"The boatbuilders first requirement was for oak and very special oak at that. Most of the wood in a boat is curved and, while you can bend oak after steaming, it is impossible to bend very heavy pieces. So shipbuilders have always valued grown crooks -- oak that has grown crooked. One of the reasons why so many park trees were planted in days gone by is because an oak growing crowded in a forest will grow up straight and clean, with few of the treasured crooks. An oak growing free in a park sends out huge branches and these twist about and have plenty of crooks in them."
from THE FORGOTTEN ARTS by John Seymour