Yachts 40’ and larger rely on three primary types of propulsion: conventional submerged propellers, surface-piercing propellers and pod-style propulsion, which in turn are associated with three system types: IPS Volvo and Zeus CMD for traditional diesel, and ABB Marine for electric power.
A certain segment of high-powered craft also relies on water jets. Herewith, is a brief summary of the advantages and drawbacks of each system.
Story Alain Brousse and Franck van Espen Photos Matthieu Carlin The basics of propulsion systems MOVING FORWARD XP Technical Propulsion Systems-YUS73:XP Technical Propulsion Systems-YUS73 14/05/09 15:52 Page115 116 TECHNICAL
DIVIDED INTO TWO SUB-CATEGORIES, V-drives and in-line drives, inboard drive trains are the most common systems found on yachts. Their popularity is due to their simplicity and low maintenance requirements.
In this configuration, a propeller is attached to a stainless steel shaft that is supported externally by struts; the shaft line is guided through a stuffing box, which ensures that the system is watertight, and connects to the transmission and engine via a coupling flange.
A reduction gear establishes a ratio between engine and shaft revolutions per minute, and allows operation in forward, reverse or neutral. A rudder, placed aft of the propeller, allows steering the boat with precision.
Other than requiring a precise shaft angle, the system is straightforward, reliable and suitable for most hull types. Maintenance is relatively minimal and focuses mainly on the stuffing box and the rubber bearings that help maintain shaft alignment.
Over time the stuffing box’s Teflon braid becomes less effective and must be replaced periodically, which is uncomplicated as long as the shaft line easily disconnects from the engine. Rubber bearings also must be replaced regularly to minimize vibrations.
Although corrosion issues are inevitable with underwater metal appendages, sacrificial zinc anodes and a properly grounded engine help reduce the problem significantly. This drive system’s main drawback is performance limitation. Aside from exceptional cases, such as the famous 60-mph Monte Carlo Offshorer designed by Carlo Riva, Bob Hobbs and Cal Connell, this mode of propulsion seldom allows boats to go over 40 knots or otherwise requires so much additional power that it makes more sense to use surface drives.
Within the past decade, however, we have seen new types of hulls with half tunnels that house the propellers. One important function of this design is that it reduces propeller shaft angle, which gets the boat to plane more quickly.
Additionally the tunnel helps funnel the water flow and creates a vortex effect that amplifies power. Thirdly, it helps reduce drag by covering the upper half of the propeller and protects it from floating debris.
Finally, it allows for a lower center of gravity that makes the boat less susceptible to pitch.
Inboard drivetrains
ADVANTAGES
•Low maintenance and
•nearly unlimited life
DRAWBACKS
•Underwater appendages are subject to impact shock
•Relatively noisy, even with today’s technology
•A cumbersome set-up, although the V-drive configuration helps minimize the problem
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THIS TYPE OF PROPULSION IS MOST common on yachts 100’ or longer, with a few exceptions, such as tenders by Wally, Tresco and some semi rigid ribs.
Many Italian builders, including Overmarine and Arno, use waterjet drives frequently on their larger models, while AB Yachts uses them exclusively throughout their range of yachts from 58’ up. The New Zealandbased Hamilton brand in 1957 first introduced a waterjet model named Chinook.
Since that time water jets have evolved greatly and now work in conjunction with powerful engines. Nowadays waterjets are found on fast ferries and catamarans used for passenger transport.
Although the system requires more moving parts than conventional inboard propulsion, it remains a relatively simple mechanism.
Water enters through an intake unit under the hull and is funneled through a tunnel housing an impeller (that serves as a pumping unit) before being discharged as a high-velocity jet through the stern.
Hydraulic jacks direct the exterior nozzle whose orientation determines the boat’s direction. Occasionally manufacturers use fixed waterjets as boosters, particularly in triple engine configurations that include two diesel engines and a gas turbine, to produce very high speeds.
This system was installed on Moonraker, a Frank Mulder design built by Norship in 1992 and on The World is not Enough, another Mulder design built by Millennium Yachts, allowing both yachts to reach speeds in excess of 65 knots.
