For just a casual bottom job use a palm sander they vary in price the one in the picture was close to $300 but it is top of the line. You can sand all day and your wrist will not burn and I've had it for 5 years.
Mike Shappell www.themanshed.com TMS-20 Builder G-Cat 5.7 - Current Boat NACRA 5.2 - early 70's