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Will marine diesels go serpentine?

Jan 22, 2013

Considering the much larger installed base of automobiles compared to voyaging boats, it is not surprising that engine developments often occur first with cars and then make their way to the marine engine world. One piece of automobile technology that for the most part has not fully transitioned to the marine diesel is the approach for taking power off the engine and running alternators and other auxiliary devices. Marine diesels still largely use V-belts, while the automotive world moved to serpentine belts some years ago.

The difference between the two devices is easy to see when you hold a V-belt up next to a serpentine belt. The V-belt has a distinctive V-shape — wider at the top or outer edge, narrowing toward the bottom of the belt where it fits into the groove in the engine take off pulley and the drive pulley of the device being powered by the belt.

A serpentine belt, on the other hand, takes a different approach. It is a flat belt, without the defined vertical profile of the V-belt. Rather than using the edges of the belt to create friction like a V-belt, a serpentine belt is essentially flat, usually with raised cords of material that add strength and surface area. Whereas a typical V-belt has about a half inch of surface area to connect with a drive pulley, a serpentine belt has up to three inches of contact area. The result of these differences is that the V-belt concentrates its force in a small area, while the serpentine belt spreads out the pressure over a larger area. This means there is less force trying to pull the pulley out of alignment and less wear on the pulley bearings.

John Stevens of Electromaax, based in Niagara Falls, N.Y., and Ontario, Canada, which designs and manufactures high-output alternators and marine charging solutions, said that belt technology has developed quite a bit over the last decade. “The automobile industry got rid of V-belts years ago,” Stevens said. He points out that a serpentine belt can carry a greater load than a V-belt and with less wear and tear on the pulleys. Some voyagers are adding multiple high-alternators to provide more charging power and a serpentine belt can power multiple alternator setups more efficiently than a V-belt. Serpentine belts also eliminate “belt dust,” can prolong engine life, and produce less noise.

V-belts still work, of course. As Bob Hansen, CEO of Hansen Marine Engineering, an engine and generator dealer in Marblehead, Mass., said, V-belts have been around a long time. “The V-belt is old school, but they have some advantages,” Hansen said. “The V-belt is easier to align and less expensive to manufacture. With serpentine belts, alignment is critical.” If misaligned, a serpentine belt won’t wear properly. “If a serpentine belt is aligned right,” Hansen said, “it will pull more power than a V-belt.”

According to Mike Alfano, director of operations for diesel dealer and engine service provider Mack Boring, Inc., another reason that many marine diesels still use V-belts is because many small marine diesels that haven’t been upgraded with high-output alternators are only driving two fairly low-demand accessories. “In the marine world you are only driving an alternator and a water pump,” said Alfano. Automobiles, on the other hand, need to drive an alternator, a water pump, an air conditioning compressor and a power steering boost pump.

To Hansen, one of the biggest reasons for sticking with V-belts is the issue of replacing a broken belt. As Hansen points out, breaking a V-belt isn’t such a big deal in many places in the world because so many engine shops will have spares on hand. Breaking a serpentine belt, however, is a thornier issue as there is less likelihood of finding a suitable replacement or a mechanic who can install one properly.

As Alfano points out, voyagers tend to be prepared for gear breakdowns. “Most cruisers are sensible enough to carry spares,” Alfano said. “That’s the secret, to be prepared.” Alfano also noted that the simplicity of the V-belt lends it to an emergency jury-rigged replacement. “In the old days of cars, you could use pantyhose for a replacement belt. It’s also possible to use rope or a piece of canvas.”

So, as marine engines are fitted with power-hungry alternators and other accessories, will the simple, reliable V-belt ever be ushered out of service and be replaced by the serpentine-type belt? If it does, you can be sure self-reliant voyagers will find some way to jury rig a serpentine belt in an emergency.

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