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Old 01 August 2012, 19:14   #1
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Breaking strain of a bow eye

I've been thinking about replacing my current anchor line (10mm 3 strand nylon, which can be a bugger for tangles if it has been shaken up, as I found out yesterday when dragging it out in the garage to dry off) with some Anchorplait.

I don't really anchor much, so it's mainly a safety item and the reason for thinking about changing it is that it's less likely to tangle in an emergency deployment situation. I was already planning to go to 12mm, but I wondered about going to 14mm for a bit of overkill.

However it looks from here

https://www.jimmygreen.co.uk/p/techn...g-strain-guide

like the breaking strain of 12mm Anchorplait is already 3.3 tonnes, and I suspect a bow eye will let go at much less than that in very rough conditions if the boat is really jerking on the line, anybody care to hazard a guess at what a typical bow eye (usually about 8mm stainless loop) would fail at?

Further to that, assuming it's less than that, my thinking is that 14mm would have substantially less stretch for a given load, leading to higher snatch loads in rough conditions, and I maybe should stick with 12mm as the best compromise.

Any thoughts welcome. Space in the anchor locker is not an issue.

Ta
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Old 01 August 2012, 19:41   #2
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I know it can be pricey but good quality multiplait deploys and repacks so much better than nylon, if you can afford it I'd go for 16mm, much better on the hands for hauling in, with plenty of stretch, so no need to worry about snatch,
I've got 100m of the example myself

50 METRES X 12 MM MULTIPLAIT / OCTOPLAIT - NYLON 8 STRAND MOORING / ANCHOR ROPE | eBay
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Old 02 August 2012, 01:11   #3
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If you're worried about snatching and you have plenty of space then put a rubber spring on it.
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Old 02 August 2012, 01:17   #4
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For a 7m vessel it is recommended that you have:
9kg with 10m of 8mm chain and 20m of 12mm warp (30m of overall length). This may be reduced by up to 20% (but not the length) ( I would recommend the reduced diameter as its only a light RIB)
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Old 02 August 2012, 01:58   #5
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Originally Posted by Silverfox
as its only a light RIB

Haha, you've obviously never weighed your VM Will, mine weighs 1600kgs......:-)

I was surprised at how heavily built they are.

Simon
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Old 02 August 2012, 03:31   #6
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Ta for the replies. The reason for the original question is that I don't really want the bow eye to be the weakest point (because if you're dead ship, and you rip that off, you've then nothing to tow from).

Another question: which is best out of rope spliced to chain, and rope spliced around a thimble and joined to chain with a shackle (obviously with the shackle pin secured).

I've just got my current rope/chain joined with a bowline, and I'm not convinced it wouldn't chafe over time with movement, and I think that the same problem would affect rope/chain spliced joins. Any thoughts?

I feel happier with a thimble spliced into the rope (and it also means I could take it off and use it for towing if need be), but I can't splice multiplait so I'd order a made-up line, and the deals available on rope/chain spliced together are much better

I think I probably know the answer, but is there any difference between the 4 a metre Anchorplait and the 1 a metre Ebay nylon multiplait apart from the pretty stripes?
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Old 02 August 2012, 05:18   #7
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Only ever seen one bow (deck )crappy chromed cleat fail
And that was a fully swamped speedboat which was been panick pulled out of the water by the owner who had decided to (borrow / nick ) our tractor ,
the nylon rope and remains of the cleat then hitting his 16 year old son in face causing severe facial injurys .

Think there is more chance a bow eyes (nuts)working them self loose over time with any snatching action than actual breaking out unless it's got no decent backing pad or washes behind whilst anchoring unless its badly worn ,

If you are worried about the bow eye failing why not run a rope or bridle fastned from the transom , running down the length or underside the hull and then through the bow eye ,
That way the main strain is taken on the transom but the bow eye is just acting as a guide or fair lead.
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Old 02 August 2012, 05:42   #8
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It's definatly worth having either a thimble or a rubber sheath spliced in if possible, I'd say the pound a meter stuff should suit your needs,
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Old 02 August 2012, 05:57   #9
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Quote:
Originally Posted by Dragonhawk ficht View Post
I know it can be pricey but good quality multiplait deploys and repacks so much better than nylon, if you can afford it I'd go for 16mm, much better on the hands for hauling in, with plenty of stretch, so no need to worry about snatch,
I've got 100m of the example myself

