GL: Diesel/Electrc Propulsion (was RE: AN interesting concept for a trawler)

[Phil Little]

Diesel electric is unsuitable for boats our size.
   
  Substituting an 70% efficient electric generator/motor set for a 99% efficient direct shaft connection to the propeller would only reduce performance and increase fuel consumption, for no perceptable improvements.
   
  These systems are best used for distributed power train systems where the prime mover cannot be directly connected to the load, such as a diesel locomotive or a ship with newer drive technology, such as azipods and thrusters.
   
  In the case of large ships, the best way to utilize azipods is via electric motor in the pod. Large ships can add enough extra power to cover higher parasitic losses in the electrical generation equipment.
   
  In large ships, such as the QEII, multiple smaller diesels each running a generator, can be located in more space-efficient arrangements, rather than the huge steam turbine powerplants located in a large central engine room.
   
  The electrically-coupled drives also allow infinitely variable speed and power control, making them very useful in complex shiphandling situations.
   
  For pleasureboat applications, however, our engines are easily connected to the props, speed is controlled with engine throttle, thrust is controlled with rudders, and short duty cycle devices like bow thrusters need only batteries, which discharge at a high rate but can be recharged over long periods between uses.
   
  Even our new IPS drive sytems (Mercruiser, Volvo) are mechanical gear transmissions for reasons of efficiency and cost.
   
  Also, in a boat, no energy can be recovered by dynamic braking because a boat doesn't need brakes!
   
  I do not think we would want this extra complexity in our engine rooms!
   
  Phil Little
   
  
D C *Mac* Macdonald <k2gkk at hotmail.com> wrote:
  In 2005, my wife and I were on the 40th cruise of the new
(at the time) "Jewel of the Seas" which uses total electric
propulsion driving "azipods" which are remarkably similar in
appearance to the new IPS drives. The prime mover for the
generation of the electricity is two turbine engines, which
are the same as used in the DC-10 aircraft, if I remember
correctly.

The vessel has NO rudders, only the azipods that rotate
through 360 degrees. There are several HUGE thrusters
in the bow area for docking purposes. As the azipods rotate
to any direction, they are used as stern thrusters during
docking.
It is fascinating to stand on the "docking" side and watch this
monster ship just move straight sideways to the pier. Crew
toss "monkey's fist" with small line and then successively
larger lines follow until the main hawsers (4+ inches) get
hauled down for looping around the monster bollards. At
this point hydraulic (I presume) winches are used to pull
the shore into the pier.

* D C "Mac" Macdonald * * m/v Another Adventure * * '95 Carver 355 ACMY * *
Grand Lake - OKlahoma * * USPS & AGLCA (#217) * > Date: Tue, 9 Oct 2007
14:59:33 -0700> From: jdolenickmd at yahoo.com> To: great-loop at lists.samurai.com>
Subject: Re: GL: AN interesting concept for a trawler>> Many of the new cruise
ships 100,000 tons + are diesel electric.
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