David,

Thanks for your introduction to marine engines.
From my experience with VW SDI and TDI engines
I like to give you some more details to answer
your statements.

>Incidentally it would appear from one of the
>illustrations on the website that the RPM of
>these motors will be below 4000, which is in
>accord with marine usage.

The max RPM is limited to 4500, which is anyway
the maximum RPM on vehicle Diesel engines.
Compare

http://www.vw-marine.com/deutsch/motoren_tdi115-4.html
with
http://www1.vw-online.de/technik/4_pumped/rechts2.htm

or

http://www.vw-marine.com/deutsch/motoren_tdi150-5.html
with
http://www.vw-nutzfahrzeuge.de/deu/technik/111kw.html

Are there any difference in power/torque diagrams?
(150 hp app.. 111 kW; 115 hp app.. 85 kW)

>Anyway, what I'm trying to get at is that these
>engines will be considerably more expensive,

VW will sell nothing for cheap, you should know,
but VW Marine isn't on the market yet. No one knows
the prices for the engine and where to buy. You
will get to now it beginning next year.

>heavier,

Really, not much. There is the enhanced oil pan,
some covers and the water-cooled turbo and exhaust
manifold. What does it take, 10 pounds, 20 pounds?

>and less powerful than the equivalent automotive
>engine.

This is really not true, compare the links. I got
some more detailed descriptions in German language.
As time will come I will send the details.

Regards
Helmut
'80 Vanagaudi