Towed generators
Mark Anderson
I have a spare small prop (10 x 8) and 3/4 in. prop shaft from a
previous boat. I'm considering towing this from a cable to a taffrail
mounted generator on my sailboat. Is there any experience out there
with homemade versions of this technique for generating power underway.
E.g. can I go direct to an old car generator, perhaps thru V-belts to
increase the rpm, and a regulator? Figuring a 30% slip, this prop
should spin at about 500 rpm at 5 kts.
--
Mark Anderson
Riparia
"The trouble with good ideas is that they soon degenerate
into a lot of hard work" - Anon.
Tom Friend
Devil's advocate:
Corosion will be your worst enemy. Any shorts induced by such white fuzz
will cause your next problem- electrolysis of the prop & shaft. I think
that isolating the prop & shaft electrically would be a Good Thing.
Hmmm. Why not just connect a generator to your main prop? The generator
would be more protected from the elements, and I'll bet your prop is bigger
and in a better location to extract energy from the passing water.
Please follow up here if you do decide to do this- it does sound like it
will degenerate into lots of hard work. ;-)
Paul Mathews
Capt Billy Bones wrote:
>
> Mark
>
> I went through the same questions you are asking and tried several
> techniques of which most of them failed or just were not efficient enough.
> I finally purchased a 28 or 32 volt permanent magnet motor, which are hard
> to find for about $200 and attached a An Evenrude outboard utility prop on
> a 4' shaft and trailed it on a stiff line. It worked wonderful. ......
Don't forget a series diode, unless you want the motor to draw current
whenever the prop revs drop below a certain point.
For easy adaptation, important motor characteristics are:
Permanent magnet type
Low series resistance: less than 3 Ohms is good, efficiency suffers as
R rises
Low rpm per Volt: You want something like 30 rpm per Volt, so, you
could use motors rated for say, 360 rpm at 12V, or 2700 rpm at 90V, or
anything in between. However, motors rated for the higher Voltages will
tend to have too high series resistance.
Spooling motors from big magnetic tape drives used to be the surplus
type of choice, but these are quite rare these days.
--
Paul Mathews, consulting engineer
AEngineering Co.
opt...@whidbey.com
non-contact sensing and optoelectronics specialists
Capt Billy Bones
Mark
I went through the same questions you are asking and tried several
techniques of which most of them failed or just were not efficient enough.
I finally purchased a 28 or 32 volt permanent magnet motor, which are hard
to find for about $200 and attached a An Evenrude outboard utility prop on
a 4' shaft and trailed it on a stiff line. It worked wonderful. It gave
about 1 amp per knot above 3 knots. In port I attached a prop to the motor
and hoisted it into the rigging and I got up to 10 amps. Had to replace the
brushes a couple times. I may still have one of the motors around if your
interested.---if they didn't get sold with the boat !!!! This system is
very similar to the Hamilton Ferris system.
--
Smooth Seas
Capt. Billy Bones
wiz...@worldnet.att.net
Mark Anderson <ande...@teleport.com> wrote in article
<1996102722...@ip-pdx15-22.teleport.com>...
Paul Kamen
You'll have a lot of torque coming up through that cable!
If I were building a towed generator, I'd be inclined to put the generator
inside the towed rotor hub. There'd be a set of "stator" vanes to balance
the torque on the non-rotating forward half of the hub, and the actual
propeller or rotor would be on the rotating back half of the hub. The
rotor would recover the rotational energy from the stator, just like
turbine blades.
That way the towline could be light and flexible, since it would only
have to carry tension and electricity, instead of all that torque.
Hope that helps, even though it didn't have much to do with your question,
except that you should be concerned with the torque-carrying cabability of
the towline.
--
fish...@netcom.com
http://www.well.com/~pk/fishmeal.html
-"Call me Fishmeal"-
Paul Mathews
Bob Richardson wrote:
>
> ande...@teleport.com says...
> >
..... I'm considering towing this from a cable to a taffrail
> >mounted generator on my sailboat. Is there any experience out there
>
> It will work. It will also work well as shark bait. Towing generators often
> get snapped up by curious/hungry shark. Make sure you have a system to
> retrieve your prop when the wind and waves get too big. One technique is to
> have a large can (plastic or tin) that can be slipped onto the line. ............
In over 25,000 mi, I never lost a towing prop to a shark. However,
chafe requires constant vigilance. I suspect that many claims of shark
damage were instead due to chafe.
