Eyebolt for anchor fixing

[Keeping Up]

I've been contemplating fitting a new eyebolt for attaching the anchor rope, to bolt through a bulkhead and maybe provide a stronger fixing than the existing welded attachment. But how big should it be? I've looked on eBay, and an M10 bolt which is about the size I was contemplating, seems to have a SWL of just 230 kg which seems far too low.

 

Any suggestions, folks?

[jodansgang]

Hi there, Clas Ohlson, M10 stainless eyebolt, breaking load 3500kg, catalogue number 31-860-3 and the price is £6.99. Hope this helps.

[Higgs]

I've been contemplating fitting a new eyebolt for attaching the anchor rope, to bolt through a bulkhead and maybe provide a stronger fixing than the existing welded attachment. But how big should it be? I've looked on eBay, and an M10 bolt which is about the size I was contemplating, seems to have a SWL of just 230 kg which seems far too low.

 

Any suggestions, folks?

 

10mm sounds a little weedy, possible 17mm. Just trying to remember the ones I've removed, I'm still guessing but 10mm definitely doesn't sound meaty enough.

[Alan de Enfield]

Just a suggestion - but get as big a 'plate' as possible to go between the bolt and the nut, Will help spread the load and stop the eye-bolt pulling thru.

[Keeping Up]

Hi there, Clas Ohlson, M10 stainless eyebolt, breaking load 3500kg, catalogue number 31-860-3 and the price is £6.99. Hope this helps.

 

 

Excellent, that's the sort of thing I was hoping for.

 

How come it is shown as having a breaking load of 3500kg, when at least a couple that I checked on eBay, also 10mm stainless steel, showed a SWL of just 230 kg.

 

Is it that they allow a 10x safety factor between the SWL and the breaking strain?

[Ex- Member]

I've been contemplating fitting a new eyebolt for attaching the anchor rope, to bolt through a bulkhead and maybe provide a stronger fixing than the existing welded attachment. But how big should it be? I've looked on eBay, and an M10 bolt which is about the size I was contemplating, seems to have a SWL of just 230 kg which seems far too low.

 

Any suggestions, folks?

 

Our front doors curtain rail is suspended on Stainless steel M8 eye bolts. M10 is nowhere near sufficient IMO and would probably rip through sheet steel bulkhead if under great stress.

 

I would have at least M20 bolt with a good 50/60mm clearance through the eye. 25mm for a wide beam and then use a thickening plate like on the welded loop below.

 

 

 

Ours is welded, but not just a loop a loop on a 5mm plate welded to a 5mm bulkhead.

 

Edited March 3, 2013 by Julynian

[jodansgang]

I don't know KU, it does suggest in the catalogue that the working load is one quarter of the breaking load (875kg). Again, hope this helps.

Edited March 3, 2013 by jodansgang

[GUMPY]

These items normally rated at 6:1 so a 100kg swl is a 600kg breaking

However there is another standard that demands 10:1

[ditchcrawler]

With Eye Bolts the design of the bolt and angle of pull also come into the equation. It really is horses for courses. Some have shoulders and take a higher side ways force, some are only good for a straight pull like lifting equipment. some can be pulled at right angles which are probably what you will need.

http://www.hoistquip.co.uk/documents/pdf/3.pdf

[smileypete]

Couple of sections of thick steel angle back to back then a rated bow/D shackle through them, with pin securely wired or pinned so it can't loosen. Then splice in a rope thimble on the end of the rope. A shackle can be forged which is a lot stronger than casting.

 

cheers, Pete.

~smpt~

Edited March 3, 2013 by smileypete

[RobinJ]

10mm sounds a little weedy, possible 17mm. Just trying to remember the ones I've removed, I'm still guessing but 10mm definitely doesn't sound meaty enough.

Surely a narrowboat has a SLW of at least 4tonnes?

So at 4000Kg, a good breaking strain has to be at least 40000Kg!

Edited March 4, 2013 by RobinJ

[Chris Pink]

Where does that figure come from?

[Higgs]

Surely a narrowboat has a SLW of at least 4tonnes?

So at 4000Kg, a good breaking strain has to be at least 40000Kg!

 

 

I think you're giving me credit for more understanding than I actually have. My sense of how suitable an anchor point is, is more down to intuition and what I remember of fittings I've removed in the past.

 

Talking numbers will go right over my head , I'm afraid.

[RobinJ]

Where does that figure come from?

I edited the wrong one.

I meant 8000Kg, i.e. 2 x the SLW!

[Chris Pink]

I am curious where you get a pull of 4 tonnes on an anchor rope?

[Timleech]

I've been contemplating fitting a new eyebolt for attaching the anchor rope, to bolt through a bulkhead and maybe provide a stronger fixing than the existing welded attachment. But how big should it be? I've looked on eBay, and an M10 bolt which is about the size I was contemplating, seems to have a SWL of just 230 kg which seems far too low.

 

Any suggestions, folks?

 

I suggest it should be rated to match or exceed the strength of the weakest link in the rest of your ground tackle.

 

Tim

[RobinJ]

I am curious where you get a pull of 4 tonnes on an anchor rope?

I am assuming (incorrectly of course) that the weight of the boat is hanging off the rope!

Clearly what is needed is some idea of the force exerted by a particular current on a boat (I assume braodside would be the highest figure).

