In my opinion the Z drive is a poor propulsion system for a long range pleasure craft. The efficiency is not all it is cracked up to be. I ought to know, as I drove a single screw Z drive 300 hp John Deere (turbo)equipped boat for 8000 miles. It is hard to know for sure what the economy OUGHT to be but it seemed to me that there was about a 15%, maybe 20% penalty using the Z drive versus a direct shaft to the engine. In a commercial environment where that kind of penalty may not be a big issue I can really see the advantage. But, for a small boat intended to go long distances the loss of range is something to be carefully considered. The Z drive leaked hydraulic fluid as I had to put in about 50 gals over the course of the 8000 miles. Strangely enough when the boat was in cold water it leaked very little hydraulic. Serious leakage started in the Caribbean and stopped again when the boat was just north of Cabo San Lucas, Baja Calif. The leakage was estimated at 1 gallon for every 100 miles run or about 2 gals a day, in warm water and about 1/10 of that in cold water. In order to find the leak I put paper towels and bilge pads in likely and unlikely places under and around fittings and could never find a trace of a leak. Yet hydraulic fluid continued to accumulate in the sump, near the Z drive. I had to assume the leak was down in the sump itself, but I could never prove that. The boat is now back in cold water of the PNW and I assume that the 1/10 of a gallon leak is hardly noticeable now. Other design issues that I was suspicious of: The surge tank used to hold excess hydraulic fluid, did not seem to be baffled, like it had been intended for a fixed installation on shore. The surging in the tank appeared to create some frothing of the fluid, most noticeable when the boat was rolling hard in a rough sea. Some of the documentation indicated that the fluid should not be excessively cooled in the heat exchanger or it would lower overall efficiency. Typical temperatures were about 110f in warm water, where the book indicated much higher ideal temperatures of about 150f. If the heat exchanger system had been set up to hold a higher temperature then the leaking would have most likely been discovered much earlier, when the boat was still in cold water. Since most boats are located in water too cold for this kind of leaking, it may be safe to assume that any hydraulic system which is running at elevated temperatures will show signs of leaking (if it will leak at all) that are not occurring at lower temperatures. This is something to be wary of. By the way, this was a Thrustmaster Unit. I don't think their unit was to blame for the problems. More likely installation mistakes. What this would seem to mean is that if a Z drive is to be competitive the installation has to be first class and all fittings have to be accessible and maintenance has to be routine. Surge tanks, baffled to prevent foaming. Temperature controlled heat exchangers. All fittings accessible. Wrenches to fit the biggest fittings. Not pipe wrenches, the fittings can worth several hundred dollars apiece. Filters mounted where they can be replaced without spilling the contents all over the engine room. Chafe guards where adjacent lines touch. A filtering system to guarantee clean fluid when refilling the surge tank. The 50 gals of leaked fluid had to be pumped out of the sump and poured back into the original 5 gal buckets, an awful mess. Capt. Mike Maurice Wilsonville, Oregon (Portland)