See full version: A closer look at Azipod propulsion
Side thrust: With Azipod propulsion, the full propeller thrust can be directed freely in any direction, whereas in fixed shaft-line rudder arrangements thrust decreases rapidly as helm angle increases. The paper states that, generally, a conventional rudder can produce only about 40 per side thrust compared to maximum ahead bollard pull thrust. The figure for flap rudders is up to 60 per cent. more
The aforementioned aspects are one reason why Azipod propulsion features are so commonly used as a solution on large cruise ships since Comfort Class requirements are easier to fulfill than would be the case with conventional shaft-line rudder propulsion arrangements. [links]
The more effective and safer turning capability of Azipod propulsion has been verified in the study by full-scale and full-speed turning circle tests between sister-ships MS Fantasy, with conventional propulsion, and MS Elation, with Azipod propulsion, which recorded 38 per cent reduction in tactical diameter. here
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Today, Volvo Penta has the widest range of pod drives powered by diesel engines, ranging up to 1,000 HP. Caterpillar is a relative newcomer to producing pods (though they previously could be mated with some Zeus offerings), but they have a similar range. Cummins Zeus has a somewhat more limited model line, and to make sure there’s no confusion, is no longer joined at the hip with Mercury Marine. Their agreement to supply integrated power systems known as Cummins MerCruiser Diesel Marine was dissolved several years ago. ZF Marine, meanwhile, has ceased producing its POD 4000, but you may still run across them in used power boat listings.
The pod itself articulates to direct propeller thrust, so no rudders are needed. And the part of the pod below the waterline is designed to shear free of the engine without leaving a hole in the boat, in the case of a catastrophic grounding. Most pod drives come in pairs, but there are a few single pod rigs, too (see Testing the Single Pod 34, to gain some insight into how a single pod works in a SeaVee 340i).
Wondering what a pod drive is? Here’s an explanation, and an overview of the advantages and disadvantages of their use in recreational boats.
So now that we know what a pod is and which there are to choose from, what’s so good about them? And, would a pod-driven boat be right for you? Let’s find out.
Conventional tugboats have been designed with large-diameter, fixed-directional propellers for providing the desired levels of thrust. This approach has resulted in relatively deep drafts for harbor tugboats, often preventing their use in shallow inland waters. The fixed direction of thrust limited the tugboat to handling vessels only by pushing or pulling them parallel to the centerline of the tugboat's hull. Accordingly, not only could the tugboats not apply thrust in any direction, other than fore or aft, but they also lacked the necessary transverse stability to resist heeling, with a significant danger of capsizing if subjected to any transverse force. In ship handling and docking of large vessels, tugboats are typically tied alongside either parallel to or at fight angles to the vessel's centerline (this is the normal method in most U.S. ports), a rapid change in the application of tugboat thrust normal to the vessel's centerline cannot be achieved without completely reorienting the tugboat. This also imparts excessively high torque to the rudder. Such an operation also requires handling of lines by the boat's crew, and involves considerable time. In some instances, such an operation may become impossible because of insufficient space between the ship and the dock, or because of other vessels or restrictions in the vicinity. Extreme care must be exercised to ensure that the tugboat is not subjected to transverse loads by its own actions or by loads imposed by the vessel being assisted, through the towing hawser which could tip and capsize the tugboat. here
Moreover, tugboats have had increasing power levels of parallel propulsion machinery installed, partly to meet demands for high thrust levels in handling ships and barges, and partly to hold the tug in the proper position using opposing thrust and rudder action. While these problems have been undesirable, they have not been solved by resorting to a brute-force approach.
By one estimate, podded propulsors are 14% more efficient compared to conventional propulsion: 6-8 % from a more efficient hull, 4-6 % due to reduced appendages, and 1-2% by tilting the propeller into the flow. Additionally, the azimuthing pods can turn 35o at full speed, and a full 180o at slow speed or stop. This contributes to unsurpassed maneuverability in littoral waters. Podded propulsion systems can offer advantages in outfitting and fuel costs compared with conventional systems,
For high craft speeds surface-piercing propellers fitted either to a specialised surface drive system, or to a Z-drive, give the highest efficiencies. However, conventional surface-piercing propellers are extremely power-absorbing at low speeds. One reason for this is that because these propellers are designed to be run semi-immersed their diameter is large compared to a conventional propeller. Thus until the craft has achieved planing speed the propeller is normally excessively immersed such that the flow and torque requirement are excessively high. A second factor, which is less well understood, is that at low speeds and high power the blades are running at a high lift coefficient, the vapor cavity behind the blade is wide and the distance between the external surface of one blade cavity and the propulsive surface of the succeeding blade is small. Thus the blade is effectively pushing against a vapour bubble with an evident loss of thrust. These two factors in particular cause craft fitted with surface drives to have considerable difficulty getting onto the plane which means they have to be fitted with excessively powerful engines. As a result of the limitations imposed by these drives their usage remains restricted and their cost is high. Also, such propellers are normally mounted well behind the hull which renders them vulnerable to damage when manoevreing or at berth. In most cases, the propeller cannot be raised sufficiently to enable the craft to be beached. here
Such a steering and manoeuvering system for water-born vessels with two individually turnable propulsion units arranged at the stern portion of the vessel and mutually spaced athwartships. These units may be such as jet units, turnable so-called thrusters or turnable propeller units of the "AQUAMATIC", "Z-DRIVE" type or the like, (but not propeller units with a stationary propeller shaft and a separate rudder). more
Further variants may be developed for maritime surveillance, resource detection, passenger and cargo transport.more
Dornier Seawings flew its new-generation Seastar amphibian for the first time on 28 March from its base in Oberpfaffenhofen, Germany. [. ] Dornier says the aircraft will be offered in various configurations including cargo, passenger, special missions and VIP transport.
Trans Maldivian Airways currently offers transfer services to more than 80 Maldives resorts, flying over 1 million passengers per year to their holiday hideaways.[links]
This is their main terminal at Velena International Airport: [links]
In North Carolina, many of the old-school sportfishing boatbuilders that initially shied away from pods due to the perceived negative impact on fishing, have started incorporating pods into their designs. Their customers want the ease of use and performance of the pods and are willing to overlook some of the downsides of pod systems. [links]
When owners create a wish list for their yacht, a good number of those requirements are determined by the vessel’s propulsion system. Speed, efficiency, fuel economy, maneuverability and greener technology directly influence design decisions.
Spencer Yachts is another example of the change within the industry. Its 70-foot Penta Gone showed just how valuable the new drive systems are and how the pods can be incorporated into boat designs. Pod drive systems are now standard on many other top-of-the-line sportfishing models from builders including Freedom Boat Works, Jarrett Bay Boatworks and Viking Yachts.
Thrust from pods is horizontal, meaning that 100 percent of the thrust goes to driving the boat forward. This creates significant operational efficiency over traditional systems that tend to waste thrust vertically due to the angle of the inclined shaft. Some pod manufacturers report a 15 to 20 percent increase in efficiency.
A few owners understand the potential drawbacks of pod technology, including initial higher purchase costs and maintenance costs. Pods are complicated systems and there are currently fewer resources—both in terms of personnel and boatyards—that specialize in pod maintenance. more
The long list of benefits is changing the game with luxury motoryachts in all sizes. Pod drive propulsion systems already power big boats, as they have large commercial vessels, including cruise ships, ferries and tugboats for some time. Commercial vessels benefit from the control, precision of movement and fuel efficiency that pod systems provide. more