Agree that you'll want to haul her in at times. I gave up with the
various bucket and funnel methods for stopping the spinning.....things
get hung up on the twists in the line. I found that I could simply haul
it in fast using a good pair of gloves....there is a limit to the torque
produced.
--
Paul Mathews
Ramon Gandia
Mark Anderson wrote:
>
> I have a spare small prop (10 x 8) and 3/4 in. prop shaft from a
> mounted generator on my sailboat. Is there any experience out there
> E.g. can I go direct to an old car generator, perhaps thru V-belts to
> increase the rpm, and a regulator? Figuring a 30% slip, this prop
> should spin at about 500 rpm at 5 kts.
Mark:
I see two problems with the approach. First, the
rope would have to be proper lay, or the prop the proper
rotation so the tow line does not unravel. You would need
to use 3-strand rope.
The taffrail mount would need to be gimballed.
Lastly, the rpm. I do not think an old automotive
generator would be a good choice, due to low efficiency. I
do know an automotive alternator will often work at dead idle,
even with air conditioner and headlights on. This means that
it produces enough amps -- perhaps 30 or 40 at idle.
But an automobile that idles at 550 rpm will turn
the alternaor at 3 or 4 times that speed, for, say 2,000
rpm for full output.
There is the problem of getting enough horsepower,
thru a rope tow line, to couple enough energy to the alternator.
A larger prop, a heavier line come to mind, but add drag.
I think a better choice would be a smaller alternator,
one with an external regulator. See what you can get out of
it when at 500 rpm or less, using a rheostat for field
control. I doubt if it would put out enough amps to be a
concern even with no regulator; also, it might not overcome
the drain of the field current. Thus you need to measure
net alternator amperes, not just the main output lead.
Some alternators have more than 3 phases; it might
be possible to rewire the stator to double or quadruple
the output at low rpm. It would last forever (the stator
anyway).
Pulleys and belts are possible, but I think you will
stall the prop or huckle the tow rope. Also, there is a lot
of friction on something like this, and it is difficult to
mount -- and maintain -- out in the open.
Some suggestions for sources: Low rpm permanent
magnet DC motors. 28 volt ones are common in the surplus
market; to power pumps, actuators and the like. Look
around old aircraft salvage yards and see what you can dig
up. Series or shunt would motors are useless as they
will probably consume more current than they put out. When
you get it, take a good look at the insides. In a d.c.
motor, the winding spins and the brushes bring out the output
from the commutator. Take it to a motor rewind shop and see
if they can rewind the armature, or reconnect the windings
to improve low rpm output.
Wind driven generators for airplanes. I had one in
a 1939 Taylorcraft (but not in 1939, this was in 1966). I
bought the unit from Wag Aero, Inc....I think in New Berlin,
Wisconsin, south of Milwaukee. Guy owns it is Dick Wagner.
He might have some more around. You don't want a new one,
I don't think....$$$$ but a good place to start asking. Also,
little gravel airports with old derelict planes and junkboxes
of parts....look there too. This genny was small, about
3-4 inches in diameter and maybe 8 inches long. Weight was
about 8 pounds or less. Air driven prop was about a foot or
so diameter. There was a switch for the whole thing, and a
switch for the field winding. No regulator (optional), so
you monitored the output and turned it off if not producing
net generator output. I recall my plane would do 87 MPH
with the thing off, and drop to 82 MPH with the field on !
Judging from the vibration, I would say it was turning
between 200 and 500 rpm, but who can tell? Well, here is
where Dick Wagner comes in. He might have an old brochure
that says the rpm. If it needs 174,000 rpm, then useless
for you, but if 200-400....hmmmmm. In a plane, loss of
electrical power is trivial (this type of plane), but in
a boat, maybe not. You want a reverse current relay or
a diode, and you probably need a pushbutton to excite the field
before it puts output to close the relay. The pushbutton would
basically bridge the field to the 12 volt battery (thru the
rheostat) so it will start charging on demand, but not
draw the battery down in a calm. I can tell you how to
accomplish this once I have some basic facts from your
particular unit.
Large, old alternators. These are more likely to
have the extra windings you need. Seems like the newer
ones are simplifying their internals. But, look around.
A good place is the yellow pages and see who in your area
rebuilds automotive alternators. Those shops have a vast
area of knowledge, AND, they generally have 100 or more
different types floating around in various stages of
disrepair. Any of these would make a good candidate for
rebuilding and maybe rewinding or reconnecting as well.
Go to an older shop with old guys in it, because the newer
shops merely replace brush/regulator units, diode plates
and bearings. Anything else, they trash the thing as the
local wrecking yards sell them alternators by the half ton.
