ASD vs conventional FPP propeller and rudders for 50+m AHTS tugboat

Discussion in 'Propulsion' started by mabdulhaq, Sep 23, 2010.

  1. mabdulhaq
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    mabdulhaq Junior Member

    Hi,

    50+m AHTS tugboat (towing and cargo handling) is under tendering at present. offers include conventional FPP and rudders with 500HP bow thruster. there are opinions that reducing or even eliminiating bow thruster if we use ASD propulsion with FPP where no rudder is needed and that will give much better maneuverability. we consider CPP completely not suitable for us being so remote from shipyards and proper docks.

    other opinion says that this is true only by small vessel (30m range) otherise in our case achieved maneuverabilty is the same in both propulsion cases esp if the bow thruster with conventional propeller is big enough about 700HP

    any hint what is better from experience, also less maintenance intensive.

    FIFI1 running via PTO from the main engines requires twin disc MCD clutches when using conventional solution...is this the same using ASD with FPP?

    is it not better for maintenance to have fire pumps completely separated from main engines then we do not worry about MCD clutches

    thanks

    Mohamed
     
  2. powerabout
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    powerabout Senior Member

    How much bollard pull are we talking?

    The fire pumps ( if going to be classed as fire vessel) will need the main engine power or you will need enormous electric motors to drive them?

    Re propulsion there's a choice of cheapest to build versus cheapest to operate..whats it going to be?

    If you cant get a slip to fix a cpp how are you going to deal with an ASD?
     
  3. mabdulhaq
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    mabdulhaq Junior Member

    thanks for input

    60 tons bollard pull ahead about 50m long vessel to have big deck area.

    will be classed for towing, supply, FIFI, pollution recovery

    we are in an area where maintenance is a problem, that is why we avoid cpp although we know it is the best for controlling the vessel.

    remaining two options: ASD with FPP, no rudder and small bow thruster or conventional FPP with rudder and big bow thruster.

    ASD with FPP might be better than conventional FPP with rudder with smaller vessels but in bigger vessel 50m + if we add 500 HP bow thruster to the FPP and rudder is this still true??.

    I would go for a higher boat price if then the operating cost will be less with less breakdowns but needed also acceptable manueverability esp. to land people with basket from the FSO to the tug at marginal weather conditions.

    where is the building cost less? and where is the operating cost and maintenance problem less? which is better for manueverability conv. or ASD both with FPP

    thanks

    Mohamed
     
  4. apex1

    apex1 Guest

    It is a bit odd to avoid the CPP in favour of a more complex and much more difficult to repair system.

    The CPP fails at the prop blade, because that is the weakest link in the chain, by design. A single CPP blade can be replaced by divers when need be.

    The CPP saves many tonnes of fuel per day, compared with the two other systems.

    On top of that, the CPP has by far the lowest op. cost. And is close to, or below the FPP with gearbox, in purchase price. The ASD is much more expensive.

    So, when Voith or Schottel are out of discussion, as is here, the CPP is the only one logical and economical choice.

    Regards
    Richard
     
  5. mabdulhaq
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    mabdulhaq Junior Member

    thanks Apex 1.

    it is the first time i hear that CPP requires less maintenance.

    all those to whom I spoke including experienced boat Maters had expressed unhappiness about the maintenance requirements in spite of the fact that CPP provides the best control over the vessel.

    problems with CPP can range to even oil spill from the propeller, this is what I have been told.

    new thing I learnt from you is that the new build cost of CPP is the lowest of all and the ASD is the higest of all.

    any other ideas i would be grateful.

    regards,

    Mohamed
     
  6. apex1

    apex1 Guest

    The entire Scandinavian fishing fleet relies on CPP propulsion exclusively. If there would be ANY problem with them, nobody would buy one. Fishermen have nothing to give away, and they don´t like to spend much on service and maintenance either.
    And they have some really nice conditions up there, with ice, storms and dragging nets in all conditions.

    Pick your choice who might be right!

    Not only is the maneuverabilty much better with a CPP, the fuel efficiency is better too by some multitude.

    Regards
    Richard
     
  7. mabdulhaq
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    mabdulhaq Junior Member

    thanks Richard.

    I believe you.

    i might be getting my advice from people who are too old to cope up with the new types of propulsion systems.

    some of them are pilots dealing with mooring and mooring operations of VLCC/ULCC and Masters of chartered tugboats working for us. they claim that the best thing for this part of the world away from shipyards and dry docks is to stay conventioonal with FPP and rudders. They claim that with CPP if you have a problem you will end up needing to take the tug to a shipyard/dry dock.

    could it be that the situation with fishing boats is different than tugboats used for towing and supply operations???

    thanks for your advice. I appreciate it very much

    Mohamed
     
  8. apex1

    apex1 Guest

    No Mohamed,

    there is nothing new with CPP´s. They are in use for 80 years now.

    The fact that you can easily replace a damaged blade makes them much easier to repair than a damaged FPP. Being far away from yards and service facilities is just another point in favour of the CPP.
    With a gearbox problem you end up in the yard for sure. CPP´s usually have not even a reduction gear on such big installations.

