It's the overall hull design and the features (bulkheads, smaller cockpit etc) that make a rough water boat. Until more recently the right features were rare to find in a boat less than 16 feet, not because it was impossible but because kayak manufacturers hadn't seen a clear market to design such a boat. But there is a solid consumer base for these boats and the manufacturers have responded.
There are plenty of transition and rec-ier type boats in 14 ft that don't perform nearly to the level of boats like the Alchemy and the others like it, and would not be recommended for someone wishing to push their skills for big water. But that is because of the overall hull design and issues like larger cockpits that would make an on-water recovery more difficult, not because of the length alone.
Touring Kayak Paddles
Bent Shaft Canoe Paddles
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