Nordhavn Diesel Electric Hybrid

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Deleted User YDKXO

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Following on from the Nordhavn thread below, I found THIS on the Nordhavn website

I know this was discussed on another thread and I think the conclusion was that a diesel electric powered boat would be less efficient but it seems that Nordhavn don't agree. I also like the redundancy built into the system in that each of the 2 props is driven by 2 electric motors and either diesel engine can drive any of the electric motors so it's virtually mechanically unstoppable. I also like the fact that the diesel engines can be located anywhere which gives the designer more freedom when designing the interior spaces

How about hooking up the electric motors to IPS drives?
 
Interesting stuff, but note you need to turn on both engines to get maximum cruise, so one 200 hp engine produces enough poke to crusie at 9.5 knts but you need the main 400hp and the 200 hp coupled up to go another two knots,......hardly efficient, I bet the main engine through normal drive would give 11.5knts or am I missing something ?
 
Not sure I understand it either but the point of the diesel electric drive is that the diesel engines are always running at their most efficient rpm which, apparently, more than compensates for the greater mechanical efficiency loss of the system compared to direct diesel engine drive. But, yes, it does seem a mite inefficient to fire up an additional 400hp motor to get an additional 2 knots but I suspect that the 9.5-11.5 knot range is close to max hull speed for a 72 footer so the extra 2 knots uses a lot of hp. I guess though that for the vast majority of time on passage, the boat only uses the 200hp motor and cruises at less than 9.5knots and the second motor is an additional engine that the owner specified for safety and, having made a decision to specify it, he thought he might as well have a big engine to get the extra 2 knots. I guess on a long passage, an extra 2 knots could make the difference between out running a hurricane or not. Even so, a total of 600hp is not excessive for a 72 footer
 
Don't diesel trains work on the same principle? The diesel engines constantly powering the generators? They presumably only use this because its more efficient than direct diesel power
 
I'm pleased to see that a manufacturer agrees with the proposition I offered on the recent thread.
To be fair, the diesel/electric train scenario is more economical due to the fact that having overcome inertia the power requirements to maintain a given speed are a lot lower than to maintain a boat's speed where much greater frictional losses and water resistance occur.
 
I shared a lock with a diesel-electric narrowboat recently. The first thing that I noticed was the unusual amount of engine noise when he was moored up. I thought that he was charging his batteries but apparently the engine runs at 3,500 r.p.m. all the time, even when the propellors are stopped. The owner was also unhappy with the design because the engines go straight up to these revolutions when started and he did not like to do this with a cold engine. He also thought that it might cause the bores to be glazed, running at high speed with no load.

I am interested in innivations but I do not feel tempted to try this one.
 
Dave
I'm pretty sure that the d/e narrowboat was no operating correctly. D/e is supposed to be very efficient at cruising speeds but it makes no sense to run a diesel at 3500rpm when there's no load on it. The owner's concens about start up are also quite justified.
AFAIK the diesel of a d/e boat should idle normally when the electric motors aren't taking any current. When you want to move off you move a lever to the 'Go' position, the engine comes up to speed and you then use the 'electric throttle' to set your desired speed. That's unless the motors are DC and work off a big lead acid battery bank. In which case the engine may need to run at that speed to power a very big alternator. Even so, when the batteries are fully charged, the diesel should then come back to idle.
Quite ready to be corrected by someone who knows more about d/e than I do.
 
I saw a hydraulic system fitted to a catamaran, one engine mounted sideways, two hydraulic motors in the hulls, very compact and the engine also drove a hydraulic generator, brilliant system, but not with the built in redundacy of this system, it's excellent.
 
Re: More info

This also means of course you can have soft engine mounts, silenced engines etc. etc. a very quiet boat, almost as quiet as a sailing yacht!
 
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