    The working conditions for a fishboat and a tug have quite some similarities.
    Both operate under extremely different conditions with as extremely different power demands. And in both cases, the CPP´s provide a flexibility and fuel efficiency no other propulsion can challenge.
    Therefore one can say, no that is not the reason, they are not wider spread. It is the ignorance and bias which makes them a bit rare.

    Go for it, you will have the best conventional tug in the region. And by far the most economical to operate! And here we are talking about 30% to 50% fuel savings over the year, not pennies. (depends on conditions of course)

    Regards
    Richard

    BTW
    CPP`s don´t require less maintenance, they require zero! The hub is filled with grease which lasts for a decade before it should be replaced. And the actuator is a service free device, apart from a drop of oil here and then. Most are never touched once installed.
    But don´t compare Chinese crap with European CPP systems! (Though I am not aware of Chinese CPP`s)
     
  9. powerabout
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    powerabout Senior Member

    I'm not sure the CPP is nessesarily the best on fuel for that application IF you have fixed speed engines?
    If you want to save fuel and run on one engine when transitting the other cpp is closed so causes massive drag.
    If you are on standby duty at the platform your fixed speed engine at zero pitch is useing plenty of fuel and being killed as it has no load on it.

    You will need to describe what engine/gearbox combinations you have looked at.
    Medium speed or high speed
    Fixed speed or variable/fpp or variable with cpp and combinator electronic controls
    The best for fuel consumption is a 4 engined 2xcpp vessel as standby is now done on one engine, transit on 2 and towing on all 4.
    Will the vessel be DP as well?
    Diesel electric vessels are the cheapest to operate but the more expensive to build yet the payback is very quick, you also get more contracts as you have the lowest overall fuel consumption, cheaper engines, fast to rebuild etc etc so more payback as the years go on
    Voith Schneider do a complete diesel electric package. An 80m dive vessel was just completed here in Singapore with their package
     
  10. apex1

    apex1 Guest

    Why would you have fixed speed engines?

    Why would you fix the pitch for max. drag instead of min. drag? And why would you run on one engine, when running on both is much more economic?

    When you are on stdby your CPP on one engine is the most efficient system you can imagine! And by far the one with the least wear and tear on the machinery.

    Although a D/E system is very efficient and has some merits, it does not outperform the twin engine CPP setup! Let alone the disadvantage on purchase and regular replacement cost.

    Same is valid for you 4 eng. proposal. Nonsense, sorry.

    The question here was obviously for a fairly cheap installation which is easy to operate and maintain, not for additional complications and cost.

    You are not familiar with CPP systems mate!

    Regards
    Richard
     
  11. powerabout
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    powerabout Senior Member

    And you are not familiar with the industry this vessel is in or the job that it will be doing
    You are talking single engined fishing boats with owner operaters watching EGT gauges with full manual CPP controls, non DP etc and there I agree 100% with what you say


    "I would go for a higher boat price if then the operating cost will be less with less breakdowns but needed also acceptable manueverability esp. to land people with basket from the FSO to the tug at marginal weather conditions".
     
  12. powerabout
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    powerabout Senior Member

    mabdulhaq
    One other thing you can do as I know one AHTS vessel operating in Africa and got the job as it was built with azipods ( including bow azi)that can be removed through the deck and hence can be repaired alongside with a crane as there is no dock available in the area.
    Its a common propulsion system you would find on a harbour tug.
    I assume your need a pair of engines about 2500hp?
     
  13. apex1

    apex1 Guest

    Oh you might be surprised, I am familiar with these jobs! You are not! How can you ask for DP when a conventional FPP setup was a possible choice?

    http://www.youtube.com/watch?v=UYRE9zN6Mgc
    I was on board when this shot was made.

    I was not talking fishing boats, I used them as a example. Why should one watch the EGT permanently? You really have NO clue about CPP`s

    And to come back on topic:

    Read the first post again, then we can discuss further.

    Harbour tugs use Shottel drives or Voith Schneider systems, not Azipods!

    Some AHTS have Azipods though. But recommending them as a alternative to FPP or CPP propulsion in as senseless as your D/E recommendation was, because that is just what they are. Another D/E system, but substantially more costly, than the conventional.

    No buddy, you have not understood what Mohamed is looking for, I fear.
     
  14. mabdulhaq
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    mabdulhaq Junior Member

    thanks.

    engines about 2500hp each, total about 5000hp.
    azipods? do you mean azimuth thrusters? is that not the same as ASD and there are L and Z type of them?

    bow thruster will be required in our case as well for sure to come close to the FSO parallel.

    thanks and regards,

    Mohamed
     
    Last edited: Sep 24, 2010

  15. mabdulhaq
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    mabdulhaq Junior Member

    also please elaborate a little more on the Azipod one in Africa and how is it made to be taken out from deck? do you mean that was part of the contract with the builders?

    Mohamed
     
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