Did I finally come up withe use for electric drives?

Discussion in 'Hybrid' started by Stumble, Mar 17, 2015.

  1. powerabout
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    powerabout Senior Member

    Yep sounds good to me and maybe save some fuel if you can run the bow one on the gen set
    Similar concept is done with some offshore vessel when on stanby away from anything
    the house gen set runs a single azi
     
  2. Powerconversion
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    Powerconversion Junior Member

    For PSV i mostly disagree about the design of fully dieselelectric design.
    Two diesels with shaftgens and dieselelectric (frequency controlled) bow and stern thrusters would be my selected choice.
    Worst green profile design I ever seen was an PSV with frequency controlled mainprops while thrusters was star/delta starters.
    Meaning they would have 10% + losses between genset and propeller during transit and they would run tunnel thrusters at fixed RPM during DP operation (min 130kW) instead of 0RPM and just a few kW.
     
  3. powerabout
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    powerabout Senior Member

    most reliable is shaft gens I agree but they suck fuel as you must have your 2 large propulsion engines running with no load so that design is ancient history.

    99% of PSV are now built Full DE with stern azi so only 4 thrusters to make Dp2 and 4 or more gen sets each being smaller then the old ME shaft gen story so way cheaper to operate.
    Some are going DC bus so that saves even more fuel as you can run variable speed gen sets.
    Now add LNG powered engines and they are clean and use less fuel
    You will start to see some oil fields say no more MGO and LNG only
     
  4. Powerconversion
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    Powerconversion Junior Member

    DC bus and variable speed has 3 disadvantages. 1 is that you need customized generators to maintain an high frequency before the rectifier in order to keep an stable DC voltage. 2 you need complex controlls, and the bigest of all is that you can't have as quick ramps anymore since you need to increase the RPM's on the diesels before you can increase power-output on propellers and this can only be overcome by introducing battery's to take care of transient need's. Battery's introduce more weigh, more losses, more control's and less payload.
    Taking PSV's as an reference is not really a good idea, we have to remember they 99% get there fuel for free from the charterer so they don't really care for other than maintenance cost and keeping an "green" profile to be attractive on the market of political correctness.

    If you where going to sail 6-12 hours out to sea what would be most economical? drives with Generator sets or conventional propulsion?
    It's an reason why tankers and container vessels don't use diesel electric, it's an reason DP vessels use it, but PSV's are a streetmix and I disagree about making them fully DE.
     
  5. powerabout
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    powerabout Senior Member

    every one agrees shaft drive is the most efficient way to convert diesel to prop thrust

    You might disagree with making a PSV full DE but the industry doesnt

    The client has always looked at the fuel consumption and when bidding for jobs old fashioned design doesn't get hired especially now that there are at least 4 boats for every job worldwide.
    Perhaps if your PSV has very long passage to make and very little standby then they might look at older designs but pollution regs still push them out.
    Vessel maintenance is a cost to the vessel owner so the less fuel you use the less there is. More importantly less fuel is less pollution.
    Smaller engines are cheaper and faster to rebuild and perhaps you can continue working while doing a rebuild, something you cant do if you only have 2 large engines and you are also off hire.
    Siemans or ABB I forget which has several vessels out there with 3.5mw batteries in them. Space and weight is not now an issue because you cant have double bottom tanks so ballast cavity. The battery / capacitor is something the DP industry is looking for hence there is money being spent in it.
    DC is spreading, I'd say many of the new vessels on the drawing board today will be DC

    http://worldmaritimenews.com/archiv...supply-first-ever-dc-power-grid-on-board-psv/
     
  6. Powerconversion
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    Powerconversion Junior Member

    I been involved with delivering diesel electric where we measured 20% loss from diesel to prop. Still got a job. You will need to look a real long time to find a old shaftgen design with same level of losses. There is established a "truth" in the industry that DE is better withour any case by case study.
    Fuel consumption and maintenance don't necessary go hand in hand, but an DE system can use powermodes withch enable the drive to controll torque and rpm to maintain a fixed power eliminating power variations on the generatorsets reducing mechanical stress.
    Siemens has it's bludrive+ system and originaly it did not involve battery. It was added later when they found out that they could not keep good enough ramprates on thrusters when demands where changing. Most supply vessels are on DP under the rig for 20min or less and are using 6-10hours to get out to the rig where they will deliver it's load.
    Most advanced stuff I been involved with was an anchorhauler that had conventional engines but with PTO/PTI so it could supply the vessel with SG's during transitt, clutch out the engines and running DE during DP operation and run DE and mainengines into the prop same time if need of all the 40 000hp it had. I see this as the untimate system, but such a pricetag.
     
  7. powerabout
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    powerabout Senior Member

    that AHTS sounds nice as best of both worlds
    20% loss from prop to engine is not the argument and not the design brief, its the fuel consumption of a medium speed say 3-4mw diesel with a tiny prop load versus an engine working at best load for the prop load.
    Lets talk DSV, under the rig for sometimes months
    Having worked boats and rigs, it does happen a drop and go but most along side jobs go for hours, many over night and then you are on standby for days trashing your ME running them at idle load.
    What percentage are you under way...10% or less of the vessel life?
    So where is fuel consumption the most important?
     
  8. Powerconversion
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    Powerconversion Junior Member

    A pure PSV is not on standby for days. Often they are not equiped with Fi-Fi or have high rescue class for high number of people. A multi role vessel equiped for ROV operations or similar should have DE. A pure PSV are much more than 10% of vessel life under transit and even if it did it would run much higher loads during that period of it's life than it would during DP operations. Maybe using 4000kW during transit and maybe 300kW during DP if weathers where calm and 1500kW if rough. While charters where high I did see an tendency to make PSV's DE for the lowest cost possible and using fake clamins like nice Cosphi if using AFE. It's a lot of gimmick out there witch don't really work.
     

  9. Powerconversion
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    Powerconversion Junior Member

    Have a cutout from side view where u can see the general arrangement.
    Sadly no single-line diagram.
     
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