Rule of thumb with an I/O (so I've been told) ... if you use say a 21
aluminum, then use a 19 steel. In other words, decrease the pitch when
switching to steel.

I'm not sure that's entirely accurate from my own experience. I had a
aluminum 19 on my 190hp Merc and it ran WOT at about 5400RPM (when I bought
the boat). The manual states 4400-4800rpm for WOT.

I read and heard that the adjustment was (rule of thumb) 1" pitch/200 rpms.
So I increased the pitch to 23 with a SS prop, and I'll be damned if WOT is
at about 4600rpm now...perfect. Maybe it would have been different if I
stayed with aluminum, I don't know. YMMV

--Mike

"bowgus" wrote in message
...
Rule of thumb with an I/O (so I've been told) ... if you use say a 21
aluminum, then use a 19 steel. In other words, decrease the pitch when
switching to steel.

"gudmundur" wrote in message
...
I currently have a 13.75 inch X 15 pitch aluminum prop on my 70 hp
Evinrude. The prop was really beat to death by it's previous owner, and
it is needing replaced. I use this boat for diving and skiing mostly, it
runs about 30 knots at present, and yanks me up out of the water quickly.
I was looking to go stainless, but they all seem to have a much higher
pitch, like 19 or more. What could I expect from say 13.25 X 21? I would
guess it would lug my motor down, and be very poor on pulling a skier up.