Volvo Penta - DPH
The DPH has long been the workhorse outdrive for the company's D4 and D6 engines. While the DPH was being re-engineered Volvo Penta took the opportunity to also improve oil flow and reinforce the suspension fork. We’re told the new version of the drive unit will also better handle the high loads that are often seen in boats from 30' to 33' with single engines.
Sterndrives Are Efficient
Sterndrive lower units are far more efficient than conventional inboards at delivering thrust. The sterndrive lower unit --which moves torque through two 90-degree turns --has always required more beef to handle diesels. That is why the DPH was specifically designed to handle the high torque produced by the D4/D6 engines.
In this view the counter rotation of the forward and aft prop is clearly demonstrated as well as the central hub gearing.
Unlike other sterndrives, the DPH has "thru-the-drive" exhaust which exits the unit above the props and therefore does not disturb them. This design also carries fumes away under water and reduces noise. To handle the steering forces at high speeds, the unit has built-in external hydraulic steering cylinders. Further, the DPH has a drive-by-wire patented X-act steering system which enhances both control and feel.
In this port side view of the DPH drive the hydraulic steering drive is clearly visible. The shadowing shows the 50-degrees of travel as well as the sacraficial anode on top of the anti-cavitation plate.
Historically corrosion has been the Achilles heel for all outdrives in saltwater. To fight this natural phenomenon Volvo Penta uses a "saltwater-grade aluminum and multi-layer paint process."
The Volvo Penta DPH props maintain resistance to the elements through its use of a high-strength, nickel, aluminum, bronze propeller design.
The light blue coloring indicates the cooling water intake and its direction of flow through the drive up into the engine. The red coloring indicates the cooling water's exit from the engine and eventually through the vent of the drive below the anti-cavitation plate. Also clearly visible are the internal drive shafts and gearing systems that are the heart of this sterndrive.
The patented propellers are specially designed for the characteristics of the D4 and D6 engines. Developing propellers for Duoprop differs considerably from conventional drives with single propellers. The counter-rotating front and rear propeller are designed to share the work load to increase bearing and transmission life. Volvo Penta states that it is the first engine manufacturer using the same alloy in its Duoprop design outside conventional inboard applications. This is important for the operator because it means that fouling should be no worse on the DPH props as compared to inboard units. The company says that corrosion resistance is "excellent" with full electric isolation to the propellers.
In this view the specifically engineers angles and shapes of the forward and aft props are clearly evident. Note that each prop is of a different size and the blades vary in shape to maximize power transfer.
Due to directional thrust, the DuoProp makes maneuvering at low speeds and docking far easier. That’s why single engine applications with the sterndrive are preferred vs. a conventional inboard installation. The propellers are offered for speeds ranging from 25 to 55 knots. Volvo Penta says that each propeller set is tailored for the engine’s particular speed and gear ratio, thus providing high efficiency with a good margin against cavitation. Because the Duoprops are completely systematic, it makes propeller selection easy. Volvo Penta says that each propeller pair is tailored for the engine’s particular speed and gear ratio, thus providing high efficiency with a good margin against cavitation. The Duoprops are completely systematic, meaning that the application and speed dictates which set of Duoprops the boat builder selects for installation.
DPH with Powertrim Assistant
Powertrim Assist is an option on Volvo Penta DPH units with EVC. Depending on RPM, Powertrim Assist trim the drive automatically to adjust the lower unit according to operator settings. The system has five set points for drive angles at five different engine rpm. Fully manual override is available at any time.