__________ are attached to the keel, which extends athwartships.

Frames are structural components of a vessel's hull that provide shape and support. They are typically attached to the keel, which is the backbone of the ship, and extend athwartships (side to side across the vessel). This arrangement helps to maintain the integrity of the hull and supports the overall strength of the vessel as it faces various stresses while on the water.

By attaching to the keel, frames help distribute loads evenly along the hull, aiding in buoyancy and stability. The configuration of frames allows for the hull to resist compressive forces and maintain its shape under different conditions, such as waves and turns.

Other choices, such as planks, bulkheads, and strings, serve different purposes in the construction and functionality of a boat, but they do not specifically attach to the keel in the way that frames do. Planks are typically used for sheathing or covering, bulkheads act as partitions within the vessel, and strings refer to longitudinal members that provide additional structural support but don’t necessarily create the same framework attached to the keel as frames do.