Most Efficient Boat Propulsion

Discussion in 'Sterndrives' started by tom kane, Dec 4, 2014.

  1. tom kane
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    tom kane Senior Member

    S/P props can not run in that ideal position most of the time they are submerged at the start or going slow until the boat reaches ideal crusing and are subject to many varing sea conditions and loading. Most propellers can work half in and half out of the water with varing results depending mostly on diameter, for instance an unloaded boat. Google S/P propellers and see the different ideas on what a S/P propeller looks like they vary depending on purpose. Most of them would create masive drag run submerged so you would need to be able to change their positioning.
     
  2. tom kane
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    tom kane Senior Member

    Define "most efficient according to our forum members opinion ".
     
  3. myark
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    myark Senior Member

    From personal experience with Mercruiser and chatting with NZ dealers, I've come to the conclusion that stern drives are designed to serve the first owner well but after 5or 6 years you have had the best out of them.

    The second problem is, that with all the good intentions in the world getting them serviced in NZ is difficult and repaired properly, nearly impossible, more moving parts in terms of things moving up and down, side to side and the like whilst spinning at high speed has got to be a factor when compared to shafts. things will wear, rubber will perish etc etc, ignore regular maintenance at your peril for this reason

    I read in a boating forum
    "I think they're the devil's own work. The two sterndrive boats i've had have cost me big money in repairs despite annual servicing, and most people I know with them have also had issues. I think one problem is that small failures can cost so much to repair. I had some slight pitting around the drive shaft seal, and the solution was a new lower drive leg at over £3k! Shaftdrives on the other hand are virtually fit and forget, and i've not had a hint of an issue in 10 years of shaftdrive ownership."

    For those seeking, efficiency and dependability, The pivotal drive is the answer.
    Shallow Water Capabilities with a trimmable propeller shaft and no fixed underwater appendages, your craft will require significantly less draft than conventionally powered hulls. You'll have greater access to shallow water areas.
    The propeller shaft to enhance performance and versatilty, the propeller shaft angle is vertically adjustable, even while underway. This allows the helmsman to achieve the optimum propeller thrust angle depending on load and sea conditions at any given time.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Tom if you're interested in "the most efficient" of anything, the forum members haven't a clue as to what you might think this means, without some guidance in this definition. A multiple list of requirements will require a priority list, suited for your definition of overly broad, difficult to describe term.
     
  5. myark
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    myark Senior Member

    A child could understand what Tom said.

    "Which boat propulsion system is the most efficient for all purpose boating?"
     
  6. gonzo
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    gonzo Senior Member

    There is no common definition for efficiency. A surface propeller would never be used on a tug. On the other hand, a large, slow turning propeller would not be efficient on a light displacement boat. A child would not be able to comprehend efficiency. That is simply and invitation to argue instead of explaining what you mean by efficiency.
     
  7. tom kane
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    tom kane Senior Member

    Just about every thread has someone saying that "it won`t be efficient" I am sure most of the forum members understand what a general discussion is.
     
  8. gonzo
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    gonzo Senior Member

    Efficient for what- speed, acceleration, fuel consumption at a certain speed, towing? Efficiency is understood. What it is efficient at is something you haven't stated.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Precisely. What are you looking to make efficient, the build, the costs in material, labor, propulsion loses, wave making, specified use, particular speed, is economy or practicality a consideration or just a wide open discussion about the potential for various conflicting elements the point. A free sailboat is pretty efficient, from some points of view, then so could be one, of any other number of possible scenarios. An argument could be made for mini atomic reactors, maybe one of the C4 decaying isotope units, used on satellites (no moving parts). Parameters are the basis for any reasonable discussion. Unless you buy into this premise like Myark, at which point I vote for self sustained hamster wheel drive, clearly delineated in one of Dave Geer's books, "The Nature of . ." I think.
     
  10. myark
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    myark Senior Member

    All purpose boating is not a tug or a mini atomic reactors or a C4 decaying isotope units, used on satellites


    "Which boat propulsion system is the most efficient for all purpose boating?"
     
