Model Boat Mayhem - Forum

Please login or register.

Login with username, password and session length.
Pages: [1]   Go Down

Author Topic: Bollard pull - what does it mean!?  (Read 6374 times)

justboatonic

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,338
  • Location: Thornton Cleveleys
Bollard pull - what does it mean!?
« on: September 22, 2011, 08:25:45 PM »

Can someone explain this please?

I 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!?  {:-{

Ta
Logged

wartsilaone

  • Guest
Re: Bollard pull - what does it mean!?
« Reply #1 on: September 22, 2011, 08:51:02 PM »

Hi Justoatonic. This should shed some light on the subject.

http://www.vht-online.de/vht2008/pdf/Bollard-Pull.pdf
Logged

Shipmate60

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,223
  • You bark - I will bite!!!
  • Location: Fareham
Re: Bollard pull - what does it mean!?
« Reply #2 on: September 22, 2011, 09:07:22 PM »

The Bollard Pull is exactly as it says, the amount of force (pull) that a tug can exert on a static object.
It is basically a comparison test between tugs.
It is only usually used before and after refit to ensure the Main Engines are developing the full rated power under load.
On a working tug there are other factors to consider as in: Towing by the main winch if it is self rendering, the load tested capacity of the bollards if side towing etc.

Bob
Logged
Officially a GOG.

ZZ56

  • Guest
Re: Bollard pull - what does it mean!?
« Reply #3 on: September 22, 2011, 10:13:13 PM »

if you go down to a marina and put your hand on a boat (might not want to do this with the owner standing there) you'll find you can push it fairly easily for its size.  Forty tonnes of bollard pull is more than enough to shift a handymax-size freighter.  Some of the big anchorhandlers have 200 tonnes of bollard pull. 
Logged

irishcarguy

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,374
  • Happiness is running from a grizzly and escaping
  • Location: Calgary N. W. Alberta, Canada
    • Britishcars International. org.
Re: Bollard pull - what does it mean!?
« Reply #4 on: September 28, 2011, 07:14:03 AM »

Hi shipmate60, It is obvious you know a lot about tugs & towing, could you tell us a bit more about the winches & towing hooks & bollards etc.for us landlubbers. I have never been on a tug so any information would be welcome, thanks, Mick B. P S = I am building the Smit Nederland at present.
Logged
Mick B.

Shipmate60

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,223
  • You bark - I will bite!!!
  • Location: Fareham
Re: Bollard pull - what does it mean!?
« Reply #5 on: September 28, 2011, 03:48:47 PM »

That is a huge question what is it you actually want to know.
BTW ex Tug Engineer.

Bob
Logged
Officially a GOG.

irishcarguy

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,374
  • Happiness is running from a grizzly and escaping
  • Location: Calgary N. W. Alberta, Canada
    • Britishcars International. org.
Re: Bollard pull - what does it mean!?
« Reply #6 on: September 28, 2011, 04:59:50 PM »

Hi Bob, I guess most anything to do with towing. Whats rendering, what happens on side pulls. How do you know where to put the bow of the tug when you want to push instead of pull, questions along those lines, there is a lot more to towing than what we tend to see, even in how you signal back & forth etc. Mick B.   
Logged
Mick B.

justboatonic

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,338
  • Location: Thornton Cleveleys
Re: Bollard pull - what does it mean!?
« Reply #7 on: September 28, 2011, 07:20:33 PM »

Thanks for the info and clarification!

Sorry for the delay acknowledging, I thought I had thanked but obviously not!  %%
Logged

Shipmate60

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,223
  • You bark - I will bite!!!
  • Location: Fareham
Re: Bollard pull - what does it mean!?
« Reply #8 on: September 28, 2011, 08:12:00 PM »

Mick,
In a harbour most tug moves except ships are done with the tow alongside the tug.
This uses the bollards and the capstans to tighten the wires.
For ship moves the wires are attached either to the foredeck bitts or after deck bitts through a Panama Lead. An oval hole in the gunwhales that has a wider 
curved steel band to ensure the wire wont fray.
Ships being docked/undocked usually have a tug on bow and stern plus 1 midships rigged to push/pull the hull.
For longer tows the towing winch is used, most of these are "Self Rendering".
This means that the load is set on the winch and if this is exceeded the winch will pay out cable till the load reduces to the set load.
Modern winches will then "remember" how much cable was paid out and when the load decreases rewind this length not exceeding the load setting.
The cable is paid out from the winch through a "Gog" or "Gog Rope" on the after deck. This is usually near the stern and is to stop the cable getting anywhere near 90 degrees neer the superstructure which can pull the tug over (being GIRTED).
The Towing winch is ALWAYS set to a load less than the breaking strain of the towing cable. If an older cable is used then this is further reduced.
If towing directly off the towing hook a "Gog" systen is still used and the hooks have an emergency release, usually in the wheelhouse.
On an open sea tow the cable will be in the water, not straight to the towed vessel. In effect the weight of the towing cable is what is doing the towing. This also gives a damping effect and would usually be carried out on the towing winch again with a "Gog" arrangement or a purpose made Towing Bridle which is attached via the after bollards port and starboard if no self rendering winch fitted.

Phew

Bob
Logged
Officially a GOG.

dave301bounty

  • Guest
Re: Bollard pull - what does it mean!?
« Reply #9 on: September 28, 2011, 08:34:57 PM »

Bollards and pull ,big tugboat engines and a straight pull ,the previous fella will have said it all ,but I did work on tugs at the shipyard after a refit and the bollard pull was a very important fact ,then in the 1960s a straight pull of 16 tons was enormous ,and carried out under very strict supervision in the docks .just think that once you have the vessel moving ,no matter how large ,the vessel moves quicker ,  stopping is the problem ,hope you get your information of this ,but the previous fella being an ex tug engineer will know too .
Logged

farrow

  • Guest
Re: Bollard pull - what does it mean!?
« Reply #10 on: September 28, 2011, 09:12:09 PM »

Reference to Iriscarguy, when a tug goes in for a push pull postion, the vessels master/pilot tells the tug where to secure and push on. Some vessels especially weak hull ones like passenger vessels have specially reinforced areas for tugs and are clearly marked with sometimes a built in towing point.
Logged

irishcarguy

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,374
  • Happiness is running from a grizzly and escaping
  • Location: Calgary N. W. Alberta, Canada
    • Britishcars International. org.
Re: Bollard pull - what does it mean!?
« Reply #11 on: September 29, 2011, 08:47:12 AM »

Thank you all That was what I had in mind how the whole thing was worked out,I will go to bed tonight a little better educated than when I got up, all thanks to you guys. Sometimes we do our jobs every day & never give it a thought that other people have no idea what it is that our jobs entails. Mick B. 
Logged
Mick B.
Pages: [1]   Go Up