So here is what I did. I had a bottom full of blisters that the previous owner had covered up with a nice thick layer of new gelcoat. Didn''t discover this until I went to repair what I thought was a few medium sized blisters. What a surprise. I used a pressure washer with a sand pick-up. The sand pick-up is a hose connected to the end of the pressure washer wand, it''s attached to a hose that goes into the bag of sand (you pcik the grit but talk to the sand supplier, they usually have the proper suggestions). The venturi effect of the high pressure water sucks the sand up the tube blows it into the hull. It''s very easy to control the impact against the hull simply by distancing the wand. There is NO dust! There is also no heat build-up. A word of caution through, it takes a lot of sand to do a 30 ft hull. The finished hull has a course surface (like sanding with 80 grip paper), perfect for the layers of repair epoxy and barrier coats. But befoe you go to this length, I would suggest that repairing the few blisters you have by hand would probably be the best bet.