Thanks everyone for the great ideas! I did try Brian's suggestions and bought a flour sifter and combined it with a new home made tool- couple pieces of scrap metal attached to my drill as a power mixer. I found I did get an improvment in the hBN/epoxy mix and fewer and smaller 'sand pebbles' in the finish. But still unacceptable as a boat finish. Time for plan 'B.' I'll resand and paint over it for now- the boron nitrate/epoxy will make a nice undercoat for a good white paint finish- just won't get the increased lubricity. (Wew, this boat building vernacular is tough to learn...) I got excited with the sifter/egg beater combi and didn't read Etienne's suggestion closely enough. I think he's on to something by heating the resin and holding off on the hardener till the hBN is mixed well. I'm going to try that next and of course before I do this again I'll take Dan's suggestion and pony up for the .70 micron stuff.
Michael in B.C.