What SurferKris said.
I'd add that any painted surface moving through the water can see performance gains by being rubbed in the direction of flow. Was involved in surface treatment tank testing for racing yachts in the late 80s when this became a hot topic.
The down sides are a glossy off the gun or moulded finish is more durable than a sanded finish and the rubbed surface will require continued maintenance. Sanding opens up the paint exposing the solids in the guts of the paint, this is less scratch resistant and slightly porous so you will need to take better care of a rubbed/sanded product. Also care needs to be applied not to sand down to raw fibres, this may lead to osmosis on boards but is far less likely on fins.
"Sanded" has been around for decades. 1st "shortboard" was a '91 SeaTrends made in Stevenson, WA. Randy French design. Bottom finish is "sanded" texture. Something to do with improving laminar flow resulting in improved performance. Fast board. Even by modern standards. Still have it. Sitting in storage since '96. Thing scared me. Replaced it with a board at the other end of the spectrum. Mistral Screamer 2. Slow and forgiving.
Old Guy....
Seatrend 9' '23", 1986, 13 lbs., was sanded bottom to rail deck with 220. Was linear, before crosshatch.
Great simple explanation of wet'n'dry sanding.
Yes it's been around for ever, but I reckon that he did a good demo
Old Guy....
Seatrend 9' '23", 1986, 13 lbs., was sanded bottom to rail deck with 220. Was linear, before crosshatch.
But was it fast?
Did it spin out?