Z Drive

[Slowtack]

I am looking at options for replacement of my VP2003 and 120SB saildrive. I have seen some limited online information on a system using a "back to front" Beta engine and a "Z" drive transmission. This would seem to result in a design that might offer a more or less similar prop depth and location to my existing system with a comparatively straightforward shaft & tube installation that would not require modification of fuel tank etc. Any info from actual installations/owners very welcome.

 

[scottie]

V drive
Yes it can be done but has its complications
High engine stern gland under engine? P bracket prop clearance different set up affects resale prices cost of V drive etc
Better to stick to saildrive

 

[prv]

Why do you want to avoid a saildrive?

Pete

 

[Tranona]

Replacing a saildrive with any other form of transmission is a major job as you need to remove the saildrive bed and build new engine beds, stern tube and P bracket. A V drive may enable you to get the prop in the same place, but you will end up with the engine very high and all the service points at the rear.

There are alternatives, the most obvious is a complete replacement using a current Volvo D1 30, which is relatively straightforward. You may well find you can get a very good deal from a Volvo dealer for this change. Assuming it is the engine that needs replacing then other engines such as Beta can be mated to your existing drive. However whether it is a good idea to link a new engine to a 30 year old drive is questionable. Although drives are in general very reliable and long lived, if they do fail they are virtually impossible to repair both technically and economically. The 120 drive is no longer available as a replacement so you would need to change to a 130 and this is a £5k job.

Bit of a rock and a hard spot, but long term the new complete unit is the way to go.

 

[Slowtack]

I am not looking to avoid saildrive per se but looking at available alternatives as regards initial and lifecycle expense and reliability.
The main disadvantages of saildrive are higher initial cost, higher lifecycle cost, frequent critical component replacement tasks, inaccessibility of key components while afloat and system complexity.
Based on reported problems with more recent Volvo products I am not sure that VP is the way to go.
Beta engine with the old Volvo saildrive is postponing the inevitabe I think and the lifecycle issues remain.
Engine plus gearbox for a simple shaft system is less expensive both in terms of initial cost and lifecycle costs.
The Z drive is new to me but seems of interest in that the enabling modifications at first sight appeared simpler than the saildrive to standard shaft conversion.
The saildrive to standard shaft conversion will require an aquadrive or similar unit to limit the final shaft slope whereas the Z drive could avoid that element.
I am not concerned about engine service points as I have pretty good engine access front and rear.

 

[PCUK]

As already said, it is a vee drive. Z drive is totally different being an outdrive.

 

[Tranona]

Bit unclear about what you mean by Z drive. That term is normally used to describe outdrives through the transom of a power boat and I have difficulty in envisaging how you would use that configuration in a yacht.

So, I assume that you are talking about a V drive gearbox which sits forward of the engine and the shaft runs under the engine through a conventional stern tube and a p bracket. If that is the case a complete installation is highly unlikely to be any cheaper than a new saildrive package and would require, as I suggested major modifications to the boat. V drives have a very chequered history and most people who have them fitted desperately try to find a way of eliminating them and fitting a conventional straight drive. Can't think of the last production yacht that used such an arrangement as the introduction of saildrives effectively removed what little packaging advantage they had. Designs that did use them such as Nic 35s did so because they had deep wide bilges to cope with the extra depth and the hull design required the prop to be forward but without the (then) bulky engine intruding too far into the saloon. Never very satisfactory and changed in later boats.

If you don't like VP then you can have a Beta (or a Nanni or Vetus) with the drive they fit, or a Yanmar. Not sure about what the supposed problems are with "more recent" Volvo products as their current range of small engines is vastly superior to the one you currently have. The drives are also better, particularly in the anode mounting area. Saildrives now dominate the new boat market because of their packaging advantages, greater refinement and lower overall installation costs. Not convinced that on average (having had both systems) a saildrive is any worse long term other than if it does fail economic repairs are not usually possible. However, given the tens of thousands in use over the last 35 years or so, it seems failures are rare.

 

[Slowtack]

V drive is what I meant
Many thanks Tranona for your insights