2000 Johnson 150hp Oceanpro Prop Slip

[reiddo1]

On slip and prop pitch, think about it. If the prop is operating near the surface, the distance from the density of water to the density of air is in the inches or fractions thereof. When you use a shallow pitched prop, the distance traveled per revolution is minimal so the force exerted against the water (thrust per rpm) is reduced meaning that there isn't much pressure differential between the rear of the blade and the ambient air. As the pitch is increased, that thrust per rpm is increased and there is more of a suction from the prop which, when adequate reaches through the available water to the ambient air and you have ventilation. Ventilation is a form of prop slip. The other part is how fast you can move the water before it forms a vacuum and the density of the water is reduced (addition of bubbles) reducing the available thrust.....cavitation. The lower the pitch the lower the water movement per rpm, the lower the cavitation.



Light, fast boats can move water very fast and have little slip. Barges can't and do!

So are you implying I am have cavitation with that prop even though the AV plate is not above the water at WOT. I could lower the engine a hole or two and see what happens.

 

[Texasmark]

What's in front of the lower unit can influence the quality of the water stream being received by the prop. If you have turbulence caused by the hull you have bubbles and you have increased slip. To turn with 0 slip, like a screw turning in a block of wood, you need solid water entering the blades......course you will never achieve 0 slip as the water obviously, gives under pressure.