testing boats

Discussion in 'All Things Boats & Boating' started by horry_bv, May 18, 2009.

  1. horry_bv
    Joined: May 2009
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    horry_bv New Member

    hi
    i am new and unfamiliar with all the terms used for boats, boatparts,etc.

    someone told me about some tests made, with the boat anchored or binded with a rope to the waterside, and running at full throttle. (or something simmilar..)

    how is this test and what is it about?

    thanks (and sorry for the bad english too...)
     
  2. masalai
    Joined: Oct 2007
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    masalai masalai

    At a guess, how strong is the rope, how well is the deck cleat to which the rope was attached, how well the anchor was bedded in the ground... no real useful purpose as that is not testing the boat in anticipated operating environment (except for it being in the water) as the usual purpose is for it to be in motion, which is an entirely different set of stresses and forces...

    Do not quote me on this as I am NOT an engineer, nor otherwise qualified to make evaluations, just using some uncommon sense...

    Others will probably come along and with great delight endeavour to demonstrate the foolishness of my comments - but without defining their demonstrable qualifications - caveat emptor....
     
  3. horry_bv
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    horry_bv New Member

    the rope must be stong enough, it must not brake....

    the test is made to evaluate a force of the boat/engine, i am a little bit confused, maybe the force with which the boat pulls on the rope at full throttle....but can't this force being calculated in a simplier way?
     
  4. horry_bv
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    horry_bv New Member

    i couldn't find nothing on the internet about this tests, but this friend told me they are very common, but maybe they are called in a certain way, or i don't know...
     
  5. masalai
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    masalai masalai

    It appears that someone was trying to measure "static thrust" which relates to the propeller/impeller mechanism and not really relevant in a boat as other things have greater significance on performance and usefulness of a particular boat to a desired purpose - to put it crudely "wanking" and displaying lots of splash/noise where curious people can come and observe the "action" in the hope/expectation of the boat breaking free and doing something "dramatic":D:D:D:D

    None of the deck cleats are designed or capable of handling this sort of load, and for tugs and other special purpose towing vessels, bollards are built into the design to facilitate towing of heavy loads, and the crew must be specially trained and skilled for that purpose and they do not test by making fast to a jetty or other such structure... as that would just be damn stupid and bloody dangerous...

    To measure static thrust complex strain gauges must be employed and usually on another floating device and away from "public" observation if ever done that way - mostly just the drive mechanism is tested in a specifically designed test tank or by computational methods... Definitely outside my ken...
     
  6. mydauphin
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    mydauphin Senior Member

    This is an old testing method use to determine many things; including hull resistance, bow wake etc... It is typically used on slower displacement boat. A scale showing force is used on line to determine forces necessary to pull hull through water. Amazingly it doesn't take a lot of power to move a big boat in calm water. I once move a 70 foot boat with 19 foot boat, 70 hp and a rope tied to cleat.
     
  7. Guest625101138

    Guest625101138 Previous Member

    The test is done to measure the "bollard" pull for tugs or vessels intended to tow something. It can be calculated but it is more accurate to actually do the test to verify that the tug meets specification. Also verifies that it is not more than specified as this has implications for the tow line and the bollard on the towed vessel.

    Rick W
     
  8. gadfly2
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    gadfly2 Junior Member

    On larger vessels, particularly tugs, this is a test of the ability of the vessel to tow other objects. The result of the test is known as 'bollard pull' and measured in tonnes.

    regards
     
  9. masalai
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    masalai masalai

    OK so it seems other replies suggest towing another moving vessel in "still" waters to assess wave-making and resistance through the water - That is logical, but to test the towing capacity of a tug against a FIXED object seems to be bordering on stupidity - to my mind - towing a VERY LARGE vessel and having strain gauges fitted at either end of the "tow-rope" seems acceptable....
     
  10. Guest625101138

    Guest625101138 Previous Member

    Brian
    You are wrong here. I have seen large vessels in strong winds actually taking large tugs backwards while the tug is at full throttle - not a nice situation if you own the berth. It is not uncommon to have older tugs undertake bollard tests to verify their pulling capacity as they age and the engines get in need of an overhaul.

    This can mean the difference between needing 2, 3 or 4 tugs to berth a large bulk carrier. These vessels have huge windage when partially deballasted and feel no pain when striking your average quay side. They need to be precisely controlled.

    Bollard pull is vitally important to any harbour tug. The tug master needs to know what the limitations are. Also ship's bollards have a load rating and the owners might be upset if the tug pulled the bollard from the deck because it had unspecified pulling power. These things need to be known through actual testing.

    Rick W
     
  11. masalai
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    masalai masalai

    Rick, what I mean is testing the static pull against a "fixed" structure like a jetty or other object firmly cemented to land could be quite dangerous, as opposed to testing bollard pull against a giving floating object where give may result in a little movement rather than catastrophic destruction due to failure of an object being used to stay affixed to immovable land secured "pull point"

    I did not intend to imply an impossibly large towed vessel as a test, just one that would allow the strain gauges to measure the bollard pull required for assessment....
     
  12. Guest625101138

    Guest625101138 Previous Member

    Brian
    It is done against a fixed point. A quay or berthing dolphin has to be able to withstand very large forces.

    This might give you an idea:
    http://www.steerprop.fi/bollardpullcode.pdf

    This is what happens when the mooring bollards are not up to the job:
    http://www.youtube.com/watch?v=6E-onRMBp3I
    You would not test your bollard pull with these.

    This is the sort of hook used for bulk carriers:
    http://www.nautilusengg.com/pages.php?info=single_mooring_hooks.html
    A large tug will have a bollard pull of say 70t so hooks like this are meant for those sorts of loads and more. The breasting dolphins that some mount to might have to absorb impact from a 500kt vessel moving above 0.3m/s. THey need tremendous strength and shock absorbing ability.

    I can send you close ups of these sort of structures if you are interested.

    Rick W
     
  13. masalai
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    masalai masalai

    No need, Just passing interest, Thanks...
     
  14. Knut Sand
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    Knut Sand Senior Member

    If I recall; Bollard pull test: Rescue boats/ life boats shall have adequate power to tow a liferaft at some speed. Liferafts are certified and tested at full load of persons/ weight and the fixtures for ropes/ tow lines are also verified this way, achieved speed is also registred.
    So the test of the boat is done with the boat connected to the quay via a scale measuring the pull, to check/ verify that the boat is able to tug rafts of certiain size.

    Or for Tug boats, same problem, other loads, much bigger scales....:D
     

  15. masalai
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    masalai masalai

    What aroused my original rejection of testing bollard pull by connecting the boat to be tested to a quay leads one to question who would risk the whiplash in the event of a failed rope, bollard or uprooted quay or other risk factors... (I cannot think of a "safe place" to do such in the Port of Brisbane for example - yet quite a few volunteer coastguard vessels - 35ft grp powerboats - are fitted with bollards specifically for towing ashore recreational boats that come to grief)

    Therefore I display my ignorance in these matters at the commercial end of the scale and ask are there special testing facilities? and in general interest terms where and how are these tests done... Strain of load gauges are not the issue for me as that technology is not unfamiliar - - the matter of testing some of the specialised ocean going tugs and of the medium size tugs used to manoeuvre vessels to their berth for loading discharge etc. is where/what I seek in enlightenment
     
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