Propeller design of boats vs. airplane

[peresah]

I'm a curious civil engineer who has just returned from an evening walk by the harbour.

I noticed that the propellers of boats appear to be designed differently (e.g. shorter, rounder) compared to airplane or wind turbine wings (long, slim airfoils).

If this is true, can anyone elaborate on the physical background behind these design differences? I guess it may be related somehow to the differences in the density and compressibility of water and air.

Thanks in advance

 

[MiketheEngineer]

I believe it has to do with their Reynolds numbers, density, practicality, water cavitation, rpms and strength of the prop design.

A 5' diameter plane prop could not turn at 2000 rpm in water!! First it would break - second it would cavitate and go nowhere.

Check out your old hydraulics books

 

[MikeHalloran]

Google "Turbinia" for some fascinating (okay, to me) history on steam turbines. Some of it will get you to the nightmares they had getting all the turbines' power to the water. (Nine screw propellers on three shafts)



Mike Halloran
Pembroke Pines, FL, USA

 

[peresah]

Thanks for your explanations and suggestions. I think that settles my curiosity for now