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{\Large Low-carbon Marine Propulsion -- without nuclear ships}
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{\Large Notes by David JC MacKay}
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{\Large\tt{www.withouthotair.com}}
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{\Large June 2011}
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%{\large (minor updates added \today)}
\chapter{Low-carbon Marine Propulsion}
Useful numbers.
What is thrust of container ship in newtons?
\marginfig{
\begin{center}
\begin{tabular}{@{}c@{}}
{\mbox{\epsfxsize=53mm\epsfbox{../../images/IanBoyleContainerShip.jpg.eps}}}
\\
\end{tabular}
\end{center}
\caption[a]{
The \ind{container} ship\index{ship!container}
{\em Ever Uberty\/}
at Thamesport Container Terminal.
\ianboyle.
}\label{everuberty}
}
When the container ship in \figref{everuberty}\index{container ship}
transports 50\,000 tons of cargo a distance of 10\,000\,km, it
achieves 500\,million\,\tkm\ of freight transport.
The energy intensity of freight transport by this container ship is
\eccol{0.015\,kWh per {\tkm}}.\nlabel{everuberEff}
In 2002, 560 million {\tonne}s of freight passed through British ports.
The Tyndall Centre calculated that Britain's share of the energy cost
of international \ind{shipping}
is {\Red{4\,kWh/d per person}}.
\section*{}
Total global dwt: 828.845 million in 2002
(Maritime Statistics, 2002 DfT)
\section*{}
{\nqs{ The energy intensity of freight transport by this container ship is
0.015\,kWh per {ton}-km}.}
The {\em Ever Uberty\/}
-- length 285\,m, breadth 40\,m --
has a capacity of
% 5364 TEUs?? (accroding to another website)
4948\,\ind{TEU}s, deadweight 63\,000\,t, and a
% gross tonnage 69\,000\,t, << THIS IS NOT A MASS
service speed of 25\,knots; its engine's normal delivered
power is 44\,MW\@.
One TEU is the size of a small 20-foot
container -- about 40\,m$^3$. Most
containers you see today are 40-foot
containers with a size of 2\,TEU\@.
A 40-foot container weighs 4\,tons and can carry
26\,tons of stuff.
% its engine is MITSUBISHI-SULZER
% "12RTA84C-UG" 49MW
%12RTA84C-UG, which can develop
%43,740kW at NCR (48,600kW at
%MCR). Service speed is about 25 knots.
% Normal continuous rating,
% Ship freight:
% was that 44MW delivered or consumed?
%4948\,TEU transported at 25\,knots by Ever Uberty's 44\,MW engine.
%Assume it is 50\% efficient.
%1 TEU is 13 tons.
% Gross tonnage 69\,000\,t.
% Actual mass transported $13 \times 4948 = 64324$\,t.
Assuming its engine is 50\%-efficient, this ship's energy consumption works out to
{0.015\,kWh of chemical energy per {\ton}-km}.
% ((44 000 kW) / 64 324) / (25 knots) = 0.0147740186 kWh per km
% http://www.mhi.co.jp/en/products/detail/container_ship_ever_uberty.html
\myurlb{www.mhi.co.jp/en/products/detail/container_ship_ever_uberty.html}{http://www.mhi.co.jp/en/products/detail/container_ship_ever_uberty.html}
Further info:
Number of tanks
Ballast: 24
Fuel oil: 17
Lubricating oil: 10
Slop: 4
Fresh water: 4
Diesel oil: 4
Sludge: 1
Potable water: 1
Waste water: 1
Tank capacities
Ballast: 23,662 t
Bunker: 9,124 t
Freshwater: 481 t
Fuel oil: 8,538.02 t / 9083 m³
% source: http://www.scheepvaartwest.be/pagina269.html
length 268,00 m between perpendiculars
beam 40,00 m over all
max draught 12.70 m
freeboard 11.500 m
depth (ie sum of draught and freeboard) 24.20 m
25 knots.
5364 TEU
or
4291 ``at 14t''
world fleet container ships
http://www.container-transportation.com/container-ships.html
4670 purpose-built box vessels, with total capacity of 12.2 million TEUs. The number increased to about 13.7 million TEUs in January 2010. Detail about the vessel number of each capacity range are shown in the following table.
Size range (TEU)
Vessel number
Total capacity (TEU)
0-499
384
124.000
500-999
823
610.000
1000-1999
1261
1.780.000
2000-2999
725
1.839.000
3000-3999
332
1.142.000
4000-4999
451
1.978.000
5000-5999
286
1.575.000
6000-6999
172
1.119.000
7000-7999
29
213.000
over 8000
198
1.757.000
%\item[\npageref{IntlShip}]
{\nqs{Britain's share of international \ind{shipping}\ldots}}
Source: \citet{Tyndallt3.24}.
