http://members.cox.net/sholley1/electric.htm

"A few years back I was impressed when I saw a "dock maintainance
barge" tooling around the cove in our Marina under the power of a
little 12 volt trolling motor. It was small, old, but the persistance
of the little thing moved the barge around quite well. I proceeded
down to my boat, and embarked on the following procedure to go
sailing."

"NOTE: There is no neat formula or correlation between thrust and
horsepower. However, I read a comparison that measured a 6 hp gas
outboard produced just over 130 lbs of thrust, so that would class the
107 Motorguide in the realm of a 5 hp gas (give or take a little).
Thats not a lot of power, but ample for my needs. I don't know how I'd
fare towing in another boat, but I'll include towing in "tests to
come"."

http://www.geocities.com/Yosemite/Fo..._outboard.html

Auxilliary Power Requirements with Electricity

"A typical trolling motor is designed to push a displacement hull at a
maximum of about 2 to 3 miles per hour. Therefore, I determined to use
the highest thrust 12 volt electric trolling motor that I could
purchase and see where that would lead. In this case, a Motorguide
model T47 motor with a 36 inch shaft length was commonly available at
the local Kmart stores. This motor draws about 50 amps at maximum
speed and is rated to produce 47 pounds of thrust. Replacing the
propeller with a two blade (power) design from the three blade (weed
free design) included with the motor should result in the required
combination of low shaft speed and high thrust. This motor, combined
with a bank of two new fully charged group 27 deep cycle batteries,
could operate at maximum thrust for about 2.5 hours. In theory, the
calculations said that this combination would propel my Com-Pac at
just under three knots. This would meet my stated goal of a 5 mile
range under power with some safety margin."

For whatever it is worth to you, I can drive my 16 ft sailing skiff at 3.6
mph using an Endura 30 drawing 30 amps.

BS

"Mic" wrote in message
...
http://members.cox.net/sholley1/electric.htm

"A few years back I was impressed when I saw a "dock maintainance
barge" tooling around the cove in our Marina under the power of a
little 12 volt trolling motor. It was small, old, but the persistance
of the little thing moved the barge around quite well. I proceeded
down to my boat, and embarked on the following procedure to go
sailing."

"NOTE: There is no neat formula or correlation between thrust and
horsepower. However, I read a comparison that measured a 6 hp gas
outboard produced just over 130 lbs of thrust, so that would class the
107 Motorguide in the realm of a 5 hp gas (give or take a little).
Thats not a lot of power, but ample for my needs. I don't know how I'd
fare towing in another boat, but I'll include towing in "tests to
come"."

http://www.geocities.com/Yosemite/Fo..._outboard.html

Auxilliary Power Requirements with Electricity

"A typical trolling motor is designed to push a displacement hull at a
maximum of about 2 to 3 miles per hour. Therefore, I determined to use
the highest thrust 12 volt electric trolling motor that I could
purchase and see where that would lead. In this case, a Motorguide
model T47 motor with a 36 inch shaft length was commonly available at
the local Kmart stores. This motor draws about 50 amps at maximum
speed and is rated to produce 47 pounds of thrust. Replacing the
propeller with a two blade (power) design from the three blade (weed
free design) included with the motor should result in the required
combination of low shaft speed and high thrust. This motor, combined
with a bank of two new fully charged group 27 deep cycle batteries,
could operate at maximum thrust for about 2.5 hours. In theory, the
calculations said that this combination would propel my Com-Pac at
just under three knots. This would meet my stated goal of a 5 mile
range under power with some safety margin."

On Sun, 29 May 2005 21:32:39 GMT, (Mic) wrote:

http://members.cox.net/sholley1/electric.htm

"A few years back I was impressed when I saw a "dock maintainance
barge" tooling around the cove in our Marina under the power of a
little 12 volt trolling motor. It was small, old, but the persistance
of the little thing moved the barge around quite well. I proceeded
down to my boat, and embarked on the following procedure to go
sailing."

