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  1. #11
    Join Date
    Dec 2012
    Location
    Gone cruising
    Posts
    2,265

    Default Re: Windlass ripped from hull

    If you have overloaded the windlass to the point where it can rip out, the bow roller would also be damaged, at least on most boats I see with charter logos on them.

    Also, the windlass has (or should have) a clutch, which if properly maintained and used will prevent windlass overload - it will simply slip on the clutch while the motor spins and the chain won't move. This is an excellent safety feature. Unfortunately most people these days forget the clutch, use the down button instead of releasing the clutch to deploy the anchor and due to forgetting there is one, never service said clutch (which needs regular regreasing, a simple and quick process). The clutch can be overtensioned though, and if you haven't used it yourself, probably was, in which case it will have little use.

    So it's quite possible you've got a boat with previous damage and/or a clutch that was never serviced, or not set correctly by anyone (unless you did so). But you're unlikely to be able to prove any of this now.

    As for pulling the boat with the windlass. We habitually do so in under 15 knots wind and ours can handle it (and if not, the clutch will slip and inform us of this, without anything being damaged - thus the 15 knot figure). The important part here is to never let the chain go taut though. In light winds the chain has catenary, and you just pull up the catenary, pause until the weight of the chain moves the boat forward and repeat. Taut, unsnubbed chains are dangerous, because the slightest wake from another boat will cause enourmous shockloads with a well set anchor that still has some scope out, and if you have a large enough anchor (not typical for charter boats), even while breaking it out.

  2. #12
    Join Date
    Mar 2005
    Location
    East Sussex.
    Posts
    21,085

    Default Re: Windlass ripped from hull

    No damage to the stucture, but I have had a mounting bolt break at the back of the windlass I think it had been a bit slack and the head of the bolt came off. I always use a snubber to take the load off the windlass when anchored. It would require enormous force to break the thick fiberglass windlass platform which on my boat is reinforced by a 30mm thick plastic raiser on top of the fibreglass and 19mm plywood plus big load spreading washers underneath. Years ago before the raiser was fitted I anchored in Palon harbour on Nisiros in a strong Meltimi wind and a big swell. Unable to get a line ashore I had the boat swinging on the snubbed chain all night and stood anchor watch. Only the following day when the wind had dropped did I get a line ashore and after a further night I had to break out the anchor. Once I had the bow over the anchor I found that it was buried so deep in the mud that the 1000 watt windlass could not pull it out. It came up eventually by using the swell to get in a foot or two of chain when the bow went down so that the bouyancy of the boat pulled the anchor up a bit when the bow rose. Even that did not move the windlass.

    I suspect that the OP had a boat where the windlass mounting was already weakened and waiting to fail. Did the charter company provide a chain hook and snubber rope as part of the boat's equipment?
    Last edited by Norman_E; 22-06-19 at 20:56.
    Working on immortality - One day at a time.

  3. #13
    Join Date
    Dec 2007
    Location
    Boat: Falmouth. Work: Cambridge
    Posts
    1,346

    Default Re: Windlass ripped from hull

    Time for some numbers. Firstly, what is the shear strength of bolts holding down a windlass?

    Assume 8mm diameter stainless bolts, to a fairly low spec, say grade 50. Use the calculator at https://www.amesweb.info/Screws/Metr..._Strength.aspx and the the very conservative grade of 5.6 (== grade 50, assumed to only 60% loading). Probably you have 7.8 (it's what a windlass manufacturer should have selected). These low grade bolts nonetheless gives an ultimate tensile strength of 18.3 kN.

    Now the geometry of the windlass attachment. The bolt will fail in shear not tensile unless the mounting point is way above the attachments. Shear strength is - this is just a 'rule of thumb' - about 50% of tensile. So call it 9kN. You have 4 bolts and the load should be shared pretty equally provided the bolts are done up properly and in correctly designed holes. Thus you should expect 9 x 4 = 36kN force on the chain before failure.

    What is the force due to anchoring? Take the US ABYC guide, for which an online calculator is on the much respected Alain Fraysse's website http://alain.fraysse.free.fr/sail/ro...ces/forces.htm. Let's assume a 42' (12.8m) monohull. To get 36kN of force you need about 76 knots of wind. To put 36kN in contact, the WLL of 10mm grade 40 chain (consistent with a 42' boat which is about normal for a charter yacht) is 1.25 tonnes, ie about 13kN. according to William Hacket.

    So did the OP really exert a force on the anchor chain equivalent to a wind well into hurricane force 12? I very much doubt it. The charter company must have either fitted sub-standard equipment, or poorly maintained that equipment, or most likely both. And if they really believe that the OP did expert such a force, they are bound to replace all the chain on that boat. Do you suppose they did?
    Last edited by jdc; 23-06-19 at 14:40.

  4. #14
    Join Date
    Mar 2002
    Location
    Greenwich
    Posts
    7,244

    Default Re: Windlass ripped from hull

    Quote Originally Posted by jdc View Post
    Time for some numbers. Firstly, what is the shear strength of bolts holding down a windlass?

    Assume 8mm diameter stainless bolts, to a fairly low spec, say grade 50. Use the calculator at https://www.amesweb.info/Screws/Metr..._Strength.aspx and the the very conservative grade of 5.6 (== grade 50, assumed to only 60% loading). Probably you have 7.8 (it's what a windlass manufacturer should have selected). These low grade bolts nonetheless gives an ultimate tensile strength of 18.3 kN.

    Now the geometry of the windlass attachment. The bolt will fail in shear not tensile unless the mounting point is way above the attachments. Shear strength is - this is just a 'rule of thumb' - about 50% of tensile. So call it 9kN. You have 4 bolts and the load should be shared pretty equally provided the bolts are done up properly and in correctly designed holes. Thus you should expect 9 x 4 = 36kN force on the chain before failure.

