Required Bollard Pull for a Harbour Tug

Discussion in 'Boat Design' started by Rob Moody, Oct 12, 2008.

  1. Rob Moody
    Joined: Dec 2007
    Posts: 5
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Cape Town

    Rob Moody Support Vessels

    Can anyone provide me with info on calculating the required bollard pull of a harbour tug.

    Also any info referencing justificaton in the choice of using either a Voith-Schneider or Azimuth propeller. Note the tug in consideration will probably be used >95% of time for berthing/unberthing ships. On the odd occasion these movements could be with a 'cold' ship.

    Largest ship under consideration is about 23,000 tonne deadweight in a 20 knot wind.

    At present there is a range of tugs (Voith and Z-Drive) being used, the max with a bollard pull of 35 tonne. However, max size that is presently being handled is about 14,000 tonne deadweight.

    Any input would be appreciated
     
  2. Kay9
    Joined: Oct 2006
    Posts: 589
    Likes: 26, Points: 0, Legacy Rep: 279
    Location: Central Coast Oregon US.

    Kay9 1600T Master

    I wouldnt go with anything less then 10,000 LBS bollard pull. If your intrested I have listings for many ship assist tugs here in the US that are for sale in the 60K to 260K range that would do this job.

    Also either drive you mentioned will work nicely. Most of the time the assist vessel (tug) is positioned prior to the move for a specific direction of pull. The assist vessel is then re-positioned for the next pull. So even an old fashion single screw tug will do the job nicely and might save you millions in cost over a new Z-drive.

    K9
     
  3. Guillermo
    Joined: Mar 2005
    Posts: 3,644
    Likes: 185, Points: 63, Legacy Rep: 2247
    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    After inspecting a 130+ tugs fleet in 6 countries I've found Voith propulsion being presently the favourite for most harbour tug masters. Then azipods.

    The attached empirical formula (see downwards) is widely used for determining the required bollard pull. A record of safe towing in Canadian waters has been established using the following K values at a towing speed of six knots.

    (a) for exposed coastal tows K = 1.0 to 3.0
    (b) for sheltered coastal tows K = 0.75 to 2.0
    (c) for protected water tows K = 0.50 to 1.5

    A quick and rough estimative for engine's power in BHP is 100 to 125 times the bollard pull in tonnes.


    Also the following formula allows a direct rough calculation of BHP (Break Horse Power) but taking no account for external factors such as wind and waves:

    BHP = 2D/3*v^2 /120
    where:
    D = Displacement of the tow (t)
    v = towing speed in knots

    To pass from BHP to bollard pull in tons you may use:

    Fixed pitch propeller: (freewheeling) BHP / 100 = (t)
    Fixed pitch propeller and kort-nozzle: BHP * 1.08 / 100 = (t)
    Controllable pitch propeller: (freewheeling) BHP * 1.125 / 100 = (t)
    Controllable pitch propeller and kort-nozzle : BHP * 1.26 / 100 = (t)


    Another formula to roughly determine the requested Bollard Pull under consideration of aerodynamic resistance and Seas state:

    Bollard pull (tons) = ((D^2/3 * v^3)/7200 + Cmv*B*D1)*K

    where:
    D = Displacement of the tow (t)
    v = Towing speed in knots
    Cmw = coefficient for the mean wind speed
    B = Width of the tow (m) (transverse to movement)
    D1 = Height of the wind facing area above water level, incl. Deck cargo (m)
    K = Factor 3 - 8, depending to the circumstances

    This formula should only be used during following two situations:
    • Ordinary towing conditions (BFT. 4)
    V = 6 knots
    Cmw = 0,0025
    K = > 3
    • Keep on station during heavy weather (BFT. 10-11)
    V = 3 knots
    Cmw = 0,015
    K = 8


    I hope this can be of use.
    Cheers.
     

    Attached Files:

  4. Ad Hoc
    Joined: Oct 2008
    Posts: 6,457
    Likes: 532, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    I've always used the rough rule of thumb, 75kg pull per 100HP.
     
  5. mhdarya
    Joined: Jan 2009
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Iran

    mhdarya New Member

    Bollard Pull calculation

    is any good source for calculation of Bollard Pull?
     
  6. prem.shankar
    Joined: Feb 2010
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: India

    prem.shankar New Member

    Bollard Pull Calculations Excel Sheets and Software

    Hi

    I can see there is a dying need for some authentic source for bollard pull calculations. I have developed excel templates and a software for calculations using industry accepted rules, like DNV, Nobledenton, OPL, BV and KR Rules, and am in the process of testing it. Would highly regard if anyone can take the pain of using them and providing valuable feedback.

    Best regards
     
  7. prem.shankar
    Joined: Feb 2010
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: India

    prem.shankar New Member

    I have developed standard excel templates following industry standard rules like DNV, Nobledenton, OPL and KR Rules. I am looking for people to use them and provide me feedback.

    brgds
     
  8. Guillermo
    Joined: Mar 2005
    Posts: 3,644
    Likes: 185, Points: 63, Legacy Rep: 2247
    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    I can check them against an extense database of known bollard pulls for existing units.
    Cheers.
     
    1 person likes this.
  9. prem.shankar
    Joined: Feb 2010
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: India

    prem.shankar New Member

    Hi Mr. Guillermo

    Thanks a lot for the offer to help.My software gives the required bollard pull for towing a Barge using a tug, and then helps in selecting the proper tug for the operation. It is different from the Bollard Pull estimated during the design of a tug. I am into Marine operations, and calculations for bollard pull required by a barge are very commonplace in the industry. I hope your database can work for such 'tug-barge' operations as well. Please advise. Thanks :)
     
  10. Guillermo
    Joined: Mar 2005
    Posts: 3,644
    Likes: 185, Points: 63, Legacy Rep: 2247
    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    So you are talking not bollard pull but the pull required to tow a barge, which is not exactly the same thing. Anyway I may have a look at your spreadsheet. Cheers.
     
  11. prem.shankar
    Joined: Feb 2010
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: India

    prem.shankar New Member

    Thanks Mr Guillermo. Will send you soon.
     
  12. jachoudry
    Joined: Aug 2012
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: United Kingdom

    jachoudry New Member

    see lots of info about tugs having a bollard pull of say, 40 tons. That doesnt seem a lot to me when you consider tugs can pull ships displacing anywhere up to 3000,000 tons. So, obviously, 'bollard pull' doesnt mean the tug can only pull something weighing 40 tons.

    So what does bollard pull mean? Does it mean 40 tons will pull the tow hook off the deck? Or what
     
  13. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,493
    Likes: 474, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    lol....obviously it means the force that can be applied, think of the strain that needs to be applied by a crane to lift 40 tons off the ground, the bollard pull is analagous, but in the horizontal plane, like the draw-bar pull on a tractor.
     
  14. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,493
    Likes: 474, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    The weight of the vessel is not so great a problem as windage and tidal movement, one man can push a vessel weighing hundreds of tonnes away from a dock if it is only inertia that needs to be overcome.
     

  15. Ad Hoc
    Joined: Oct 2008
    Posts: 6,457
    Likes: 532, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    It means that a propeller is rotating but no forward movement. Just like a fan. A fan doesn't move..but you feel the "thrust"...the air moving from the fan.

    If you placed that 40 tonne on ice...would you need 40 tonne of pull, to move it, or less. If less how much less?

    Well, lets say the coeff of friction between the ice and the 40 tonne 'block/mass' is say 0.05, it means the force required to pull the 40 tonne block would be just 2 tonne.

    So, no, it doesn't mean only able to just pull something weighing 40 tonne.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.