  11. jehardiman
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    jehardiman Senior Member

    The real issue with an adaptive surface propulsion control system is what you have to know how far in advance to allow the system to respond properly. Using a ground effect vehicle as an example, it is feasible to make an attitude controls system that senses the ground and obstacles ahead and either determines that they are overflyable or avoids them. With modern ranged ground sensing LIDAR merged with sub-millimeter radar, LRGA, and a MPP backbone server, doing this on the ground is possible...think advanced DARPA ALV. But as I said, ground vehicles are dirt simple, and that is because it is dirt...static...it is not changing in the few seconds before you get to it. Waterborne craft, especially those that have to interface with the wave profile, have it harder because the surface is changing in elevation and slope constantly.

    Because of this hulls are designed to interface with the surface in one of 3 ways, profile, platform, or mixed response. Mixed response is what a normal buoyancy supported hull does; depending on the wave encounter frequency the hull either responds to the wave profile (waterplane dominates: a barge) or doesn't (mass dominates: SWATH). Platforming and Profiling are what high speed and most dynamically controlled vessel do. In Platforming, hull is controlled at a fixed height above the still water surface with very little vertical motion either by design in planning hulls, air pressure in hovercraft/SES or by control surfaces in hydrofoils. Once the waves reach a certain height and length, it is possible for high speed craft to Profile where the hull is controlled to follow the swell surface with considerable vertical motion.

    However, craft that rely on Platforming or Profiling usually cannot transition from one to the other. There will always be a point where the wave profile cannot be mitigated by the design or the control system. It becomes a matter of being able to sense the wave surface with enough fidelity in enough time to respond. In the design postulated, even with the best modern sensors I know of, there would always be some randomness that could not be sensed far enough in advance to move the control/propulsion system to the optimum. This problem is very close to what some of the AC teams were trying last year with the wind.

    http://www.sail-world.com/Cruising/...-Oracle-Racings-wind-mapping-technology/66144

    Some day there might be the capability to get a good enough estimate of exactly where the water surface will be at the propeller the necessary time in advance. I know that in my own experience with real time sensing systems we had to wait for computing power to catch up with the theoretical concept.
     
  12. myark
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    myark Senior Member

    Of course they do
     
  13. myark
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    myark Senior Member

    So what is your choice of a propulsion system that is the most efficient for all purpose boating?"
     
  14. myark
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    myark Senior Member

    I have owned several jet boats and found reliable but lost HP redirecting through to the jet pump.
    I had spent many times taking small stones out of the grill and problems in the Waikato River and lakes with weed infected areas and sometimes at sea after a storm would pick up floating derby in the jet units.
    I have also had many boats with outboards which are also OK but cannot travel in shallow water and expensive also has the weed problems.
    Stern legs the same but they are more unreliable.
    A simple boat we used to ski behind had a straight prop direct drive and went like a rocket but it could not travel in shallow water and could damage the shaft when approach the boat ramp to retrieve .
    This is why I have studied Toms pivotal drive system for some time and found to be the most efficient, I like the very simple system that can be made at a very low cost with DIY maintained and the fact no lost HP power from motor to prop and it actually eats weed and turns to thrust and can drive straight up on to the beach if need or over submerged logs or sand banks similar to a jet unit.
     

  15. tom kane
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    tom kane Senior Member

    Thank`s myark and we are just touching on some of the advantages of being able to lift or jack propulsion systems such as steerable and jackable tractor drives or common old stern drives. Easy..
    It appears many boaties miss the pleasure of boating in the quiet places because they are restricted to deep water. It takes a long time for some people to catch on the different ideas especialy if it means competition in business oportunities. Many experts try to baffle the public with meaningless maths and theory which do not work in practice and they or anyone else do not realy understand. There is no use complaining about a product if you can not see how to solve the problem to suit yourself. Every one can look in a dictionary to see what efficiency,or efficient means.
     
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