Shakedown cruise yesterday after a year in the slip. Bottom paint was applied a year ago, which usually lasts for two seasons. Pulled out of the slip but was only able to reach 3.2 kts. @ 2200 rpm. (56 hp Yanmar and usually can cruise at 5.0 kts @ 2200 rpm) Continued to open area, and after 45 minutes or so was able to increase speed to 4.1 kts @ much higher rpm (3100 rpm). Even with boat pointed downwind in 15 kt wind, I was only able to see a 0.1 kt increase in speed. The loss of power occurred throughout the full rpm range. Also no black smoke. I went below to visually examine the spinning of the propeller shaft. All seemed normal for the rpm. I strongly suspect the loss of power is being caused by an unusually large buildup of crud (barnacles etc) on the hull and propeller. My question is whether anything else might be going on before I go to the expense of a short haul and powerspray.