h a l f b a k e r yIdea vs. Ego
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What if we pulled ships across the ocean using cables like
trams in San Francisco. With no engines, they could haul a
heavier payload. The on-land engine could be a combination
of elements that are not practical on the ocean. Maybe
solar-
diesel hybrid. The cable would basically have knots
in it.
During off-load the ship would let go of the knot letting the
rope slip through a ring that would catch another knot once
off-load is complete. Hopefully before the next ship
arrives.
Cable Ferries
http://en.wikipedia.org/wiki/Cable_ferry
[EdwinBakery, Dec 07 2012]
Green Answers
http://greenanswers...ner-ships-are-ocean
90000 Ships on the ocean at any given time [Brian the Painter, Dec 08 2012]
The biggest container ship uses 1,660 gallons of heavy oil fuel an hour
http://gas2.org/200...as-50-million-cars/
It's incredibly efficient, turning 50% of the energy into movement. [Voice, Dec 08 2012]
Diesel contains 138,700 BTU per gallon
http://en.wikipedia...iki/Fuel_efficiency
[Voice, Dec 08 2012]
Common cruise speed is 25 knots, or 28.76 miles per hour. Let's round up to 30
http://wiki.answers...container_ship_burn
[Voice, Dec 08 2012]
Skin friction calculation
http://en.wikipedia..._drag#Skin_friction
[Voice, Dec 08 2012]
It needs shark skin
http://rsta.royalso.../1929/4775.abstract
[Voice, Dec 08 2012]
Now I'm way over my head
http://ittc.sname.o...Skin%20Friction.pdf
[Voice, Dec 08 2012]
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Welcome to the Halfbakery. |
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You'd have to weigh the extra mass of the cable against the possible efficiency increases from a single large fixed engine. The cable would be extremely heavy if it is even physically possible (I have my doubts), and marine diesels are already fairly efficient. |
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That being said, the idea isn't completely without merit. Over a shorter distance, it might work. The major savings would actually be economic, not energetic, as it would allow smaller crews on a given ship, since navigation would largely be a non-issue, and engine maintenance would be limited to a couple of pumps or similar. |
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You do realize that cable-pulled boats are nothing new, right? They used to have those all over the place. |
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And yes, obviously it's much more efficient. Your proposal for solar is unnecessary, electric motors are already extremely efficient. This is why they use/used cable pulled boats in the first place. Since the cable-pulling winch is on land and stationary, it can just pull its power from the grid. |
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The problem with your proposal is that over a long enough distance, the cable would end up being partly underwater in the middle of it, and would pull the boat downwards into the water as well as along it. The downward pulling force could be an issue with freight, as they load up as much weight as they can onto a boat, the boat need only float and not sink. So that extra downwards force from the cable would limit what you could carry. |
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I'll put up some calculations on those two issues later. |
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and of course one of the biggest issues with cable crossings is that the cable gets in the way of thru-traffic, which is one of the biggest reasons they don't use them anymore. Of course, this could be solved by having only one-cable system, where the cable is either retracted on the winch when no boat is crossing, or at the point where it will start pulling boats, but simply sunk at the bottom of the sea, and then boats could lower an anchor/arm and grabit it and pull it up to hook up to the system. THAT of course would then raise issues with the cable and sewater and corrosion. Steel cable + seawater = rust. |
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The weight of the cable is easily solvable by making the cable slightly buoyant. It could be a metal cable braided into the sheath of a hose filled with Styrofoam. Or something like that. |
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Like EdwinBakery said though, it would block shipping. This would be idea for the Chinese to use in the Spratley Islands though, I guess. |
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Welcome to the 'Bakery, [Brian]. You've come up with a
classic halfbaked idea here, so have a bun for getting off
to a great start. |
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My only input at the moment is that the power source
would have to be huge and capable of generating
unthinkable torque. Solar, internal combustion, or a
combination thereof would be impractically inefficient if
built to that scale. A massive electric engine powered by a
nuclear reactor would be a good option. |
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The weight of the cable with respect to the boat can be solved by buoyancy. You'd actually want to balance it so it floats about 20m below the surface except where buoyed by a ship, which should minimze cross traffic issues. |
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The weight of the cable with respect to the driving engine is another story. |
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And, [alter], once you go electric it doesn't matter what the power source is. Solar is just as good as nuclear, as long as there is enough of it. |
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People seem to misunderstand, buyancy will not help with the cable, the farther away you go the more "downward" it will pull from the ship's point of view. This is sort of like my chord-through-the-earth-tunnel problem I think I posted here with calculations. Once you start pulling on that cable, it will straighten and form a direct line between the two points of the ship and the winch, and after a certain distance that straight line will simply go below the curvature of the earth, and hence, underwater. From the point of view of the boat, it will be pulling both forward AND DOWNWARDS at an angle.
