A 19 pitch 4 blade prop is equivalent to a 21 pitch 3 bladed prop. If you go
back to a 17 pitch 3 bladed. you should increase your rpms by 6-800.

--
Bill
Chesapeake, Va


"Shawn Willden" wrote in message
...
I have a 20' Bayliner, a 1990 with a 5.0L Merc and (I think) Alpha 1
outdrive. The engine has been modified with a 4BBL carb (now a marine
one,
for those who followed my earlier travails!) which should give it about
230
HP (as comared with 200HP with the original 2BBL).

After getting the engine fixed up with the right kind of carb, I took it
out
on the lake last week and while the engine seems to run well, there's
absolutely no way the boat could have gotten an adult out of the water on
skis. Top speed is pretty good (nearly 40 mph, and this is at an
elevation
of over 5000 feet) but the boat is really slow to dig its way up onto
plane. As you might guess from the subject line, I suspect the prop.

This boat apparently came with, and was pretty much always run with, a
three-bladed 17 pitch prop. This spring, however, the former owner
trashed
the prop on a sand bar. Before he sold it, he purchased a new
four-bladed,
19 pitch aluminum prop (don't know what the diameter is, but it looks
about
the same as the previous 17-pitch prop, which he left in the boat). My
suspicion is that this prop is just too much for my engine to turn, but I
don't really know if 2 inches of pitch make that much difference.

At plane, with a wide-open throttle (assuming the throttle cable is
adjusted
correctly), the engine peaks out at 3500 rpm. According to a Mercruiser
manual I have, it should run to about 4200 WOT.

So, before I go buy a prop, what do you all think? Should this engine be
able to handle a 19 pitch? Actually, I'll buy a prop anyway, because it's
cheaper than looking into deeper engine problems, and if it gets me
acceptable performance, I'll stick with it. However, if the current
performance indicates that there might be other problems, I'd rather know
sooner rather than later, even if I decide not to do anything.

Thanks for any help,

Shawn