I can answer a couple of the questions posed about the Z-drive, since it is being installed in Anjumal. Since I have not taken delivery, I'll have to leave the cost of ownership questions for a few years, but I agree it is more complex than a simple propeller shaft and glands. Higher maintenance costs seem likely. >From: "C. Marin Faure" <cmfaure@earthlink.net> >1. What does it do to the draft of the boat? It sounds like it could be >more than the conventional >shaft and prop design. It added about 6" of draft (6' went to 6' 6"). Some was due to locating it low enough to be able to swing 360 degrees without hitting the bottomside when in the 180 direction. >2. What is the cost compared to the conventional engine(s)-aligned-to- >shaft(s) layout used in our boats today? About $100,000 extra on a 440HP propulsion plant. >3. What sort of maintenance and repair considerations are there? It is a very rugged unit, but still has much more complexity than a drive shaft. I expect it will be more costly to maintain. There is a separate hydraulic pump and hydraulic motor to control the rotation of the drive, the lube oil requires an 8' gravity head on it to provide positive pressure so lube oil leaks out, rather than sea water leaking in. It has an automatic torque disengagement so the shaft releases if the prop gets stuck (log stuck under the prop). I have it very well protected behind a massive keel and it is built to last for full time operation as in a tug or boom-boat, so my trawler usage will be comparatively light duty. See pictures at http://www.anjumal.com/constphotogallery/03-08/6515%20021101%20Stbd%20quarter.jpg - from stern w/o rudder http://www.anjumal.com/constphotogallery/03-05/Z%20and%20Sherry%20m.JPG - close-up with Sherry in picture http://www.anjumal.com/constphotogallery/03-05/Z%20&%20Underside%20-m.JPG - close-up from stern In the picture at http://www.anjumal.com/constphotogallery/03-08/ER%20drive%20train%20m.JPG, the blue parts are the engine room side of the Z-drive. At the top is the hydraulic fluid tank. Under it, the small blue cylinder is the gear head. Moving toward the foreground is the universal joints and the green torque clutch, before getting to the transmission and engine. (the blue hydraulic pump in the very foreground is a different pump for the stabilizers, windlass, and bow thruster.) >4. What is the cruising efficiency of this type of system? My Z-drive is also coupled with a speed nozzle around the prop. The result is a break even or slight gain over a conventional drive. Of course the nozzle could be added to a fixed prop for all gain. Without the nozzle it was estimated at about a 10% loss if I remember correctly. I have coupled the Z-drive with a full rudder. At speed the rudder is used to steer. At idle the Z-drive is used to maneuver, along with the bow thruster. If people are interested in results once I have been using this, let me know and I'll send a progress report later on. A picture of the Z-drive is on my web site at http://www.anjumal.com/mv.htm see the bottom of the page. -Wray MV Anjumal Portsmouth, NH