Hull speed as determined by the 1.34 x square rt of the LWL is not a hard number, just an approximation or rough guideline.
Below is a portion of an in interview with Gary Mull:
He was casually asked whether the maximum speed of his intriguing new boat design was 1.34 times the square root of the waterline length.
"I wish people would quit saying that," he retorted with intensity. "There's no such thing as a maximum speed under sail. There's a point at which the speed-versus-resistance curve begins to get very, very steep. At low speeds, a certain increase in horsepower gets you a fairly good increase in speed - but at high speeds, doubling the horsepower only gets you a very slight increase in speed. Usually somewhere around 1.34 times the square root of the waterline length - the sailing waterline, not the static waterline - that speed/ resistance curve starts to get very steep. But there's no absolute limit."
"But," he was asked, "doesn't the quarter wave start to build up higher than the cabintop?""No! That's not so!" he exclaimed. "I've never seen such a thing. That's all magazine talk. That's not naval architecture. I'm continually seeing this 'maximum speed under sail' or 'maximum speed-length ratio' or whatever-the-hell, and it's totally meaningless to naval architecture, as an absolute maximum. It does have meaning, because the speed-resistance curve does get very, very steep, as I say; but it seldom gets absolutely vertically asymptotic."