8/17/2019 SSicdh 2016

1/19

5/13/20

Slow steaming

Source MAN

Since beginning of the worldwide shipping crisis mostshipowners tried to keep ships in operation because this has

been proven better than lay off. To achieve this many of them

especially for container ships has decreased the ship speed and

derated the engine power. To reduce the speed of a

containership from f.e. 25 kn down to 18 kn the power demand

of a fixed propeller decreases down to about 30% of nominal

power, a power range which will be very sensitive for slow speed

2-stroke engines and can be only managed by special additional

measures also for ship new buildings.

 A common problem occur because of the over proportional

decreasing of the charge air pressure, which leads to a lack of

air and especially for slow speed 2 stroke engines in the range

of 60% to 40% engine power to increasing temperatures of

exhaust gas and on combustion chamber components and

below 40% engine power to a continuous need of running the

auxiliary blowers. Both results are not wanted.

Slow steaming

8/17/2019 SSicdh 2016

2/19

5/13/20

Some researches for fast container ships 5 years ago found outthat the most economical ship speed seems to be 50% of the

nominal ship speed, i.e. for about 10% of MCR. But also it has

been stated that as lower the fuel prize as higher the most

economocal ship speed. That means that for the current fuel

prizes the optimal speed will be higher than 50%. But generally

the engine maker have given the permission for new modern 2

stroke engines for continuous operation down to 10% of nominal

engine power but for the operation range below 60% they require

special measures. Until now there is no strict definition of „slow

steaming” and so called “Super slow steaming”. But it seems to

be common sense that propulsion power below 60% of MCR

means low load or slow steaming and power below 30% MCR

“superslow steaming”

Slow steaming

Generally following problems can occur for l ow load operation:

Main engine

Decreasing of turbocharger efficiency and significant drop of charge air

pressureIncreased E-consumption because of increased or continuous operation ofauxiliary blowers (2 stroke)

Malfunction of auxiliary blowers respective e-motors, broken ventilator fansSticking of piston rings, fouling, coking of piston top land

Fouling of air receivers (back flow)Malfunction of no-return valves or flaps in air receiver (2 stroke engines)

Soot fire in exhaust receiversHot corrosion in the range of 40 to 60% engine power on exhaust valves,piston etc. (2 stroke)

Low temperature corrosion on combustion chamber components like valves,piston rings, cylinder liner below 20 to 40% load

Increased cylinder oil consumption and overlubricating (2 stroke)Limitation by barred range because of torsional or axial vibrations (2 stroke)

Slow steaming

8/17/2019 SSicdh 2016

3/19

5/13/20

 Auxi li aries

Increased load of auxiliary engines (2 stroke)Decreased fresh water generation by engine cooling water (partly)

Low temperature corrosion in exhaust gas boilers (partly)Soot formation and fire in exhaust gas boilers

Decreased and too low steam production in exhaust gas boilers (partly)Ship

Decreased propeller efficiencyFouling of propeller and ship hullLubrication losses in aft end propeller shaft bearings

Many of these deficiencies can be compensated by operationalmeasures. But effects caused by propulsion engines charge air

pressure can only be deleted or reduced by measures and changes onthe turbocharger systems. Here has to be divided between long time ortime limited measures.

Slow steaming

Long time measures are the selection of smaler enginesbecause of less investment expenses or derating of engines for

significant reduction of fuel consumption. Less fuel consumption

can also be achieved by installing smaler or less numbers of

turbochargers and if possible by the adaption of charge air

cooler, compression ratio, injection and valve timing and exhaust

gas boilers.

Reduction of fuel oil consumption can also be achieved by time

limited measures but this can be not done on all engines and

causes normally higher specific fuel consumption at higher ship

speed. These measures can be easier carried out at electronicalcontrolled engines by optimizing valve and injection timing.

8/17/2019 SSicdh 2016

4/19

5/13/20

Further on the use of turbocharger turbines with variable

geometry (i.e. variable nozzle ring blades) will be possible or

cut off of one or two turbochargers if more are installed. This

can also be achieved by a sequential (register) turbochargingwith two different sizes of turbochargers, if one turbocharger

can be switched off. Important in this case will be that the cut

off turbochargers will be turned and lubricated. Possible is also

an installation of an exhaust bypass or alternatively an

installation of a power turbine which can be operated at higher

than 85% load.

 All mentioned measures have impact on the IMO NOx

certificate and must be certified separately.

