A brace, perpendicular to the keel, that helps maintain the beam (breadth) of a marine vessel against external water pressure and that may serve to support the rail
To cross, as a purpose; to oppose; to run counter to; to contravene; hence, to frustrate or defeat
a crosspiece spreading the gunnels of a boat; used as a seat in a rowboat hinder or prevent (the efforts, plans, or desires) of; "What ultimately frustrated every challenger was Ruth's amazing September surge"; "foil your opponent
If you thwart someone or thwart their plans, you prevent them from doing or getting what they want. The accounting firm deliberately destroyed documents to thwart government investigators. to prevent someone from doing what they are trying to do (thwart (13-19 centuries), from thvert)