Then I always did start from worst principles and worked downwards!

[Chris Pink]

A narrow boat weighs a lot more than 4 tonnes.

[Albion]

A narrow boat weighs a lot more than 4 tonnes.

Agreed but you're not hanging the boat up by the eye, only resisting the forces on the anchor when it is deployed. This will be cushioned by the stretch in the rope, the speed of grip of the anchor flukes in whatever surface they find and the stretching of the catenary loop of chain so it won't even be a snatch load applied. In a past job I had to obtain some calibrated eye bolts for an industry that I worked in and was amazed at the difference between the rated spec and the results obtained form testing those same eye bolts in our labs. The actual breaking load was way above the rated and certified load, as others have said.

Roger

[Chris Pink]

I have no intention of hanging my boat by its anchor fixing. I was simply curious about robinj's figures.

 

Though it could be a new approach to mooring; vertical marinas where you simply hang your boat up when you are done.

 

So what is the bollard pull on an anchor?

 

And, I assume more important, the snatch load as an anchor bites.

[john6767]

Slightly off topic to the OP's question, but where exactly to people tend to locate an eye bolt for the purpose of fixing the anchor rope?

[Albion]

I have no intention of hanging my boat by its anchor fixing. I was simply curious about robinj's figures.

 

Though it could be a new approach to mooring; vertical marinas where you simply hang your boat up when you are done.

 

So what is the bollard pull on an anchor?

 

And, I assume more important, the snatch load as an anchor bites.

Perhaps something similar could be done at visitor moorings, it would increase the available space significantly at the expense of stuff falling out of the fridge

I don't think that anyone can exactly define the load applied except by calculation knowing all the detail of the boat, currrent flow etc, etc for each case. As you suggest, instant snatch load after the boat has got up some headway in a signifcant current will be so much more than anchoring in a gently flowing, muddy bottomed river. I guess you have to make a call based on the type of situation that you expect to find (worst case) in the type of boating that you anticipate doing. However, there is no point in a huge eyebolt if the anchor warp is the weak point in the chain (to use just an example).

Roger

Roger

[Rich]

I've been contemplating fitting a new eyebolt for attaching the anchor rope, to bolt through a bulkhead and maybe provide a stronger fixing than the existing welded attachment. But how big should it be? I've looked on eBay, and an M10 bolt which is about the size I was contemplating, seems to have a SWL of just 230 kg which seems far too low.

 

Any suggestions, folks?

 

I was foolish enough to ask a question of this type some while ago. The best suggestion came from Tony Brooks and perhaps he will repeat it on here.

[Keeping Up]

Thanks for the suggestions so far. I'm not in any hurry so I'll wait and see if any more other comments come in then decide what to do (which may even include unprating some of the other tackle).

 

For info I currently have a 26kg Danforth anchor, with 20 metres of very very old and rather heavy chain, then 5 metres of 20mm diameter rope. The existing fixing is a short length of 10mm diameter steel, bent into a semicircle of about 50mm diameter and welded both ends to the foredeck to make an eye. I don't know how strong the welds will be as the loop was really only intended as a bow-fender hanger, but I do know that all the welds on the boat are pretty good.

 

My thoughts were to make a fixing of known good strength under one of the bow cockpit seats, with an eye through the bulkhead at the front of the cockpit (which is a general locker, not a water tank nor a gas locker). The bulkhead is 4mm thick and I had intended to put a washer of say 10cm diameter of 6mm steel to prevent the nut from pulling through.

 

The boat is a narrowboat and weighs about 20 tons.

 

Incidentally the chain came about because I asked my friend who owned an old Severn & Canal Carrying Co boat if he knew where there was any spare chain; he said he had a short length amongst the ballast in the bilges of his boat, and I was welcome to have it. We pulled on the visible end, and just kept on pulling. The "short length" turned out to be about 20 metres long, and fortunately there was no sign of rust; it feels like weighs around 50 kg.

[Albion]

Thanks for the suggestions so far. I'm not in any hurry so I'll wait and see if any more other comments come in then decide what to do (which may even include unprating some of the other tackle).

 

For info I currently have a 26kg Danforth anchor, with 20 metres of very very old and rather heavy chain, then 5 metres of 20mm diameter rope. The existing fixing is a short length of 10mm diameter steel, bent into a semicircle of about 50mm diameter and welded both ends to the foredeck to make an eye. I don't know how strong the welds will be as the loop was really only intended as a bow-fender hanger, but I do know that all the welds on the boat are pretty good.

 

My thoughts were to make a fixing of known good strength under one of the bow cockpit seats, with an eye through the bulkhead at the front of the cockpit (which is a general locker, not a water tank nor a gas locker). The bulkhead is 4mm thick and I had intended to put a washer of say 10cm diameter of 6mm steel to prevent the nut from pulling through.

 

The boat is a narrowboat and weighs about 20 tons.

 

Incidentally the chain came about because I asked my friend who owned an old Severn & Canal Carrying Co boat if he knew where there was any spare chain; he said he had a short length amongst the ballast in the bilges of his boat, and I was welcome to have it. We pulled on the visible end, and just kept on pulling. The "short length" turned out to be about 20 metres long, and fortunately there was no sign of rust; it feels like weighs around 50 kg.

That sounds very robust as they say that it is the chain that does most of the work rather than the anchor.

Roger