The Pershing 115, which also features the system, has a top speed in excess of 50 knots. One of the advantages of waterjets is that they allow reversing at higher engine speeds, thanks to a deflector scoop that drops down over the nozzle to stop or reverse the jet’s thrust vector. The maneuver is completely safe, as long as the passengers are forewarned.
A 165’ Mangusta going at a speed of 38 knots can come to a full stop in less than 265 feet. Waterjets are suitable for shallow-draft planing hulls to augment high-speed capabilities.
It is a relatively simple fitting that requires but one entry point in the hull bottom and an exit point at the transom. These units often are found on hulls where surface-piercing propellers have reached their limits.
Waterjets
ADVANTAGES
•Produces no vibration
•Low noise level
•Excellent maneuverability
•No submerged appendages
DRAWBACKS
•Maintenance and repairs are a bit more involved than in other systems and can require working underwater
Rolls Royce Kamewa waterjet
Rolls-Royce began in 1904 as a luxury car maker, but this prestigious label also has become associated with technology in the aerospace, energy and marine industries. Rolls Royce’s marine division includes a branch dedicated to Kamewa waterjets, available in three series: the FF series works with engines from 300 to 1,800 hp. The recently introduced A series is dedicated to high-performance vessels.
Built in aluminum, these directional waterjet units can work with engines up to 4,000 hp. Finally, the S series is reserved for commercial applications on vessels such as cruise ships and ferries and can be coupled to engines generating as much as 30,000 hp.
Hamilton Jet
For the past 46 years Hamilton of New Zealand has installed about 30,000 waterjet systems available in two series.
The HJ series includes eight models suitable for engine power from 350 hp to 1,200 hp that with triple installation can boost speeds to 58 knots. The second series, HM, includes six models equipped with impellers, ranging from 1’3” to 2’6” in diameter. These are designed for boats from 65’ to 195’ in length and with 4,500 maximum horsepower.
Additional information available at rolls-royce.com/marine/products/propulsion/waterjets
For more information visit hamiltonjet.com XP Technical Propulsion Systems-YUS73:XP Technical Propulsion Systems-YUS73 Arneson surface drives
Although the concept for surface drive dates back to the 19th century, Howard Arneson revolutionized offshore racing by fully developing the Arneson surface drive as an alternative to other drive systems. California’s Arneson Industries manufactures and distributes its surface drives throughout the world.
Builders of sport yachts such as Baia, Magnum, Pershing, Overmarine and Arno have been clients for decades. The complete range includes 13 models (ASD6 to ASD16), that can be coupled to engines from 300 hp to 2,400 hp.
Arneson also sells a conversion kit for boats equipped with Mercruiser Bravo engines and conventional drives. Although it is rare, Arneson surface drives also can be found in combination with turbines.
More information is available at arneson-industries.com
118 TECHNICAL BEFORE BECOMING STANDARD on many series sport yachts, this type of propulsion was most common on race boats, where they proved to be very efficient. The extension of propeller shafts out through the boat’s transom locates them well aft, producing about 20 percent more horizontal thrust power than traditional inboard propellers.
With few exceptions, most builders opt for articulated drive systems for superior steering, motion and trim control. When they are optimally mounted, surface propellers are immersed only half way to significantly reduce appendage drag. Surface-piercing propellers also can be much larger than submerged propellers, making them more efficient.
It is easy to spot boats equipped with surface-piercing propellers because they usually “kick up” a telltale spray known as a rooster tail. This type of propulsion is well adapted to boats up to 90’ and engines with a maximum of 3,000 hp, therefore it is unsuitable for very large yachts.
For larger units with planning hulls, builders usually prefer waterjets; such is the case with the Mangusta range, equipped with Arneson surface drives up to 80’, and then Kamewa water jets for models 92’ and larger.
ADVANTAGES
•Reliable
•Efficient
•Allows for shallow draft
DRAWBACKS:
•Maneuverability can be an issue
•Cost
Surface-piercing propellers Fabio Buzzi designed this drive system for high-performance boats. A few production boats such as the Mas 42, the XSR 48 and the Sunseeker XS Sport use this drive system that works more or less like the Flexidrive, with a rudder located just aft of the propeller.
