Spring on the hardstand has a familiar rhythm. Boats come out, hulls get pressure cleaned, and owners queue for the one shore power outlet still working at the end of the row. If you are doing your own antifouling, cut and polish, or gelcoat repairs, that wait eats into a weekend you have already paid the yard for.
A boat maintenance generator solves that problem, as long as you match it to the tools you plan to run. A Gentrax 3.5 kW generator, rated at 3.0 kW continuous, handles most DIY refit jobs, one heavy tool at a time. It weighs 28kg, which matters when you are carrying it across a gravel yard to the cradle. Welding is where it reaches its limits, and we set those out plainly below.
Here's what you need to know about power draw, safe setup, and fuel on the hardstand, using figures from the Gentrax owner's manual and the Outbax product listing.
» MORE: Inverter generators explained
What Can a Gentrax 3.5kW Generator Power on the Hardstand?
The Gentrax GT3500 Inverter Generator delivers 3.0 kW continuously and 3.5 kW at peak. In practical terms, that covers one high-draw tool, such as a rotary polisher or heat gun, plus a small companion load like a dust extractor or work light.
Rated Output Versus Maximum Output
Rated output is what the generator supplies all day. Maximum output is a short burst for motor start-up. Plan around the 3.0 kW rated figure. The manual warns that exceeding the rated load can damage the unit, shorten its life, and void the guarantee.
Starting Watts and Running Watts
Motor-driven tools draw a spike of current as they start. Queensland's Electrical Safety Office notes that motor-driven appliances can draw two to 10 times their rated load at start-up.
On the GT3500, the red overload light and the green output light both come on for about four seconds when a motor starts. The manual says this is normal. If the red light stays on, the load is too high and power to the tool is cut.
Here’s what one of our customers said about the Gentrax GT3500 Inverter Generator:
“Received today, ripped out of the box, topped up the oil and fuel, pulled 3 pulls and fired up beautifully. Runs quieter than I was expecting. Thank you Outbax for a great product.”
Why Pure Sine Wave Output Matters for Your Tools
The GT3500 uses digital inverter technology to produce pure sine wave power, the same smooth waveform as household mains. That protects variable speed polishers, battery chargers and inverter welders, whose electronic controls can misbehave on rough power.
Table 1: Gentrax GT3500 at a glance
| Specification | Gentrax GT3500 |
|---|---|
| Maximum output | 3.5kW |
| Rated output | 3.0kW |
| AC voltage and frequency | 240V, 50Hz |
| AC outlets | Two weatherproof 15A outlets |
| DC output | 12V 5A, battery clips included |
| Engine | 149cc air-cooled four-stroke petrol |
| Fuel and tank | 91 RON unleaded, 5.7L |
| Run time at 50% load | 4.1 hours (Outbax listing); 6.2 hours (manual) |
| Engine oil | SAE 10W30, 0.9L |
| Starting system | Recoil |
| Noise level | 62dB at 7m |
| Dimensions | 565 x 320 x 470mm |
| Weight | 28kg |
| Warranty | 12 months |
Sources: Gentrax user manual (3.5kW model) and the GT3500 product listing, October 2026. The run time figures differ, so plan around the lower one.
How Much Power Do Sanders, Polishers, and Heat Guns Draw?
Most marine refit tools sit well inside 3.0kW on their own. Trouble starts when two high draw-tools run together. Check each tool's rating plate, then add the figures up before you plug in.
Table 2: Typical power draw of hardstand tools
| Tool | Typical rated input | On a GT3500 alone? | Sensible pairing |
|---|---|---|---|
| Random orbital sander | 300 to 450W | Yes | Dust extractor |
| Belt sander | 750 to 1,200W | Yes | Dust extractor |
| Dual action polisher | 700 to 1,000W | Yes | Second polisher or work light |
| Rotary polisher | 1,200 to 1,600W | Yes | Small dust extractor |
| Heat gun at full heat | 1,800 to 2,000W | Yes | Work light only |
| Shop vacuum or dust extractor | 1,000 to 1,400W | Yes | One sander or polisher |
| Angle grinder | 900 to 2,400W | Usually | Nothing else for larger grinders |
| Small inverter welder | Varies with amperage | Light work only | Nothing else |
Typical ranges for common consumer and trade tools. Always confirm against your tool's rating plate.
Sanders for Antifouling and Hull Prep
Orbital sanders are the easiest load on the generator. Pair one with a dust-extracting vacuum, because antifouling dust contains biocides you do not want drifting into the water. The NSW EPA publishes guidance on applying antifouling paint at marinas, and most yards set their own dust capture rules.
Polishers for Cut and Polish Work
A rotary polisher at full speed draws roughly 1.2 to 1.6kW. That leaves room for a vacuum or lights, but not a heat gun. Dual action polishers draw less, so two people can work the topsides on one generator.
Heat Guns for Decals, Vinyl, and Gelcoat Repairs
Heat guns are deceptive. They are small, yet many draw close to 2kW at full heat. Run one alone or with a light, and switch Eco Mode off.
» MORE: How to calculate your generator power needs
Can a 3.5kW Inverter Generator Run a Welder?
Sometimes. A small inverter stick or MIG welder used at low amperage for light repairs may run within 3.0kW. Heavier work, such as stainless rail repairs or aluminium fabrication, needs a larger generator.
What Size Generator Do You Need to Run a Welder?
The welder's rating plate decides the answer, not its advertised amperage. Look for the rated input power in kVA, or the effective input current, often shown as I1eff. Multiply I1eff by 240V for an approximate continuous draw. If the result is above 3,000W, the GT3500 is the wrong generator for that job. Many welder makers also list a minimum generator size in their manual. Use that figure if it is higher.
