On Thu, 09 Jul 2009 19:13:59 +0700, Bruce In Bangkok
wrote:

I can see what you are doing but I still don't see an advantage - this
is not to say that "I wanna do it that way" is not a valid reason. But
it seems to me:

I don't know what sort of electric motor you plan on using but the one
boat installation I saw used raw water cooled motors. There was a
fairly extensive cooling system with at least one over temp warning
system per motor. The one or two water cooled generators I have seen
exhibited severe corrosion in only a few years of use. will water
cooled motors have the same service life and a low speed, small,
diesel engine?

Yes, I guess "I wanna do it that way" is a valid reason. Hadn't
thought about it, but that is part of it.

The plan is to use a fork lift raise/lower motor. This is the exact
same motor as used in electric cars, but with a much heavier case. It
will develop 35 HP at 120 VDC and about 8 HP at 24 VDC. No need for
water cooling. Oh, a extra plus is the motor, like all DC motors, will
work in "reverse" as a generator under sail.

Not sure what you mean about the severe corrosion you've seen in water
cooled generators. I've seen a bunch of marine generators over 30
years old still running and looking good.


I wonder about the high power/low power control systems. What is the
advantage of this? with the diesel auxiliary I might use idle to back
out of a slip or to creep up on the anchor rode but that is generally
a very small percent of the engine's operating time. In addition,
especially inside a marina, I have frequently seen a need for almost
full power in maneuvering, particularly when the current is running 3
or 4 knts through the marina.

First, with those kinds of currents you mention it would definitely be
a situation to use the high power mode!! :-)

Low power mode would not be like idle. It would be closer to the way
it seems some manufacturers, particularly Hunter, put small engines
in, like a 10 HP diesel in a Hunter 33 a friend had. Or, if you
prefer, it would be like a max range power setting. Remember we're
talking 3.5 to 4 kts on battery only. A couple more batteries and it
could be 4.5 to 5 kts, probably with about the same "range" with the
added Amp Hours. Remember, battery only is for short time use. Max
range would probably be 4 to 8 miles, but you really wouldn't want to
do that because you'd have to use the generator to recharge. Better to
go into high power mode.


Okay, let's look at how low power, battery only, would be used. As I
had mentioned, right now we're at a marina in Slidell, LA due to a
care-giver situation. It's about 2 miles to the lake. We could use
battery only to get to the lake, sail about, etc., then maybe low
power back. In a way it does make sense because when we get back we'll
plug in and recharge "free" (fixed rate electricity).

If we moved to a nearby marina, our trip to the lake would be about
1/4 mile. Now this would make more sense to use low power. Someone not
cruising, day sailing or overnight weekending, in this situation could
use electric only and recharge when they got back. There'd be no need
for anything else unless they take occasional cruises.


Our normal sailing mode is cruising and anchoring out, with occasional
marina stays. There are times when we travel some in canals, so the
high power generator mode is needed. IOW, there are times when we need
to play motorboat for hours, days or maybe even weeks at a time.

Low power battery mode:

Yes, we know how to drop and weigh anchor under sail, but sometimes
there's little or no margin for error. Easier and safer to douse the
sails and flip a switch. Getting in and out of "port" when needed for
supplies, clearing in/out, etc. Ever try to creep though reefs
visually under sail?

Rather than go on, just look back how you use your engine. If it's say
less than a 1/2 hour a day if cruising or less than an hour
day-sailing, pure electric would work for you. Think about how nice it
would be to flip a switch and have instant power for whatever reason.
Maybe the winds are light and you want to come about and your boat is
one of those that's reluctant or very slow to do so in light
conditions. Hard over, flip the switch, come about, flip the switch
off.

The 110 VAC generator gives another plus of power for A/C if you want
to burn the fuel, fast charging with a large charger, etc. Heck, I
might pull the propane stove and put in an electric one. I wonder how
that would compare to "cooking with gas", fuel and cost wise?

It seems to me that saving space is the biggest advantage of a
diesel-electric drive. You do get rid of the gearbox but do you need a
speed change between the motor and the propeller?

As I had mentioned, it would take a recduction for much better
propellor efficiency. A chain drive would be cheapest, but a bit
noisy. Notched belt would be much ore expensive, but quiet. One could
maybe find a "gearbox" surplus or junked or... The motor brushes can
be electricly swapped for reverse.


In short, is there a distinct advantage in the diesel-electric drive?

I don't think there is a "distinct" advantage and in some cases a
disadvantage. It depends on one's boating style. Our case I feel there
is an advantage. Wayne had mentioned his trawler - in his case I would
say big disadvantage. As mentioned before, I've had lots of experience
with electric power and with "green" power - solar and wind. Whenever
you use those you have to look at your needs and wants and decide if
it's for you. You can't just turn on stuff or jump into your electric
car and drive it like a combustion one. You have to do a bit of
"resouce management". Most folks want "energy on demand" and are
unwilling to put up with the "work" to use or the waiting sometimes.


I'm not trying to start an argument here, I know what the advantages
are for a diesel-electric drilling rig, for example, and I'm trying to
figure out if there is one for a small engined sailing boat.

No argumant, Bruce :-) I know where you're coming from. It's a complex
subject with all kinds of "gotcha's". I wish it were like in the
movies, where they have a 2 X 2 ft. solar panel on a 20 passenger
electric transport and it runs it at 90 MPH all day and even all night
(from starlight???). It just doesn't work that way in the real world.

Other than a dinghy, I wouldn't even consider an electric power boat.
Well, maybe a slow 'African Queen' type on a lake or bayou for short
weekend use.

Rick