Pod drives, twenty years later, are they as good as was promised?

Volvo Penta IPS drive, painted with Propspeed antifoul

What are pod drives

Pod drives are basically just another form of marine propulsion, they join outboards, shafts and outdrives, pods came very late to the recreational marine market, about two decades ago Volvo debuted the IPS (Inboard Propulsion System), previously pods were used in commercial shipping and cruise liners. Not long after Volvo debuted their IPS, Mercruiser joined the pod market with the Zeus drive, I believe it was a collaboration between ZF gearboxes and Mercruiser, or possibly Mercruiser taking the drive to the market, at least one part of the Zeus drive is made by ZF. ZF have their own pod drive, although its use seems to be reserved for much larger boats, usually in the 24 metre plus yachts.

Engine options when using pod drives vary, Volvo will only be coupled to Volvo engines, I have seen Zeus pod drives on Cummins and Caterpillar motors. As for the high end boats using ZF pods, owing to the huge horsepower required to propel them, they mostly seem to be coupled to Man and MTU powerplants. I have never seen or known of any pod drive being used with a gasoline/petrol motor, what is worth mentioning is hybrid drive setups, this is where one pod can have two power plants driving it, one conventional diesel and the other could be electric for example. I have not seen any yet but I understand they are being used or possibly at least tested in some commercial operations.

The major benefits of pod drives is because of their low drag & hydrodynamic efficiency, a smaller engine can be used to propel boats that were previously equipped with shaft drive, the potential benefits include longer range, increased interior space for the boat using the same footprint, it allows boatbuilders to experiment with different designs and layouts, pod drives are mostly quieter too in my experience, that does obviously vary a bit from boat to boat.

Too many who have never tried pod drives will tell you about how bad they are, unreliable, nobody can fix them etc. As usual, let me tell it how it really is. Pod drives have some unique features and some in common with other propulsion systems.

Forwards and backwards

IPS drives are unique in that their propellers face forward towards the bow of the boat, Zeus and ZF face the stern, on reading, forward facing propellers are meant to be hydrodynamically superior, I could not comment one way or the other, the Volvo drives for sure appear to be further towards the centre of the boat, on the whole, IPS equipped boats seem to be faster or have higher cruising speeds, but that could also be due to the boat design, both high performance sports yachts and more traditional designs both use pod drives.

Mercruiser and Volvo both make outdrives that face the bow of the boat, I have only seen these installations in single engine boats and are aimed at water skiing and wakeboarding, the idea being that they replace centre shafts, the usual power package for these types of boats.

Mercruiser Bravo 4, forward facing outdrive (not a pod drive)

Multiple engine installations

Pod drives are always installed in multiple engine configurations, First impressions: Wajer 38 & Boat review Sea Ray 470/475DA, both of these boats have twin pods installations, Volvo IPS for Wajer and Mercruiser Zeus for the Sea Ray, triple or even quad installations are possible. The Absolute 70 and Lazzara LSX 75 have quad Volvo IPS pods. Things have moved on from when the original quad engine boats were conceived, new drives can be coupled to considerably more powerful engines and even hybrid propulsion systems, so where once were four motors are now two.

Quad IPS drives on a 75 Lazzara LSX

Pod drives do not have to be close coupled, the drives can be mounted much further away from the motors using jackshafts, this allows designers to alter handling and balance characteristics and engine room layouts.

Twin propellers

All pod drives use counter rotating twin propellers, so one propeller moves clockwise and the other moves counter clockwise, outdrives have used this for decades. The twin propellers offer greater efficiency by wasting less energy, adding to improved hydrodynamics of the pod design equates to less fuel consumption, the twin propellers also generate more thrust, this is great for low speed maneuvering, actually this thrust has its own problems, see below.

Steering & trimming

Pod drives act independently of each other, steer at different angles, one drive to another and be in different gears, forward and astern on different drives. The pods themselves work as their own steering system, like outboards or outdrives, there is no separate rudder. Pods cannot trim, there is no mechanism to raise or lower them, trim tabs must be used, a major difference between Zeus and IPS is Zeus have the trim tab incorporated into the drive itself. The tabs when left unused for a while will actually fall on their own accord, the moment the joystick is touched they immediately return to the fully retracted position.

Joystick control

One of the main attractions to pod drives is the joystick control, it allows you to make low speed manoeuvres with all the grace of a ballet dancer. For me Volvo definitely has the edge here, they have a special low speed mode which limits engine power available so you can't overdo it and their joystick design is vastly more ergonomic than the original "tractor tyre" of the Zeus drive.

Volvo IPS joystick

In the case of the Zeus drive, the joystick is used for autopilot control also, this is a nice feature which finds its way into the Mercruiser Axius joystick control for sterndrives, the autopilot feature on the keypad is standard, you just need a Mercury antenna for GPS and heading data, it works very well, IPS requires a separate autopilot control.

The joysticks can also be interfaced with some bow thruster systems, this makes true lateral parallel docking possible, you can still do it without but it needs practice, in my experience all the pod drives have a tendency to lead the stern sideways first.

In the even of a joystick failure, which actually rarely happens, you can still use the motors without it, docking and low speed is much more akin to sterndrives with their vectored thrust because under normal helm control the pods move in unison and not independently of one another.

