The propeller does boil the water. It is a scientific fact and I shall offer
irrefutable proof:

http://www.brooklyn.cuny.edu/bc/ahp/MBG/MBG4/Joule.html

Quotes:

"In the following years he took to measuring the amount of heat generated by
every mechanical process he could think of. He enclosed wooden paddles
inside an insulated container and used a falling weight to turn a shaft and
churn the paddles. Friction caused the water in the container to heat up,
and Joule measured the heat change. From this the work done could be
compared with the amount of heat that had been produced.

By 1843 he was ready to publish. Called the mechanical equivalent of heat,
this is value for the amount of work required to produce a unit of heat, and
is calculated as 41,800,000 ergs. (One erg is the work done in moving a one
gram mass through a one centimeter distance)."



So, as one can plainly see that in the mid-1800's it was recognized that the
churning of propellers heat the water. In the case of the cavitating
propeller, the slippage is so great that the energy that would normally go
into propelling a great ship forward goes, instead, into raising the caloric
content of the fluid medium surrounding said propeller causing boiling and
cavitation.

Hence, the propeller boils the water, causing cavitation.

My tea kettle has a propeller in it and boils water quite quickly with no
application of heat.