At low speeds the friction of the hull's skin is a greater source of resistance to forward progress than are the waves formed by the hull's forward motion. So a long narrow boat with a high theoretical hull speed but a large wetted surface will require more energy to paddle at low speed than a short fat boat with a minimal wetted surface. In extreme cases, such as flatwater racing kayaks, they can only be handled by expert paddlers. Touring kayaks hulls must be flattened out to increase initial stability, and, with it, wetted surface area. A kayak's volume is sometimes expressed in gallons or in cubic feet, but more often as simply high, medium, or low.
Volume is influenced by a kayak's length, beam, prismatic coefficient, and depth or deck height.
A high volume kayak is one that will hold tons of gear and a big paddler. For long distance touring you'll need to have sufficient volume to pack camping gear and supplies. A high volume boat is usually slower and heavier than a low or medium volume boat, but also drier and more comfortable. In strong winds a high volume kayak, with its higher bulk out of the water, will be more difficult to control than a lower profile lower volume boat. Your physical size is also important in choosing your kayak's volume.