Too much thrust

I don't think I have ever seen this problem mentioned, if you are not careful, the low speed thrust that pods develop can be a nuisance, there is simply so much available, some typical examples of this;

• Shallow water, all those propellers spinning cause the seabed to stir up, you can clouds of sand and mud under and behind the boat, under most circumstances it's not usually too much of a problem, I have however seen filthy raw water filters full of sediment caused by shallow water operation, this is more of a problem at low speed, when cruising, the particles do not have enough time to reach the filters. The draft on pod drives in surprisingly deep, pods can be fitted in tunneled hulls reducing the draft.

• Mediterranean style berthing,  with their ropes in the water and all that thrust, more than one rope has been caught around the propellers.

• Other moored boats, you would not believe just how even large boats can be made to dance and bounce when being subjected to all that moving water, this is especially interesting when you are in an engine room trying to look at something and are suddenly tossed around like cork, ask me how I know. 

Collision damage & draft

This is the part that the naysayers will often go on about, "if one of those drives hits something, you´ll sink instantly", or similar., well pretty much hitting anything hard enough with any drive system, be they shafts, outdrives, jets or outboards is going to ruin your day. Volvo and Mercruiser approach damage to the pods themselves in different ways. Mercruiser Zeus, at least most I have seen get mounted more in tunnels in the hull, so they are not really exposed in the same way as IPS, Zeus has a plastic "shear skeg" on the lowest part of the drive, in the event of impact, this plastic part is design to break off, reducing the amount of damage or shock to the drive.

Volvo treats impact damage differently, the drive faces forward and is not mounted in tunnels, Volvo have quite exact measurements for hull thickness and reinforcement of the IPS drives, on the inside of the hull, the drive is mounted using a pair of rubber rings of sorts, stacked one above the other, sounds crude but acts like a shock absorber in case of impact.

Corrosion

I have never seen any pod drive suffering from corrosion, a lot of the boats that have them installed are on the larger side and so dry docking for extensive periods of time is less common, all year round in the water is quite normal. Its not surprising that the drives hold up well, the components in the water are made on bronze alloys, Mercruiser uses the well tested Mercathode anti corrosion system that they use on their outdrives, Volvo have a separate anti corrosion system that is not mounted directly to the drives, I do not know when it became available, I have seen larger, newer boats with it fitted on the transom, but not older ones. The drives themselves are protected by anodes, IPS have a hidden anode and Zeus use huge anodes on the trim tabs.

Reliability

I have heard and read a lot of stories of boatowners having huge problems with pod drives, I have to admit, that surprisingly I have not had these bad experiences or really know anybody who has, by and large in the yard, we have not had huge problems, it seems the issues are geographic, by that I mean that the people experiencing problems were in areas that had little dealer support nearby, not all yards and dealers are able to service and repair pod drives.

The earlier Volvo IPS drives have been incredibly reliable as far as I am concerned, mostly coupled to D6 motors in various power outputs, in both recreational and commercial service the drives had been very robust. I actually think Volvo have shot themselves in the foot with their latest pods, they have done away with pol level dipsticks and replaced them with oil level and quality sensors and these have been a pain, they are incredibly sensitive, the least amount of oil outside of the required amount sets off all manner of alarms with messages leading you to believe your drive is full of water and about the grenade.

I actually think the Zeus drive is more complicated, with its steering and trim system incorporated into the drive, it requires three different oils if I remember correctly, the early drives had a bulletin issued for replacing the nuts that hold the drive in place and also a few of the distribution manifolds that control steering and trim were getting blocked and causing a loss of hydraulic pressure, the system works at extreme high pressure, the hoses are specially made to operate at these pressures and cannot be substituted, there are no aftermarket or parallel parts as far as I know.

In both cases, you do need the intervention of a qualified service agent or dealer to perform maintenance, not all dealers will be approved. One thing I would like to mention, not related to the drives themselves, more the motors that are coupled to them, in the case of Zeus the most popular motor is Cummins, the QSB and QSC motors, they are belters, with a long history or good service and large service support, they are reliable and robust.

I am not always Volvo Penta's biggest fan but I have to admit the D6 motors are actually pretty good, smooth and very easy to live with, Volvo also write very good manuals, of their modern motors, the pod drive motors in my experience give less problems than the sterndrives, although conventional shaft is still the system with least service calls. I have not had enough time with the larger engines to make any real deductions, the new powerful D13 motors for the currently largest IPS professional package looks promising, the previous D12 shaft drive was and still is a very good engine.

Summary

Whatever your opinion on pod drives, they are here to stay, indeed since their introduction to the recreational boat market, they have penetrated so hard that many boats now only offer pods as the powertrain, there are a few that also offer outboards too, but, I think this is more to do with market demand in the US rather than much else.

Hybrid drives will eventually find their way into recreational boats. There is no doubt some of the features they offer are fabulous, my personal favourite is the GPS "anchoring", Skyhook from Mercruiser and Dynamic Positioning System (DPS) from Volvo, they hold the boat on station at the touch of a button., very useful when you want to retrieve or put out fenders and lines and have the boat stay where you want, or, waiting for the fuel dock when its windy.

I suppose, the question is would I want a boat with pod drives? What with my dislike of too many electronics and making things more complicated than necessary, well, the answer is yes and no. It comes down to the individual boats, some are so good, the Wajer 38 and Windy SR52 Blackbird are just two examples, both of which I would be overjoyed to have, however, could they be as good with other propulsion systems or even exist if it were not for pod drives?

I hope you have enjoyed reading this post. Please feel free to follow me on social media.