By the way, with the parts I just mentioned, which
you can get for $15 to $25 (under $8 or so if you are an
alternator shop), you can rebuild an alternator and put it
on the sales shelf for $120. Total investment and cost,
including labor, shipping, stocking, and the cost of an old
alternator that is not gouged out internally, would be
not over $30. Nice profit, eh? NAPA does this with their
mexican rebuilts. They pay some poor latino $4 per DAY
to work in this shop, and their cost per alternator is
only about $15.....core is zero as they ask for one when
they sell you the $120 unit..... maybe I am in the wrong
line of business!
At any rate, avoid the parts-replace-only shop, and
go to some old geezer that still knows what to do. There will
be some, as often these shops do motors and starters as well,
and when a 1932 buick drives in with a bum starter or genny,
you have to MAKE all the parts for it! Here is where the
experts save the day and the parts replacers say "What year
car did you say it was ? Let me look in my book.....sorry,
I don't have it here." The old timers will say, "Sure, bring
it on down and I'll give it my best shot." Then, heh heh,
you can tell them that you don't really have a 1932 buick,
but instead have this OTHER problem.....
Lastly, an alternator shop will test the thing for
output current, and can test out the field currents, etc
all at the RPM you want. In my opening statatement I said
you probably did not want a generator, but an alternator.
However, you can never tell, after going thru the pile of
stuff there you might found that I am all wet and there
is a 1932 Buick genny there that is just the ticket....
Oh, and put some kind of hooks out there on the
shaft or prop hub. You might catch a 600 pound Mackerell
or tuna! Or Jonah the whale.
--
============================
Ramon Gandia, Nome, Alaska |
AL7X S/V Seven Stars |
tel 907-443-2437 fax 2487 |
============================
Bob Richardson
ande...@teleport.com says...
>
>I have a spare small prop (10 x 8) and 3/4 in. prop shaft from a
>previous boat. I'm considering towing this from a cable to a taffrail
>mounted generator on my sailboat. Is there any experience out there
>with homemade versions of this technique for generating power underway.
>E.g. can I go direct to an old car generator, perhaps thru V-belts to
>increase the rpm, and a regulator? Figuring a 30% slip, this prop
>should spin at about 500 rpm at 5 kts.
It will work. It will also work well as shark bait. Towing generators often
get snapped up by curious/hungry shark. Make sure you have a system to
retrieve your prop when the wind and waves get too big. One technique is to
have a large can (plastic or tin) that can be slipped onto the line. The can
will then slide down and cover the spinning prop, thus making it easier to
haul it in.
Kevin J. Hansen
We did around 20,000 miles with a towed generator. I got a surplus 72
volt DC motor (fairly easy to find) and drilled a cross-hole through the
shaft for a shackle. We tied a chunk of fairly stiff double braid (to
resist the torque) to that - about 75 feet.
The prop that worked best was from a 25 horse Evinrude outboard; epoxy to a
3 foot long SS shaft, and I poured about 5 pounds of lead around the shaft
just ahead of the prop. (Use a pop can for a mold). If you don't have
enough weight, the prop comes summersaulting out of the water when you're
going fast, tangling the line in the process. You have to make sure it
stays in the water.
The prop is used BACKWARDS. It doesn't matter if it is nicked or bent a
little.
This produced about 5 amps at 5-6 knots, and provided thousands of
amp-hours for our 3 year sojourn. The 100-120 amp-hours per day were
sufficient for autopilot, radios, refrigeration, and lights. On one very
fast passage from Tasmania to NZ, the batteries were fully charged when we
arrived, with no other source of charging!
The biggest problem was getting it in if we had to; the torque and drag
made it a fairly hazardous operation. It prevented us from fishing (after
one truly humungous snarl when the lure hit the propellor). Other than
that, the occasional replacement of bearings (once) and brushes (3 or 4
times) were all the maintenance required.
When used with a homemade prop, we got up to 15 amps as a wind generator
with this arrangement. Brushes didn't last long at this amperage, however.
Not bad for a $75 investment!
Kevin J. Hansen
kjha...@alaska.net
James A. Chamblee
I used the tow-behind generator made by Hamilton Ferris on two
trans-Atlantic crossings. I found it to be very reliable; and generated
plenty of juice.
It was vastly superior to a wind generator; because the output was
higher underway, and it wasn't a constant worry hanging in the rigging
someplace. Since much of my cruising was done in trade winds, the
relative wind speed across the boat was only about 10 MPH, making a wind
generator virtually useless.(But they are useful at anchor)
My generator was hung on the taffrail in 3/8" rope "gimbals", w. about
75 ft. of 3/8" braided line to a 3 ft. shaft with an outboard prop
mounted. It turned up about 500 RPM at 6 knots of boat speed.
