Yup, SMOOTH is fast, as Jackdaw has stated.
The most important area for such smoothing is on the all the 'leading edges' of the boat and for 1/3 the way back from that leading edge to whatever and far away from the leading edge the trailing surface is. Baby's ass smooth.
Teflon based paints work best for this: Baltoplate (Interlux), the various offerings of VC, VC17, etc. as the low friction teflon and the ability to 'burnish' these coatings is unparalleled for 'FLAT and smooth' and low friction.
Burnishing is the 'smearing' of semi-soft coatings into a highly polished and very flat surface. The burnishing is usually done with high grade clay filled 'magazine paper' ... the shiny paper thats found in high quality magazines. Flat sanding removes such expensive coatings; burnishing smears the finish to be smooth and doesnt remove any coating.
The 1987 Americas Cup boat 'Stars and Stripes' used a scientific coating called 'rivelettes' ... a molded polymeric coating similar to shark skin ... the microscopic 'roughness' provided microscopic 'cavitation' (producing microscopic gas bubbles) at the hull surface which lessened hull drag/friction.
Before the age of environmental awareness ... top tier racers used to apply slowly eroding soap coatings that increased the 'wetness' of the water at the hull surface. Of course such boats trailed soap suds in their wake and such is why such practices are now strictly illegal ... but were at that time very FAST in practice.
Also too some boats just after 'the soap times' experimented with 'air porous hulls' and used hand operated air compressors to force air through the hull into the water which reduced friction ... and is still prohibited in racing circles.
Some 'modern' design boats ( Tunnel hulled boats ) 'naturally' trap air under the hull for friction reduction ... some of the ultra-fast sailing ILYA scows and some of the mega-ultra fast Aussy skiffs. You watch the stern wake for the apparent amount of air bubbles visible to set the correct amount of heeling which traps the greatest amount of air under the hull's flat or tunneled bottom.
For the average person, SMOOTH and FLAT is the 'fastest', especially smooth and flat at the leading edges and (at least) about 1/3 the way back from those leading edges - bow, keel, rudder.
