Will a metal boat always displace more water than a fiberglass boat?

Not necessarily. The amount of water displaced by a boat depends on its weight and design, not just the material it's made from. A heavier metal boat can displace more water than a lighter fiberglass boat, but if the fiberglass boat is larger or designed to carry more weight, it could displace more water. Ultimately, displacement is determined by the volume of water pushed aside, which is influenced by the boat's overall weight and shape rather than material alone.