%\item[\pageref{freight458}] {\nqs{\Figref{freight458}}}.
{\bf Energy consumptions of ships.}
The five points in the figure are a container ship (46\,km/h),
% 25\,knots),
a dry cargo vessel (24\,km/h), an oil tanker (29\,km/h),
% 15.5\,knots),
an inland marine ship (24\,km/h), and the NS Savannah (39\,km/h).
% To set the scale of ship sizes,
% a Panamax -- the largest ship
% able to get through the Panama Canal
% -- typically has a displacement of 65\,000 \tons.
% The new aircraft carrier being built in the UK also weighs 65\,000 \tons.
\begin{description}
\item[Dry cargo vessel]
0.08\,kWh/\tkm.
A vessel with a
grain capacity of 5200\,m$^3$ carries
3360 deadweight \tonnes. (Deadweight tonnage is the
mass of cargo that the ship can carry.)
% Dry cargo vessel, optimized for fuel consumption:
% 3360\,dwt.
% Length: 91\,m, breadth 14\,m, draught: 5\,m.
% , gross tonnage 2460\,t. This is not the displacement!!
It travels at speed 13\,kn (24 km/h); its
one engine with 2\,MW delivered power
consumes 186\,g of fuel-oil
per kWh of delivered energy (42\% efficiency).
\myurlb{conoship.com/uk/vessels/detailed/page7.htm}{http://conoship.com/uk/vessels/detailed/page7.htm}
% Just one engine.
% Onboard power supply: 300\,kW.
% Emergency power: 70\,kW diesel.
%
% Oil is about 46\,GJ/{\tonne}, which is 13\,kWh/kg.
% So 186\,g/kWh is 2.4\,kWh per kWh (or 42\% efficiency).
%
% OK, this can go in my freight chapter:
% Energy per cargo-distance (counting the power of the main engine alone)
% is
% (ignoring the engine efficiency) 2000\,kWh/2460\,t/24\,km = 0.034\,kWh/tkm
% 2.4 $\times$ 2000\,kWh/2460\,t/24\,km = 0.08\,kWh/tkm.
%% 0.0805
% If we include the onboard power supply, assumed to be going at
% 150\,kW on average, as part of the power cost too,
% we get 7.5\% more cost, or 0.087.
\item[Oil tanker]
%
% One
A modern oil tanker
uses 0.017\,kWh/\tkm\
\tinyurl{6lbrab}{http://www.lindenau-shipyard.de/pages/newsb.html}.
Cargo weight 40\,000 t.
Capacity: 47\,000\,m$^3$.
Main engine: 11.2\,MW maximum delivered power.
Speed at 8.2\,MW: 15.5\,kn (29\,km/h).
%% 28.7
% Length 188\,m, width 32\,m. Draught: 10\,m.
% Marine engine efficiencies are about 42\%.
% What's its transport efficiency?
% Crude oil is 1192 litres per {\tonne}, so yes, it takes 40\,000
% {\tonne}s at 29\,km/h, using 8.2\,MW. Express that as a loss
% per 1000\,km: the energy of the
% fuel required to transport 40\,000 {\tonne}s a distance of 1000\,km is
% 2.4 $\times \frac{1000 \km}{29 \km/\h} \times 8200\,\kW$
% = 680\,000\,kWh.
% (The factor of 2.4 accounts for engine efficiency.)
% (This is 0.017\,kWh/tkm.)
The energy contained in the oil cargo is
% 13\,kWh/kg $\times 40\times 10^{6}\,\kg =
$520$ million $\kWh$.
% So that's a loss of
%\[
%\frac{ 680\,000 }{ 520\times 10^{6} } = 0.0013 \,\mbox{per 1000\,km}.
%\]
% Roughly one thousandth per 1000\,km means that roughly
So
1\% of the energy in the oil is used in transporting the oil one-quarter of the way
round the earth (10\,000\,km).
\item[Roll-on, roll-off carriers]
% 13 kWh chemical energy per kg
% 0.013 kWh chemical energy per g 77g fuel per kWh chemical
The ships of Wilh.\ Wilhelmsen
shipping company
% especially roll-on, roll-off carriers)
% use 150\,g/kWh (fuel), and emit 468\,g/kWh (\COO).
%% fuel consumed was 395,703 t, COO emitted was 1,232,990, from 25 ships in 2006.
%% check: pr 395703/18.0 * 44 1,000,000
%% check: pr 150/18.0 * 44 367
%% inconsistency might be because the emissions include auxiliary engines.
%%
% Their \COO\ emissions per tkm range from 10\,g/t-km
% for the oldest ships
% to 5.5\,g/t-km.
