http://sites.mercurymarine.com/porta...che ma=PORTAL


Three- vs. Four-blades?

Four blade propellers usually:

a.. Plane the boat faster than 3-blade propellers
b.. Keep the boat on plane at a lower speed
c.. Give improved mid-range speed at the same RPM as a 3-blade propeller
d.. Provide quicker acceleration than most 3-blade propellers
e.. Run smoother than 3-blade propellers
f.. Have better holding power in rough conditions
g.. Are less likely to ventilate in sharp turns
h.. Provide better low speed handling
i.. Are not quite as fast on the top end as a comparable 3-blade propeller


http://www.marinepartsman.com/about-...ousings_1.html

The 4 blade design (stainless steel) is popular with boaters who are looking
for a good hole shot, better acceleration, and better bow lift (higher trim
angle) to reduce boat drag (too much of boat in water- reducing top end
speed). Important: 4 blade designs allow your boat to stay on plane at a
lower rpm, producing a slower cruising speed without loss of plane of the
boat in rough seas and conditions. Renegade props (4 blade) are of an
excellent design -allowing better top end, speed, with minimal drag.

http://www.boatsunlimitedny.com/products/propellers.php

Number of Blades
Some propellers have three blades, while others have four. Which should you
chose? Generally, a 3-blade propeller provides good performance in most
circumstances. A 4-blade propeller, however, can provide better performance
in rough water or with high mounting heights (such as Flats boats). This is
because a 4-blade propeller has more blades to hold the water when air may
be present in the water, which is more common in rough water or with a high
engine mounting height.



San Juan 23:

http://www.geocities.com/Yosemite/23..._tips/d06.html



PROPELLER CHOICE - The pitch of the stock propeller for most small 2 cycle
outboards is designed to push a light aluminum fishing boat at planing
speed, not a 1.5 ton displacement sail boat hull at 5 knots. On a planing
hull the engine can rev freely and cool properly pushing a light load within
its designed RPM range. When using the stock propeller to push a
displacement hull like an SJ23, the engine will generally operate in the
bottom half of the RPM or torque range. This overloads the engine resulting
in overheating and accelerated wear. Be very wary of the throttle setting
on your own outboard. Find the setting that produces maximum speed with
minimum throttle. Notice that you can increase the throttle with very
little more speed. To solve this problem you could change from a 2 bladed
propeller to 3 bladed propeller or install a finer pitched propeller,
usually 3 blades. Either change will achieve more push and longer engine
life but with more noise. The fine pitched propeller, especially if it has
three or four blades, is excellent for accelerating, towing, punching into a
current or waves and really comes into its own when backing up or stopping.
These propeller blades are generally round shaped (like a lily pad) versus
the screw shaped propellers designed for speed. It should be noted that a 4
cycle engine generates more torque at a lower RPM than is a 2 cycle engine
and is therefore is a better choice for pushing a displacement hull.

Tested on Beneteau:

http://www.bruntons-propellers.com/a...performance%22