One side effect – hailed in some circles and reviled in others – is that these same systems can be used to control those engines and transmissions without mechanical cables and pulleys. This technology, first developed in the aviation world, is called fly-by-wire, meaning that electrical signals transmit the helmsman's wishes to the machinery. Thus, clean new helm designs with only a single control lever per engine – rather than the standard black shift and red throttle for each – are becoming more common. These electronic controls are available on everything from outboards to big diesels. Older hands make require some time to adjust to the simplicity, but most experts say it's a better system.

CUMMINS MERCRUISER DIESELZeus pod with aft-facing, contra-rotating propellers, integrated trim tab above and protective skeg below.

POD-DRIVES

Some of the products appearing on the market in recent years are downright futuristic. By now you've probably heard of Volvo Penta's IPS system, and Cummins Mercruiser Diesel's Zeus system. While there are some significant differences, they both have one radical element in common: two or more steerable drive pods under the boat, connected to gas or diesel engines right above them in the engine compartment.

A computer uses sophisticated software, tuned for each boat model, to interpret the movements of a joystick at the helm and determine in which direction the pods turn and how much thrust is applied. The pods are not physically linked together. The reason they can maneuver the boat so effectively is that they can be turned in different directions, such as one in forward and the other in reverse. While still relatively new, many people who have driven pod-equipped boats say that they completely eliminate the need for a bow thruster. They many also reduce the learning curve for new boaters when it comes to docking.

When sophisticated new precision autopilots are connected to this computerized system, the boats become capable of precise station-keeping, holding an exact heading and position while standing still, as you might while waiting for a bridge to open. They can compensate well for wind and current combinations by using high-precision GPS receivers.

Pod drives have other attributes. They eliminate the long shaft and strut assemblies hanging down underneath the boat, which create drag. The companies therefore claim that the propellers bite into "clean" water that is not disturbed by turbulence, and are therefore more efficient. Volvo Penta claims efficiency gains of up to 30 percent over a shafted inboard installation on the same model boat.

Both pod drives are installed so that the pods will break off cleanly in the case of a major underwater collision or very hard grounding, and are designed so that a break-off does not hole the boat. Volvo Penta says there have been several accidents with IPS boats – hard groundings – and that the drives sheared off as designed, leaving the boats floating and intact. There are an estimated 2,000 IPS-equipped boats already in the water, which itself is a testimonial to the design.

Another advantage of pod drive designs is that they save space inside the boat. The engines are installed in a compact package right above the drives, typically right near the stern of the boat. This gives interior designers more room to work with. Grand Banks says that the Zeus installation saves so much room they were able to add a second stateroom to the design.

THE FUTURE

Pod-drive technology is developing rapidly, with new models appearing in both higher and lower horsepower configurations. Volvo Penta, which was first on the scene with its diesel-powered IPS, has just rolled out new versions compatible with its larger gas engines and with some much higher powered diesels for bigger yachts.

Mercury Marine has taken the pod-drive concept and applied it to sterndrives – a natural evolution – by removing the tie-rod that connects the two sterndrive legs and using a Zeus-like computer to move the two independently. Early demonstrations of this configuration, called Axius, show that it can provide maneuverability similar to the original systems. Mercury plans to have it in production in 2008, and Volvo Penta is expected to bring something similar to market for its sterndrives.

Another innovation to look for is a configuration in which pods and engines are separated. Already in use aboard large cruise ships, this configuration uses large electric motors inside the waterproof pods to drive the propellers directly, powered by large diesels inside the hull that serve as generators, providing electricity to the pods via heavy cables. One major advantage to this arrangement is that you can now separate the engine and pod unit, giving the interior designer even more flexibility. Most marine architects must design around the weight of the diesel engine, but this configuration would allow the designer to put that heavy diesel virtually anywhere.

Systems like this are expected to break into the production market, though it may take several more years – another thing to look for as engine technology marches forward.