% 5.5 / 468 = 0.011752 kWh delivered per t-km mult by 2.4
% ok so 5.5-10 means 0.028 to 0.05 kWh per t-km
deliver freight-transport with an energy cost between 0.028 and 0.05\,kWh/t-km
\tinyurl{5ctx4k}{http://www.wilhelmsen.com/SiteCollectionDocuments/WW_Miljorapport_engelsk.pdf}.
\end{description}
%% C5A Wingspan: 222 ft 9 in (67.89 m)
%% Empty weight: 380,000 lb (172,370 kg)
\newcommand{\kitefig}[1]{%
\begin{center}
\mbox{\epsfxsize=50mm\epsfbox{figs/kite#1.eps}}
\end{center}
}
\newcommand{\kitefigb}[1]{%
\begin{center}
\mbox{\epsfxsize=85mm\epsfbox{figs/kite#1.eps}}
\end{center}
}
\newcommand{\kitefigc}[1]{%
\begin{center}
\mbox{\epsfxsize=75mm\epsfbox{figs/kite#1.eps}}
\end{center}
}
\subsubsection{Kites and method 2}
Let's make clear how everything is oriented:
the wing of the kite would circle round
rather like one blade of a standard windmill, in a circle
that's face-on to the wind.
\begin{figure}[h]\figuremargin{
\kitefigb{side}
}{
\caption[a]{Method 2: Side view of a kite extracting power by pulling
on a string while twizzling gradually downwind.}\label{kfigside}
}
\end{figure}
\Figref{kfigside} shows a side view, when the kite has just passed
12 o'clock.
I haven't discussed the details of how to reel a real kite back in.
In practice, the trajectory followed by the kite would not have
to be circular.
\subsubsection{Kites and method 1}
There is another way of extracting power from a
kite, analogous to the {\em{horizontal}\/} load on the glider
in the updraft.
In a standard wind turbine, this load, which acts in a direction
opposite to the wing's velocity,
is supplied by
torque from the generator in the hub of the wind turbine.
In the case of a kite, a load opposite to the wing's velocity
could be supplied by attaching to the
wing a little wind turbine that generates power from the large apparent
wind generated by the rapid motion of the kite through the air.
\begin{figure}[h]\figuremargin{
\kitefigc{side2}
}{
\caption[a]{Method 1: Side view of a kite extracting power by twizzling
in a circle, and generating power with an on-board mini-turbine.}\label{kfigside2}
}
\end{figure}
\Figref{kfigside2} shows a side view, when the kite has just passed
12 o'clock.
The kite now perpetually moves in a circle.
The miniturbine mounted on the kite does
not need to be super-big. The speed of the kite is perhaps
ten times the windspeed, and power of a turbine
scales as speed cubed times area,
so the frontal area of the miniturbine can be one thousand times
smaller than that of an equivalent standard wind turbine;
% area v**3 = power
as a ballpark figure, the diameter of the miniturbine might be
about one thirtieth of the kite's length.
I haven't quantified
this cartoon of how kite power could work.
The aim of this qualitative description is to give a feel
for the kite power options, so that it becomes plausible that
the power-extraction limits for kite power
are much the same as the limits for standard wind turbines.
\citeasnoun{MilesLoyd} describes an idealized model under which both
kite power methods -- drag power production and lift power production --
produce, when optimized,
the same power from a kite with a given lift-to-drag ratio.
The power from a single kite increases as the square of the
lift-to-drag ratio.
Under this idealized model,
%\myquote{
``a kite the size of the C-5A [an enormous military
transport plane]
with a wing area of 576\,m$^2$
\ldots\ would produce 22\,MW in a 10-m/s wind''
% }{
\citeasnoun{MilesLoyd}.
% }
A quantitative discussion for method 1
would have to describe how the weight of realistic on-board
miniturbines is supported; and would account for the efficiency of those
miniturbines, which presumably dissipate in turbulence
some of the energy harvested by
the kite.
A quantitative discussion for method 2
would work out the optimum speed for
the kite to move downwind (\citeasnoun{MilesLoyd}
% Saul said
says it's $v_{\rm wind}/3$);
and would specify in more detail how the kite is reeled back in.
For both methods, a quantitative discussion would need to
keep an eye on the drag force associated with the rapid motion of
the piece of string through the air.
\citeasnoun{MilesLoyd} describes results from
a detailed realistic model of drag power production.
A kite the size of the C-5A, on a 400\,m tether,
would produce 6.7\,MW in a 10\,m/s wind.
The tension in the tether would be
up to 3.2\,MN.
\section{Other applications}
\subsection{Tide}
Saul pointed out that the same kite-power methods could be
applied to tidal power also, using underwater kites.
With method 2, the whole power generation part of the system
could be located in the dry, on board an anchored barge.