Separate pod incidents in 2019 have led to a host of industry-wide problems with azipods on cruise ships. The technical issue on the Carnival Vista is associated with the bearings on one of the ship’s two azipods. During the present repair all four bearings on the two azipods will be replaced.
I have the idea that the complex and therefore vulnerable azipod technology in combination with the huge forces with which they have to deal are in the long run not really up to the task for which they are intended. A simple shaft and propellor with one only moving part for the propulsion is so much more reliable and almost indestructible.
I have no idea about the reliability of one or the other. The Mermaid system where the functions of a propulsion motor, main propeller, rudder and stern thruster are combined in a single unit is a more traditional design. Hard to compare although the Mermaid propulsion looks simpler but that can be deceptive.
Your statement is true but given propulsion pods have been around since introduced in the 1980’s I doubt if things will revert to shafted propellers. The propulsion pods have just too many advantages. They eliminate the need for separate steering gear, and stern thrusters. They require less space. They tend to generate less onboard noise. Being electric, they integrate easily with diesel electric plants. Reliability has improved since they were first introduced and will likely continue to do so. The pluses far out weigh the teething pains of development.
One of the problems is that cruise ships continue to get larger putting more, and more strain on said equipment.
I have the idea that the complex and therefore vulnerable azipod technology in combination with the huge forces with which they have to deal are in the long run not really up to the task for which they are intended.
That is what I meant to say, having to replace ball bearings is a sign of excessive wear and tear.
I attended in the late sixties the sea trials of the side-stone dumpers Cetus and Taurus with the installed Voith Schneider propellers that build the new lengthened piers into the sea at Hook of Holland. With these propellers the ship could move sideways as the stones were hydraulically, from the middle of the ship, shoved out over the side. Impressive demonstration of the capabilities of such systems.
I know, and it’s not the first ship with ABB’s units to require repairs. However, I was referring to @Dutchie’s earlier remark about “industry-wide problems” as there are two major suppliers of podded propulsion units and, of those, ABB has been more reliable while Mermaid has all but disappeared from the market.
To my knowledge, ABB’s new XO lineup should solve some of the issues encountered in the previous generation.
Actually Mermaid is the only comparable product to ABB’s Azipod product line; they are both so-called podded propulsion units with the propulsion motor within the rotating gondola. Siemens has a similar product (SISHIP eSiPOD) but to my knowledge they have not managed to sell it yet. The rest are Z-drive units with bevel gears.
Captains of harbor tugboats are lyrical about the VSP because of the maneuvering flexibility. A disadvantage is that they can only handle relatively small powers of up to 1 MW.
For forward motion in open seas, a standard screw and rudder are simpler mechanically. Other than the rotation if the shaft nothing else is moving, whereas with the VSP the mechanism is constantly varying the angle of attack of the blades in order to provide an average thrust. It is imaginable that more frequent maintenance due to wear is required.
It is essential that cruise ships must have excellent maneuvering characteristics especially at low speed, because they are supposed to call quite often at small ports in remote places where there are no facilities such as deep berthing quays, powerful tugs, etc. Because of that, they are mostly fitted with azimuthing propellers that make it possible to maneuver the ship effectively in a very confined area.
A disadvantage is that the steering of an AZIPOD propelled ship is not intuitive and different from handling of ships with conventional propulsion units because there are several limitations and in general AZIPODs must be handlied with great care and gently. Ship masters and senior officers as well as sea pilots must be specially trained. If not handled properly damage will be the result. For instance high power at low speed usually leads to harmful heavy vibrations that may reduce life time of mechanical components. Maintenance wise the critical issues of these systems are seals and bearings, the result might be leakage, insufficient lubrication etc.
Carnival Vista destroys Messina, Italy marina - “AZIPODs must be handlied with great care and gently”.
Probably the result of a lack of training or they didn’t pay attention?
Just to make it clear, these are ABB Azipod propulsion units (in this case, 6.5-megawatt VI1600 units fitted on an icebreaker):
Azipod has exactly two moving major parts: the propeller (always electrically-driven, always fixed pitch) and the gondola which rotates about the vertical axis.
The only non-intuitive thing with Azipods is that if you operate with full manual control with the joysticks, they work like outboard motors rather than rudders - you turn the lever to port and the vessel turns starboard.
My mistake, that was only valid for the VSP systems of course.
I understand that already for some time podded propulsion systems have been installed on ice-classed vessels that were employing the double acting principal whereby a ship navigates stern first in ice and conventionally in open seas. That makes this concept the preferred propulsion systems for icebreakers.
Manoeuvring with azipods is exactly what you say. My first experience I was told to use only one for a while and imagine I was sitting in the stern of a small boat manoeuvring with a tiller controlled outboard motor. Then as I got used to it manoeuvring with both.