Sanding, Sanders, Sand paper... I've Sanded Enough Already!

90% of all boat work, seems to involve sanding.

Of what involves sanding...  Seems to involve sanding the same pieces, repeatedly with little visible change until they are painted.

The irony of Re-painting something that has already been painted, is that unless the existing paint is the same type as what you are painting with, and in relatively good condition it ends up coming off...  Which means sanding with a rough grit, over an area that has been gone over thoroughly in days gone by.

The difference between Sanders, make a big difference in the amount of time it takes to do a job.

Dual Action and Random Orbital Sanders spin and oscillate with a path that doesn't put inline scratches into a surface and makes it easier to get something smooth.  A grinder, or polisher/sander that doesn't take a different orbit can scar the surface you are working.  That may or may not be a big deal depending on how far you are along in the painting process. 

For bulk material removal, and general shaping I like a Makita 9227c with an 8 inch vinyl pad.  They remove a lot of material quickly, which can be a very good or very bad thing. 

 If you have scratches that are in a straight lines, or circles the next finer grit follows the same way and keys into them and they don't go away.  That is why a coarser grit on a R.O.S. looks like the next finer grit, on a hand block.

Of the Random Orbital Sanders, there are a few differences...  You can have square pads, or round pads, and even long board pads.  There are differences between the size orbits the pad moves, a fine finishing sander may be 3/32nds, while other sanders have a 3/16th orbit and even in very fine grits will show rings in the finish.

I'm going to assume at this juncture, that you are equipped with only electric supply and not a large air compressor suited for keeping up with pneumatic tools.  If you have air, I like Dynabrade DA's, and Hutchins inline sanders. 

I've found that the Dewalt product line does a decent job for a relatively inexpensive cost when only electricity is available.  Most of the time a 5 inch random orbital sander fits where you need to sand on a boat, though a 6 inch pad does a flatter job. 

The Porter Cable 6inch Orbital sander, is another companion...  They don't last all that long if you put them into 8 hour days, and lean on them at all... but do a lot of work due to the larger orbit and greater power than 5 inch sanders have.

1/4 sheet square pad sanders have a place too, as they vibrate.  Vibrating means that you don't have swirl marks.  On small parts, and inside corners they can make lighter work than what would otherwise need to be hand sanded.  I use 80 grit, and 220 grit almost exclusively on these.  80 grit for paint stripping, and fairing in putty/high build primer.   220 grit for all finish sanding and paint de-nibbing.

As far as sandpaper goes, cheap sandpaper doesn't last very long or cut as fast as decent paper.  3M gold, is about the price point where you are paying for what you get, which is... decent sand-paper.  I use 3m Gold from 80 grit through 320 grit, in a combination of hookit backing, and sitckit depending on the tool. 

In 40 grit, you can spend a little more and buy Norton Blue-Mag, but for most work Green F weight 3M production paper works good enough for the cost.