"NOTE: There is no neat formula or correlation between thrust and
horsepower. However, I read a comparison that measured a 6 hp gas
outboard produced just over 130 lbs of thrust, so that would class the
107 Motorguide in the realm of a 5 hp gas (give or take a little).
Thats not a lot of power, but ample for my needs. I don't know how I'd
fare towing in another boat, but I'll include towing in "tests to
come"."

http://www.geocities.com/Yosemite/Fo..._outboard.html

Auxilliary Power Requirements with Electricity

"A typical trolling motor is designed to push a displacement hull at a
maximum of about 2 to 3 miles per hour. Therefore, I determined to use
the highest thrust 12 volt electric trolling motor that I could
purchase and see where that would lead. In this case, a Motorguide
model T47 motor with a 36 inch shaft length was commonly available at
the local Kmart stores. This motor draws about 50 amps at maximum
speed and is rated to produce 47 pounds of thrust. Replacing the
propeller with a two blade (power) design from the three blade (weed
free design) included with the motor should result in the required
combination of low shaft speed and high thrust. This motor, combined
with a bank of two new fully charged group 27 deep cycle batteries,
could operate at maximum thrust for about 2.5 hours. In theory, the
calculations said that this combination would propel my Com-Pac at
just under three knots. This would meet my stated goal of a 5 mile
range under power with some safety margin."

A number of years ago I replaced the gas outboard on an Irwin 24 with
the cheapest trolling motor at the local Walmart. This was on Lake
Lanier, not in the ocean, but it was more than sufficient for driving
this boat in and out of the marina. I am not sure what the thrust
rating was, but I paid $150 for both the motor and a deep cycle
trolling motor battery. With a solar panel on the cabin roof I never
needed shore power to keep it charged up enough for going in and out
of the marina 2 or 3 times a week.

The boat I am building now (a 7 meter Eco7 catamaran) will have two
electric trolling motors for auxilliary.


Weebles Wobble
(but they don't fall down)

On Mon, 30 May 2005 04:07:00 -0400, tedwilliams wrote:

On Sun, 29 May 2005 21:32:39 GMT, skddjl (Mic) wrote:

///
"NOTE: There is no neat formula or correlation between thrust and
horsepower.///

There is in fact a formula which relates thrust to horse-power and
water speed.
Simply put: thrust in lb. =
( power in watts / speed through water in MPH )
X 0.1 scaling constant

Example: 1/2 HP = 373 watts,

water speed 1 MPH

thrust = 373watts /1 mph X 0.1 = 37 lbs

water speed 2 MPH:

thrust = 373watts / 2 mph X 0.1 = 18 lb thrust

Notice that the big unknown is the water speed. Even if a boat is
anchored, the propeller will push water at 1 mph or 2 mph depending on
its size, pitch etc. You can take 1 mph as a lower limit - usually
higher. This is higher than the other unmentioned
losses - motor efficiency 90%? prop efficiency 80%??

Brian Whatcott Altus OK

Ted wrote:


Hmmm, the math is pretty simple. We measure the output power of motors or
engines in Hp. 1 Hp = 746 watts. 5 Hp = 3730 watts. To produce 5 Hp at 12
volts would require 310.8 amps. (Assuming no IR, friction, and windage
losses) That requires some pretty heavy duty wiring. I doubt that I could
lift a true 5 Hp 12 volt motor.

Ted,

See http://www.electricmotorsport.com/PA...pecs.htm#Page5

This motor (ETEK) is capable of 9HP continuous, and only weighs 21
lbs. Of course, it only puts out about 2HP max at 12V, but you can
get over 9HP at 48V. You are right about the amp draw at 12V of course.

I remember reading in a recent "cruising world" about a new
production day sailer in the 36-40ft range that relies on electric
propulsion and a genset to charge the rather large battery bank.

