On Aug 3, 9:43 pm, Evan Gatehouse
wrote:
....
On a cat a SIMPLE D/E system would almost seem to work rationally
(like Glacier Bay "do away with the batteries philosophy"), but I LIKE
the redundancy of twin engines instead of a more complex
genset/motor/controller system
....

One of the joys of yachting for me is that it is supremely and
unapologetically irrational . I certainly don't want to discourage
folks from finding beauty in systems and practices even when they are
hard to rationalize.

Like you, I like the redundancy of twins. I can attest that it has
been comforting to know that when one engine eats the bearings on its
salt water pump and spits them all over the engine room or drops its
propeller into the depths that my boat still has propulsion.

The Ossa (Glacier Bay) system looks interesting and could drive twin
props with multiple gensets so it might be pretty durable. I have
read their tech paper (http://www.ossapowerlite.com/tech_library/
fuel_efficiency/fuel_efficiency.htm). If you take them at their word
the system might well use less fuel in typical service than an old
mechanically governed over sized diesel system with a fixed prop that
was significantly undersized for its average service would... I can
imagine a scenario where it would be an easy system to rationalize (a
large yacht with big hotel needs and big fuel bills). On the other
hand, I was a little taken aback by the argument that claimed a long
commercial history of d/e propulsion because of its inherent
efficiency and also claimed that efficiencies of their system were the
result of very recent advances in technology and their proprietary
systems. I suppose you just have to take them at their word for the
second bit as their tech paper has no sources or verifiable numbers on
efficiencies. My understanding of the history of marine diesel
electric is different from theirs. I know that for the past hundred
years or so d/e systems have been used by navies and commercially for
a number of very good reasons. Those reasons include the ability to
run under water (submarines), to operate quietly (ASW) , to provide
quick changes in power over a wide range (tugs), to provide for
multiple, remote or vectorable thrusters (platforms), to provide for
big hotel needs (cruise ships) and so on. However, I don't think it
is historically correct to put fuel efficiency, per se, in that
list. This is certainly one of those cases where I would love to be
proven wrong. The siren call of a relatively cheap technological fix
for the woes of small boat propulsion and power generation is
strong. But, caveat emptor.

-- Tom.