[Public-list] weight distribution and electric power

[Gordon Laco]

Yes, very interesting topic.

I used to teach at Georgian College's School of Marine Technology and so had
a terrific library at my disposal.  It was fun trying to figure out hard
numbers for the various options.

With regard to the water generator, I used thrust figures for various revs,
blade orientation, pitch, area, etc. and tried to work backwards to get
figures for a water DRIVEN prop (as opposed to a water driving).  Blade area
is key, and since you can assume that slippage will happen in a similar
ratio to thrust producing props - the big problem is getting the revs high
enough and with enough torque.  Skene's Elements of Yacht Design is a book
with useful data on this topic.

I too look forward to what our colleague comes up with in an actual test.

Gord #426









> Gordon-
> 
> I did the same math and came to the same conclusion. Why go to electric and
> then install a generator? In fact, I looked at exactly the same ones...honda
> air cooled gensets.
> 
> I could never quantify the drag of the water generator. There are no hard
> numbers out there on it. It's even tough to compare apples with apples when
> comparing diesel power and electric power, because the diesel gives up a lot
> of its available power in losses, where the electric has much lower losses,
> and generally more available power. By available I mean that the electric
> motor has very different torque and power characteristics which make its
> power more available.
> 
> It's a very touchy-feely thing, which is unfortunate. And it has a lot to do
> with your expected usage profile and how long you expect to go before
> selling. There are significant resale value implications.
> 
> At the end of the day, there is a lot more Q per pound in internal
> combustion. But if you can deal with the lower Q value per pound, electric
> can be pretty doggone nice. Simple. Quiet. No smell. Always ready to go.
> Pretty slick...
> 
> Personally, I am very interested to see how Dan's project turns out. It may
> work very well, in which case I'd say it might be something for others to
> consider too. I just didn't have the guts to try it like Dan has. Let myself
> be talked into sticking with internal combustion...a decision I half regret.
> 
> 
> Later,
> 
> JB
> 
> On 9/29/06, Gordon Laco <mainstay at csolve.net> wrote:
>> 
>> I did a bit of figuring on this issue back when considering an electric
>> aux
>> in my old boat.  The water generator is not an inconsiderable drag while
>> sailing.  I fell back on looking at fitting a small Honda generator, which
>> would have done a fine job but there I was back with gasoline but this
>> time
>> in addition to the extra batteries and lower thrust the e motor could
>> deliver...
>> 
>> Gord #426
>> 
>> 
>> 


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