    What is the force due to anchoring? Take the US ABYC guide, for which an online calculator is on the much respected Alain Fraysse's website http://alain.fraysse.free.fr/sail/ro...ces/forces.htm. Let's assume a 42' (12.8m) monohull. To get 36kN of force you need about 76 knots of wind. To put 36kN in contact, the WLL of 10mm grade 40 chain (consistent with a 42' boat which is about normal for a charter yacht) is 1.25 tonnes, ie about 1.3kN. according to William Hacket.

    So did the OP really exert a force on the anchor chain equivalent to a wind well into hurricane force 12? I very much doubt it. The charter company must have either fitted sub-standard equipment, or poorly maintained that equipment, or most likely both. And if they really believe that the OP did expert such a force, they are bound to replace all the chain on that boat. Do you suppose they did?
    If it’s anything like the windlass fitting on our boat the bolts won’t have failed but the fitting they are attached to will. It may just be a shelf held to the hull by being glossed in or bolted to fittings glassed in and the wood in the shelf may not be strong enough.

  5. #15
    Join Date
    Jul 2003
    Location
    West Australia
    Posts
    11,567

    Default Re: Windlass ripped from hull

    In any case I think you have a right to assume the charter boat is reasonably fool proof and if not then instruction should be given before departure. I would suggest charter company are just trying it on and you need to resist paying for the damage. Indeed publicize the name of the charter company. ol'will

  6. #16
    Join Date
    Jul 2003
    Location
    River Itchen, Southampton
    Posts
    6,897

    Default Re: Windlass ripped from hull

    Quote Originally Posted by jdc View Post
    Time for some numbers. Firstly, what is the shear strength of bolts holding down a windlass?

    Assume 8mm diameter stainless bolts, to a fairly low spec, say grade 50. Use the calculator at https://www.amesweb.info/Screws/Metr..._Strength.aspx and the the very conservative grade of 5.6 (== grade 50, assumed to only 60% loading). Probably you have 7.8 (it's what a windlass manufacturer should have selected). These low grade bolts nonetheless gives an ultimate tensile strength of 18.3 kN.

    Now the geometry of the windlass attachment. The bolt will fail in shear not tensile unless the mounting point is way above the attachments. Shear strength is - this is just a 'rule of thumb' - about 50% of tensile. So call it 9kN. You have 4 bolts and the load should be shared pretty equally provided the bolts are done up properly and in correctly designed holes. Thus you should expect 9 x 4 = 36kN force on the chain before failure.

    What is the force due to anchoring? Take the US ABYC guide, for which an online calculator is on the much respected Alain Fraysse's website http://alain.fraysse.free.fr/sail/ro...ces/forces.htm. Let's assume a 42' (12.8m) monohull. To get 36kN of force you need about 76 knots of wind. To put 36kN in contact, the WLL of 10mm grade 40 chain (consistent with a 42' boat which is about normal for a charter yacht) is 1.25 tonnes, ie about 1.3kN. according to William Hacket.

    So did the OP really exert a force on the anchor chain equivalent to a wind well into hurricane force 12? I very much doubt it. The charter company must have either fitted sub-standard equipment, or poorly maintained that equipment, or most likely both. And if they really believe that the OP did expert such a force, they are bound to replace all the chain on that boat. Do you suppose they did?
    And you assumed no sikaflex. The numbers would be even higher!

  7. #17
    Join Date
    Jul 2003
    Location
    River Itchen, Southampton
    Posts
    6,897

    Default Re: Windlass ripped from hull

    Quote Originally Posted by William_H View Post
    In any case I think you have a right to assume the charter boat is reasonably fool proof and if not then instruction should be given before departure. I would suggest charter company are just trying it on and you need to resist paying for the damage. Indeed publicize the name of the charter company. ol'will

    Spot on.

  8. #18
    Join Date
    Jan 2004
    Location
    Med
    Posts
    5,874

    Default Re: Windlass ripped from hull

    more info needed before we start suggestion the charter company at fault.
    coinciding most charter boat are within four years old the windlass would had been fitted at the factory ,
    and they would had fitted many hundred if not thousands , that not to say a shoddy repairs hasn't been done since fitted very rarely read of windlass just falling off .
    but I have seen one windlass plus cleats ripped out when a power boat roared off at speed still attract to another boat anchor chain .
    I no fan of charter company they get away with murder but I also seen the way charters miss use boats so it could easily be the fault of another charter who missed used it , but who to say and how do the OP prove it ?
    its no different then when a charter return and a dive goes down and says the keel damage .
    personally I think the OP now has a problem on his hands , he could ask for a report by a independent surveyor but that would cost him more then the repair .
    Warning forumite dyslexia near by
    www.bluewatersailorcroatia.webs.com

  9. #19
    Join Date
    Nov 2009
    Location
    Home UK Midlands / Boat Croatia
    Posts
    18,881

    Default Re: Windlass ripped from hull

    Quote Originally Posted by RupertW View Post
    If it’s anything like the windlass fitting on our boat the bolts won’t have failed but the fitting they are attached to will. It may just be a shelf held to the hull by being glossed in or bolted to fittings glassed in and the wood in the shelf may not be strong enough.
    Indeed so Rupert. I would expect that in all cases the failure point will be the sub-structure that the windlass is bolted to rather than the windlass or the bolts.

    Richard

  10. #20
    Join Date
    Aug 2011
    Location
    On the Celtic Fringe
    Posts
    13,985

    Default Re: Windlass ripped from hull

    Quote Originally Posted by jwilson View Post
    Even if you abuse the system the windlass should stay attached.
    When did the laws of physics change?
    Cynical Scottish almost retired engineer.

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