New Hybrid: Small diesel/ Big OB in 33' S/D Hull.

Discussion in 'Boat Design' started by rustybarge, Oct 28, 2013.

  1. rustybarge
    Joined: Oct 2013
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    rustybarge Cheetah 25' Powercat.

    Hi All,

    Large engined planing and semi-displ boats are designed to run at the best continious rating of the diesel engine, EG: A 300hp/ 2500 revs/ 6.5gal.hr for the modern Volvo/ cummins turbo engines.

    In a 5 ton boat of about 33'/10mtr that will return about 2mpg, or about €350/ 100 nm in Europe.

    The problem: An ordinary middle class person can hardly afford the cost of fuel.
    But running a 300hp engine at tickover/7kts will wreck the engine.

    The concept: A S/D hull with a small diesel to give 7kts (30-50hp/1 gal.hr).....and a big petrol 300hp outboard to give 'run for shelter' capibilty.

    Why?
    Normally Cruise at 7-8 kts with diesel. In a beam sea drop OB, speed up to 15 kts to stop rolling.
    Big Ob's are light (250kg) and cheap, but will give the desired max speed, tilt out of the water no corrosion/ drag.
    Small diesels are very economical and light, and cheap to purchase.

    So A new sort of Hybrid;small Diesel/ big outboard ( or maybe Merc. petrol inboard)

    What do you think?
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    So what to do about the drag from the diesel's propellor when it goes off-duty ? In any event, a four-stroke or DFI outboard won't suck much gas at the lower end of the rev range, or damage the engine either.
     
  3. rustybarge
    Joined: Oct 2013
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    rustybarge Cheetah 25' Powercat.


    looking at the Suzuki 300hp leanburn, it uses 10ltr/2.5gal.hr at 2000revs to give 8kts cruise on a 8mtr by 2.7mtr 1.5ton rib. (3mpg, less on heavier hull)
    http://www.suzuki-marine.co.uk/docs/Ribcraft 7.8 - DF300A (Lean Burn).pdf

    The Yanmar 75 diesel weighs 215 kg, and at cruise revs of 2200revs will consume less than 1 gal/hr at 7 kts in a Jetten 37' weight 11.5 tons. (7 mpg)


    weights: the suzuki is 275kg, the Yanmar is 215kg. = 490kg.( 300+75=375hp)

    volvo 350hp d6 is 770kg.........

    So saving of over 400kg, and nearly twice the range at 7-8 kts at 1gal/hr with the diesel. You could run both engines together so cancelling out the drag on the shaft drive diesel, or the diesel could use an outdrive lifting out when the OB is in use.

    Cost:
    350 Volvo £43,000.
    Suzuki 300hp: £23k + yanmar £8k= £31k.


    Handling: At displ. speeds a S/D hull will roll in a beam sea. Stabilisers cost a fortune (£70k), flopper stoppers are impossible to bring aboard single handed in rough conditions, especially entering a harbour.

    With my concept you will normally cruise at 7-8kts at 1 g/hr giving amazing range, in a beam sea you start the 300hp OB to speed up to 15 kts.....no rolling!!

    PS: the Suzuki 300hp leanburn(4000rev) exactly matches a Volvo 300hp(2500) diesel with 6.5 g/hr at cruise.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Much depends on what the desired speed is most of the time, if you are proposing this two-speed idea as a remedy for excessive rolling at lower speeds in beam seas, and you are otherwise only going to be motoring at 7 knots, it looks like a dud idea to me, you'd be better off with a dedicated displacement design that is stiffer in roll, than a boat that is less efficient going at that speed, such as a semi-displacement hull.
     
  5. rustybarge
    Joined: Oct 2013
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    rustybarge Cheetah 25' Powercat.

    At 7kts the difference between the drag on a Displ. hull and a S/D would be negligible, in fact the flat sections on the s/d would damp out roll more than the round bilges on a true displ. design.

    So the concept of a two speed design has several good reasons, but mainly from a financial view point: fuel consumption. The ultimate set up would be a v8 petrol 300hp merc. shaft drive as the big cheap/ light 'fast speed' engine located centrally in the hull, and a small diesel driving the same shaft/propellor as a donkey/wing engine.

    In fact a 75hp diesel with reduction gear and lots of torque, turning the coarse pitch propellor of the v8 would get good grip on the water at low revs.

    I remember seeing a dual input/ single output gearbox somewhere, with separate clutches, or even a simple chain drive onto the main prop shaft would be more than ample.

    A very large range will be possible at 7kts/1gal.hr, making further saving by filling the tanks at low price locations.

    The Uk is the spiritual home of the s/d hull form, as far as I know the concept has never crossed the Pond to the States.

    What hull would make a suitable choice?
     
  6. eyschulman
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    eyschulman Senior Member

    There is one problem with your thinking about running a diesel at lower rpms and load. It is old school and wrong. Check out boatdiesel.com and Tony's tips at Seaboard marine. A modern diesel will last much longer if run at lower loads and rpm provided the coolant temps are in range and at the end of the day the motor is brought up to 80% or greater load for 10 min. Yes you will hear a lot of old school telling you otherwise but it is plane wrong. What do you think a modern M1 motor is? Its the same motor that produces much more HP with a different chip at different RPM. It is basically meant to run 24/24 at full load( significantly less than same motor at M4). So what this means is you can get a M4 motor to run more like a M1 by not pushing the throttle and rpm up there.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    So the predominant usage will be at 7 knots ? It is certainly a novel idea to have a monster engine in reserve to speed things up in the rough to lessen rolling !
     
  8. rustybarge
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    rustybarge Cheetah 25' Powercat.