Completely locked in the running position, it includes a unique and ingenious exhaust system with a vent located just above the propeller, which helps boost its forward thrust action. Trimax XP Technical Propulsion Systems-YUS73:XP Technical Propulsion Systems-YUS73
TECHNICAL 119 SDS France Helices
This 20-year-old company, specialized in propellers, developed its own surface-piercing propulsion system. Its complete propulsion package in bronze and stainless steel includes corrosion-resistant drives, propellers, hydraulics and steering equipment. Five models are available according to boat size and engine power.
More information is available at francehelices.fr Flexidrive by Flexitab
The Victory Design Studio and the University of Genoa’s marine engineering department perfected this Italian-made surface drive. The unit includes a composite element with a rudder that envelops the upper half of the propeller and is adjustable up and down for optimum trim relative to speed.
Three models are available according to boat speed and configuration. For now, maximum engine power is 2,800 hp.
For more information, see http://www.flexitab.com
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ADVANTAGES
•IPS requires less horse power to achieve the same speed compared to conventional propulsion
•This in turn results in improved fuel economy
•Precise maneuvering is ideal for tight quarters
•It is possible to install two, three or four IPS units
DRAWBACKS
•Propellers are exposed to possible damage from floating debris
•Certain hulls lean more sharply into turns
•Cost
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WITH THIS TYPE OF PROPULSION SYSTEM, propellers are mounted on swiveling pods that extend below the boat. Independent engines, operating each drive, draw their power from an array of batteries recharged by generators. This system offers many advantages, including increased maneuverability, space savings for more interior volume, reduced fuel consumption, low engine noise and almost no vibration.
Large maritime companies have ordered pod systems from manufacturers such as ABB to reduce their operating costs; the yachting industry who took notice has begun applying the technology to units 130’ and larger.
Companies such as Volvo Penta and Cummins-Mercruiser also developed versions designed for boats from 30’ to 80’. The difference is that they rely on conventional engines, and the fuel economy they provide is thus a bit less noticeable. Pod drives
IPS Volvo Penta
In 2005 the Swedish company Volvo Penta launched the revolutionary Inboard Performance System, or IPS, designed for boats in the 35’ to 75’ range.
The Volvo Penta engineers’ primary goal was to significantly reduce fuel consumption. The pod system inspired them, and they opted for forward-facing counter-rotating propellers that pull rather than push the boat and can thus operate more efficiently in an undisturbed water flow.
Pods rotate in either direction from the boat’s long axis creating a variety of possible angles (unlike stern drives that are always parallel), which allows lateral thrust, an attribute that is particularly valuable when maneuvering away from a dock. In fact, the system’s associated joystick makes maneuvering a breeze.
The system allows for more powerful acceleration and a 15 to 20-percent increase in efficiency as compared to conventional drives. Requiring less horsepower, the IPS, which also weighs less than conventional engines, allows greater speed with less fuel consumption.
Another big advantage that boat builders appreciate is that the compact engines and drives require much less space than conventional installations, which provides additional space to expand accommodations on the lower deck.
One possible drawback is that with their inclined position in a V-hull configuration, the IPS drives and propellers can encourage the boat to lean more into turns. However, Volvo Penta engineers have proven very willing to work closely with boat builders to make sure the IPS requirements become an integral part of hull design.
One of the recommendations is that the angle at dead rise aft on the ship’s amidships not exceed 20 degrees.
A more significant drawback is that the forward-facing propellers have no protection whatsoever. A built-in safety measure included in the system allows a damaged pod unit to separate completely from the hull in the event of a substantial impact while keeping water from intruding.
The currently available product range includes 2 x 250 hp (IPS 350) to 2 x 515 hp (IPS 900), and more options are planned. Since it is possible to mount the IPS system in triple and quadruple configurations, this technology is now available on larger units. For example, the Lazzara LSX 92 features the IPS in a quadruple configuration.
This was from the Yachting International Magazine which is a fantastic luxury yachting magazine. If you liked this article you should perchase the magazine as there are a large number of excellent articles in this publication every month.
