prop striations?

What purpose do the striations serve on this prop:
http://www.boatdesign.net/gallery/showphoto.php/photo/20171

 

What you see is milling traces. Since the tool leaves circular traces when moving along the prescribed track, light is reflected differently along those tracks. This can be particularly obvious if looking at the "rough cuts", before the finishing steps are completed.

 

Looks like more than milling traces to me. If you look at the base of each blade, you can clearly see how the striations come to a defined stop. The size and spacing is identical on each blade, and they throw shadows.

 

Looks like grooves from initial, coarse milling with a large diameter ball cutter to me. Probably done with a CNC mill. Additional, finer milling would follow with a smaller diameter cutter, probably several more stages of milling.

 

Yep, first pass and then you stress relieve again. Otherwise the blade will walk on you.

 

Thank you all. I have never seen a prop of this scale being milled. I also saw the depth and stairstep of the shadow closer to the hub and thought maybe someone was reinventing the wheel. Thank you all for clearing that up for me.