Matt Colie wrote:
You are correct about Turbinia. I was told that their thinking was that
this could be an alternative to a larger radius (a problem with the
higher than expected shaft speeds) but still a chance to put all the
horsepower into the water. Turbinia was not the only vessel with this
feature.


IIRC the screws on Turbinia looked rather odd.


Problem: A marine screw propellor creates thrust by accelerating a
column of water. The second prop will be in the column "wash" of the
first and have much less mass to accelerate.


Yes and the aft prop will also be operating in turbulent &
aerated flow. Nontheless it can be made to work and I think
the idea of using a higher pitch for the aft prop is a good one.



Do you have horsepower left over at flank? (Up against the govenor with
less than best admission or partial throttle...)


Wouldn't it be the other way around? Governor less than full
advance with the engine at top RPMs and full throttle?


Fresh Breezes- Doug King