Originally Posted by jwalker
I don't understand the logic of a 4 blade prop in your situation. You were trying to reduce the load on the engine to get it back into the power band and a 15" pitch sounded about right as a starting point but then you add a blade so you're effectively spinning 1 and 1/3 propellers so increasing the load on the engine.
But the blades are smaller, and are cupped less.
I'm not sure what the surface area differences are for a given size perhaps a prop guru could shed some light on that ..
Because of the so called 'dark art' that are props, I think a big range of factors can have quite an impact, including the usuals such as hull weight deadrise & hull form, motor torque etc, and not to mention the depth in the water, I mean moving an engine up or down an inch can absolutely transform the perfomance of some engines, as I have experienced, thats why trial and error seems to be the best way to find that ideal match I suppose,.. so in the end therefor, its not just about physics and maths as the interaction of some of these variables doesnt always give the result expected.
Another example was when I tried a 21 pitch on my Honda 90 , It ran as sweet as a nut on a 19", so I went for glory and a few extra knots .. big mistake
I could barely get that motor to spin above a fast idle, the transformation was unbelievable .. and heres a thing, the alloy prop which that engine came with was actually slightly better that a stainless equivalent, giving a superior hole shot... wierd eh ?
I'm tellin ya .. theres voodo in them things