Making the cable buoyant will just make it curve upward a bit in the middle compared to being perfectly straight . |
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//the power source ... would have to ... generating unthinkable torque |
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No, not really. It's not hard to push a ship around, especially at low speeds. Hasn't anyone gone boating? It will need to be big if it's a really big ship, but a big distance won't necessitate more torque. Distance will only create the need for more torque when you, again like I said, go so far that the cable is underwater. The cable being underwater will create drag as it moves, which would require more torque. But as long as you're not so far that the cable is above water, no additional torque is necessary. |
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Did some calcs, and it turns out that the "chord", the length of the cable from winch to ship, will be 8000 * sin(.0075 * Distance) where Distance is the earth-travelling distance (the arc) between the two in miles, assuming a spherical earth with a radius of 4000 miles. The depth of the cable below the surface will be 4000 - (4000 * sin(.0075 D)) where D is again distance. The angle of the cable from level, or the angle at which it enters the water is 90 - ((180 - .015 D) / 2). |
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OK, maybe made a mistake, my chord is coming out longer than my arc when I plug in for 1 |
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Dangit! I did something wrong there |
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Anyway, the one time a while aago when I did it for any imaginary tunnel through a chord of the earth (for a train that rolls downhill then up, with ideally no energy input, obviously though some to beat friction - or for a cool kind of canal) and I did the calculations correctly, I remeber that I found that at 60 miles of earth distance, you're one mile below the surface |
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//buyancy will not help with the cable// Yes it
will. If the cable were neutrally bouyant then,
yes, if it ran from Ireland to New York it would
just try to cut a groove in the seabed as it went
around the Earth's curve. |
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However, even a very modest amount of bouyancy
will easily overcome this "cheesewire" effect. The
maths is annoying, but imagine this: stretch a
wire between two towers a mile apart, and put as
much tension on it as you like. It will still sag by
way, way more than a foot in the middle, under
its own weight. Now turn things upside down:
even a modest amount of bouyancy will "raise" the
centre of that mile of floating cable by a foot. |
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Roughly speaking, the Earth curves by one foot
per mile. So, problem solved. |
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A greater problem, though, is the drag on the
cable. How big will this be? |
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For a big ship, I am guessing that much of the
resistance comes from hull drag - the friction
between the water and the sides of the ship. This
drag should be proportional to the area of metal
in contact with the water. |
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A big ship has something like a million square
inches in contact with the water. A smooth cable
of one inch diameter (which would be ludicrously
thin), stretched between Ireland and N.Y. (3000
miles) will have about 500 million square inches in
contact with the water. |
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Thus, the energy needed to tow a boat across the
Atlantic will be at least 500 times greater than the
energy needed by a regular ship. |
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So, the idea will not be energy efficient unless
there are at least 500 ships being towed at any
one time. |
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But it gets worse. A 1-inch cable will be utterly
incapable of furnishing enough tension to move
itself (let alone any ships, which are insignificant).
So, you need a bigger cable, which means more
drag, which means a bigger force, which needs a
thicker cable... and you have to keep on going
until the square/linear ratio catches up and saves
you. You're going to need a cable at least a few
feet in diameter. |
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So, let's be optimistic and assume we can get
away with a cable only a foot in diameter. This
will have a drag equal to 6,000 big ships. So now
we need 6000 ships in constant motion to make
this worthwhile. |
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Then there's the cost of the steel (or whatever) to
make the cable. If it's steel (fitted with floats, as
necessary), then the 3000 mile, 1ft thick cable will
weigh about 5 billion pounds, or 2.5 million tons.
At a cost of about $1000/ton, this would cost $2.5
billion. I guess that's affordable. |
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So, the only fundamental thing preventing this
working (aside from the hazard to other shipping)
is the problem of needing to keep at least 6000
ships attached to it all the time. |
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I assumed everyone would use this new oceanic
crossing thus 6000 ships should be easy to find. Also
the buoyancy for the cable comes from the ships as
well as buoys so less buoys are needed than one
would think. Trains have a similar issue where around
long bends the train tries to drag over the center
cars to the inside of the corner. this is solved by
adding engines every so many cars. |
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<snip> partially completed math
We'll just have to calculate the drag of moving a
hydrogen (you'll never procure a sufficient quantity
of helium) balloon and multiply it by the number of
balloons needed.
We'll also need to add the
cost of producing hydrogen and decide on a cable
thickness based on the number of ships.
How
do I calculate drag? Do I multiply drag coefficient by
the cross section? |
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//So, the only fundamental thing preventing this
working (aside from the hazard to other shipping) is
the problem of needing to keep at least 6000 ships
attached to it all the time.// |
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Perhaps, but remember that you gain an advantage by
powering all of those ships via a land-based power
source. You could use, say, nuclear power instead of
the bunker fuel that ships typically use. So it may not
be technically energy-efficient, but it could easily be
/fuel-efficient/, as well as cleaner and cheaper to
boot. |
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Keep in mind the container ships also don't carry any
fuel. Huge savings there too. I get the cable would
need to be thick, that is a problem but I'm curios
about how ships will cross paths with the tram?
