Lazzara's drivetrain system with enclosed shafts

Not sure about the particular setup on that boat. However, many of the Lazzara models are known for having a lot of cavitation related vibration when getting up on plane from too little blade tip clearance, too small propellor tunnels, and/or the underwater exhaust getting into the prop.

I've run three different Lazzaras equipped with IPS drives; an LSX 75, an LSX 92 and the 76 Skylounge. No cavitation issues. No difficulty in planing. Good running boats!

They weren't referring to IPS drives. IPS drives wouldn't have the problem described.

If this is the system CaptJ is referencing, that 'fence' likely isn't enough to channel the exhaust straight back at slower speeds, such as coming on plane; the props could very easily draw exhaust into the stream. Once on plane, that lip should prove effective in channeling exhaust to aerate the aft running surface.

My mention of vibration etc. refers to all of the NON IPS lazarra's. I survey seatrialed one 68' that the vibration was so bad, both hull and engine surveyors ran out of the engine room and demanded all stop because they feared the engines were going to be ripped off of the engine beds. I have pictures of an after the build exhaust modification from the factory, that they have done on some boats.

In the link shown, those are enclosed shafts and then a skeg underneath it. Some fast SF builders have been using enclosed shafts for a while. You have more to service at haulout and accessing everything. MY guess though would be that in a very moderate grounding where a lot of boats would just ding props, on this Lazarra system you'd be bending shafts because the first thing to hit is the skeg with appears to be part of the shaft tube.

Lazzara pushed the envelope often times. Innovativeness often brings risks and issues with it. The problem was that the boat on which they were testing their ideas was one going to a customer. Somewhere between genius and mad scientist. I look at how shallow their drafts are on some larger boats, such as 4'6" on 85' and 4' on 76' and the natural consequence of that is cavitation if not compensated for in other ways.

My boat has an enclosed shaft system, although less hydrodynamic than the Lazzara. I read something about increased efficiency, but I don't entirely understand that. If you remember, the stern tube extends all the way to the struts. I believe this is more robust and does offer some limited protection to the shaft. I'm not aware of any other pros or cons.

I've tried enclosing shafts with a 1/2" wall split tube but didn't see any measurable difference with or without the tubes during sea trials. If exposed shafts get covered in growth it would probably be different. This was with 3" shafting and 5" OD tubes on a 47+ knot sportfish.