Slow

steaming

Source Wärtsilä

8/17/2019 SSicdh 2016

5/19

5/13/20

Engine Designers revised Low Load Bulletins

Slow

steaming

Source Wärtsilä

Slow Steaming

8/17/2019 SSicdh 2016

6/19

5/13/20

Slow Steaming

Slow Steaming

8/17/2019 SSicdh 2016

7/19

5/13/20

Slow Steaming

Slow Steaming

8/17/2019 SSicdh 2016

8/19

5/13/20

0

20

40

60

80

100

120

140

6 8 10 12 14 16 18 20 22 24

Expenses(US$/nm)

speed v (kn)

Expenses US$/nm = f ( v; SFOC)

fuel cost

charter cost

total expenses

Slow

steaming

Source MAN

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

speedfuel/nm

fuel/h

Load

Speed and Fuel Consum ption / nm as a Function of Engine Load and SFOCand fuel Consumption / h as a Function of Load and Load & SFOC

speed

fuel/nm

Fuel = f ( Load)

Fuel = f ( Load ; SFOC)

Source MAN

Slow

steaming

8/17/2019 SSicdh 2016

9/19

5/13/20

The graph shows the operationalvariable costs given a surpluscapacity exist in the actual fleet.

I.e. reduction of schedule speedresult in no additional capital costor additional charter party cost.

Container vessels have the mosteconomical speed at ~50%speed which equivalents ~10%engine load.

To obtain full flexibility underthese conditions, the vesselsmust be able to operate from10% engine load to full load

without any restrictions.

Costs per Nautical mile as function of vessel speed

0,0

20,0

40,0

60,0

80,0

100,0

120,0

140,0

0,0 5,0 10,0 15,0 20,0 25,0

Vessel speed

    U     S    D

ME FO Cost

Cyl LO cost

Fixed cost per nm

DG FO Cost

FO cost per nm for TC cleaning

Additional DG FOCost low load

OFB FO Cost lowload

Total Cost

Costs per Nautical mile as function of ME load

0,0

20,0

40,0

60,0

80,0

100,0

120,0

140,0

0 20 40 60 80

ME Load Percent at constant load

    U     S    D

ME FO Cost

Cyl LO cost

Fixed cost per nm

DG FO Cost

FO cost per nm for TC cleaning

Additional DG FOCost low loadOFB FO Cost lowloadTotal Cost

Slow

steaming

Source MaerskOFB Oil Fired Boiler 

Long term load< 10 %

?

Not recommended

(means load < 40 %) NO

 A

contamination of 

exhaust gas system

Slide Valves

(100 T€ for 8S70MCC)?

NO

Long term load>= 40 %

?Do nothing, recommended:Slide Fuel ValvesMonitor gas ways

YES

(means 2-stroke) NO

Main Engine4-stroke

?

< 25 %: Switch to MDO Temporary Load-ups Retrofit recomm.: 2-st charge air cooler  TC-Modification

YES

Radical De-ratingby cylinder cut out

YES

•Temporary load ups

for cleaning gas ways• Frequent TC-Cleaning

(means load between 10 and 40%) NO

• Over-lubrication

• Bore polishing• Piston ring blow by• Scavenge fires

YES

YES

NOLoad dependantLubrication (200 T€)

Slow steaming

8/17/2019 SSicdh 2016

10/19

5/13/20

OneTurbocharger 

?

YES NO (means 2 -4 Turbochargers)

 A

Max Load 40,60,70%(2,3,4,TCs) 125 T€ / ship 1-2 d modific. Time Risk 1 of 2 c ut out:

High thermal load

Flexible LoadDemand

?

Cut out of 1 TC

Installing fixed gate Stocking of TC-Rotor  NOx Measurement Crankcase Bearing calc.NO

Cut out of 1 TC

Installing Swing Gate TC-Rotor in situ External seal air NA NOx Measurement Crankcase Bearing calc

Load option 100 %

250 T€ / ship Risk of TC Bearings fail. Risk 1 of 2 cut out:

High thermal load

YES 1

PTO generator 800Propeller refit 400

External Options

YES

Flexible Load

Demand?

Optimize TC for Part Load

8/17/2019 SSicdh 2016

11/19

5/13/20

Slow

steaming

Source MAN

MC/MC-C engines require 2hrs per day at least 75% load

ME/ME-C engines require 2hrs per week at least 75% load

Load up cycle:

Load up, 10 40% engine load 30 minutes

Load up, 40 75% engine load 60 minutes

Load down 30 minutes

From a cylinder performance point of view load up is NOT necessary.

High load limi t to be evaluated for for turbine and boiler cleaning purposes

Slow steaming

Source MAN

8/17/2019 SSicdh 2016

12/19

5/13/20

Gas channel in the exhaust valve seat

Gas channel in the exhaust valve seat Blades of turbocharger nozzle ring

Fouling of exhaust gas passages

conventional fuel valves

Slow steaming

Slow

steaming

8/17/2019 SSicdh 2016

13/19

5/13/20

Between 30 and 40% load the auxiliary blower may switch

on

and off quite often, which may damage the blower.

Select a different speed range.

Below 30% load the Auxiliary Blower will operate continously.

For continous load the Auxiliary blower is not designed.It could be worn out very quickly.

Have a spare blower on board.

