T-Pain Is On A Boat: Re: [Electric Boats] RE: 5KW or 10 KW

Yes I agree, it was very enjoyable hearing his truthful perspective on EP.
Coming from a powerboat background, I like sailing for the peace it brings to the table.
With that said, I want to own a sailboat with an auxiliary motor, not the other way around.

A friend I sail with has a 6 HP 2 stroke Yamaha on the back of his boat. When we go out
he uses it to get out of the marina & clear the channel. Once the sails are hoisted the motor
gets turned off & doesn't get fired up again until we reach the channel on the return trip.
Frankly I hate the sound of the thing but love the smell, brings me back to a simpler time:)

Thanks to everyone that has responded to the question. Frankly when I go this
route, I probably will install a 10K unit instead of a 5. Price wise, very little
difference between the two. Although most as I do enjoy the peace of sailing,
there are times when the tides do run against you so having a little extra kick in
the way of EP isn't a bad thing.

Bob

--------------------------------------------
On Thu, 3/13/14, Orest Iwaszko <orestyko@hotmail.com> wrote:

Subject: Re: [Electric Boats] RE: 5KW or 10 KW
To: electricboats@yahoogroups.com
Date: Thursday, March 13, 2014, 9:35 AM

you can always count on Carter to put a sensible
summary in a real world perspective.
Whew that was hard to put into
wordsfor comparison my stats
full speed 2.6 mph
8 Ton
boat with 2.25 KW peak
.28kw/Ton I never use more than 1.2KW to
achieve my 2.5mph for fishing = .15
kw/Ton
Its single screw and backing up while docking
between boats requires the diesel if windy.
Orest
On 2014-03-13, at 8:41 AM, Carter Quillen
wrote:

Bob,
This
is definitely NOT a stupid question but I think you may be
asking the wrong people. When it comes to final decision,
you have to ask YOURSELF what it is YOU want and need for
YOUR boat and then decide how you want your boat to be able
to perform. Let's not forget, there was a day when
people sailed all over the world with no auxiliary motors at
all.
Although
you won't find a bigger proponent of electric propulsion
for boats than me, there is one question I always suggest
people ask themselves when considering an electric
conversion. Do you have a sailboat with auxiliary power or a
power boat with auxiliary sails. If the answer is the
latter, you probably want to stick with diesel. Or at the
very least go with a hybrid system that includes a
properly sized generator.
On
the issue of sizing, I would concur with often quoted rule
of thumb for approximately 1 kW/ton. This should give you
plenty of power for any situation and if you think you need
more for your particular boating application, then you might
want to consider sticking with diesel. But I also believe it
is quite reasonable to get by with considerably less than 1
kW/ton if you determine it will work for
you.
On
the lower end of the spectrum, there are many people that
use Mincota trolling motors to get in and out of their slip
on some pretty big boats, then rely on their sailing skills
after that. I have been pushing a 20 ton boat with a 7
kiloWatt peak motor,(.35 kW/ton) that I almost always
operate at 4 kiloWatts, (.2 kW/ton) for almost a 1000
miles now. It is fair to say it's a bit slower than most
people would want but it works
for me and I've always been able to maintain control of
my boat, albeit in slow motion sometimes, even in some
pretty adverse conditions.
So
get all the advice and opinions you can and study all the
wonderful data you can get from this site and others, then
decide for YOURSELF what is right for YOU. With proper
expectations, there is hardly a wrong
choice.
Capt.
Carter Quillen, P.E.www.shipofimagination.com

On Wednesday, March 12, 2014 8:15 PM, bob
jennings <sabre281@yahoo.com>
wrote:
Thanks Eric for the time
you put into this email.
It gives me things
to think about.

Thank you
Mike & Brian also!

Bob

--------------------------------------------
On Mon, 3/10/14, ewdysar@yahoo.com
<ewdysar@yahoo.com>
wrote:

Subject:
[Electric Boats] RE: 5KW or 10 KW
To: electricboats@yahoogroups.com
Date: Monday, March 10, 2014, 4:27 PM

Hi Bob,
Good questions.
Short answer, a larger
motor will not
use less amps to drive your boat at a given

speed. It will probably not run cooler at the same
given amperage (different motor, different
design, who
knows?).
My
30' 10,200 lb Bermuda 30 ketch uses 5.1kW
(measured as draw from the batteries) to motor
at 6 kts at
full throttle. At 5kts
(2500W), the motor windings of
my
Propulsion Marine 5.5kW drive never get to 80C, Motenergy
says the max temp for the ME913 motor is 150C.
At full
throttle, the 6.8hp of power
going into the electric drive
powers my
boat 1/2kt faster than the old 12hp diesel could
push the boat at full throttle. At
28'and 8000lbs,
do you think you
need more power than that?