However, it is not without difficulties:
* In substantial seas, the prop tends to briefly leap out of the water;
causing the tow line to kink up.
* Large fish or sharks occasionally attempt to devour the prop. The
shaft discourages the severing of the line due to this problen.
* Recovering the line and prop back aboard takes about half an hour;
because as the line gets shorter, the prop leaps from the water like a
hooked gamefish periodically and severely kinks the line while airborne.
While this is spectacular at the time, it takes a long time to remove
all the kinks when the line is back aboard.
* The generator must have roller bearings to take the load of the tow,
which in my rig was about 50-75 pounds of force pulling on the armature.
A normal generator is not designed for this force (or any force in that
direction for that matter).
I don't think I would do it again, however. Solar power is better and
more convenient than either towed or wind-blown.
I hope this is helpful.
Rod Mc Innis
Oh, I just love these "what if" threads!
Paul Kamen (fish...@netcom.com) wrote:
: You'll have a lot of torque coming up through that cable!
: If I were building a towed generator, I'd be inclined to put the generator
: inside the towed rotor hub. There'd be a set of "stator" vanes to balance
: the torque on the non-rotating forward half of the hub, and the actual
: propeller or rotor would be on the rotating back half of the hub. The
: rotor would recover the rotational energy from the stator, just like
: turbine blades.
Interesting concept, but I do have a few nits about it.
1) Having the generator inside the hub would certainly increase the
size of the hub. This large hub would certainly add to the drag of
the unit.
2) If the "stator" vanes didn't exactly counter the "rotor" blades,
then the entire unit would try to rotate, which would "wind up" the
tow cable (which now includes the power cables). I suppose you could
intentionally mismatch the rotor/vanes so that you would know which
direction it would want to turn, and thus have the tow cable handle it
(a cable will resist a torque in one direction, but will unravel
against the opposite torque).
3) It would be possible to let the generator assembly spin, but then
you would need to have slip rings for trasnfering the power out. Gets
complicated, especially when you consider.....
4) SEALS! No, not the marine mammals, the things you need to keep the
water out. If the stator doesn't turn, then all you need is the main
shaft seal. However, if you want to the stator to be free to turn,
well, now you have a much more difficult sealing problem.
5) Electrolysis. If you are just getting mechanical energy from the
towed prop, then it can be neutral with respect to the water. Heck,
it could be electrically isolated. But if you want the prop hub to be
the generator, and pass electrical power up the tow cable, then you
will have to have an electrical potential difference between the boat
and the towed array, just to get current to flow. This potential
difference could cause electrolysis between the boat and the
genertor.
All in all, I would thing that the added drag from the large hub,
and friction losses due to the seal requirements would make this less
efficient than just transfering torque up the cable.
: Hope that helps, even though it didn't have much to do with your question,
: except that you should be concerned with the torque-carrying cabability of
: the towline.
Make sure that the torque "tightens" the cable twist, rather then
loosens it!
Rod McInnis
Paul Kamen
rmci...@adobe.com (Rod Mc Innis) writes:
>1) Having the generator inside the hub would certainly increase the
>size of the hub. This large hub would certainly add to the drag of
>the unit.
My guess (a somewhat informed guess, if I say so myself) is that the drag
from a very large hub, if it's reasonably faired, will be very small
compared to the drag from the blades.
>2) If the "stator" vanes didn't exactly counter the "rotor"
>blades, then the entire unit would try to rotate....
Good point. The stators could be carefully "trimmed" for neutral torque,
but this would assume the generatore torque varies with the same function
of speed as the rotor/stator torque. It would, at the very least, dictate
the exact electricla load for each speed. Maybe the counter-rotating
design, which wouild be torque-balanced over a wide range of electrical
loadings, is better that the stator/rotor concept.
>3) It would be possible to let the generator assembly spin, but
>then you would need to have slip rings for trasnfering the power
>out.
Now I'm thinking non-rotating in-hub generator, with counter-rotating
blades. I don't think the seals or the electrical isolation are really a
big deal. After reading some posts about the problems handling a towline
that's trying real hard to twist up, I think it's still worth pursuing a
torque-free design.
Bob Richardson
In article <55ap60$8...@enquirer.corp.adobe.com>, rmci...@adobe.com says...
>
>
> Oh, I just love these "what if" threads!
