He asked me the same silly question. The longer the boat, the faster? I read this about two years ago. I agree with Matt.
Here is an answer by Matt, a maverick boat designer.
"Longer boats are commonly regarded as being 'faster' than shorter ones. The reality is, as usual, more complicated. I would rather say that longer boats have a higher potential speed; you still need to supply the energy to achieve that speed. If you don't feel like working that hard ( and it can be real hard in a headwind and sea) then you will go slowly, and the guy in the shorter boat will keep up with you just fine at the same power output. Sorry, here comes a little math: A boat's speed (in knots) can be expressed as a factor of the square root of its waterline length (in feet), V / sqrtL, the Speed-Length Ratio (or Taylor Coefficient). With variations from other factors, generally a boat is most efficient (best speed from least effort) at S/L ratios around 1.0. The maximum speed a boat will usually reach under sail or paddle ('hull speed') is close to a S/L of 1.34."
Well, that is only 1/4 of the full text. Click here for more. Search for "Some Design Factoids"