Gear box question

Discussion in 'Inboards' started by Steve in SoCal, May 17, 2007.

  1. StianM
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    StianM Senior Member

    What about using two convencional engines running two convencional gears and two convencional proppelers.

    Both gears fitted with PTO/PTI and generator/motor.

    Top speed using both motors and low speed using one motor that runn a generator trough the PTO that powert the PTI on the oposite gear.

    You would not nead anny speed control since as long as the generator and motor has the same number of poles they would runn at the same speed.

    If the load on the propeler is high it will consume more amps and therefor they would share the load betwen the two proppelers perfectly.

    The proppeler speed would go up and down with the engine RPM since they HZ would go up and down with it.

    This is just from the top off my head that I did not do anny serious reaseartch about, but it should/could work and it's not exstremly expensive or complicated.

    You don't nead clutches or pulleys.
     
  2. alan white
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    alan white Senior Member

    A belt drive is not so efficient. It would generate more btus than chain or gears.
     
  3. FAST FRED
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    FAST FRED Senior Member

    "A belt drive is not so efficient. It would generate more btus than chain or gears"

    As long as a belt is not slipping the losses are mostly hysterisis , the rubbers resistance to bending and un bending.

    For an experiment the fact that belts would cost .00001 of a custom engineered and then manufactured gear box might need to be put into the "efficiency" equation.

    FF
     
  4. Steve in SoCal
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    Steve in SoCal Junior Member

    While belts may not be the ideal from all aspects they have a few big plusses. The span between each segment is easily accommodated, the weight is very low in comparison to other options and, the failure mode is far safer than the others.

    Gear trains would be cost prohibitive and chain is a good idea on paper but between stretch, environmental effects and weight it is a distant second. The gear and chain systems would weight considerably more 3-5 times as much on average. The radius of the pulleys have an impact on the belt life and heat rise, using the largest pulley possible has always been part of the equation.

    The other ideas add layers of complexity that defeat the purpose of the systems straight forward approach. While this is not perfect it is viable and that is a huge stumbling block to overcome. There are some remarkable minds working on truly heady design concepts, problem is they are way too expensive to produce. A product has to be marketable to be valid and this is a niche market to say the least.

    The whole exercise started with my desire to solve a conundrum about an issue I had with a boat I have been thinking about building for my own use. My desired cruising grounds include vastly different kinds of operations from dead slow to damm the torpedo's full speed ahead. My own desire to operate my engines with the utmost efficiency to my wallet and their longevity. Then I began to think that there are several kinds of boats that fit in the power dilemma. How many boats under 60 tons with big engines use all or even half their rated power a high percentage of the time, not many. I don't think the market is large but a few boaters with an eye towards reducing cost would perhaps like an option. Maybe not an ideal solution but a real product that is not too costly or requires major re-engineering of systems.

    That is the design and why it is as configured, it gives the best flexibility in installation and application.

    Steve
     
  5. alan white
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    alan white Senior Member

    I was wrong about belt efficiency. Thanks for the informative reply, Fred.

    Also, to Steve, it has taken me a while to understand your idea. At this point, I see more what you're thinking about. Declutching mechanisms must be available off the shelf. I liken your limited consumer market niche to the market Cadillac went after with their 8 cylinder/4 cylinder engine, which bombed in the marketplace, but was actually a brilliant idea for the same reasons you would want to have peak efficiency at a broader range of speeds.
    A single decoupler with clutch synchronizer is probably the one item that would solve the question of viability. Surely such animals are out there able to withstand multi-hundred HP power transfer. The manufactured unit would be easier to design, a simple bevel gear in a rotating cage between the two belt pulleys in the center location and a means to apply pressure to a band around the bevel gear between. Really a planetary cluster, it would be constant mesh and so solve the problem of engagement shock.
    given that an item such as that would be expensive one-off, the choice would, I suppose, be a single declutching set-up on one pulley in the simplest form (reversing gears will still turn), followed by a declutching coupling on both pulleys (gears don't turn but more complicated and expensive). If two decouplers, why not located on the prop shafts instead of the central location, and save belt wear? Perhaps more expensive, I don't know.

    Alan
     
  6. Steve in SoCal
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    Steve in SoCal Junior Member

    Hi Alan,

    The only problem with clutching on the shafts is I know of nothing that would work in that situation. You would have to mount bearings on the prop shaft and have some way to lock the pulley when engaged. For a high torque and horsepower use this would have to be made. I can think of a method to achieve the results; the shaft would have to be keyed or splined where the clutch hub mounted. The pulley would have holes bored into it on the web below the rim and the clutch would have fingers that slide into the holes. This approach may be desirable as you say, it would stop all motion except the bearings at the shafts.

    You could incorporate that system into a replacement flange for the shafts that would be the least intrusive method. The production of the parts is not as big an issue as it may seem, I know several job shops with capabilities to do 5 axis work in small batches. But it is a far more expensive solution than I originally conceived.

    The comparison to the ill fated 8-6-4 is understandable. The same idea reared it head at Mercedes a few years ago with about as much success I should add. While not ground breaking technology, this concept is designed to manage power with the flexibility not offered in a simple twin engine boat. As I have learned there are many ways to achieve the goal of dividing power, at higher cost and complexity let alone weight and size. This is not something for the big mega yachts where the size and cost factors don't prohibit grand ideas. This was conceived for the 40-100 foot or so boats with modest engine rooms that don't have the ability to carry the weight or room to pull off another option.

