Thoughts on this drive system

Discussion in 'Powerboats' started by Willallison, May 24, 2002.

  1. Willallison
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    Willallison Senior Member

    I think you might have just become my hero Mike!!:D :cool: :D
     
  2. Portager
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    Portager Senior Member

    ESLRF

    Peoples reactions to eye safe laser range finders never cease to amaze me. ;)

    Cheers;
    Mike Schooley
     
  3. Willallison
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    Willallison Senior Member

    It's not just the ESLRF that gets me going - it's the package which it's mounted to..... including those three little pop-guns up front!:D
     
  4. Portager
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    Portager Senior Member

    Stern Drive Efficiency

    I called my local Arneson Dealer and chatted for awhile (he keeps his boat next to the Phantom).

    He told me that he did a side by side comparisons of Arneson Drives and Stern drives on identical Fountain boats. He said that even though the Arneson drives were driven by diesels that weighed 2,000 lbs more than the gas driven stern drives, the Arneson could stay on plane at lower speed, had a higher top speed and had better cruise efficiency and range even after taking into account the lower specific fuel consumption of the diesel versus gas engines. The Arneson Drives could also turned sharper.

    He said the Arneson Drive will perform better at moderate or cruise speed than a stern drive because the drag is much lower and you can optimize the engine speed by adjusting the drive depth.

    Normally I would think he is bias because he sells Arneson Drives, but at the time he ran these tests he was a Mercury dealer. He has now converted all his boats to Arneson Drives and he no longer sells Mercury. I think that says a lot.

    The cost of the ADS6 drive, complete with the steering cylinders and everything you need for installation is US $7,200.

    Cheers;
    Mike Schooley
     
  5. Willallison
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    Willallison Senior Member

    I sent a short email to Arneson and they basically said the same thing as your local dealer - that by trimming the drive you can optimize engine speed and prevent over-reving / over loading. But - ever the sceptic - I can't see how this can be achieved on a slower moving vessel.
    A boat running at say 18 - 20 knots in sloppy conditions is going to be rising and falling continuously as it negotiates each wave. Ipso facto, the surface drive must run deeper and shallower as this happens, so surely you are going to be faced with an engine which is heavily loaded one second, then under loaded the next.......
    I've read a number of magazine articles over recent time which extoll the virtues of the surface drive, but I'm yet to come across one with a direct comparison between boats which are virtually identically rigged, with the exception of the drive. And whilst all are impressed with the higher top speeds attained, none of the articles mention the mid-range.
    My interest has come about because I'd like to incorporate a surface drive, or similar, in a design project which I'm currently working on - but obviously I need to be sure that it is appropriate for the task.......

    By the way, thanks Mike for taking the trouble to ask around on this issue for me - it's most appreciated
     
  6. Portager
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    Portager Senior Member

    Drive Load Variations

    I think your overlooking two things.

    First the drive is operating in the wake area and at 18 to 20 knots, the waves are knocked down in the wake area. Well at least it works that way on the Phantom, or it would if we could go that slow. :)

    Second the flywheel plus the drive provide angular momentum, which averages out the load variations. On the Phantom, we don't notice any load variation and we go out in some pretty rough seas.

    Cheers;
    Mike Schooley
     
  7. Willallison
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    Willallison Senior Member

    hmm... that's true, but then the Magnum is a pretty big, heavy boat which, I would imagine doesn't pitch a great deal. It's not so much the waves coming through the wake that I was thinking about. The props on a surface drive are what - about a metre aft of the transom? So as the bow rises to meet a wave, so the prop will be forced deeper into the water. And as the bow drops off a wave, so the props will be lifted clear of the water.
    This is all pure conjecture on my part and I'd clearly love to be wrong as I'd like to incorporate them in my design project(mostly 'cause they ARE very cool!:cool: )
    I liken the situation to a boat that my parents own. It's a 26 ft deep v with a pair of Optimax Merc 225hp outboards mounted on a pod, which locates the motors about a metre aft of the transom. Before we bought the Optimax's the boat had a pair of 200hp Merc's which were mounted so high that the water pick-ups were remote mounted at the bottom of the hull. The motors ran props which are designed to be ventilated. But the boat was unable to hold plane at anything below about 25 knots and in a seaway (and here is my link to surface drives) the engines would continuously over-rev or load up as the props were lifted clear or submerged.
    Having said all that, I find it difficult to believe that there are an increasing number of pleasure boats being fitted with surface drives if they are as intractable as I've suggested......
     
