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From: Glenn Williams (no email)
Date: Wed Aug 01 2007 - 18:50:18 EDT
<<<<<If you follow your argument to its logical conclusion one would say
that a 2 blade prop would provide more thrust than a 3 blade prop of equal
diameter and pitch. I doubt that is true.
I hope you would agree that 3 blade props are not 'better' than 4 blade
Props>>>>
Here's what Gerr says about number of blades:
"This brings us to the question: how many blades? Surprisingly, the ideal is
one. A single blade does not have other blades disturbing the water flow
ahead of it. But trying to get a single blade propeller to balance is sort
of like trying to clap with one hand. Two blades are the logical answer.
Both sailboats that need to reduce drag and high speed powerboats sometimes
use two bladed props. The problem with two blades for ordinary craft is that
you'd need a whopping big diameter to get all the blade area required to
drive you effectively. Enter the standard three-bladed prop. This
configuration has proven to be the best compromise between balance, area and
efficiency.
Of course there are props with four, five and even more blades. They are
useful for two reasons. First, with their extra blades you can get more area
with less diameter. So if you needed a 20 inch screw but only had room for
an 18 incher, you could use say, a four bladed prop.
THE FOUR BLADER WOULD GENERATE ALMOST AS MUCH THRUST AS THE THREE-BLADER.
IT WOULD NEVER BE QUITE AS EFFICIENT BECAUSE WITH THE BLADES CLOSER
TOGETHER, THEY SCRAMBLE UP EACH OTHERS WATER FLOW - LITERALLY GETTING IN
EACH OTHER'S WAY"
The capitals are mine, not Dave Gerr's.
Cheers
Glenn.
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