    Steve
     
  7. Frosty

    Frosty Previous Member

    You keep talking about belts. What kind of belts do you mean toothed or V?.

    How will you tension it and worse how will you replace it --remove a shaft?

    A V belt handles about 3 HP--How many HP are these engines.
     
  8. Steve in SoCal
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    Steve in SoCal Junior Member

    Jack,

    V-Belts can carry a bit more power than that but, the belts I am talking are mm pitch timing belts. These are timing belts that have a rounded tooth profile. They transmit high power and run quietly.

    You would have to remove or at least unbolt the flange to replace a belt. I would put a spare belt on each shaft when I did the install. That is common practice with machinery using these belts.

    Steve
     
  9. Frosty

    Frosty Previous Member

    You would have to completely stop the vessel or the shaft would pull out. And lock it or you would be working on a turning shaft.

    You would need to back the shaft out far enough to get the puller on.

    I think this is a messy idea and probably why its not done. Its a good idea but it would need a special gearboxes to do it properly.



    Doing this on a budget is not possible in my opinion.

    I once saw a very profesional boat built in America with a hydraulic motor bolted to the side of the main drive shaft. In case of engine failure the Hydraulic motor was chained to a sprocket already fitted to both shaft and motor. A chain was fed around and snapped up with a split link. The hydraulic motor was driven by 1 of the constanty running generators that both had hydralic pumps on for windlass and bow thruster.
    The vessel would reach 5-6 KTS in this set up.

    With a large ratio and a deep pitch shaft speed will be less than 100 RPM

    Apparantly the gearbox itself is unharmed by this.

    Which i think was your original question?
     
  10. Steve in SoCal
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    Steve in SoCal Junior Member

    Jack,

    I don't know the details of disconnecting a shaft on a typical boat but you raise a good question. I was under the impression that a shaft would move back half an inch/12-13mm by unbolting it. Yes the boat would have to be stopped or the shaft immobilized to break the flange loose. To change a belt with a spare on the shaft would be an easy task. I don't understand the special gear boxes? Hyd is an option for a get home drive, this is based more on using it as a primary drive.

    Steve
     
  11. Frosty

    Frosty Previous Member

    Steve --your very first opening page had the solution.

    You suggested generators driving motors. Now I dont know if you mean AC or DC--it doesnt really matter, but that would be the answer.

    Just shut down one gen and run the motors (which ever) on the one gen.

    The QE 11 has this arrangement. I think its a bloody clever idea. She used to have turbines but they were a bit of a problem so were ripped out and instead she had 9 BMW generators.

    So standing on anchor skeleton staff=one gen.

    You want to move it --start a couple more.

    Guests come aboard--start another and so on.

    She would pull Full ahead on 7 or maybe 8 meaning she could always have one in state of repair.

    Your belts would mean you had to have same rotation. You would also by tensioning them put a side strain on them wich ,--well may not be a good idea.

    You would have to supply the dead gearbox with oil pressure because you are putting thrust up into it even though it is not delivering torque it is taking thrust. This could be easilly achieved by fitting an external pump supply.

    Turning motion from just dragging the prop through the water is not as critical,-- as the shaft is wanting to come out rather than push in. Thats one reason why you have to lock some boxes.

    You need to have a serious conversation with your choice of gearbox manufactureres.

    Unless your going round the world your fuel saving will not justify your idea.
     
  12. StianM
    Joined: May 2006
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    StianM Senior Member

    I don't know if you noticed my last sugestion on top off page 4.
    I gues a shaft generator and motor on the PTI/PTO could be replaced by hydraulic pumps and motors. It would cost less and take less space.
    [​IMG]

    It would convert alot off energy into heat.

    I see you really want fixed pitch proppelers because it's cheaper, but how mutch cheaper is it? dos it defent the extra cost off a gearbox with forward, rewerse and nutral?

    On low loads the engines will lose the turbopreshure and lose some off it's efficensy. I wonder is a sequensial turbocharger system could make the engine work at low load is it's actualy designed for this power.

    You have two choices and one is to make the engine work well over a wider range witch would mean some modifications.

    Another is to manage the engines power trough a advanced propulsion system.
     

  13. Steve in SoCal
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    Steve in SoCal Junior Member

    Jack Frost and Stian,

    You guys are both right that the method to do this correctly is an alternative to the two engines and two prop shafts. The cost factors is a big issue as is the weight and size of these components. The idea of using Diesel electric has always appealed to me, the weight and size is a factor as is cost on the DE solution. The hydraulic system could be an alternative but as you say Stian, the heat load and loss of energy in wasted heat is fuel out the tail pipes.

    As for the price of transmissions vs. Controllable propellers I don't know if the price favors one or the other. On a smallish boat with high revving engines you would have to use some reduction drive between the engine and shaft.

    I don't know if there is one clear best way to do this. Each method has its pluses and each has it negatives. One thing is clear, it is not common on smaller boats to do anything like this. That is part of the challenge; some of hardware looks to be very costly yet, by replacing other standard items the cost be greatly reduced.

    I am going to sit back and think about all the information I received on this idea. I have yet to hear anything from Ossa and that is a bit disappointing. I will research the electric side a bit more. As far as pay back on the cost, the drive system is a small part of the overall cost to build and a large part of the on going cost to operate a motor boat. Saving fuel at the onset pays dividends.

    Thanks,
    Steve
     
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