Fig 5.8 Calculation of the frictional resistance
Reynolds number: Rn = V = velocity of yacht in m/s For hulls: L = 0.7-L,
For keels and rudders: L = mean chord [ keel: 1.45 m ] [ rudder: 0.5 m ] v = kinematic viscosity
[ hull: 408.6 N ] [ keel: 93.6 N ] [ rudder: 34.0 N ]
p = water density [ salt water at 20 'C » 1025 kg/m ]
2 2 2 Sw= wetted surface [ hull: 25.2 m ] [ keel: 4.4 m ] [ rudder: 1.3 m ]
For total frictional resistance — add the contributions from hull, keel and rudder. [ 536.2 N ]
always be obtained by multiplying by the so-called dynamic pressure 0.5 • p • V2 and a representative area, here normally the wetted surface Sw.
The values computed for the YD-40 are at 3.5 m/s, or 6.8 knots, the same speed as in Fig 5.4. By adding the contributions from the hull, keel and rudder the total friction is obtained as 536 N, also given in the bar of Fig 5.4.
Viscous pressure Fig 5.9 shows a typical pressure distribution on the hull at a given resistance depth, ie along a certain waterline. It is seen thai the bow and stem pressures are higher than in the undisturbed water at this depth, while
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Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.