>
Well, what if you just took advantage of a free wheeling prop. I know a few
boats that did. That seems much easier, safer, and inclined to produce more
power.
A 19" prop rotating moderatly fast can be geered up to spin your generator.
Mark Anderson
Paul Mathews <opt...@whidbey.com> wrote:
> Agree that you'll want to haul her in at times. I gave up with the
> various bucket and funnel methods for stopping the spinning.....things
> get hung up on the twists in the line. I found that I could simply haul
> it in fast using a good pair of gloves....there is a limit to the torque
> produced.
If hauling in is a problem, why not briefly heave to?
Rod Mc Innis
Paul Kamen (fish...@netcom.com) wrote:
: >2) If the "stator" vanes didn't exactly counter the "rotor"
: >blades, then the entire unit would try to rotate....
: Good point. The stators could be carefully "trimmed" for neutral torque,
: but this would assume the generatore torque varies with the same function
: of speed as the rotor/stator torque. It would, at the very least, dictate
: the exact electricla load for each speed. Maybe the counter-rotating
: design, which wouild be torque-balanced over a wide range of electrical
: loadings, is better that the stator/rotor concept.
How about a variable pitch on the stator blades, where the pitch was
controled by the torque from the tow line?
Rod McInnis
Mark Anderson
Paul Kamen <fish...@netcom.com> wrote:
> big deal. After reading some posts about the problems handling a towline
> that's trying real hard to twist up, I think it's still worth pursuing a
> torque-free design.
For some reason I didn't get a feed on the posting leading to
counterrotating or other torque free generators. Sounds great, but
we're deviating from the K.I.S.S. school. If the problem to be solved
is a twisted up towline, why not use 1x19 cable rather than dacron line?
Or, if you can cope with the storage, how about several sections of
tubing with bayonet locks between them?
Certainly belting off the main propshaft could be the best solution.
It's protected, it's larger so more power. You'd probably want a clutch
to completely disengage it from your gearbox. Unfortunately you'd
always have the props drag unless you used an adjustable pitch prop.
Feather completely when not trying to generate. Dialin what you want
the rest of the time. But those props are expensive.
Fabbian G. Dufoe
Paul Kamen (fish...@netcom.com) wrote:
: Now I'm thinking non-rotating in-hub generator, with counter-rotating
: blades. I don't think the seals or the electrical isolation are really a
: torque-free design.
What's the advantage of having a long tow line? Why not have
something configured like a trolling motor that mounts on a bracket on the
boat? It would seem to be much easier to tilt or raise the generator out
of the water just as you would an outboard than to haul in a tow line that
was spinning at 500 RPM or so. A solid mounting would resist torque a lot
easier than a system of trimmable vanes, wouldn't it?
--
Fabbian G. Dufoe, III
350 Ling-A-Mor Terrace South | email: sf6l...@scfn.thpl.lib.fl.us
St. Petersburg, Florida 33705 |
813-823-2350 | 27 deg 44.5 min N, 82 deg 38.3 min W
Paul Kamen
sf6l...@scfn.thpl.lib.fl.us (Fabbian G. Dufoe) writes:
>What's the advantage of having a long tow line? Why not have
>something configured like a trolling motor that mounts on a bracket
>on the boat?.....
I guess the idea is to minimize size and weight of structural parts. But
it would be interesting to see if a "regenerative" trolling motor could
be built, perhaps at only a small cost increment above a standard
trolling motor. (Offhand I'd think the propeller pitch would be all wrong
for power generation, not to mention the blade camber. So most likely a
propeller swap would be necessary when changing functions)
Rod Mc Innis
Fabbian G. Dufoe (sf6l...@scfn.thpl.lib.fl.us) wrote:
: Paul Kamen (fish...@netcom.com) wrote:
: : Now I'm thinking non-rotating in-hub generator, with counter-rotating
: : blades. I don't think the seals or the electrical isolation are really a
: What's the advantage of having a long tow line? Why not have
: something configured like a trolling motor that mounts on a bracket on the
: boat? It would seem to be much easier to tilt or raise the generator out
: of the water just as you would an outboard than to haul in a tow line that
: was spinning at 500 RPM or so. A solid mounting would resist torque a lot
: easier than a system of trimmable vanes, wouldn't it?
The mounting.
You would have to have the mounting pole long enough to reach the
water at all angles of heel and wave action. At the stern, the waves
passing by can make it a long way down to the water. Add a good heel
and you might need a 20 foot pole to keep the generator in the water
all the time.