For a day sailer that is typically connected to dock power every
night, electric seems like an interesting way to go. A genset and
a large house battery bank are pretty nice things to have on a sailboat
anyway, and you have eliminated a bulky and heavy diesel inboard that is
only good for propulsion and charging batteries.

If you start google searching you'll find that there is a lot of interest
in hybrid/electric conversions for autos and boats. There is a lot of
info available and quite a few people experimenting.

Now if we could only get someone to produce a 2,400 lb keel which was
also a huge battery bank (sigh). Either that, or a really affordable
large fuel cell (sigh again).

YMMV

Don W. (Who is toying with the idea of converting a Catalina 27 to electric
and getting rid of the 9.9HP Yamaha 4-stroke)

On Mon, 30 May 2005 11:49:12 -0400, ted williams wrote:

[bw]
There is in fact a formula which relates thrust to horse-power and
water speed.
Simply put: thrust in lb. =
( power in watts / speed through water in MPH )
X 0.1 scaling constant

[tw]
You are 100% correct in the theoretical thrust relative to speed.

///
Using your example, at a thrust which produces 37 lbs at 1 MPH could be
easily overcome by a modest breeze against the surface of the vessel that
produced more than the 37 lbs of force provided by the motor.

If the net effect of the breeze against the vessel surface produced 74 lbs,
the vessel would travel backward at 1 MPH.
Regards,
Ted

Hmmmm... the formula gives a value for thrust, given some water speed
and input power.

What it DOESN'T give, is a value for boat speed given thrust at a
given input power.
That would need knowledge of air drag and hull drag which do not
enter here.

However, if you could find the drag at given hull speeds, e.g by
towing the hull and measuring the force required, THEN you could
say how much thrust would be needed ( = drag) at that speed and hence
what power would be needed at that speed, ignoring the losses I
mentioned earlier.

Sincerely

Brian Whatcott

snip

I had a look at the page and found a few odd things. The math for a motor
has not changed since they were invented. Only the efficiency in which they
convert input power to mechanical energy has improved.

Take a look at the 24 volt motor shown on:
http://www.electricmotorsport.com/PA...pecs.htm#Page5

Motor output is 15Hp max and 8 Hp continuous.

Well, this is *not* a 24V motor. It can be operated on 24VDC, but will
not reach its maximum rated output. It is a 50VDC motor, look at the
specifications box.

To get 15 Hp at 24 vdc assuming no losses, you would need 466.25 amps. The
motor is rated at a maximum motor current of 330 amps for 60 sec. You might
get the equivalent of 15 Hp for 5 seconds before it was toasted.

8 Hp would require 248.67 amps continuous at 24 vdc. brush life for that
current rating isn't given. What would it be? I don't know, maybe 24 hours
or less. It appears that brush life drops exponentially with current

Take another look at the page. The charts are for the same 50VDC motor
operated at three different voltages. The charts basically give you the
performance characteristics at the stated voltage - you can't
extrapolate from them.

The chart looks correct as it takes into account the losses in motor
efficiency. But the chart does not jive with the text below it. Notice the
chart only shows up to a tad over 4 Hp for a motor that the text below the
chart clearly states 15 Hp max, 8 Hp continuous.


The motor is rated for 150A continous. At 48VDC, that's 8HP at about
3100 RPM. That 150A continuous input would net you 4HP at about 1350
RPM. Half the voltage, half the VA, half the horsepower.

The 48 vdc motor is similar. A claimed maximum Hp of 15 Hp which would
require only 233 amps within the stated rating of the current limit for the
motor but think about the brush life, it is off the chart. When you look at
the chart, again it appears that brush life drops exponentially with
current.

8 Hp would require 124.3 amps. Still lots of amps.

Per the chart, it requires 150A. You're right, that's a lot!

