A towboat for river barges is tested in a towing tank. The towboat model is built at a scale ratio of 1:13.5. Dimensions of the model are overall length \(3.5 \mathrm{~m}\), beam \(1 \mathrm{~m}\), and draft \(0.2 \mathrm{~m}\). The model displacement in fresh water is \(5500 \mathrm{~N}\). Estimate the average length of wetted surface on the hull. Calculate the skin friction drag force of the prototype at a speed of 7 knots relative to the water.