Increased Engine RPM - More horsepower available! Increased blade tip to hull clearance. Improved engine operation. Reduced noise and vibration. Reduced "Prop Walk". "No Barnacles" option if installed on a stainless shaft with no zinc. Minimal increase in drag as compared to a "standard" 2 blade. Guaranteed or your money back (See additional conditions under "No Barnacles") EFFECTIVE APRIL 1, 2011, THE PROPELLER PRICE WILL INCREASE TO $325. WE APOLOGIZE FOR THIS INCREASE BUT THE COST OF SILICON BRONZE HAS MORE THAN DOUBLED SINCE THE PRICE OF $310 WAS ESTABLISHED.

Finally, a 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 RPM.
• Increase oil flow and thus pressure by increasing cruise RPM.
• Increase coolant flow by increasing cruise RPM.
• Prevention of Marine Growth through controlled galvanic activity.

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 8.6% greater that the original 2 blade design and 11% less than a CDI or Perfect Pitch propeller.  The propeller is investment cast of Silicon Bronze for durability, prevention of marine growth, 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.

 

No More Barnacles!

The normal installation procedure for the Indigo Prop is the same as with any propeller. Install it on its shaft with a shaft zinc on the shaft for galvanic protection. As an option, it can be installed without a zinc. Marine growth is the greatest deterrent to propeller performance. Coatings applied to a propeller do not remain effective and by the end of the season, the boat will hardly move as a result of a fouled propeller. With a "normal" bronze propeller, a zinc is installed on the stainless steel shaft to serve as a sacrificial anode. This is necessary since the bronze propeller attached to the stainless steel shaft in a saltwater environment creates a galvanic couple [a very noble metal (shaft) electrically connected to a less noble metal (prop) immersed in an electrolyte (saltwater)]. A small electric current is generated and flows from the propeller to the shaft. The electrical activity created by this current flow on the surfaces of the propeller will prevent marine growth from growing on the propeller, however the propeller will sacrifice itself and be ruined in just a couple of seasons. The addition of the zinc (a metal which is less noble than either the shaft or propeller) to the shaft prevents deterioration of the propeller as the zinc is then sacrificed. However, the propeller surfaces no longer experience the galvanic activity and thus become fouled with growth. The Silicon Bronze alloy used in the construction of the Indigo propeller gives the best of both worlds. The material is such that the propeller can be installed without a sacrificial zinc and therefore generate a controlled amount of galvanic activity and thus stay clear of marine growth. With this low level galvanic activity there is still some very minor sacrificing occurring on the surfaces of the propeller but the deterioration is greatly reduced. It is estimated that an Indigo propeller installed in this manner will have a service life of about 6 years. View actual un-edited images of an Indigo propeller after six months immersion in salt water (April - October 2002). More Propeller Images (65k)