> -----Original Message-----
> From: Ken Williams
> Arlid:
>
> The electrical system was designed by Mickey Smith, as you suspected.
> Mickey and I have a funny history together. Decades ago, when I
ran a
> computer game company (Sierra On-Line), Mickey was our representative
> from Intel.
REPLY
Yes I remember Sierra On-Line.
My fouir year eold daughter learned how to use computers while playing the Mother Goose game.
> Here's a question for you: I had always thought there was a direct
> correlation between horsepower and fuel. Aren't the hydraulic
> alternators consuming exactly the same amount of fuel that an
> equivalent generator would?
REPLY
You are correct!
In addition most hydraulic systems have an additional 5% loss compared to a purely mechanical drive.
However taking an additional 5 - 10 HP from your main engine does not shift it far along the power curve relatively to wher it is just driving the boat.
The little extra fuel burned is not as much as would be consumed in a genset delivering the same electrical power as single phase 120 or 220V AC at 60HZ.
1800 RPM is not the optimum RPM for the engine blocks used for gensets.
I'm not aware of anyone doing detailed studies complete with a lot to data comparing the two methods.
Alternators actually produce 3 phase power which is then rectified to DC. A technical argument can be made that this is actually more efficient per unit of fuel burned that the single phase AC output used in smaller gensets.
Nordhavn owners usually speak of their output as "free electricity", but I'm not sure it is. In my case, I'm happy to have a little extra load on the engines. With twins, I'll be consuming only about 90hp per engine much of the time. I'm not sure constant under-loading is good for an engine.
REPLY
Here again you are quite correct. All engines have only a narrow range of RPM in which is it most efficient.
Therefore the close you come to running the engine at that RPM and loaded appropriately the better.
Deriving your electrical power from the propulsion engine in a manner which is essentially independent of the exact RPM is th ebest solution to cruising power.
> As to the house battery bank: . we'll have 1,530 24v amp hours.
> That should be enough for our use. 99% of the time it will just be
> Roberta and I on the boat, and we're pretty conservative on using
> power. On Sans
Souci, our 62,
> the primary power consumer at night, while at anchor, was the sat TV
> positioning unit. I always had to power it off, and the Fleet 77,
> before going to bed.
REPLY
Being conservative with using power is the key. In your case I am suer the systemwil perform nicely and meet your expectations.
I have run into some people that want a similar system but expect to use power in a profligate manner as if they were ashore in a luxury condo. They expect to air condition the entire vessel day or night.
> "...How do you split the load between the genset and the inverters
> when you have central air using chillers?...
>
> It has been a few weeks since I looked at the electric panel. I need
> to do some investigating to answer this question. I'll look this afternoon...
>
REPLY
I will look forward to hearign from you later.
Very best regards
Arild
| Williams, Ken |
2006-11-19 14:40:59
|