Mark explained it well. You're looking for a more maneuverable kayak. Shorter boats are inherently more nimble but don't base your decision entirely on length.

Traditionally longer sea kayaks had a very flat keel. The ends were effectively pinned in the water and would track like freight trains. Some more modern designs instead have a significant curve to their keel, what we call "rocker." This frees up the stems and allows them to turn easier. The cross section of the hull also matters. A deeper "V" will bite the water more than a rounder bottom.

For an extreme example, compare the Wahoo flat water race kayak (top) with the open water Panthera (bottom). Both are 18 feet long (+/-). The Wahoo hull is very flat in profile from stem to stern. It tracks quite stiffly (it understeers, to use the car analogy). My 18' long Panthera, for instance, can practically spin within it's own length at lower speeds. The stern is very loose (oversteers).