Keith Hughes

Ted,

There was another page somewhere with brush life vs input current. Its basically
an inverse exponential, which is why the motor is rated at 9HP at 50V. It is
capable of putting out higher power outputs, or of putting out 9HP at a lower
voltage, but the brush life drops dramatically at the higher currents. Looking
at the 48V chart, it appears that the motor makes 9HP at about 155A. Now looking
at the bottom of the chart is says that the brush life at 150A continuous is 500
hours. Now if we drop back to 5HP at 48V, we need about 90A. The chart says
that the brush life at 100A continuous is 2000 hours. That is about the same as the
TBO of a gasoline engine.

Another interesting feature of this motor is that the brushes are removable
as snap out unit, and can be changed in about a minute according to the literature.

A Yamaha 9.9hp is capable of making about ten HP on the max throttle setting,
but I almost never run it wide open because it makes too much noise, and things
start vibrating. Also, the higher power settings just result in the nose of the
boat rising further in the air, and the outboard trying to bury itself in the
water with an increase of only a knot or so. I'd bet that the average power
setting is more like 4-5HP.

So, for a _day_ sailer, with 15 minutes of motoring to get out of the slip, and
another 15 minutes of motoring to put it away, it appears you would need about
45AH at 48V, (180AH of 12V), X 3 for battery life, or 4 ~120AH batteries. As you
noted that is a BIG house bank. Also, as you noted, you are discharging them
at a pretty fast rate during the discharge cycle. However, if you have a DC genset
that is capable of producing 3-5KW, you can start the genset, and use it to power
the motor continuously. Also, with that big house bank, and a 3-5KW inverter you
can have some pretty snazzy AC appliances on the boat meaning that you can do
away with the alcohol stove, and power a microwave and an AC fridge. If you run
the genset, you can probably even power a small AC unit some of the time.

Oh, and another nice feature is that the motor can be driven as a generator by
the prop while you are sailing, although you may need a pretty fancy switcher
circuit to take advantage of the variable voltage.

Of course, all of this is going to weigh more than a 99Lb outboard, but you
hever get something for nothing.

Just thinking online,

Don W.



Ted wrote:
On Mon, 30 May 2005 15:35:59 -0700, Keith Hughes
wrote:


To get 15 Hp at 24 vdc assuming no losses, you would need 466.25 amps. The
motor is rated at a maximum motor current of 330 amps for 60 sec. You might
get the equivalent of 15 Hp for 5 seconds before it was toasted.

8 Hp would require 248.67 amps continuous at 24 vdc. brush life for that
current rating isn't given. What would it be? I don't know, maybe 24 hours
or less. It appears that brush life drops exponentially with current

Take another look at the page. The charts are for the same 50VDC motor
operated at three different voltages. The charts basically give you the
performance characteristics at the stated voltage - you can't
extrapolate from them.


Ahhh, thanks. What threw me were the same Hp readings for all 3. I thought I
was looking at 3 different motors.

Normally, when a motor specification is given (such as for say an MD408), it
is given ratings at 250 VDC. I thought I was looking at 3 motor specs. I
only gave it a quick look and assumed it would was like all the other motor
specs I have read but for different motors. Didn't realize it was the same
motor. The article was a far different method of presenting motor specs than
those by GE, Westinghouse, Reliance, etc. I am accustomed to reading
industrial motor specs and they all follow a similar format.

For instance older older MD type motors are ususally rated at 250 VDC. You
have to know they are rated to withstand 500 VDC and extrapolate the Hp and
RPM at 500 VDC.

Today, motors are rated typically at 500 VDC. The typical AC source to the
drive is 3 phase 460 VAC at 60Hz. Now when you go overseas to say China,
their standard voltage is 380 VAC at 50Hz. You won't get much over 400 VDC
from a 380 VAC source. In this case, we take the standard motor speed and KW
ratings and derate them for the 380 VAC source. What might require a
standard 50 Hp motor for an application here may require a standard 75 Hp
motor in China.

Older CD motors are rated at 250 VDC and can't commutate 500 VDC. They are
what they are and you can't exceed the specs.

