At planing speeds, how is the boat's trim affected?

At planing speeds, a boat achieves a level trim supported by dynamic lift, which is the reason this choice is the correct answer. When a boat is moving fast enough to plane, the shape of the hull and the speed generate lift that elevates the boat, allowing it to run on top of the water rather than pushing through it. This results in a flat or level position on the water, optimizing efficiency and minimizing drag.

In this trim position, the weight distribution is balanced, which enhances the boat's handling and stability during high-speed operation. Operating at a level trim enables better fuel economy and performance, as the hull has less resistance from the water.

The other options do not accurately describe the condition of the boat at planing speeds. A bow-down trim might occur at lower speeds or when the boat is not properly trimmed, but not during planing, where the dynamic lift keeps the hull level. Increased drag occurs when the trim is not optimal, while instability is typically a result of improper weight distribution or trim rather than a characteristic of the planing condition itself.