Coincidentally, I believe that the Motenergy
ME913 is the motor in Electric Yacht's
"10kW"
drive. In my
opinion, that is a little over-stated.

The motor is rated for 125A continuous, so a
typical
48V system maxes at 6.2kW
continuous. Moving up to 72V
will
only get one to a 9kW continuous rating, so I read 10kW
with a grain of salt (yes, I know that they
state 10kW as
"maximum current"
but what does that really mean?)
.
Even so, the Propulsion Marine drive in my boat
that
uses the same major components as the
EY system was
conservatively rated at 5.5kW
on purpose to allow for less
than optimal
cooling in the bilge of an auxiliary sailboat.

With

all that said, I believe that using peak current ratings
(1
minute rating or 5 minute rating) is
misleading in the
marine market. In a
car or motorcycle, peak ratings
make more
sense (when was the last time that you drove your
car for 5 minutes at full throttle?).
But we "set
and forget"
boat throttles, running for long periods at

90% or more (gas and diesels) or 40-50% (electrics).
Nobody wants to hit the throttle to
combat a strong
current and have the motor
do a thermal shutdown 4 or 5
minutes later.
Since we operate our drives in a

continuous mode, we should only be looking at continuous
ratings. Please note that the most
important single
specification for sizing
an electric marine drive has proven
to be
displacement. Length of the boat (LOA) does not
appear to have much of a direct correlation to
how much
power you need because LOA
doesn't say much about the
boat's
design.
Back to
the
group's recommended ratings, 1kW per ton of
displacement will power a typical displacement
boat to
90-95% of theoretical hull speed
with a properly matched
driveline.
You can put in more motor, but it really
doesn't do much besides raise your cost.
There are
some in this group that
believe that a larger motor is
actually
less efficient being driven at a lower percentage
of it's design, though I believe that may
be more
theoretical than
practical.
Going

back to my boat, the
ME913 (remember that Motenergy says
125A
continuous) will push the boat to 95% of the
theoretical hull speed at 106A as long as
I've got power
and it will never
overheat. With 8kWh of Lithium, that

would be 69 minutes from a full charge to 80% depth of
discharge including losses to Peukert's
Effect. If
I doubled my battery back
to 16kWh (320Ah @ 50V), I could
run at full
throttle for 140 minutes and still not overheat.
I've posted my detailed performance
observations
many times here and my
measured "watts to knots"

efficiency is better than any verifiable performance
numbers
that have been posted here for a
mid-size sailing auxiliary.
However,
beating the performance of my boat should be
doable. She's a
full keel, prop in an aperture,
rudder
that is a 3" thick slab of teak, and her hull is
far from fair so a modern design should do
better.
We've got a rare
collection
of practical information about
electric boats in this group.

We've discovered that D. Gerr's
calculations
don't work well for what
we're doing here (his
predictions are
more than 300% off for my boat, and D. Gerr

himself admitted that his work is more applicable to
faster
boats). We've got electric
boaters with hundreds
of hours (or more) of
electric motoring experience. We
know
how much power it really takes to push boats like ours
to practical speeds. We've got a
number of vendors
that are a reasonably
reliable lot (as vendors,
they
probably have at least a subtle
bias). We've got a
number of
experimenters that want to build a better, or at
least a different, mousetrap. There is
more unbiased
practical experience in the
field of electric marine drives
here than
anywhere else on the planet. There are also
a lot of unsubstantiated opinions too.
But if you go
slow and read
carefully, you can collect enough real

information to build or buy an effective electric drive
for
your boat. So welcome and feel
free to ask
anything.
Fair
winds and smooth
seas,Eric1964 Bermuda 30
ketch, 5.5kW
Propulsion marine drive, 8kW
LiFePO4 battery
packMarina del Rey, CA
---In electricboats@yahoogroups.com,
<sabre281@...>
wrote :

Maybe this is a
stupid question but
I've wondered about the

advantages/disadvantages to having a 10 kw motor vs. 5
kw.
My boat is 28', 8000#'s of
displacement so let's
assume hull speed
is 6 knots at full throttle. From what

I've read I know the 5kw will do the job. If you
wanted
to motor lets say at 3.5-4 knots for
a long period of time
would a 10KW unit run
cooler & use less amps from the
battery
bank when compared to a 5kw?

Thanks,

Bob

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