With a long pole, the torque at the mounting point could be rather
high, which would necessitate a substatial mounting pad.
Rod McInnis
Peter W. Meek
Fabbian G. Dufoe <sf6l...@scfn.thpl.lib.fl.us> wrote in article
<55phug$8...@ns1.thpl.lib.fl.us>...
>
> What's the advantage of having a long tow line? Why not have
> something configured like a trolling motor that mounts on a bracket on
the
> boat? It would seem to be much easier to tilt or raise the generator out
> of the water just as you would an outboard than to haul in a tow line
that
> was spinning at 500 RPM or so. A solid mounting would resist torque a
lot
> easier than a system of trimmable vanes, wouldn't it?
I think long tows allow the axis of the blades mechanism to be closer to
normal (in the technical sense of being closer to parallel) to the water
flow. I know that power driven props work better (or at least differently)
when the propshaft is other than parallel to the flow.
----------
--Pete <pwm...@mail.msen.com>
http://www.msen.com/~pwmeek/
Fabbian G. Dufoe
Rod Mc Innis (rmci...@adobe.com) wrote:
: You would have to have the mounting pole long enough to reach the
: water at all angles of heel and wave action. At the stern, the waves
: passing by can make it a long way down to the water. Add a good heel
: and you might need a 20 foot pole to keep the generator in the water
: all the time.
If conditions are such that sometimes you need a 20-foot pole to
keep the generator in the water all the time the solution might be to let
the generator come out of the water some of the time. What I'm suggesting
is that you may get all the electrical power you can store from having the
generator submerged only by the crests. In that case you don't need to
design for submersion in the troughs as well.
Also, keep in mind that the mounting bracket doesn't have to be at
the top of the transom. If the boat is large enough that that would
require a 20-foot pole it might make more sense to mount the bracket
lower. A lower bracket that allowed the generator to be raised vertically
would reduce the torque on the mounting pole.
Another technique that would reduce the required pole length would
be to allow its angle to be adjusted so it could remain vertical
regardless of the boat's angle of heel.
Although I was thinking of a generator designed from the ground up
I wonder what would be required to convert an off-the-shelf trolling motor
to this application. Any permanent magnet DC motor will function as a
generator if you spin the shaft. Would it be enough to mount a different
pitched prop and put a diode in the circuit?
Trolling motors typically have pretty weak plastic props. I
believe their shafts are pretty standard, so if someone could point me to
an inexpensive metal prop that would fit my trolling motor I could
experiment with this.
Ramon Gandia
Various sailor types wrote:
> What's the advantage of having a long tow line? Why
> not have something configured like a trolling motor
> that mounts on a bracket on the boat? It would seem
> to be much easier to tilt or raise the generator out
> of the water just as you would an outboard than to haul
> in a tow line that was spinning at 500 RPM or so. A
> solid mounting would resist torque a lot easier than a
> system of trimmable vanes, wouldn't it?
>
> You would have to have the mounting pole long enough
> to reach the water at all angles of heel and wave action.
> At the stern, the waves passing by can make it a long
> way down to the water. Add a good heel and you might
> need a 20 foot pole to keep the generator in the water
> all the time.
>
> With a long pole, the torque at the mounting point could be rather
> high, which would necessitate a substatial mounting pad.
I think such a device could be fashioned out of a defunct
outboard motor. Remove the power head and put in an alternator
and a coupling to the shaft coming up from the lower unit.
Assume a 15 amp output; or about 200 watts. This is aprox.
1/4 horsepower, so I think you want to scrounge up an o.b.
unit that is 1.5 to 3.5 hp max. It does not need reverse
in the lower unit, but a neutral would be good.
My only concern would be for friction in the gearing, etc.
The gear ratio should be about right. Pick the largest
diameter, lowest pitch prop you can find. The contraption
can be mounted far lower in the water than an operating
real outboard motor would be. In a small motor, the
friction should be minimal. Worth a try.
--
==============================================================
Ramon Gandia, Nome, Alaska | To deter Spammers, e-mail address
AL7X S/V Seven Stars | is not machine readable. Convert
tel 907-443-2437 fax 2487 | by hand! ----> rfg @ nome DOT net
==============================================================
Greg Davids
Does anyone out there have any direct experience using their fixed
prop as a generator? How did your transmission feel about this? How
much juice do you get out of the system? What did you use for a
generator, and how was it mounted? Did you have any notable decrease
in sailing speed ( if you are already dragging a fixed three blade
prop, is the amount of drag with it turning a generator really that
much more than if it is locked by the transmission?)?
