The essentials in 30 seconds
- Pure sine is mandatory in marine applications. Modified-square 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 maker 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 draw.
- 2026 standards: Victron Phoenix 12/1600 Smart (~ $540 USD 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 fit an accessible ON/OFF switch.
- Skysat workshop 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 bank and the 230 V world. It converts the battery’s DC voltage into a clean sine wave, allowing household appliances (coffee maker, laptop, absorption fridge, chargers) to run. But without correct sizing, it becomes 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 by Skysat, and gives installation rules. For the battery bank that powers 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 (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 compressors, fans), 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), choose pure sine.
Sizing — workshop method
Four-step calculation:
- List all 230 V equipment used simultaneously. Coffee maker (1,000–1,500 W) + laptop (90 W) + absorption fridge (300 W at startup). Total continuous draw: ~1,400 W.
- Identify startup surge. For coffee makers and fridges, multiply continuous power by 1.5–2.0. Estimated surge: ~2,100 W.
- Choose an inverter rated at 150% of continuous draw. Continuous draw 1,400 W × 1.5 = minimum 2,100 W inverter. Round up to the next range: 2,000–2,500 W inverter.
- Check surge compatibility: a 2,000 W Victron inverter can handle ~4,000 W surge for 1–2 seconds (datasheet). Compatible with coffee maker/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 and mid-market 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 makers, 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 wired at 24 V.
- Phoenix 12/2000 Smart: ~ $850 USD ex VAT. Fridge compressor + coffee maker + tools.
- Phoenix 12/3000 Smart: ~ $1,250 USD ex VAT. Heavy continuous 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 a combined inverter + shore charger 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 banks + solar.
If you plan to replace your shore charger and add 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 shuts down on undervoltage.
- Fuse class T or MEGA 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 switch 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 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 an inverter directly on the bank voltage.
Can I use the inverter while sailing (engine running)?
Yes, in fact it’s optimal — the alternator recharges the bank while compensating for inverter draw. 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 standby (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 an inverter power an air conditioner?
Theoretically yes, but not recommended. Marine AC draws 500–1,500 W continuously. On batteries, autonomy is limited to a few hours max. Prefer a generator or shore power for prolonged air conditioning at anchor.
Combo inverter-charger or separate units?
Combo (MultiPlus) if you plan to use both functions intensively (long anchor stays + harbor stays). 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 family sailboat
Inverter installed in 2024: Victron Phoenix 12/1600 Smart (~ $540 USD ex VAT) + accessible ON/OFF switch in cabin + 200 A class T fuse. Typical use: coffee maker (1,200 W startup) in the morning at anchor, USB chargers while sailing. Average 24 h draw: 30–40 Ah (including idle loss). 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 shore↔battery in < 20 ms, continuous 230 V at anchor for long stays (1,200 W AC possible for 2–3 h), space saved in the technical locker. 6 h workshop install. Total install $2,200 USD ex VAT.
Case 3 — 8 m coastal solo sailboat
Small needs: laptop charging + phone chargers. Phoenix 12/500 Smart (~ $270 USD ex VAT). 2 h install, 80 A class T fuse + switch. Total install ~ $380 USD ex VAT. Customer feedback: "For the use I have, it’s exactly the right power — not oversized, not frustrating."
Excluded alternatives — inverters not selected
- Chinese quasi-sine inverters (250–350 USD ex VAT in 2,000 W models): avoid in marine use. Waveform degrades laptop chargers and fridge compressors 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 built-in 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 off-grid
An absorption fridge (Dometic, Vitrifrigo) draws 90–300 W in cycle, with startup surge 2–3× continuous draw. For a 200 W fridge on average:
- 24 h draw: 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, the MultiPlus 12/3000-120 combo (~ $1,850 USD ex VAT) is our standard: integrated 120 A shore charger + automatic transfer. The customer gets their AC coffee even on long anchor stays.
Skysat distributes Victron Energy and Mastervolt. 2026 USD ex VAT prices are indicative distributor pricing.