Same thing applies to the type of AC motors. To place an AC motor on an
IGBPT drive, the motor has to be able to withstand the PWM power to the
drive. Unless the motor is built to withstand variable frequency and voltage
by Pulse Width Modulation, you can heat one up real fast. VM Star is a great
Reliance built motor designed for that pupose.

My error. Thanks for clearing it up. It had me going around in circles for a
bit.

My warmest regards,
Ted

Hey, Weeb...

Are you still on Lanier? I've got an option contract on the house but
they've not exercised, just paying the renewals, as yet, so I'm still here
while I'm not on the boat refitting (which means I get about a week a month
at home)....

L8R

Skip, near the Habersham Condos

--
Morgan 461 #2
SV Flying Pig
http://tinyurl.com/384p2

"Twenty years from now you will be more disappointed by the things you
didn't do than by the ones you did do. So throw off the bowlines. Sail
away from the safe harbor. Catch the trade winds in your sails. Explore.
Dream. Discover." - Mark Twain

wrote in message
news
On Sun, 29 May 2005 21:32:39 GMT, (Mic) wrote:

http://members.cox.net/sholley1/electric.htm

"A few years back I was impressed when I saw a "dock maintainance
barge" tooling around the cove in our Marina under the power of a
little 12 volt trolling motor. It was small, old, but the persistance
of the little thing moved the barge around quite well. I proceeded
down to my boat, and embarked on the following procedure to go
sailing."

"NOTE: There is no neat formula or correlation between thrust and
horsepower. However, I read a comparison that measured a 6 hp gas
outboard produced just over 130 lbs of thrust, so that would class the
107 Motorguide in the realm of a 5 hp gas (give or take a little).
Thats not a lot of power, but ample for my needs. I don't know how I'd
fare towing in another boat, but I'll include towing in "tests to
come"."

http://www.geocities.com/Yosemite/Fo..._outboard.html

Auxilliary Power Requirements with Electricity

"A typical trolling motor is designed to push a displacement hull at a
maximum of about 2 to 3 miles per hour. Therefore, I determined to use
the highest thrust 12 volt electric trolling motor that I could
purchase and see where that would lead. In this case, a Motorguide
model T47 motor with a 36 inch shaft length was commonly available at
the local Kmart stores. This motor draws about 50 amps at maximum
speed and is rated to produce 47 pounds of thrust. Replacing the
propeller with a two blade (power) design from the three blade (weed
free design) included with the motor should result in the required
combination of low shaft speed and high thrust. This motor, combined
with a bank of two new fully charged group 27 deep cycle batteries,
could operate at maximum thrust for about 2.5 hours. In theory, the
calculations said that this combination would propel my Com-Pac at
just under three knots. This would meet my stated goal of a 5 mile
range under power with some safety margin."

A number of years ago I replaced the gas outboard on an Irwin 24 with
the cheapest trolling motor at the local Walmart. This was on Lake
Lanier, not in the ocean, but it was more than sufficient for driving
this boat in and out of the marina. I am not sure what the thrust
rating was, but I paid $150 for both the motor and a deep cycle
trolling motor battery. With a solar panel on the cabin roof I never
needed shore power to keep it charged up enough for going in and out
of the marina 2 or 3 times a week.

The boat I am building now (a 7 meter Eco7 catamaran) will have two
electric trolling motors for auxilliary.


Weebles Wobble
(but they don't fall down)

On Tue, 31 May 2005 15:37:05 -0400, "Skip Gundlach on wifi"
skipgundlach.sez.remove.this.part@earthlink.(fish catcher)net wrote:

Hey, Weeb...

Are you still on Lanier? I've got an option contract on the house but
they've not exercised, just paying the renewals, as yet, so I'm still here
while I'm not on the boat refitting (which means I get about a week a month
at home)....

L8R

Skip, near the Habersham Condos

I live in Lilburn, but have no boat currently
(building one as we speak)


Weebles Wobble
(but they don't fall down)