Slow steaming

 Auxiliary blowers failure

Concern:Auxiliary blowers not designed for continuous operation and

prone to failure

Experience: The number of failures experienced in the APMM fleet have

been limited to app 20 cases for 250 vessels/year. The failures are mostly limited to one supplier (HHMCO) and

have generally 2 sources:1. Sealing failure leading to bearing failure and impeller

damage2. Motor damage due to overheating

Counteractions:Keep a set of auxiliary blower motor and impeller on boardDo not run the auxiliary blowers continuously if no spares are

on board

Slow steaming

Source Maersk

8/17/2019 SSicdh 2016

14/19

5/13/20

Cold and hot corrosion

Concern:Cold or hot corrosion of combustion parts due to high and

low exhaust temperatures at lower loads

Experience:Cold corrosion has been seen in a few cases at loads below

20%, when the cooling water temperature has been toolow and the fuel sulphur level high (4%).

Hot corrosion has only been seen on RTA exhaust valveswhen operated at 40% load.

Counteractions1) Keep cooling water temperatures above 90 deg C

(Wärtsilä) and 85 deg C (MAN)2) Adapt the cylinder lube dosage/TBN to the fuel – i.e.

follow MAN Diesel’s guidelines for ACC also on Wärtsiläengines and older MAN engines with HJ lubricators.

3) Use TBN 70 cylinder oils above 1.5% sulphur fuels4) Keep exhaust temperatures below 480 deg C (RTA)

Slow steaming

Source Maersk

Engine load[%]

Seq. TC EGB

SFOC[g/kWh] pscav[bar] SFOC[g/kWh] pscav[bar]

25 -4.2 0.2 -1.8 0.1

50 -4.2 0.5 -4.3 0.2

Concept:

EGB installed

Opened at 70-

100%

Closed at < 70%

The Turbocharger is matched with maximum

Scavenge Air Pressure in Part Load.

If the engine is operated at above the

optimized Part Load, the valve opens and

By-Passes the surplus volume of Exhaust

Gas in order to protect the engine against

too high Scavenge Air Pressure

Slow steaming

Source MAN

Measures of improvement

8/17/2019 SSicdh 2016

15/19

5/13/20

Scavenging air receiver 

Cooler 

Com

p

Exhaust gas receiver 

V1 V2

V3

ME Turbo: DuET concept

Valve operation procedure:

Main engine start-up

1. Main engine start (only large

T/C running). V1, V2, V3: closed

2. Increased engine load (above

75%)

3. Open valve V1→V2 →V3

4. Gradually close V3

5. Both T/C running parallel

6. Increase to 100% loadCom

p

Turb

Slow steaming

Source MAN

Measures of improvement

During slow steaming at about 50% ship speed

Temperature downstream exhaust gas boiler may drop below acid dew

point

2- and 4-stroke main engines offer power reserves up to 90% at this speed

Improvement: Utilize main engine power reserves to increase temperatures by

installation of a PTO generator and stop aux. generators at sea

Slow

steaming Measures of improvement

8/17/2019 SSicdh 2016

16/19

5/13/20

Non planer blade shape

Kappel Tip Fin Propeller 3-5 % efficiency gain

Up to 14% fuel savings

Slow steaming

Source Kappel

Slow steaming

Turbocharger cut off – Bearing load increase at slow steaming

Source MAN

8/17/2019 SSicdh 2016

17/19

5/13/20

Operation with increased scavenging air

pressure at low load and lower engine RPM with 1 turbocharger cut-out has

lately resulted in reports of damaged crosshead bearing shells

Slow steaming

Source MAN

Counter measures by MAN Diesel &Turbo:

Investigate and design upgraded bearings

Make instruction for inspection and assessment of crosshead bearing condition

(Circular letter to owners has been issued)

Recommended immediate actions to ship owners by MAN Diesel &Turbo:

Continue low load operation with Turbocharger Cut-Out

Maintain normal inspection of crankcase for white metal findingsUse of endoscope for additional inspection of bearing condition

(as example during dry docking to determine which bearing to open up)

It is NOT necessary to open up bearings unless findings of white metal fall-out

Slow steaming

Source MAN

8/17/2019 SSicdh 2016

18/19

5/13/20

Higher average exhaust valve temperature may result in hot-corrosion

TBO (Time Between Overhaul) getting reduced

This calls for more frequent inspections when operating at low load continuously

S60MC-C8Running hrs 26.000

Burn away: > 11 mm(max. 9 mm)

Slow steaming

Source MAN

One counter measure:

Jacket cooling water by pass

8K98ME – TC cut-out (one out of two)

Liner Cold Corrosion observed

Slow steaming

Source MAN

8/17/2019 SSicdh 2016

19/19

5/13/20

37< >MAN Diesel & Turbo Dr. T. Greiner   Slow steaming Part 4 Latest MAN experience and actions 07.05.2013

12K98ME/ME-C as 6-cylinder by extreme de-rating

Propeller exchanged. SFOC: Potential 6-8% down

Half of the cylinders dismantled.

(2 out of 4 T.C. are cut out)

Varius levels of re-matching and EGB

(Exhaust Gas By-pass) options

The Radical Slow Steaming Option

2 cylinder engine

converted into

 

SFOC: Potential 10-13% down