Windlass ripped from hull

[smithadr]

We have just finished a weeks charter in the mediterranean. Everything fine until the last day when, upon raising the bow anchor (via electric windlass) after lunch in a bay, the rear end of the windlass (ie the part furthest from the anchor) became detached from the fibreglass platform it was bolted to in the anchor locker. This didn't happen as the anchor was being pulled up from the sea bed - it occurred after it had emerged from the sea yet just before returning to its normal position in the bow roller. The windlass motor did not trip out so after we manually rehoused the anchor into the bow roller and removed the anchor chain from the windlass we were able to turn the windlass winch in the usual way using the handheld electric device -- it would therefore appear the electric motor inside the windlass was undamaged and still fully operational.

The company we chartered the yacht from seemed to suggest it was our fault either bacause the anchor was stuck under a rock on the sea bed or because during the week we had used it to pull the boat away from the quay after being moored stern to overnight.

My thoughts/questions are:

- Surely if the windlass is ripped from the hull in this fashion it is due to not being attached in a secure enough way in the first place .... is this correct ?

- Lets say the anchor is lodged under a rock on the sea bed. If the skipper persists in trying to raise it using the brute force of the windlass, in a properly set up windlass either the electric motor should trip or the windlass clutch should slip before excessive strain is placed on the windlass hull attachments points (ie bolts as described above).

- Is it true that you should not use a windlass to pull the yacht away from the quay when leaving a stern to mooring ??

Any help greatly appreciated.

Thanks....

 

[PaulRainbow]

I'd say if it was fitted correctly and the correct thermal breaker was fitted it would not be possible to rip the windlass from the deck.

However, it should not be used for dragging the boat around, it's there for raising the anchor chain and anchor. Even when retrieving the anchor you shouldn't just drag the boat along with the windlass. The correct way is to slowly motor the boat forward, whilst retrieving the slack chain. When directly above the anchor, tighten the chain and wave action should break the anchor free, if not, engage astern and give it a pull.

Either way, sounds like the windlass was not securely mounted.

 

[RichardS]

As Paul says, the windlass must never be used for pulling the boat in any direction, or indeed, for breaking the anchor free if it is deeply embedded or stuck under a rock or whatever.

Whether such misuse could or should ever actually break the fibreglass mounting point is another question but, in my limited experience, I would say that I have been on several boats where such misuse would actually break the windlass mounts.

Richard

 

[penberth3]

I guess you're away from the boat now, but did you look for any existing cracks, i.e. dirty or weathered surfaces where the structure failed?

As the others have suggested, if the anchor was stuck, I'd expect you to notice the windlass pulling the bow down before anything failed.

 

[jwilson]

Even if you abuse the system the windlass should stay attached.

On my boat you charterers regrettably do sometimes stall the windlass motor with the anchor firmly in the bow roller, ie trying to shorten the bow of the boat with bar-tight chain between windlass and anchor. Again and again find it like this when the boat comes back. Despite large clear notice next to the windlass switches. Windlass still however firmly attached. My boat does get checks and maintenance......

 

[smithadr]

Many thanks for the really helpful replies. I should stress that our anchor didnt get caught.under a rock or anything like that ot jist seems that over time the windlass bolts must have worked themselves loose. Fingers crossed when the charterer opens up the windlass unit he will not find any internal damage and use that as an excuse to withold some of my security deposit....

 

[ProDave]

I'd say if it was fitted correctly and the correct thermal breaker was fitted it would not be possible to rip the windlass from the deck.

However, it should not be used for dragging the boat around, it's there for raising the anchor chain and anchor. Even when retrieving the anchor you shouldn't just drag the boat along with the windlass. The correct way is to slowly motor the boat forward, whilst retrieving the slack chain. When directly above the anchor, tighten the chain and wave action should break the anchor free, if not, engage astern and give it a pull.

Either way, sounds like the windlass was not securely mounted.

Bit if you take up the slack and then motor astern, the force on the chain and hence the winch would still be the same.

In this case the anchor was out of the sea, so somehow something jammed at the bow roller and the winch did not trip out, but ripped itself out of the deck.

 

[PaulRainbow]

Bit if you take up the slack and then motor astern, the force on the chain and hence the winch would still be the same.

It isn't the same. Pulling the boat around with the windlass is a bad idea because it puts excessive load on the motor, that's the primary reason boat should be driven forwards. When you're directly over the anchor it can't hold the same as when you have a load of scope, so it breaks free easily, as a rule. If it doesn't, you don't use excessive force while the rode is still on the gypsy, if it doesn't break free easily you tie the rode off, same as you would when anchoring overnight or in windy conditions.

 

[sailaboutvic]

It isn't the same. Pulling the boat around with the windlass is a bad idea because it puts excessive load on the motor, that's the primary reason boat should be driven forwards. When you're directly over the anchor it can't hold the same as when you have a load of scope, so it breaks free easily, as a rule. If it doesn't, you don't use excessive force while the rode is still on the gypsy, if it doesn't break free easily you tie the rode off, same as you would when anchoring overnight or in windy conditions.

I agree with Paul and you always tie it off no matter what before trying to set it and then finish off by using a snubber
What's I will say and this may not be the case here , I seen charterthat have they anchor caught on some thing and they draw forward under full power to try and trip the anchor , now as most of us know you can't trip the anchor in this way .

 

[jwilson]

The other thing many people do is rely on the windlass gypsy as the securing point when anchored. Windlass makers say not to do this (though for a light wind "lunch stop" I and many others do). But for longer term or windy anchoring this is very bad practice. Also it means that what's holding you is the clutch that just might slip, not a cleat that is hopefully very solidly bolted to the deck.

 

[Yngmar]

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.

 

[Norman_E]

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?

 

[jdc]

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/Metric_Bolt_Grades_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/rode/forces/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?

 

[RupertW]

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/Metric_Bolt_Grades_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/rode/forces/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.

 

[William_H]

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

 

[Elessar]

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/Metric_Bolt_Grades_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/rode/forces/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!

 

[Elessar]

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.

 

[sailaboutvic]

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 .

 

[RichardS]

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

 

[Sandy]

Even if you abuse the system the windlass should stay attached.

When did the laws of physics change?