Greg Davids
Chester Copeland
>I have a spare small prop (10 x 8) and 3/4 in. prop shaft from a
>previous boat. I'm considering towing this from a cable to a taffrail
>mounted generator on my sailboat. Is there any experience out there
>with homemade versions of this technique for generating power underway.
>E.g. can I go direct to an old car generator, perhaps thru V-belts to
>increase the rpm, and a regulator? Figuring a 30% slip, this prop
>should spin at about 500 rpm at 5 kts.
>
>--
>Mark Anderson
>Riparia
>"The trouble with good ideas is that they soon degenerate
>into a lot of hard work" - Anon.
For those who wish to try a homemade towed generator, I suggest a
slightly modified "electric" outboard of the type used by fishermen on
small boats.
Everyone should realize however that there is no free lunch. Any
energy extracted from the water (or air) to generate electricity will
be obtained at the expense of forward thrust!!!! The bottom line is
that a device that extracts lets say 1/3 hp (ie 200 watts + losses) is
equivalent to running your motor at 1/3 hp output IN REVERSE.
To get a feel for the effect, turn on your motor on a calm day with no
sails up and put it in forward at idle speed. I suggest the forward
speed obtained under these conditions represents the approximate loss
in attempting to generate a reasonable amount of electricity. By the
way, there is a very big difference between locked blades in the water
producing drag and spinning blades generating electricity and thus
producing drag.
Good Luck
James A. Chamblee
I tried generating juice from my 3 blade prop, and I was very unhappy
with it for 2 reasons:
1. It was noisier than the prop rotating on its own, and I couldn't
suppress the feeling that my shaft bearings were wearing away with every
turn.
2. I didn't like the idea of mechanical gear located deep in the hull,
which had the potential to become fouled and jam the shaft, misalign the
engine, or bend the shaft.
If God had meant propeller shafts to be used to generate electricity, he
have made them out of armature materials.
Jim Chamblee
Mark Anderson
Rod Mc Innis <rmci...@adobe.com> wrote:
> Fabbian G. Dufoe (sf6l...@scfn.thpl.lib.fl.us) wrote:
> : What's the advantage of having a long tow line? Why not have
> : something configured like a trolling motor that mounts on a bracket on the
> : boat?
>
> The mounting.
>
> You would have to have the mounting pole long enough to reach the
> water at all angles of heel and wave action. <...>
>
> With a long pole, the torque at the mounting point could be rather
> high, which would necessitate a substatial mounting pad.
The pole would need be no longer than that on a transom mounted windvane
servo rudder and they work fine. Do the solid attachment on the
centerline. On a transom hung rudder boat, this would be quite straight
forward. I like the idea. Securely attached to the rudder but
retractable. Sure you're not in free water like being towed some
distance behind, (hence reduced efficiency), but you obviate the shark,
tangle, retrieval, and maneuveering liabilities of the long tow.
Paul Kamen
ccop...@concentric.net writes:
>...To get a feel for the effect, turn on your motor on a calm day
>with no sails up and put it in forward at idle speed. I suggest
>the forward speed obtained under these conditions represents the
>approximate loss in attempting to generate a reasonable amount of
>electricity...
It may represent the energy lost, but not the speed! Remember that the
power required to move at "idle" speed represents only a small fraction of
a knot at waterline-limited sailing speeds. The point being that under
most sailing conditions, you can pull off quite a bit of power with a
very small effect on speed.
Ramon Gandia
James A. Chamblee wrote:
> If God had meant propeller shafts to be used to
> generate electricity, he have made them out of
> armature materials.
This is not entirely unreasonable. In many generators
and alternators I have seen, the armature iron is
pressed on a shaft, or at least looks like it.
Must look into this further....
Rod Mc Innis
Fabbian G. Dufoe (sf6l...@scfn.thpl.lib.fl.us) wrote:
: Although I was thinking of a generator designed from the ground up
: I wonder what would be required to convert an off-the-shelf trolling motor
: to this application. Any permanent magnet DC motor will function as a
: generator if you spin the shaft. Would it be enough to mount a different
: pitched prop and put a diode in the circuit?
I doubt that the trolling motors are permanent magnet motors. But
since they are reversible, they would have the rotor and stator
connections independant, so you could provide the necessary
excitation.
: Trolling motors typically have pretty weak plastic props. I
: believe their shafts are pretty standard, so if someone could point me to
: an inexpensive metal prop that would fit my trolling motor I could
: experiment with this.
I wouldn't worry about the strength of the prop. If it can survive
the torque when operated as a motor, I would expect it to be OK when
operated as a generator.
