Ganging Outboards - Does it work?

Discussion in 'Propulsion' started by CatBuilder, Jan 14, 2012.

  1. WestVanHan
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    WestVanHan Not a Senior Member

    I was going to mention to take the electric vs gas hp ratings with a grain of salt...

    There was a company in Germany had some new ones in crates,and some rebuilt ones but this was a year ago+.Quite a few used/rebuilt ones around.Can chase them down if you like.

    IIRC the 27 hp weighs 160 lbs. and 36 hp about a hundred more.
    The 27s powered a cat to Hawaii 6 mpg with both engines.

    Interesting thing is they are monobloc engines-no head gasket
     
  2. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Ummm, I think, CatBuilder, that you might be confusing power ratings prior to 1983 with more recent ones. My understanding is that gasoline powered outboards, at least those from major manufactuers and using the NMMA/ICOMIA 28-83 standard since 1983, are rated on the power delivered to the prop, not at the engine crankshaft.
     
  3. WestVanHan
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    WestVanHan Not a Senior Member

    I think you're right dc.

    Friends had an 85 hp factory jet outboard,it was the identical engine and tune as a 115. So due to inefficiencies it was rated at 85.
     
  4. CatBuilder

    CatBuilder Previous Member

    If you say so. I am only familiar with the inboard engine calculations of HP at the crankshaft vs the prop shaft. I had assumed the outboards were rated just like the inboards.

    Can anyone explain how the Torqueedos are claiming 9.9 equivalence then with a smaller motor? I'm baffled. Their numbers seem to fit very closely to the inboard numbers.
     
  5. CatBuilder

    CatBuilder Previous Member

    That would be great... the 27's would be plenty. A pair. They don't have parts anymore though, right? So if I blow any part of the motor, it's junk?
     
  6. CatBuilder

    CatBuilder Previous Member

    The other point I should have made earlier about HP ratings between electric and ICE is that with an ICE you need to be at 3600RPMs on a Yanmar inboard or 5000RPM on a Yamaha or Honda outboard to reach rated horsepower.

    This setting on the diesel is rarely achieved. On the gasoline/petrol outboard, 5000RPM is unfortunately, often achieved, leading to shorter engine life.

    Since the torque of the electric motor hits right from 0RPM, you can get full rated torque at the lower prop spin speeds. This means more HP at those speeds than an ICE can deliver. The electric has a flat torque curve, while the ICE has a variable torque curve over the same range of RPMs. The ICE has so little torque (and consequently HP) it will stall if you put a slight load on it at low RPMs.

    This is why we have clutches.

    Since you don't want to operate any motor at full torque rated RPMs for very long (3600 all day on a Yanmar or 5000RPM on an outboard), you are actually comparing very similar HP (or KW) at the normal cruising RPMs due to the higher torque of the electric. I used to cruise my Yanmars at 3200 max RPM. 2800 when I needed to save some fuel and still go fast. At those normal RPMs, an electric motor of 12-15KW is equivalent to the 30HP Yanmar in HP even if we don't take into account all the parasitic losses.

    Power (HP or KW) is torque x angular velocity on the shaft. (well, plus a few other terms in the equation, but that's the main part of concern here)

    Is torque also rated on the prop shaft for ICE outboards? If it's not, maybe that's how Torqueedo came up with the numbers?

    The prop spins at whatever RPMs 5000 is reduced to by the gearing on the gas outboard, and delivers 9.9HP at 5000RPM.
    The Torqueedo then looks at the situation and picks a lower cruising speed and says, OK, we are equivalent to a 9.9 at 4000 RPM which is 4.8HP or something like that?

    Any ideas how they come up with that?
     
  7. tunnels

    tunnels Previous Member

    Use you computer and crunch munbers till the sun goes down if need be but dont forget to add all the things that influance what you are looking at
    . The mounting of multiple outboards in close proccimity to each other must have a unknow effect that is yet to be discovered . Bit like aircarft mysteriously going out of control till it was discovered the air turbulance after a plane goes past ! theres still a lot we really dont know or understand about boats and boating :confused::?::D:p
     

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  8. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Minnards http://www.minardsdiesel.com/outboard.htm in Newcastle Australia claim to support these engines, the diesel outboards have been in use by Australian Defence Forces so the claim could be fair dinkum. Worth an email to confirm sales@MinardsDiesel.com . Jeff.
     
  9. CatBuilder

    CatBuilder Previous Member

    Do they even make an 18HP model of those Yanmars?? I went to Jeff's link and saw two models.

    I was told the sistership ran with a pair of 18HP diesel outboards. I think they said Yanmar, but that's not adding up....
     
  10. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    I'd agree with the other posters and with waikikin

    The Yanmar outboard engines were developed for the military so they didn't need to carry petrol/gasoline. It was petrol exploding that caused the major fires on the UK's warships during the Falklands conflict

    So they are unnecessarily expensive for you and I. However I have seen them used by Colombian fishermen so I guess some people get them cheap. I think there was a 27 and a 35 to match the conventional diesels Yanmar made at the time.

    Parsun make a bigger electric outboard it's sold in the US and powers pontoon boats

    But I'd stick to regular outboards, at least to start with, unless you've got lots of experimenting time and money

    Maybe in a few years there will be some electric car engines available. Or you could maybe marinise a golf cart?

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  11. masalai
    Joined: Oct 2007
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    masalai masalai

  12. CatBuilder

    CatBuilder Previous Member

    Oh well. Another good idea down the drain. I wish commercial products were of higher quality. The quality and business sense of various companies just seems to be going down the drain more each year.

    Is my perception of quality constantly decreasing part of getting older or is this a new thing?

    I ought to be producing good electric outboards instead of doing charters. Seems everyone wants one, but nobody makes one.
     
  13. WestVanHan
    Joined: Aug 2009
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    WestVanHan Not a Senior Member

    Did research for my friend:
    IIRC in the 90's was another Japanese or Korean brand (komatsu or Tohatsu?) and also Italian Ruggerinis...I think they had a 15 hp,dunno if they are still built or not.

    I have no idea how they come up with stuff,all I want is a side by side comparison with identical boats,showing hp and gen set size,with gps in an uninterrupted video. Have never seen such a videoe,so I'm skeptical...


    And as for being in production,for a diesel to meet US EPA standards it'd be very difficult.

    The torque and hp thing, all the arguments make sense on paper,but once again-show me.
     
  14. masalai
    Joined: Oct 2007
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    masalai masalai

    I have noticed an increasing rate post 2005 and getting progressively worse.... learn to love google and be prepared to go and have a look and pick up using CASH - seems to be the only "reliable" way to get the goods, but warranty? be prepared to be bloody vindictive and carry a big stick (or gun?)....
     

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

    masalai masalai

    Best species on the Yanmar 27hp outboard yet
     

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