Maybe a few containers could be connected with a
bar instead of a cable. The bar would be curved so as
to let ships pass over it. Or they could join the
convoy.
"Join or Die!" Like a Borg thing. |
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//I'm curios about how ships will cross paths with the
tram// |
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Hey, it's /your/ half-baked idea. |
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// once you go electric it doesn't matter what the power
source is. // |
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I rather think it does. Solar power only works while the sun
is shining, and generating enough of it to charge giant
batteries to maintain a constant current when the sun is
not obliging means building 3-4 times the collection
capacity than is needed for direct transmission. Internal
combustion has upper limits of power production before it
loses viable effeciency, which is why you have
turbochargers the size of single-wides on big ships and
Bugattis with eleven radiators. Nuclear power, on the
other hand, is not only the most efficient source of power
thus invented, but its generation capability is limited only
by the size of the pile and of the turbines that it drives
(and we can make really, really big turbines). |
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//and we can make really, really big turbines// |
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And we make those turbines for external
combustion and hydro. And they're equally viable
for concentrated solar thermal electric
generation, with molten salt heat storage. (PV is
stupid, expensive and inefficient for large scale
plants, PV with battery even worse). The first
ever 24/7 solar plant came on line July last year
using molten salt. |
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My point was that once you go electric your fuel
source decouples from your prime mover. Hence
the "it doesn't
matter" line. |
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Bammn! You've been told. (hand hurts a little) I love all the
feedback. Still curious about Cross traffic. Any thoughts? Any free
buns? (I love your buns) |
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I love your buns too, [Brian], but don't get overly
enthusiastic about it or we'll run into a ToS situation. |
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I believe somebody already fixed the cross-traffic issue by
suggesting that the cable bouyancy be set at about twenty
meters. |
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[Matt], I lounge corrected. |
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It would help quite a bit if the distances were kept lower by staging it. 1300 miles to the Azores from Newfoundland, 800 miles to Spain. |
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It would also help a lot if the cable weren't in the
water. |
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Suspend the cable from a somewhat large number
of helium balloons, hovering a few tens of metres
above the ocean. Ships can then hook onto it
through suitable descenders. |
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This will eliminate virtually all of the drag
problems. |
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How do I calculate drag? Do I multiply drag coefficient
by the cross section? What do I do after that?
Googling it, all I get is page after page of how to
calculate a drag coefficient. Drag coefficient of a
sphere in air is about .5. How can I use that to
calculate the actual drag on a balloon of x size moving
at y speed? |
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[Voice] See the Wikipedia articles 'drag equation' and 'drag coefficient'. |
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For complex, real-world objects, such as ships and cars, I think that the drag coefficient itself is sometimes simply measured directly, rather than being calculated. |
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The drag coefficient of braided cable in water has got to
be a rather complicated affair. It may look like a big
straight line, but six feet of 1 1/2" braided steel rope
(cable) actually has more surface area than, say, six feet
of human being. |
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You would coat the cable, with as smooth and low
friction a coating as possible (anti-fouling). Of
course ship hulls already have that, so [MBs]
numbers are probably fairly accurate. |
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That being said, he did neglect form drag. Based
on very little research, I believe this is actually
the dominant factor for most ships (excepting
long,
skinny craft such as racing shells or racing power
boats, and possibly catamarans in general), at the
least it is significant. Since the cable would have
essentially zero form drag, his
numbers
are probably somewhat more unfavorable than
would strictly hold. |
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Forget the steel cable. I see a carbon nano-tube cable with some floaties every couple of hundred meters or so. Beware of floatie drag as well as being a seaweed trap. |
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Maybe something across the Strait of Gibralter? |
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what if we employed the electric trolley method
where ships used their own motors while pulling
current from a cable rather than having their hulls
filled with near crude oil? |
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//what if we employed the electric trolley method where ships used their own motors while pulling current from a cable rather than having their hulls filled with near crude oil?
— Brian the Painter// |
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Maybe if there were a way to make an insulator that could be made to conduct with a magnet or something. Some insulating materials become conductors at high temperatures... |
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An inductive loop pickup could work. Or a trolley-car style pantograph to the blimp-suspended aerial cable. |
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//Or a trolley-car style pantograph to the blimp-
suspended aerial cable// |
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because constructing cable-towers in the Atlantic
(mean depth 3.3km) could be tricky. |
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Fortunately the Atlantic is a placid, benign
environment, so the (notoriously robust) blimps
will be fine. |
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To avoid HUGE transmission losses, you'd have to
go with something like 1 million Volt line with step
down transformers at increments. Otherwise there
might be... arcing. |
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As a further efficiency hike, perhaps the whole
fuel energy to mechanical energy to electrical
energy then transmission then step down then
back to mechanical energy process could be
simplified somewhat? Perhaps just put the fuel on
the boat, then turn that directly into
mechanical... you'd cut out all those horrible
conversion and transmission losses, as an added
bonus there would be some flexibility with regard
to route. |
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I predict that if this were implemented, you may
have the most efficient transport system on the
planet. |
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