Generally, the hull of the aluminum alloy fishing boat can be divided into three basic types according to the Speed-Length ratio. This is another dimensionless number. Express the speed of the aluminum alloy fishing boat in knots and divide it by the square root of the length of the waterline to get this number. For example, a motor boat with a 25-foot waterline length has a maximum speed of 12 knots and a speed-to-length ratio of 2.4. Another example is an ocean liner with a sailing speed of 28 knots and a waterline length of 1,000 feet. The speed-to-length ratio is 0.885.
Similar to ocean-going regular liners, the displacement hull of a fishing boat does not produce lift when traveling at high speeds. The maximum speed-to-length ratio of a real displacement hull is 1.34. At this speed, although the power is increased, the draught at the tail of the boat can only be deepened, but the speed of the boat cannot be increased. Rowboats, canoes, towing boats and standard sailing excursion boats all have typical drainage hulls.
For example, the waterline of a sailing boat is 25 feet, and its speed is 6.7 knots, or about 71/. mile per hour, with a speed-length ratio of 1.34 times the square root of 25. This is the "hull speed (Hull s knock pee called d)" if flying increases the sails and power, it will only cause the boat and its equipment to overwork.
The other type is the semi-displacement hull, which often has a round Russian part and a fairly wide tail plate to obtain the lift generated by the water flow below the hull. It has a higher speed than the drainage type, and the speed-length ratio can be up to 2.5. For example, shrimp boats in Maine, some brisk sailing boats, yachts and various old excursion boats. This type is also called semi-planing hull.