Knowing what I know now, I wouldn't consider anything less than 2000 watts.
I bought a 900 watt 2 stroke genny three years ago because the price was right ($120 or so, IIRC). It was small, relatively quiet, lightweight, and damn near useless to run tools.
I used it once.
Two years ago, i bought a 4000 watt four stroke generator on wheels. It was more money ($500 or so), but it has been well worth it. It has powered tools for boatwork (it is great being able to run two sanders at a time on long extension cords), while simultaneously charging batteries. It's powered guitar and bass amps at outdoor concerts, and run a movie projector. It takes up the whole cargo bay of our jeep liberty, but it doesn't get moved that often. in the spring it gets hauled to the boatyard, and it is chained to the cradle and tarped until it needs to go home again, and it has always started without complaint.
For boat use, a 2000 watt
inverter is the way to go. Lots of them here, and price aren't bad. i am kinda intrigued by the 2 KW LP powered model, for under $300.
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