Ernest Scribbler writes:

My 77 Thunderbird rode no rougher than any equivalent
conventional hull:

http://blizzard.zmm.com/thunderbird/starboard.jpg


Nice boat. Looks like it's in great condition.

According to one of the photo captions, the stainless steel
prop reduces the top speed by 5-7 mph despite both props'
being 14.5" diameter and 21" pitch. Why would two props of
identicial specification have such different performance
characteristics because of one being steel and the other,
aluminum?

My father's 95-hp 1966 Mercury outboard, mentioned in an
earlier post, had a two-blade aluminum prop. I remember
my father telling me that a three-bladed prop would've
given our 16-foot Crestliner day cruiser a lower top
speed, but would've had more pulling power (like for
towing another boat, or pulling water skiiers).

I can certainly understand why a three-bladed prop would
give a boat more pulling power than a two-bladed one. That's
intuitive. But why would a two-bladed prop offer greater
speed? I'd have thought that the more blades, the greater
a boat's pulling power *and* top speed.

It occurred to me that maybe the explanation had something
to do with more blades rendering the prop less efficient by
creating more cavitation, but it seems like that would have
a detrimental effect on both aspects of performance.



Geoff

--
"The sky was low and heavy, like the brow of a retarded child."