I had installed reinforcement strips of fibreglass at the sides of the cockpit where the sides met the deck, because I feared a weak point where I had inadvertently made a butt joint there between the sheets of 'glass covering the deck, rather than an overlap for strength.
When cured I sanded the strips with a P120 grit to blend them in with the rest of the deck.
Here the starboard strip has been sanded and the unblended port strip is also visible.
Note the portable industrial grade extraction fan placed near the sander to pick up any dust. I purchased two to use either side of the workshop when sanding; portable because I don't have room to hang a big unit on the wall.
They work really well and of course can be used on the bench or on the boat to directly suck up any nasty dust.