Variable pitch prop

[talltigeguy]

I know I mentioned it somewhere here some time ago, but the concept of a variable pitch prop would be pretty awesome to institute on a wakeboat. I was talking to an airline pilot, and I wondered how the plane slowed down so fast once it landed (this was an older prop plane), and he explained that the plane's propellers can be changed in pitch, even to the point that they reverse pitch and it puts the plane into 'reverse'. I thought I had brought this up in a thread a year or two ago, but can't find it now. I had never heard of a boat doing it.

I was on a cruise just a couple weeks ago and was surprised to find that the boat's propellers have adjustable pitch. The big diesel engines generally run at the same RPM's all the time and the speed of the cruise ship is controlled by changing the pitch on the propellers.

That would be pretty sweet to have on an inboard boat and could be used differently based on the application. You could go from wakesurf tractor to high speed barefooter with a switch something like the TAPS switch. Has anyone worked on this for smaller boats?

[chpthril]

There used to be some variable pitch props for I/Os IIRC. Never driven one or know how well they worked. I think they were really geared, pardon the pun, for the go-fast crowd.

[TeamAllen]

I remember one from Land and Sea called Torque Shift, from back in my I/O days. They don't make them any longer, I guess. I found this one http://www.aerostarmarine.com/runabouts.html.

My guess is they can't do it on an inboard because the hub of the prop is so small. The hub diameter is so much larger on the other boats because of the through hub exhaust. Thee is more room for all the parts the have to put in there to make them shift?

[IDBoating]

I was on a cruise just a couple weeks ago and was surprised to find that the boat's propellers have adjustable pitch. The big diesel engines generally run at the same RPM's all the time and the speed of the cruise ship is controlled by changing the pitch on the propellers.

Helicopters and propped airplanes work the same way. You set the engine at its happy RPM's and vary the pitch to get the air behavior you desire. The ability to have an "air brake" is a secondary benefit, but not the primary reason they have variable pitch props.

Note that this also eliminates the need for a transmission with forward and reverse gears. The shaft always turns the same direction, and the reversal is handled solely by the blade pitch. So your powertrain gets simpler but your prop gets far more complex.

[Ewok]

And when you put all the mechanicals for the drivetrain in a variable pitch prop and then hit a prop, then that really expensive and complex part needs a very expensive rebuild or replacement.