induction motors (compressor fridge, fan), medical equipment.
- Pure sine: voltage identical to the grid, powers everything without issue. 20–30% surcharge vs quasi-sine, but a worthwhile investment as soon as you go beyond basic smartphone charging.
In modern 2026 marine installations, pure sine is the de facto standard. Unless you have a very specific use case (incandescent lighting only), go pure sine.
Sizing — workshop method
Four-step calculation:
- List the 230 V equipment used simultaneously. Coffee machine (1,000–1,500 W) + laptop (90 W) + absorption fridge (300 W at startup). Total continuous load: ~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 sized at 150% of continuous load. Continuous load 1,400 W × 1.5 = minimum 2,100 W inverter. Round up to the next range: 2,000–2,500 W inverter.
- Verify surge capability: the 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 USD ex-VAT) is more than enough.
Victron Phoenix range
Entry to mid-range Victron range, pure sine, 12 V and 24 V.
- Phoenix 12/500 Smart: ~ $270 USD ex-VAT. Small uses: laptop, USB chargers, 230 V lighting.
- Phoenix 12/1200 Smart: ~ $470 USD ex-VAT. Light coffee machines, drills, small tools.
- Phoenix 12/1600 Smart: ~ $540 USD ex-VAT. Skysat’s workshop reference for 35–45 ft sailboats. 3,000 W surge (2–5 sec).
- Phoenix 24/1600 Smart: ~ $580 USD ex-VAT. 24 V version for sailboats with 24 V architecture.
- Phoenix 12/2000 Smart: ~ $850 USD ex-VAT. Compressor fridge + coffee machine + tools.
- Phoenix 12/3000 Smart: ~ $1,250 USD ex-VAT. Continuous heavy-duty use.
Mastervolt Mass Sine range
Direct competitor to Victron with MasterBus / CZone integration for configured yachts.
- Mass Sine 12/1500: ~ $720 USD ex-VAT. More expensive than Victron at equivalent power, but native MasterBus integration.
- Mass Sine 12/2000: ~ $980 USD ex-VAT.
- Mass Sine 12/2500: ~ $1,250 USD 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 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 USD 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 USD ex-VAT. 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 | Surge | Efficiency | Price USD ex-VAT |
|---|---|---|---|---|
| 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 cuts on undervoltage.
- T or MEGA class fuse in series with battery. Rated at 1.5× nominal current. 1,600 W inverter = 200 A T-class fuse.
- Accessible ON/OFF switch. Inverter in standby draws 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 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, in fact it’s optimal — the alternator recharges the bank while compensating for inverter load. Watch 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 with 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 draws 500–1,500 W continuously. On battery, autonomy is limited to a few hours max. Prefer a generator or shore power for extended anchorages.
Inverter-charger combo or separate units?
Combo (MultiPlus) if you plan to use both intensively (long anchorages + port stays). Separate units if shore charger is already installed and you only need to add an inverter. Combo wins on space/wiring, loses on maintenance flexibility.
3 real-world workshop cases — inverter install
Case 1 — Bavaria 41 cruising family sailboat
Inverter installed in 2024: Victron Phoenix 12/1600 Smart (~ $540 USD ex-VAT) + accessible ON/OFF switch in cabin + 200 A T-class fuse. Typical use: morning coffee machine (1,200 W at startup) at anchor, USB chargers while sailing. Average 24 h consumption: 30–40 Ah (including idle draw). Customer feedback: "Coffee at anchor changes the quality of the cruise."
Case 2 — Lagoon 42 offshore catamaran
Victron MultiPlus 12/3000-120 combo inverter-charger (~ $1,850 USD ex-VAT) replacing the existing shore charger. Benefits: automatic transfer dock↔battery in <20 ms, continuous 230 V power at long anchorages (1,200 W AC possible for 2–3 h), space saved in technical bay. Workshop install: 6 h. Total installed cost: $2,200 USD ex-VAT.
Case 3 — 8 m coastal solo sailboat
Small need: laptop charging + phone chargers. Phoenix 12/500 Smart (~ $270 USD ex-VAT). Install: 2 h, 80 A T-class fuse + switch. Total installed cost ~ $380 USD ex-VAT. Customer feedback: "For my usage, it’s exactly the right power — not oversized, not frustrating."
Excluded alternatives — inverters not recommended
- Chinese quasi-sine inverters (250–350 USD ex-VAT for 2,000 W): avoid in marine. Waveform degrades laptop chargers and compressor fridges within months. Attractive price point, 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 integrated ON/OFF switch: some entry-level models lack a physical power button. Idle draw (0.5–1 A continuous) then 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 away from shore
An absorption fridge (Dometic, Vitrifrigo) draws 90–300 W in cycle, with startup surge 2–3× continuous load. 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 autonomy without recharge.
For this specific use case, the MultiPlus 12/3000-120 combo (~ $1,850 USD ex-VAT) is our standard: integrated 120 A shore charger + auto transfer. The customer gets their 230 V coffee even on long anchorages.
Skysat distributes Victron Energy and Mastervolt. 2026 USD ex-VAT prices are indicative distributor rates.
