Diesel/Electric Propulsion System Design - Have your say!

Discussion in 'Hybrid' started by CatBuilder, Sep 11, 2011.

  1. goboatingnow
    Joined: Oct 2008
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    goboatingnow Junior Member

    CatBuilder, good to see you're open to new ideas.!!

    In fairness, given all your requirements, especially commercial use, You will not be fitting diesel electric to that cat, anytime soon
  2. CatBuilder

    CatBuilder Previous Member

    Which is precisely why I am exploring using a large diesel generator and industrial electric motors. You get way more than 2000 hours from them and they power air conditioners and electric heaters with ease.

    Now you see the logic.

  3. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Gee...Does a Cat need two engines ?
  4. CatBuilder

    CatBuilder Previous Member

    Huh? This post makes very little sense. Care to elaborate?
  5. CatBuilder

    CatBuilder Previous Member

    No. It doesn't need two engines most of the time. Docking is when two engines are handy. What are you getting at?
  6. keysdisease
    Joined: Mar 2006
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    keysdisease Senior Member

    LOL, No.

    There are several configurations where Cats are powereed by a centerline engine like the Prout Snowgoose pictured in one of my previous posts this thread.

    On the McGregor 36 Cats they were supplied with one ourboard bracket on one hull only. This actually worked pretty good in most conditions, but that was on a light 36ft trampoline boat.

    There have been single engined boats with a hydraulic drive in the "other" hull and even single engined boats with hydraulic drives in both hulls and the engine amidships in one hull.

    They don't HAVE to have two, but IMHO there's just something wrong about them not having two.


  7. michael pierzga
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    michael pierzga Senior Member

    so a robust engine in one hull and a robust generator in the other hull would work ? The boat would motor in a straight line ?
  8. CatBuilder

    CatBuilder Previous Member

    Yes, that works just fine, but it is fairly important to have that second prop available for docking. Catamarans (especially 45' catamarans with a big deck house) have a lot of windage. They twist up easily when approaching a dock. You need that second prop to keep things in order when docking.

    If we go for a pair of 30HP diesel engines (which I am also open to), how will we retract the props? Also, how can I fit a big generator head to one of them as well? Any ideas there?

    See... I'm not after any particular system. I'm after a reliable setup that can do the following:

    1) Lift props from the water when sailing
    2) Generate about 8-10KW (10-12KVA) of power for house loads
    3) One prop on each hull (for docking, which is frequent and in any weather with charters)
    4) Reasonable weight to keep sailing performance

    also... nice to have...

    a) Entire boat runs on diesel

    There are several ways to achieve this, so please do not be shy about suggesting ideas. I have no problem with a pair of diesels with retractable running gear and a 10KW generator head attached to one of the engines. If anyone know how to do this, please feel free to hop in.

    Electric motors with a large generator seemed to be the most simple way to achieve these design parameters. It's the retractable drives (first priority) that is the most difficult to solve.
  9. masalai
    Joined: Oct 2007
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    Location: cruising, Australia

    masalai masalai

    Hi CatBuilder,
    Maybe there is a need to refresh a bit as distractions seem to be creeping in like single engines in a pod (passable option sometimes in a sub 36 ft cat but NOT above that or in a regularly docking in differing weather conditions, big cat...

    a) how big is your CHARTER CAT?
    LOA= ??
    BEAM OA = ??
    Displacement in KG or lbs = ??

    I agree in the choice of diesel engine (Kubota) ... (NOT Common-rail - as that is dependant on high quality fuel)

    High thrust-4-stroke petrol outboards mean simplified installation, quiet running, BUT risk of propeller-aeration?

    Do your management sums and calculate the size of the genset for domestic needs and the size of the battery bank to meet the inverter loads for that - a tedious process but VERY NECESSARY...
    A 24V system may suffice for domestic, Nav & ships functions and then install a battery charger only using something like 24V delco alternators (I have a pail running of a small Kubota via belts (6000KVA = 30v & 200A) and regulators to control the voltage to the AGM batteries... or look at the options from the likes of http://www.christieengineering.com.au/Products.asp?PCat=Diesel battery chargers

    I went for 6v batteries in my bank - Should have gone for 2 volt single cells... http://www.batteriesdirect.com.au/shop/product/10148/gpl-l16-2v.html or here http://www.energymatters.com.au/deep-cycle-batteries-2v-batteries-c-153_204.html connection in series is far easier to manage than the complexities to maximise efficiency in multiple parallel banks... I use the 'Plasmatronics PL60' charge regulators...
  10. CatBuilder

    CatBuilder Previous Member

    Thank you, Masalai.

    Sorry for the distracted post. I tend to keep my mind very open during the problems solving process, then try to narrow down dozens of ideas via logic/facts/math toward the end. I was just in the "frenzy" stage of thinking and allowing any and all ideas in that can't immediately be rejected.

    I have done quite a bit of reading and conversing this afternoon with people. Does anyone have any input on this particular pod type? I think it is the same one used by Gideon of Green eMotion. It's Dutch and so is he:


    These pods are slightly under powered for my taste, but at 10KW each, they should do the trick.

