Suspenz EZ Roller "V" Rack saddles combine a kayak cradle system and roller loading assist. To load your kayak on the roof of your car, just set the bow on the rear rack and push it forward while it rolls into place. Once your kayak is centered between cradles just tie it down as if the rollers weren't there. Transport kayak bottom side down.
Rack attaches to most cross-bars (round, square, aero, factory) via a plate under the cross-bar and wingnuts - no tools needed.
Works best for sea kayaks with flat to shallow "V" hull in the cockpit area (e.g. not Eddyline kayaks).