Steven Shelikoff wrote:


I still think it's pretty easy to be fooled on some parts of the
rotation. I.e., if the blade you're watching is going down but you see
a "splash" coming up above it breaking the surface, it could just as
easily be "push" from the blade just behind it that's coming up.

Sure it is, but I'm watching that blade in "slow motion" compared to the
one on your boat, and I'm not being fooled.


The problem is that for the totally submerged blade, the portion of
where it's less efficient isn't the entire arc from 270 to 90.

True, but the only part where it approaches maximum efficiency is
@045* (give or take some degrees) to 090*

And

there are large portions within that arc where it's more efficient than
portions within the arc from 90 to 270.

Name one

Poorly posed question. (Consider a 1' dia prop with the hub submerged 2'
and we will stick with 270-090/090-270) Name a portion of the arc (in
degrees) between 270-000 where the overall efficiency of the blade
matches or exceeds the overall efficiency of the blade between 090-180,
then give it as a percentage of the total arc between 270-000/090-180
(90*). Then do the same for 000-090 versus 180-270


As for the rest, I see two main points:

1. Please explain how you can narrow down overall net sideways force to
a mere 8-9 degrees ( I would consider it closer to 135* +/-).

2. If we consider a prop (in this case, for this question, just
submerged) to be less efficient between 270-090 than it is between
090-270, how can dropping that prop (the prop is 1'dia so hub would

be @6" underwater) 2' 6" to 3', make all that much noticeable change
in the overall efficiency and arcs of efficiency, considering the
horsepower, turning it. i.e., do I think that inefficient side may
have gained some efficiency ? .... yes. Do I think I could perceive
the difference ?.... unlikely, in most cases. (9,999.99 out of 10,000
-couldn't G).

As I was starting this, I remembered I had one of those long paint
stirring thingies (propellor on a shaft) for my drill. Out to the pool!
Started just beneath the surface .... helluva splash.
Then lowered it as deep as possible (barely avoiding electrocution).
Interesting. At first, no noticeable movement, but within 2-3 sec. I
could see a moving "bulge" on the surface. To be sure I wasn't being
fooled, I tried it a number of times (whilst listening to my wife
shouting in the background about her possible need to dial 911, shortly)
with the same results.
Now I admit there is little good science here and the results are open
to discussion, but it was interesting.

otn