- Increased Engine RPM - More horsepower
- Increased blade tip to hull
- Improved engine operation.
- Reduced noise and vibration.
- Reduced "Prop Walk"
- Minimal increase in drag as compared to a
"standard" 2 blade.
- Cast from C87600 Silicon Bronze.
- Guaranteed or your money back
- EFFECTIVE JAN 10, 2017, THE PROPELLER
PRICE WILL INCREASE TO $360. WE APOLOGIZE FOR THIS INCREASE BUT THE INCREASED
COST OF SILICON BRONZE LEADS TO THIS INCREASE TO SIMPLY COVER OUR INCREASED
As part of our ongoing program of
Continuous Improvement, we have refined the geometry of the Indigo Atomic 4
propeller to yield a propeller that is even quieter and smoother than the
original model with slightly higher Wide Open Throttle (WOT) RPM to boot. The
"Radial Winglet" name refers to the change that has been made to the
geometry of the winglet. The fillet that defines the transition from the blade
face to the winglet in now on a constant radius. This moves the suction side of
the winglet (forward side) to a location that limits the impact of tip vortex
cavitation on that side of the winglet thus reducing noise in the normal
cruising RPM range.
Shown here are images of the old and
new blades to give you an idea of the subtle differences. The
"scratch" on each blade near the winglet is a scribe mark that was
made at a constant radius about the center of the propeller bore. As you can
see on the "Original Design", the winglet sort of flared out as you
traveled from the leading edge (right side) to the trailing edge (left side).
In the "Radial Design", the flare is gone and the fillet radius
between the blade and the winglet is on a constant radius from the leading edge
to the trailing edge. Admittedly, this does not really look like any big deal.
However, it turns out to be rather significant from a torque and noise
standpoint. By "rolling" the trailing edge portion of the winglet
toward the propeller centerline, we were able to remove about 3/16" of
winglet (at the greatest propeller radius) to obtain the configuration shown at
the right. This reduction in blade area at the extreme radius plus the radial
progression of the winglet fillet radius yielded a WOT increase of nearly 300
RPM in initial testing. This increase of RPM was accompanied by a very slight
reduction in thrust so a small change in pitch has also been made.
Aside from this subtle change in
geometry, the Indigo propeller remains the only propeller designed from the
ground up to improve performance of the Direct Drive Atomic 4
powered yacht. The design of this propeller has evolved from numerous
tests with a variety of 2 and 3 blade designs, all with the Direct Drive Atomic
4 as the engine of choice. Note: Some V-Drive Atomic 4 models are direct
drive in that they have a 1:1 reduction. Check name plate on V-drive for ratio.
Engines with a reduction gear (not Direct Drive) are unique in that the
propeller shaft coupling has four (4) bolts where as the Direct Drive coupling
has only three (3) bolts.
The vast majority of Direct Drive Atomic 4
yachts were originally equipped with a 2 blade, 12" diameter by about
9" pitch propeller. This application allows the vessel to achieve a
respectable cruise speed in calm waters at about 1400 RPM. However, wide
open throttle is only about 1700 RPM which leaves very little reserve for foul
weather or bottom fouling. Furthermore, at 1400 RPM, the engine is
working very hard (near maximum cylinder pressure) which leads to high loads on
rings, pistons, and bearings.
The design objectives of this propeller are:
- Increase cruise RPM to about 1900 with wide open throttle
around 2400 RPM.
- Reduce loading on pistons, rings, and bearings by
increasing RPM for a given HP.
- Increased alternator output by increasing cruise
- Increase oil flow and thus pressure by increasing cruise
- Increase coolant flow by increasing cruise RPM.
Increasing RPM can be accomplished by simply reducing pitch on
an existing 2 blade propeller but not without consequences. Most
installations have less than the recommended 15% tip clearance between
propeller and hull and at higher RPM, considerable noise is generated by
vortices coming off the tips of the blades.
Our propeller meets all design objectives. It is a
3 blade design at 10" diameter and
7.4" pitch . The 3 blade concept yields much less
propeller induced vibration yet total blade area is only about 8.0% greater
that the original 2 blade design and 12% less than a CDI or Perfect
Pitch propeller. The propeller is investment cast of C87600 Silicon
Bronze for strength, durability, and accuracy of pitch and blade
geometry. The smaller diameter and blade winglets virtually eliminate the
unacceptable noise associated with tip vortices generated at the higher
RPM. The smaller diameter and 3 blade design also leads to a significant
reduction in "prop walk" when operating in the astern direction.
DUE TO ONGOING PROBLEMS FINDING A FOUNDRY TO CAST PROPS USING
C873 SILICON BRONZE, WE NO LONGER OFFER OUR "NO BARNACLES" OPTION
A few props of each size are still available as of
Propellers are available in right hand rotation only for
3/4", 7/8" and 1" shafts. Instructions are
included for removing your existing propeller and installing the new propeller
on your existing shaft.
HOW DO I KNOW IF MY ATOMIC 4 IS
DIRECT DRIVE ? The easiest way to tell is to look at the engine
coupling between the engine and the propeller shaft. If there are three (3)
bolts holding the two coupling halves together, then you have a direct drive
Atomic 4. The engines with a reduction gear have a coupling with four bolts.
Note: Some V-Drive Atomic 4 models are direct drive in that they have a
1:1 reduction. With the V-Drive, however, do not rely on the number of bolts to
determine direct drive. Check the name plate on V-drive for ratio or rotate the
engine in forward and check the ratio.
Props installed as of Feb. 2019
Application List (To Date, vessels on which propeller is in
C&C 30 Redwing
Chris Craft Cherokee
Eastward Ho 24
Morgan 28 Out Island
Morgan 30 Out Island
Morgan 30/2 IOR
Morgan 33 CCA
Rhodes Swiftsure 33
Southern Cross 28
(If your vessel is not listed it most likely
means that no one has yet to try the propeller)
Download Installation Instructions
Send your questions or comments to me at
Call today for Credit Card orders or send
check/money order to:
Indigo Electronics, Inc.
105 Pipe Kiln Court
Williamsburg, VA 23185
Today. You never knew sailing could be so much fun!
1-800-428-8569 toll free
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