Pulleys for Cable Steering system

Discussion in 'Boat Design' started by Dhutch, Feb 9, 2012.

  1. Dhutch
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    Dhutch Junior Member

    Im looking at referbishing a cable based steering system on our narrowboat and am stuggling to find suitable pulleys?

    The system is a DIY system using a quatrent of just under two foot in diameter, with a pair of cables going through several single and then a pair of double pulleys upto the helm, where the cables are secured to a lenght of chain which passes over a sprocket mounted on the shaft of the wheel.

    Im expecting to use cable around 5mm in diameter (I have a roll-end of multistrand glavanised 5mm control cable) which is a larger than the existing cable and has a maximum bend radius of around 2inches which is about twice that of the current cable. So my plan was to have 5inch diameter pulleys, about the largest I can fit, but am unsure what material would be best for them. The existing pulleys where nylon but are now more than worn!


    Daniel
     
  2. michael pierzga
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    michael pierzga Senior Member

    You might consider changing to vectran rope and normal yacht blocks.

    Many times when I have worn sheaves to replace I have a local machine shop make them, fast and cheaper...Bronze or delrin. Always specify wire or rope because the sheave profile is different.

    http://zephyrwerks.com/

    Try googling Bronze, delrin sheaves for store bought gear
     
  3. Dhutch
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    Dhutch Junior Member

    Michael, thankyou for your reply.

    Sheave is a new word to me so I will do some googling on that and see what I can find, im in the UK, although ordering from overseas is not impossable. As you say, if it comes to it, having some made is always an option. We need three single pulleys and two twins.

    What is the thinking behind using a rope rather than cable? Or would that simply be to open up more options for pulleys?
    Currently the three single pulleys (including the two that feed the cable on/off the quatrent) are open, on the end of a post rather than in a block, which means a slack cable will fall off but I hope to switch to an enclosed pulley.

    What would you do to maintain system tension? Currently there is a single powerfull drawbar spring in one of the two cables but this means unless the system is tightened almost at the limit of the springs travel when turning in the direction that puts the spring underload with a lot of power on the other side goes slack and falls of the pulleys. Athough I guess a captive pulley would solve this.

    The nature of the boat in question means whatever system is used needs to be robust to shock loadings, fairly dirty conditions and low maintainance, as well to certain extent, an amount of abuse! The only saving grace being we have a tiller which can be fitted in emergancies.


    Daniel
     
  4. michael pierzga
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    michael pierzga Senior Member

    rope goes around bends better so you can oversize it, doesn't break strands " fish Hook", and is gentle on sheaves.


    Wire is perfectly OK...go for it if you already have a coil. Ive used wire for many years.
    If youre thinking of rope , stop by a good rigging shop to see what they have and recommend.
     
  5. kenJ
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    kenJ Senior Member

    Today's choice in ropes is totally different than in years past. For your use you don't need a real strong rope, just one with little stretch. In case you didn't find it on Google, a sheave is the part of the pully that turns and the rope/wire rides on. Google: Harkin, Ronstan, or "marine blocks uk" and take a look at your choices. Unless you need to use the wire to maintain originality I would go with rope, so much easier to use.
     
  6. FAST FRED
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    FAST FRED Senior Member

  7. Dhutch
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    Dhutch Junior Member

    Theres no requirment 'keep origanality' the boat was built by my family in 1991 and I am simply replacing the orignal worn out system, trying learn a from the previous one and make it less delicate. Narrowboats are not delicate!

    Im happy to use a suitable rope if that will provide the performance we need while being suitably durable. Non of the runs are exposed to direct light, although there is plenty of grease and grim floating about. It would also require some changed to the quadrent I presume but more on this later.

    Thoughs on a system to maintain tension?



    Daniel
     
  8. michael pierzga
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    michael pierzga Senior Member

    Turnbuckle...probably what you have now. Idler sheaves are difficult to fit.

    Steering is a simple system. No need to spend a lot of cash for anything high tech
     
  9. Dhutch
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    Dhutch Junior Member

    And just use the nateral spring of the rope for any required give, like the quadrent not being perfect etc. Sounds fair.

    Too right abouts costs. Dont mind spending money where needed but when when I had a look at that edson link and nearly fell of my chair at some of the prices for sheave assemblys!

    http://www.edsonmarine.com/marinestore/index.php?main_page=index&cPath=84_92


    Daniel
     
  10. Stumble
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    Stumble Senior Member

    Dhutch,

    Use dyneema rope, sold under the name amsteel blue, not just whatever is lying around. It is much stronger than steel, highly abrasion resistant, impervious to chemical attack, and will reduce friction in the system (it has about the same slippery index as Teflon).
     
    Last edited: Feb 10, 2012
  11. michael pierzga
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    michael pierzga Senior Member

    One problem with fabric is the eye splice in relation to avaible space. A splice eye and bury must be say 200mm long ? If space is tight keeping this splice bury out of the tuning block might present a problem. Wire ends can be crimped short.
     
  12. SamSam
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    SamSam Senior Member

    My cable system on a small boat had two springs, one on each side. Would that work? If it will, it might be easier to get two new springs so they'll be the same, instead of trying to match the older one.
     
  13. Dhutch
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    Dhutch Junior Member

    Yes, thats true. It wouldnt be an issue and the quadrent end, but im not sure of the avilable space at the wheel end between the run of the chain and the first pulley.

    Talking about the qaudrent. At present it is made of three 4mm semi-circular steel plates bolted together with spaces at 50mm centers. With the cable running on the spacers between the plates. Obvisouly if rope or cable of a larger diameter was used the plates would have to be re-spaced but would it be an issue for the rope to be running un such a quadrent, or would a suitable dyneema or vectran have enough abrasion resistance to cope? Boat use is circa 300 hours per year and I would be aiming for a cable replacment of no more than every 5 years or 1500hours.


    Daniel
     
  14. Dhutch
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    Dhutch Junior Member


  15. FAST FRED
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    FAST FRED Senior Member

    I had a look at that edson link and nearly fell of my chair at some of the prices for sheave assemblys!

    Sadly you only get get quality by paying for it.

    FF
     
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