  8. Portager
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    Portager Senior Member

  9. Jeff
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    Jeff Moderator

    Interesting - thanks very much Mike for the link to the RumRunners Yachts site - nice to see a big brother to the impressive Alsberg runabout Harry Schoell also designed.

    And thanks for taking the time to get some current Arneson info for us and what sounds like a fairly unbiased first hand comparison. Good to hear from someone who could have either and makes the switch, though it would have been even better if both were running the same or very similar engines - I would think the different thrust range, gearing, and propping of a diesel vs gas would make a difference in itself which couldn’t be ignored (I’ve been awake too many hours right now to find some numbers to back that up though :))
     
  10. Willallison
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    Willallison Senior Member

    Glad you could join us Jeff....
    The RumRunner seems to be quite a vessel!

    What we really need here is some input from an expert in the field............anyone out there?................
     
  11. Portager
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    Portager Senior Member

    More Surface Drive Info

    One of the best articles that I have found on the web is (page 1) http://powerandmotoryacht.about.com/library/weekly/aa061301a.htm and (page 2) http://powerandmotoryacht.about.com/library/weekly/aa061301b.htm.

    Since I wanted more real data than this article provides, I called Twin Disc (Twin Disc builds the Arneson Drives) @ (262) 638-4000 and talked to Dana. He said they have an extensive data packages that shows test results of Arneson Drives tested against Stern drives, inboards, outboards, ... and Water Jets. Since Twin Disc makes both Arneson Drives and Water Jet drives the last comparison should be unbiased. He said this data package is only available in hard copy, so I'll have to wait for it to arrive by snail mail.

    I asked Dana about cruising performance and he said that at all speeds above planing speed the Arneson Drive provide higher speed for a given power level or require less power at a given speed. Below planing speed they act like a normal submerged drive.

    I asked about overloading the engine at low speed. He said that provided the boat is within the design weight that isn't a problem. The surface piercing props are sized to the maximum torque required in the submerged mode. The only problem is when the boat is overweight, but then they can correct the overload condition by adding air tubes like we have on the Phantom. A new development is a butterfly valve on the air tubes that opens below a certain engine RPM and closes above. This provides much quicker hole shots.

    In heavy seas, the drives are trimmed to run with the water near the prop centerline. In this way small changes in running depth cause minimal changes in prop torque. If the drive depth increases dramatically and the engine starts to lug down, the operator has sufficient time to raise the drive and off load some torque (light weight engines require quicker response time than heavier engines with larger flywheels). The air tube with a butterfly valve mentioned above also helps in this situation. When the engine starts to lug down, the butterfly valve opens. Since the air tube is mounted just above the drive centerline, it allows the prop to suck air and off load the over torque condition.

    Once I receive the data package from Twin Disc I'll post a summary to the forum.

    Cheers;
    Mike Schooley
     
  12. Willallison
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    Willallison Senior Member

    Thanks Mike, I really appreciate your efforts.
    Do you know whether the data package that you refer to is available to the general public - or more specifically how I might go about getting a copy, given that I'm in Australia....?

    It would be interesting to see what they class as "above planing speeds". I guess that's exactly the kind of info that would be in the data package.

    This all brings up another variable to the equation. The trimmable versus fixed surface drive debate. The simplicity of the fixed system is surely its greates attraction, but given what you've said, I guess that it is more likely to suffer from the problems that I'm concerned about than a trimmable system.
    I've made a couple of enquiries with the manufacturers of the fixed units - I've not heard anything back from them as yet.....
     
  13. Portager
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    Portager Senior Member

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  15. Portager
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    Portager Senior Member

    How does that work when all your steering fluid is floating on the surface of the Ocean?

    Regards;
    Portager
     
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