Trimax and Arneson comparison

Discussion in 'Surface Drives' started by PetterM, Jun 2, 2008.

  1. PetterM
    Joined: Sep 2004
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    PetterM Senior Member

    Does anyone any direct comparison data between these drives? Have anyone fitted these drives to the same boat. Especially interested in behaviour during acceleration (around hump) and steering at low speed and intermediate speed, and high speed.
     
  2. PetterM
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    PetterM Senior Member

    I suppose this question could be generalised as pos and cons of fixed vs. articulated surface drives. Any takers?
     
  3. Steve H
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    Steve H Senior Member

    I converted my 42 Harley from fixed surace drives to Arnesons. So I guess I could answer any questions related to that specific conversion.

    Steve
     
  4. PetterM
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    PetterM Senior Member

    Would be great if you could help me with the following:
    I am interested how to two compares during:
    Low speed manoeuvring
    Steering at low planing speeds (just over hump speed)
    High speed steering
    Acceleration.

    ..and:
    Minimum planing speed?
    Maximum speed?
    What power are you running?
    Why did you convert?

    Thanks for your help...
     
  5. Steve H
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    Steve H Senior Member

    Low speed, as in dock handling? This was the main reason for the swap. It was a nightmare in a crowded marina on a windy day. It is night and day better around the dock. It handles as well as a inboard/outboard if not better.

    Low planing speed steering (just over the hump) is a little better, it wasn't that bad before.

    High speed steering is much better. The boat still has bow steer issues, but near as bad as with the fixed drives. (I'm still playing with props)

    Acceleration is about the same when light on fuel (100 to 200 gallons), but much better with heavy fuel. (400 to 600 gallons)


    Minmum planing speed if light is under 20 mph now. That is down about 5mph from before the drive swap. I must mention here that I am large using K-Planes with even larger stainless extension bolted to them. These make a huge difference.

    Max speed is about the same as before which is 48 to 50mph.

    I am running twin 415hp 502's. Twin disc 1:5to1 trans. 18X21 three blade old style Rollas.

    Why did I convert? Dock handling mainly. Boredom too. Seems like I always have too many irons in the fire. But if I knew how much work it was going to be I would have just installed a bow and stern thruster!
     
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  6. PetterM
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    PetterM Senior Member

    Thanks for your helpful replay! You have given me plenty to think about.
    Could changing the propeller rotation help you bow steer problem?
     
  7. Steve H
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    Steve H Senior Member

    Props are currently turning in. I am reasonably sure that reversing them would make it much worse.
     
  8. Rik
    Joined: Dec 2007
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    Rik Senior Member

    The Arneson will be an easier cleaner install and will work better for all around boat use.

    The tri max will require hull changes to install and will not accelerate as well nor handle the different weight load changes.
     
  9. PetterM
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    PetterM Senior Member

    I read somewhere that in high speed turns Arneson drive is more likely spin out than a fixed drive. Is this a factual? If so what’s the mechanism for making this happen?
     
  10. Steve H
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    Steve H Senior Member

    News to me. Maybe in a full race application? But those boats spin out all the time no matter if they have surface drives or not. It is usually due to operator error or a broken steering component.

    Remember: Anything that you read on the internet should be taken with a grain of salt. Especially when it comes to surface drives and this website. I did alot of research before I converted my boat to Arneson's. Most of the "advice" I got was false, kind of like urban legends. Someone starts a rumor then it gets repeated enough that it becomes fact.
     
  11. Rik
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    Rik Senior Member

    Probably a rumor started by Fabio
     
  12. Steve H
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    Steve H Senior Member


    Exactly:)
     
  13. PetterM
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    PetterM Senior Member

    Fabio spreading rumours again hehe...and I thought he was to busy getting is boat ready for the around Britain race…I do agree that there are loads of people on this site with a hidden agenda; some even use this site to slander the competition…that beside though, one can still learn a lot from people at this site.
    With regards to the Arneson spin out scenario, after thinking about it, I suppose what I was getting at was if one has a twin set-up, then in a turn the turning moment is achieved by the composite effect of both the rotation of the skeg (rudder effect) and rotation of the thrust force. Looking on from the back in a turn, the outboard propeller disc is moving towards the centre line of the boat, so that the wetted (working) swept area of the propeller is decreasing, and therefore thrust is reducing. The effect will be opposite on the inboard propeller in a turn where thrust will increase. Obviously in a turn if the outboard thrust vector is decreasing and the inboard thrust vector is increasing this will reduce the turning moment…So I was wondering if on a very fast boat this could result in a spin out? Maybe I should try to calculate the propeller forces to find out… :confused:
     
  14. Rik
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    Rik Senior Member

    The propeller rotation can be either inboard or outboard depending upon what the boat likes best.

    This is the same for any propulsion not just Arneson.

    Now if the boat is being steered by the vectored thrust as well as the rudder on the Arneson, there is in fact more control and less wheel input needed to achieve the turn resulting in less steering arc needed to accomplish the turn.

    As the boat list into the turn (assuming the boat does not want to roll outward at this speed of the turn) the relation of thrust of the outboard propeller in relation to the inboard propeller thrust will depend upon the deadrise of the boat at the stern, the displacement of the vessel and the distance of the propellers in relation to one another.

    Now you mentioned the hypnosis on a very fast boat, (relative statement) and how this would affect the situation.

    Mind you on a very fast boat, the propeller submergence on an Arneson is the same relative submergence as on an I/O and even a fixed surface drive.

    Now for a high speed turn your hypothesis of the inboard propeller thrust being able to overcome the directional thrust of both propellers as well as the resistance of the rudder forces in the turn which will in turn make the boat turn the opposite direction than the steering of the drives is nearly impossible.

    I would liken this to a hypnosis to a boat going forward and hitting a wave off center casing the boat to list to one side and the highest propeller would then loose thrust (assuming the propellers are far enough apart to make a difference) and the lower propeller would then make the boat hook port or stb.

    Mind you, this hypnosis is valid on a fixed surface drive, an Arneson, even an I/O as the submergence of the propellers below the keel is less than the height of the waves in which the boat is running.

    Not a very practical hypnosis and not reality as seen in the current flock of high speed boats. They all seem to keep going straight in the cross seas and the Arneson propelled boats do not seem to be spinning out in the turns.
     

  15. PetterM
    Joined: Sep 2004
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    PetterM Senior Member

    Rik thanks for your comments, do you by any chance work for Arneson? I wasn’t trying to have a dig at Arneson in any way shape or form, just so that’s clear. It’s commercial success speaks for it self.
    I am still a bit intrigued by the high speed spin out issue, be it with fixed or articulated surface drives. From what I have seen on videos etc it may happing with the boat going in a strait line at close to top speed. Is this a propeller issue? Or can it be caused by sudden change in propeller speed?
    Here an expemple (on a surface drive with rudder steering) http://www.youtube.com/watch?v=VNjEnDdlMoA ca 3:30 into the film.
     
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