A bigger concern is the pitch of the prop. You would need to turn
the prop pretty fast in order to get it to generate the same voltage
it would operate on as a motor.
I know you can buy 24 volt trolling motors, which would mean that
you would only have to spin it half as fast to get 12 volts. There
might be 36 volt units available, which would allow a fairly slow prop
speed.
Rod McInnis
Fabbian G. Dufoe
: since they are reversible, they would have the rotor and stator
: connections independant, so you could provide the necessary
: excitation.
: A bigger concern is the pitch of the prop. You would need to turn
: the prop pretty fast in order to get it to generate the same voltage
: it would operate on as a motor.
As an experiment I connected my trolling motor to my volt meter,
switched it on, and rotated the propeller by hand. It was easy to bring
the reading (with no load) over 12 volts for brief periods. Next I
wrapped a line around the prop and pulled it to get a longer period of
prop rotation. Voltage on the meter reached 19 volts and the prop wasn't
turning as fast as it would on the next-to-lowest speed setting with the
motor running.
I don't know whether the magnetic field came from conventional
permanent magnets in the motor or residual magnetism in the cores of the
field coils. I just know it produced respectable voltages from a
relatively slow-turning propeller.
Paul Mathews
Fabbian G. Dufoe wrote:
>
> Rod Mc Innis (rmci...@adobe.com) wrote:
> : I doubt that the trolling motors are permanent magnet motors.
ALL of the dozens of trolling generators I've built and/or inspected
have used permanent magnet motors as generators. They will charge a
completely flat battery.
--
Paul Mathews, consulting engineer
AEngineering Co.
opt...@whidbey.com
non-contact sensing and optoelectronics specialists
jklin...@aol.com
I don't understand, I got that idea of using a trowling motor to charge
batteries about 18 yrs ago and bought the biggest minkota that was made
then and hooked to an electric drill. I only got about 2.5 volts at 500
rpm. I came to the conclusion that I had to have about a 90 volt perminat
magnet motor to do the job. I sold the minkota in a garage sale before I
set sail. It had never been in the water. Jim
jdfry
Paul Mathews <opt...@whidbey.com> wrote in article
<328CE6...@whidbey.com>...
>
> ALL of the dozens of trolling generators I've built and/or inspected
> have used permanent magnet motors as generators. They will charge a
> completely flat battery.
> --
>
> Paul Mathews, consulting engineer
> AEngineering Co.
> opt...@whidbey.com
> non-contact sensing and optoelectronics specialists
>
Paul,
Got any tips for the group or ideas on where we can find plans for trolling
generators you know to work.
Rod Mc Innis
: : since they are reversible, they would have the rotor and stator
: : connections independant, so you could provide the necessary
: : excitation.
: As an experiment I connected my trolling motor to my volt meter,
: switched it on, and rotated the propeller by hand. It was easy to bring
: the reading (with no load) over 12 volts for brief periods. Next I
: wrapped a line around the prop and pulled it to get a longer period of
: prop rotation. Voltage on the meter reached 19 volts and the prop wasn't
: turning as fast as it would on the next-to-lowest speed setting with the
: motor running.
: I don't know whether the magnetic field came from conventional
: permanent magnets in the motor or residual magnetism in the cores of the
: field coils. I just know it produced respectable voltages from a
: relatively slow-turning propeller.
Hook a light bulb up to the leads to give it a load, and try your
experiement again.
Rod McInnis
Paul Hovnanian
Paul Mathews wrote:
>
> Fabbian G. Dufoe wrote:
> >
> > Rod Mc Innis (rmci...@adobe.com) wrote:
> > : I doubt that the trolling motors are permanent magnet motors.
>
> have used permanent magnet motors as generators. They will charge a
> completely flat battery.
It may be possible that some trolling motors are not permanent magnet
and
therefore not suitable for use as a generator. They may be series or
shunt wound D.C. motors. One way to tell is to see if you can reverse
the direction of the motor by reversing the battery polarity. FIRST,
make
sure that there are no solid-state devices, meters, etc. attached that
may
be damaged. If the motor does NOT reverse when the batery is switched,
it is
probably not a P.M. motor and will not work as a generator.
Without actually doing the experiment, if you have the trolling motor
schematic and the forward/reverse direction is controlled by switching
the motor
field windings (the reverse switch is conected to "extra" wires from the
motor)
it is not P.M. and will not make a good generator.
--
Paul Hovnanian hovn...@faast.ca.boeing.com
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Who is General Failure and why is he reading my hard disk?
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