How to Run a Welder Off a Generator Safely
1. Start the generator and let it reach full speed before plugging in the welder.
2. Switch Eco Mode off.
3. Run the welder on its own. Unplug grinders, vacuums, and chargers.
4. Start at the low end of the amperage range and work up gradually.
5. Stop if the red overload light stays on. Repeated overloads shorten generator life.
When to Step Up to a Larger Gentrax
The Outbax Gentrax GTX4200 Pro Inverter Generator (3.5kW rated, 4.2kW peak) gives useful headroom for light welding and is parallel capable. For regular fabrication, the Gentrax GTX6600 Inverter Generator (6kW rated) is the more realistic choice.
Table 3: Gentrax and VoltX power options for boat maintenance
| Model | Rated / peak | Weight | Tank and run time (50% load) | Price | Best for |
|---|---|---|---|---|---|
| Gentrax GT3500 | 3.0 / 3.5kW | 28kg | 5.7L, 4.1 hours | $899 | Sanding, polishing, heat gun work |
| Gentrax GTX3500 | 3.2 / 3.5kW | 37.5kg | 7.5L, 6.3 hours | $1,199 | Long days, key and remote start |
| Gentrax GTX4200 Pro | 3.5 / 4.2kW | 41.5kg | 8.8L, 6.8 hours | $1,449 | Light welding, two tools at once |
| Gentrax GTX6600 | 6.0 / 6.6kW | See listing | 6.6 hours | $2,099 | Regular welding, bigger refits |
| VoltX Topband V1200 | 1.2kW (2.4kW surge) | 13kg | 1,152Wh battery | $999 | Silent charging, lights, light sanding |
Prices and specifications from product listings, October 2026.
Here’s what one of our customers said about the Gentrax GTX6600 Inverter Generator:
“Works well, starts super easy every time. I just bought a second one!! :)”
How to Set Up a Generator Safely on a Slipway or Hardstand
A portable inverter generator is a practical hardstand shore power alternative, but a boatyard is full of fuel, solvents and people. Follow these steps every time.
1. Check the yard rules first. Many boatyards restrict where you can store and decant petrol, what hours you can run machinery, and how dust must be captured. Ask the yard office before you arrive.
2. Choose firm, level ground. The manual calls for a firm, level surface away from buildings and structures, with the exhaust clear. Keep the generator out from under the hull, cradle, covers and tarps.
3. Keep the exhaust away from people. Exhaust fumes contain carbon monoxide. Never run the generator inside a cabin, shed, or shrink-wrapped boat.
4. Earth the generator. The manual recommends earthing with a lead of sufficient current capacity. The wire and earth stake are not supplied.
5. Use a portable RCD and quality leads. The Electrical Safety Office advises running a good quality extension lead from the generator directly to the tool, and says generators should meet AS/NZS 3010:2017. A portable RCD at the outlet adds protection on damp ground.
6. Keep it dry. The 15A outlets are weatherproof, but the manual says never run the generator in rain. Keep it clear of washdown hoses.
7. Refuel safely. Stop the engine and let it cool. Refuel on bare ground, wipe up spills, then move at least 3m from the fuelling spot before restarting. Keep fuel well away from open solvent and paint tins.
At 62dB at 7m, the GT3500 is a quiet generator by yard standards, which keeps you on good terms with the owners on either side.
Run Time, Fuel, and Salt Air Care for a Full Refit Day
The product listing quotes 4.1 hours at 50% load from the 5.7L tank, while the manual quotes 6.2 hours. Heavy tools burn fuel faster, so expect a lunchtime refuel. If your yard allows it, bring a spare approved fuel container.
Eco mode lets the engine slow down under light loads, which saves fuel and lowers noise. It suits intermittent sanding. Switch it off for heat guns, rotary polishers, and welders.
Buying new before a haul out? The manual sets a break-in period of about 25 hours below 75% of rated output, followed by an oil change. Run those hours at home first.
Table 4: Gentrax maintenance schedule for coastal use
| Item | Manual interval | Hardstand tip |
|---|---|---|
| Engine oil level | Before each use | Check on level ground before every start |
| Engine oil change | First at 1 month or 20 hours, then every 6 months or 100 hours | Use SAE 10W30 |
| Air filter | Clean every 3 months or 50 hours | Check after dusty sanding days |
| Spark plug | Check and gap (0.6 to 0.7mm) every 3 months or 50 hours | Look for corrosion on the terminal |
| Fuel filter | Clean every 6 months or 100 hours | Replace if torn or blocked |
| Oil filter | Clean every 6 months or 100 hours | Drain oil first |
| Fuel line | Check daily | Look for cracks after hot days |
| Muffler screen and spark arrestor | Clean every 12 months or 300 hours | Brush off carbon deposits |
Source: Gentrax inverter generator user manual maintenance chart.
Salt air speeds up corrosion, so wipe the case down after each session and store it dry and ventilated. For long storage, the manual says to drain the fuel, add about 15ml of oil through the spark plug hole and apply a rust inhibitor to the exterior. Outbax stocks spare parts online, including the Fuel Filter for Gentrax Generator GS/GSI/GSX Series.
For quiet jobs, the VoltX Topband V1200 Portable Power Station charges cordless tool batteries and runs lights with no fuel or noise. It is rated at 1,200W and IP20, so it is not built for polishers or wet conditions.
The Bottom Line
A Gentrax 3.5kW generator is a sensible boat maintenance generator for owners who sand, polish and patch their own boats on the hard. Run one heavy tool at a time, check every rating plate against the 3.0kW rated output, and size up for welding. Set it up on level ground, away from covers and fuel, with an RCD and good leads.
If you are unsure which model suits your refit list, compare the Gentrax range at Outbax or call the team for sizing advice before the antifouling season rush.
