All About Pod Drives: Volvo-Penta IPS, MerCruiser Cummins Zeus, and ZF Marine

Wondering what a pod drive is? Here is an explanation, and an overview of the advantages and disadvantages of their uses in recreational boats.

30th March 2012.
By Lenny Rudow

Pod drives, including the Volvo-Penta IPS, MerCruiser Cummins Zeus, and ZF Marine 4000 have taken the recreational boat market by storm during the past few years. And with good reason—these propulsion systems offer several major-league advantages over traditional inboard power systems, so once a few savvy boaters got their hands on ‘em, word travelled fast.

Since pod drives eliminate shaft angle and are more hydrodynamic than shafts, struts, and rudders, the efficiency gains are significant.

So what are pod drives, exactly? They’re a relatively new power system that eliminates the need for shafts, struts, and rudders. Instead of using traditional running gear to transfer the engine’s power into thrust, a “pod,” consisting of the transmission, outdrive, and propeller(s), is mounted right through the bottom of the boat.

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 some manufacturers are using single pods.

So now that we know what a pod is, what’s so good about them, and would a pod-driven boat be right for you? Let’s find out.

Volvo Penta introduced pod drives to the recreational marine market, with their IPS system.

The advantages of pod drives are numerous. For starters, they offer an efficiency gain of between 15 to 30 percent when compared to straight inboards. Since they protrude beneath the waterline and face directly forward (in the case of Volvo-Penta IPS) or directly aft (in the case of MerCruiser Cummins Zeus and ZF Marine) there’s no efficiency-sapping shaft angle, as there is with inboards. That means thrust is directed in a straight line. On top of that, pods are more hydrodynamic than traditional running gear. Net result? It takes fewer horses—and less fuel—to propel a boat to the same speeds than it does with straight inboard power systems. Added bonus: fuel capacity can be trimmed accordingly, which saves on a boat’s wet displacement, further boosting efficiency gains.

The Zeus pod drive from MerCruiser Cummins was the second pod system to hit the market, but the first with the props facing aft.

 

Another advantage of pod drives is an increase in the boat’s useable space. The engines can be mounted farther aft in the boat (again, no long shafts are necessary) and this usually opens up gobs of space inside the hull for an extra mid-cabin berth, a large stowage area, or in some cases an entire stateroom. There’s also space saved aft of the engines, so the area under the cockpit is wide-open and available for use as stowage, fishboxes or chill boxes, fender lockers, and the like.

Handling and maneuverability is yet another major-league advantage with all of these pod systems. Since the drives articulate independently, thrust can be directed wherever you need it. This makes it possible to literally spin in the boat’s own length, turn 90-degrees on a dime, and carve tighter turns at speed. The pods are controlled by a joystick, so maneuvering is as simple as pushing or turning the stick in whichever direction you want the boat to go—there’s no more opposing the engines and jockeying the throttles to back into a slip or make a tight turn in the marina basin.

Anglers too will discover that fishing with pod drives is advantageous. And everyone will appreciate advanced functions like the Zeus Skyhook and Volvo-Penta Dynamic Positioning. With both of these systems, the boat uses a combination of GPS, electronic controls, and the pods to maintain an exact position in spite of wind, waves, and current. All you have to do is press a button, and the boat does the rest.

ZF Marine is the latest entry into the pod drive market.

 

Disadvantages of Pod Drives
But we all know that everything about boats is a trade-off. So what about disadvantages?

In truth, the pod’s list of negatives is startlingly short. First off, there’s cost. A boat’s hull and weight distribution have to be designed specifically for pod drives, so there’s a substantial cost to the boat-builder. As a rule of thumb, these systems add 10 to 15 percent to the cost of an average boat (though this should come down with time, as more and more pod boats are on the market long enough to recover design costs).

Oddly, the other major disadvantage to pods is purely psychological: it just feels weird to have those pods protruding right out from under your boat, especially for IPS with its forward-facing propellers. You’re no more (or less) likely to strike something than you are with straight inboards, but people have a hard time getting that fact through their heads.

It’s true, however, that if you do smack a log or run hard aground, the repair costs can be higher than they would be for straight inboards.

Are pod drives right for you? That’s a question that you can only answer for yourself, but a direct comparison between a traditionally powered boat and a pod boat of the same exact model has certainly led us to believe this could be the case.

Lenny Rudow

Editor’s Note: Want to learn about some specific boats rigged with pods, and how pod power helps make them better boats? Read our reviews:

 


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About the author:

Lenny Rudow

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Lenny Rudow is Senior Editor for Dominion Marine Media, including boats.com and YachtWorld. With over two decades of experience in marine journalism, he has contributed to publications including Boating Magazine, Marlin Magazine, Boating World, Saltwater Sportsman, Texas Fish & Game, and many others. Lenny is a graduate of the Westlawn School of Yacht Design, and he has won numerous BWI and OWAA writing awards.
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