    To answer your questions, my cat's dimensions can be found at the following link. It is more simple for those who need to know the size/displacement to see the link as it's in both english and metric units:


    Yes, I agree with you about outboard propellor aeration and also... much worse... total immersion of the outboards while in operation, with loss of propulsion. Not good. These reasons, along with the poor thrust of outboards in general and use of gasoline are some of the many reasons I wanted to explore the diesel/electric route.

    Outboards and a large generator are my backup plan if the electric system cannot be reasoned out.

    I have done many electric systems (all successfully) and have found that in the case where you plan the system to run 4KW/hr of heaters or 4KW/hr of air conditioning, or 4KW/hr for your electric range and refrigerator, you really don't need to plan out much else, other than battery bank size you would like to use to run those loads - or if you prefer to run them off the generator directly.

    The rest of the power demands are trivial and are used along with the 4KW/hr load. You just round up to 5KW/hr and that takes care of everything you would use on DC in a day (indoor lights, nav lights, instruments, etc..) So for this discussion, it's not entirely necessary to go through the whole tallying of DC loads and such at this point.

    So, we are talking 10KW pods (a little under powered) or 12KW motors powered by a 21-24KW generator. Generator is on 100% of the time when motoring and feeds the controllers which feed the electric motors. Generator has capacity for both motors, though you can turn one off and divert that extra power over to the house bank battery charger, or you can enjoy the reduced fuel consumption from 1.7 liters at full load for a 21KW Kuboda genset down to a little under a gallon an hour on half load.

    The secret here is flexibility. I can do whatever I want with all that power. Use it to drive the boat directly, or divert it to battery charging, or run all the air conditioners and heaters and electric stove all at the same time.

  11. pdwiley
    Joined: Jun 2008
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    pdwiley Senior Member

    You can get diesel outboards. Heavy & expensive however.

    I have seen a generator that mounted between a Yanmar engine and its g/box basically extending the engine footprint by 300mm (I think). Not sure what kW rating the go to however.

    The jet drive is something to look at. We used to operate 2 6 tonne displacement work boats. The first one we fitted with twin o/boards. The second we fitted with twin 225HP diesels driving Hamilton jet drives. This one used less fuel by far and was more manoeuverable plus nothing to hit stuff (we were operating the boats in broken ice).

    Rotating the drive leg for any propellor drive to get it out of the water is going to be an issue if you go that way. The sideways swivelling unit strikes me as having the minimal hassle WRT alignment/thrust. Stern drive legs are proven technology but unless you mount them right aft, what do you allow them to retract into and how do you service them? There's a few things I can think of but not sure if I'd want to go there. If you do mount them right aft then they'll come out of the water a lot more frequently in any sort of sea.

    I agree with you WRT robustness of the AC alternator-VFD-electric motor setup. Provided it stays dry or can survive immersion these systems have proven uptime measured in years in harsh industrial environments.

    Designing systems is such fun. Which set of compromises do you live with?

  12. keysdisease
    Joined: Mar 2006
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    keysdisease Senior Member

    This used to be fairly common in trawlers, either a belt driven or off the PTO generator unit to run house current while underway. The downside was you had to run at a fixed RPM which was determined by the pulley sizes or the PTO gearing.


  13. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    Dunno yet if it's feasible but I'm pondering if I can mount a generator at the other end if the engine. Bolting a CV-joint btw them.. makes changing a new belt a bit more complex but not too much..
  14. CatBuilder

    CatBuilder Previous Member

    I do know that engines come with specifications regarding loads off the front end that you cannot exceed without destroying the engine. Be careful here. Those loads are too small to run much more than a very larger alternator and water pump. A real generator head has to be run from the normal output shaft.


  15. masalai
    Joined: Oct 2007
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    Location: cruising, Australia

    masalai masalai

    Is it too late to consider chamfers? See "edited" image attached (image 1)

    I looked at those pods early in my planning, they looked to be the best engineered and openness in information at the time, but I could not justify cost and I was looking to have lifting legs, and no one I knew in Australia, at the time was interested in working on such and the importation cost also made life quite difficult in the case of a need to sort some things out... Worry about sealing and ingress of sea water which will kill any prospect of powered movement immediately there is a leak :eek:

    The aft end of those 'chamfers' would give you a start place to mount sonic electric outboard legs (LOOONG shaft option) and swing it sideways under the aft end of the bridge-deck on a long composits/SS shaft parallel to the fore / aft line of the hulls onto which the leg is clamped (the leg will be NON STEERING)... Your enthusiasm for redundancy would lead me to suggest an EQUAL pair of gensets, where each one would give you minimum cruising speed on both for manoeuvring, and slightly better speed with all the power sent to one leg when passage-making...

    There seems to be a thrust (torque limit?) on those sonic drive legs.... so you may have to go for something else that is more robustly mounted to give more than 10kg/metre (whatever that means) and I do not think it means lots of push for the boat - ie minimal power/thrust... It is these sort of questions that left me with diesel saildrives... (My hull is not the best for shaft drive) as per image of the Chamberlin C10 (image 2) - that is the hull-shape which I desired... http://www.catchcryhamm.com/?q=node/20 His design "Foreign Affair" is almost perfect for long distance motoring... But a little too big for me... (image #4)

    My Kubota 21hp as a genset with a pair of Delco 24V alternators for 6000KVA max... (Not now used but in reserve for the house supply when on land...) (image 3)

    Attached Files:

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