I just hauled Polaris in December for a bottom job. The plan was to just clean and then put on couple new coats of Micron 66 over the top of the Micron 66 the previous owner had used 3 years prior.
However, once it was out the boat yard pointed out that the current Micron 66 paint was peeling away from the hard (I think it was a hard paint) from 6 years prior. It was pretty obvious, especially around the water line. They told me I could paint the new Micron 66 over the old Micron 66 but that old layer was peeling away so it may not work very well.
In the end they recommended sand-blasting the bottom and starting fresh which is what I did. Put on 2 new layers of epoxy barrier paint and then applied the first layer of Micron 66 while the epoxy paint was still tacky to get better adhesion. All of this in 1 day.
Next day put on the second coat of Micron 66. And then up in the lift the next morning and paint the areas where the jackstands were.
All seemed to work very well. Here on Mississippi Gulf Coast the advice I am getting is 3-year cycle will work. With the occasional in the water cleaning of the bottom.
Cheers,
Jim