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www.marinelink.com MN31THERIGHTTECHNOLOGY : WITHCAUTION Z-Drives may be the right technol- ogy for a number of applications, butthere are issues to consider. The drives are dynamic and have a significant impact on the way the tug rides.Consequently, the hulls of the Titan class vessels are built for stability and want to ride at the surface of the water instead of cutting through the waves. Capt. Lickey described the Western Titan as ?rolly? and I have to agree. A small correction of the drives set the tug rocking ? port, starboard, and then port once more before settling into its new course. Small swells of three or four feet, the kind we had encountered as we entered the more open waters of Queen Charlotte Sound off Canada, really got the boat swaying.LESSONSLEARNEDAfter the Western Titan, Western Towboat began building its Titan class vessels with bilge keels, or rolling chocks, to counteract the ?rolling? effect of their wide, rounded hull shape. Bob Shrewsbury, co-owner of Western Towboat, along with his brother Ric Shrewsbury, said other issues they have encountered include the necessity to overhaul Z-Drives sooner than conventional drives. Because of the design of the Z-Drives themselves, operators may not get as many hours out of the gears and bear-ings. However, he said, the secret is to buy a bigger unit than you think you need. Because ocean towing vessels operate on a continuous duty cycle, operators will want a drive with enough horsepower to keep it from always having to operate at the topend of its torque. This is the lesson learned from the Western Titan, which had its drives replaced with higher capacity units early on.Still, according to Shrewsbury, maintenance and repair on Z-Drives is not much more complicated than conventional tugs. ?It?s all just gears and bearings,? he said. MN#9 (18-31):MN 2011 Layouts 9/6/2011 12:06 PM Page 31