50 METRES X 12 MM MULTIPLAIT / OCTOPLAIT - NYLON 8 STRAND MOORING / ANCHOR ROPE | eBay
I've bought from these guys in the past and if you email them, they were quite happy to attach a stainless thimble and shackle ready for chain attachment (if you don't actually need the chain) or quote for a different length of octoplait etc. I have ordered bits seperately from them and then received a PayPal refund out of the blue because they spotted the same address and put everything into one delivery for me.
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Old 02 August 2012, 06:01   #10
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Its been a long time since I did calcualtions of breaking loads, but I reckon you would pull the metal fixnig out of the GRP of the boat before it failed ....
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Old 02 August 2012, 06:02   #11
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Something to think about and i always say you can never have good enough anchor or ground gear and length of rope ,, but. ! Correct me if I am wrong
When many of the recommended anchoring calculations were made they were done many years ago when most leisure boats were wood heavy displacement boats /yachts calculated using old type admiralty pattern or fishermans type anchors using natural fibre rope in sheltered severe storm conditions ,
Modern planing hull shapes using high hold anchors (bruce )with nylon rope perhaps can get away with less .
I am Not saying that the 3x depth using chain & 5x using just rope doesn't still stand in most cases but when the original Bruce anchors were first designed they recommended using just a short length of chain for chaffing/ wear purposes on the sea bed .
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Old 02 August 2012, 17:23   #12
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[QUOTE=
like the breaking strain of 12mm Anchorplait is already 3.3 tonnes, and I suspect a bow eye will let go at much less than that in very rough conditions if the boat is really jerking on the line, anybody care to hazard a guess at what a typical bow eye (usually about 8mm stainless loop) would fail at?



Ta [/QUOTE]

The tensile strength of SS316 is 515MPa, that is, a bolt with a cross-section of 1 square meter will hold 515000000N force. The effective cross-section of a 8mm bolt is 36 square millimeter.
Multiply these, and we get approx 19000N or 1,9Tons. A u-bolt has two legs, so it should hold nearly 4 tons, provided the pull is at the right angle. I have not made any allowance for distortion of the arch; on one hand, the bending will cause it to harden so it may not deform, on the other, any distortion may weaken the bolt
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Old 02 August 2012, 17:50   #13
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Quote:
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The tensile strength of SS316 is 515MPa, that is, a bolt with a cross-section of 1 square meter will hold 515000000N force. The effective cross-section of a 8mm bolt is 36 square millimeter.
Multiply these, and we get approx 19000N or 1,9Tons. A u-bolt has two legs, so it should hold nearly 4 tons, provided the pull is at the right angle. I have not made any allowance for distortion of the arch; on one hand, the bending will cause it to harden so it may not deform, on the other, any distortion may weaken the bolt
Thanks for this, I assumed the line was weaker than the U bolt too, just didn't have any data or calculations to support that.
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Old 02 August 2012, 19:34   #14
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Its been a long time since I did calcualtions of breaking loads, but I reckon you would pull the metal fixnig out of the GRP of the boat before it failed ....
I figured that too ... sorry I should have been clearer, when I said breaking strength of the eye I meant breaking strength of the whole thing fitted into a GRP hull, not specific to the failure of the metalwork. However the metal bit is going to snap off at somewhere between 3 and 4 tons so that's the maximum and it's probably less.

It's all pointing towards anything more than 12mm being a waste of time anyway, which answers the question of which to buy.

There was an interesting anchor test in some magazine a few years back where they tested breakout force in a range of anchors and also estimated the peak loads on the anchor line on something like a 40' yacht in storm force winds. I wonder if anybody has ever done a similar thing with light planing hulls.
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Old 03 August 2012, 05:40   #15
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Haha, you've obviously never weighed your VM Will, mine weighs 1600kgs......:-)

I was surprised at how heavily built they are.

Simon
Which I've always thought is an anomaly.

Ours is 1300

Quote:
Originally Posted by Silverfox View Post
For a 7m vessel it is recommended that you have:
9kg with 10m of 8mm chain and 20m of 12mm warp (30m of overall length). This may be reduced by up to 20% (but not the length) ( I would recommend the reduced diameter as its only a light RIB)
Usually people recommend 1m chain/1m vessel + 1m. I think we have 10mm chain though. And then lots more than 20m warp!
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Old 03 August 2012, 07:07   #16
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[QUOTE="gotchiguy"]

Which I've always thought is an anomaly.

Ours is 1300
/QUOTE]
Likewise, we weigh in at 1100 so Jigsaw does seem bit lardy.
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Old 03 August 2012, 13:04   #17
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Quote:
Originally Posted by gotchiguy

Which I've always thought is an anomaly.

Ours is 1300

Usually people recommend 1m chain/1m vessel + 1m. I think we have 10mm chain though. And then lots more than 20m warp!
I've quoted the MCA guide. Doesn't mean it is right though!
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Old 03 August 2012, 15:12   #18
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Anchors-Rocna-demos-and-testing!
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