    I grew up on a small farm, and we had two tractors, a Massey Ferguson 135 which had a Perkins 35hp three cylinder engine, and a Ford 6600 80hp 4 cyl.

    the little Mf was used as a runabout, on the road, looking at animsls down the fields, mucking out stables....in fact left running at idle for several hours each day and never under load. I can remember two rebulids at about 2500 hrs.

    the Ford was used for ploughing with a four furrow plough at near max. revs max torque, and pulling heavy trailers. When I left the farm the engine was still singing at 6500 hrs.........

    I'm not a diesel engineer ( petrol is more of my thing), but what afflicts slow running diesels is cylinder glazling, causing blowback. At low revs the compression pressures are not large enough to bed the rings into the cylinder surfaces, causing the surfaces to become shiny. Then when you apply high revs the large pressure created within the combustion chamber blows past the rings and into the crankcase....very evident from the crankcase breather.

    Maybe a ECU chip could cure a ' law of physics problem, but how?
     
  9. rustybarge
    Joined: Oct 2013
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    rustybarge Cheetah 25' Powercat.

    the paradox:
    Displ. hulls roll a lot,are very slow, but are very economical.
    S/d hulls drink fuel because they only lift slightly out of the water in double figures, but don't roll because of high stability at 15kts.
    Planing hulls can't cruise when on the 'hump' between 7-15kts.

    So the two speed 'two different engines' concept utilises the advantages of a S/d hull in the displ. mode for economy, and the semi- planing mode for roll stability.

    the best of both worlds.......:cool:
     
  10. rustybarge
    Joined: Oct 2013
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    Location: Ireland

    rustybarge Cheetah 25' Powercat.

    Engine and drive systems for our dual power plant S/D hull:

    Two outdrives: one 75hp diesel, the other v8 petrol.
    Single shaft drive v8 petrol, 75hp wing diesel driving the same shaft/prop(chain/sprocket?)
    Single saildrive 75hp diesel centrally located(folding prop), 300hp outboard.
    Single shaft drive 75hp diesel with folding prop, 300hp outboard.

    What do you think are the advantages/ disadvantages of these setups?
     
  11. eyschulman
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    eyschulman Senior Member

    Re; cylinder glaze this is avoided by proper break in and bringing the motor up to higher loads intermittently. Many commercial fish boats inc. lobster and crab run at low rpm tending traps. These boats get very high hours on their motors. They do tend to run faster to and from the traps. Constant idle out of gear and no load is bad. But moderate load at lower load and rpm with intermittent high load will provided proper maintenance give a motor longer life. In the industry the life of a motor is not measured by the hours but by the total fuel burn. This concept does run against traditional diesel thinking but especially with the newer diesels which use techniques to cut back on over fueling at lower loads for environmental reasons it is probably the closest to the truth.
     
  12. rustybarge
    Joined: Oct 2013
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    rustybarge Cheetah 25' Powercat.

    I think you are totally right in what you say, there are two reasons for common rail ECU injection on diesels. To stop the rattling noise at idle , cured by the injection of a tiny bit of diesel just before TDC to dampen the 'bang', and as you say to meet environmental regs (smoke)at start up and idle.

    Are ECU common rail engines any more economical at continuous rated cruise?
    IMHO, no!
     
  13. Stumble
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    Stumble Senior Member

    I think the idea is interesting, but the installation is a bit complicated. Twin engines, twin drive gears, twin fuel tanks (of different fuel), ect is a lot of complexity.

    I would rather see a diesel-electric hybrid. With a large electric propulsion engine, then two diesel generators. Size one generator for house loads plus displacement speed operation, and the second for high speed operation. Then add a VPP prop to handle the different speeds.
     
  14. rustybarge
    Joined: Oct 2013
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    rustybarge Cheetah 25' Powercat.

    Very interesting idea, but the large windings on the propulsion motor would probably weigh quite a bit to produce 225 kilowatts of power, plus the generator windings...... Not so sure about having 400 volts dc onboard a boat!

    Green line do a hybrid boat, and the electric motor is just 7kw......
    http://greenlinehybrid.com/Greenline-33-specifications

    4kts sounds a bit optimistic in a 5 ton boat with just 7kw, taking into account the 75hp diesel only manages 9 kts flat out.

    this 75hp electric outboard would be perfect, but it's 345 volts:http://www.torqeedo.com/uk/electric...ators-and-green-boaters/technical-information
     

  15. rustybarge
    Joined: Oct 2013
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    Location: Ireland

    rustybarge Cheetah 25' Powercat.

    What's the largest hull that could be driven at 7kts/ 75hp/ 4.5ltrs.hr (1 uk gal)?

    The steel Jetten 37' by 12.6" , draught: 3'3", 11.5 tons, Cat: C(6 miles offshore) displ. boat designed for inland waterways, and sheltered coastal work. The hull form has a long keel, skeg and shallow deadrise.

    here's the performance on 75hp:
    1600revs. 5.5kts...2ltrs... 11 mpg
    2000revs. 6.5...... 4...... 7.1 mpg
    2200revs 7..... .... 6..... 5.25 mpg
    2500revs 7.5 ...... 7..... 5 mpg
    3200revs 8.3 ..... 17. .... 2.2 mpg.

    http://www.jettenyachting.com/Jetten-series/Jetten-37-AC
    [​IMG]

    [​IMG]

    I chose this as an 'worst case' example because it's a hard chine flat section sea boat, sort of similar to a S/D hull form, an fits neatly inside the marina bands in Europe of up to 12mtrs, 15mtrs,18mtrs.

    The target weight of the chosen S/D hull will probably be in the 5-8 tons range.
    So 75hp looks like it's enough to drive the boat against wind and tide at 7 kts....just?

    Is this enough power for a sea boat?
     
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