My cap rails are wide and flat as is the hatch (well gentle curve actually.)

What I want to remove is some water damage that occurred when the varnish had worn away, and the PO had not recoated.

I have some areas where the wood has grayed or darkened... I would like to remove as much of that as is gently possible. The other advantage I see of a sander is being able to work in smaller areas than I can comfortably limit my arm movement and still get work done... corners for instance of such things as the seahood and hatch... these are recessed and trying to sand into a corner is a PITA.

The cap rails are very accessible, but they are long... so if I can get to one whole cap rail on one side in a day or two... well that is just labor saving.

I'll stick to using the foam sanding pads I have for sanding the various profiles... fortunately there is not too much "fancy work" here.

Thanks for the word on the 220 and 320.

I've been starting with 80 and then shifting to about 200 for finish, using the 600 only (or 320) when touching dry varnish for a new coat.

One nice thing I have happily noticed... water beads up beautifully on a good coat of varnish.