Pros & Cons of Dee shackles vs Bow Shackles

[vyv_cox]

Vyv, re your pic at #12:
1) the cones could add substantially to the strength of any shackle (Dee or Bow). I suppose you haven’t tested the effect of a load centred on the pin vs at an end?
2) I assume that is the Allen key headed pin you raised in another post – very neat
3) What is that to the right of the pic?
GHA - nice big pic. . . (just me being me . . .)
Cheers, Andrew

1. Not sure whether the strength would be increased or not. The intention was to centre the load to avoid the edge of a skewed shackle clashing with the bow roller.
2. This is not my kit, it belongs to the owner who designed the cones. But it is the same shackle type that I use, a countersunk Wichard.
3. A Kong swivel, one size larger than mine I think, 10 - 12 mm.

 

[Andrew G]

Thanks Vyv. Re 1. as you know, with the link centred each eye takes 1/2 the load, off centre the closer eye takes more than 1/2 . This is what I meant by improve the "strength"?? I saw this in the context of your tests showing the pins and eyes to be more vulnerable - the centering should improve this?
It would certainly help passing through cheeks etc.
Night time here - I'll post more tomorrow. Andrew

 

[rogerthebodger]

With the load centred on the pin the pin becomes the weakest point due to the maximum bending moment being at the centre of the pin span. This is illustrated by the mode of failure shown in the first 3 pics on VyV's web site. If the load was off centre and the eye at the loaded end would take most of the load and I think the eye would split and fail. The bending moment on the would be reduced but the shear loan on the pin at the loaded end would be higher that shear load with the load centred.

The centring cones as shown in VyV's post would not reduce the bending moment of change the mode of failure. If the cones were spacers and the pin tightened so that the load point was clamped and the pin under tension this may reduce the bending moment in the now composite pin.

Used to design lifting equipment in a previous life when I lived in UK.

 

[afterpegassus]

The reason that bow shackles exist is so that the pin ends are within the maximum OD of the bow, thats it, the only reason.

This is not true. I looked at a selection of shackles in our rigging loft and for example the pin on a Crosby 6 1/2 ton redpin bow shackle measured 120mm whereas the max OD of the Bow was only 100mm.

You confirm that Bow shackles can be directionally loaded and I did say that D shackles "ought" to be used in linear fashion, not "cannot" so what is untrue about this?

 

[estarzinger]

Here is what US Cargo says:
"Anchor/Bow vs. Chain/D-shackle
Anchor and bow shackles are synonymous. Both names refer to a shackle with a larger “O” shape look. This design can take loads from many directions without developing significant side load. The larger loop shape does reduce its overall strength, but it is also able to handle a larger strap.

Chain shackles are also known as D-shackles, d shackles, or dee shackles. Both refer to the “D” shape design. A d-shackle is narrower than a bow or anchor shackle and generally have a threaded pin or pin close. The smaller loop is designed to take high loads primarily in line. Side and racking loads may twist or bend a D or chain shackle.
"

 

[estarzinger]

And here is what Crosby said when I asked them by e-mail . . .

"Thanks for your enquiry. Dee shackles are for a single point connection, Bow shackles are for a multi point connection."

 

[vyv_cox]

Slightly contradictory advice from the two suppliers but I'm sure they mean well I suspect that in the vast majority of cases the lever arm on a D shackle with the pin through the shank is so small that it is unlikely to be a serious effect, certainly a lot less than there is with most swivels. And if the bow will not go through the roller then there is not much option.

 

[Deleted member 36384]

And here is what Crosby said when I asked them by e-mail . . .

"Thanks for your enquiry. Dee shackles are for a single point connection, Bow shackles are for a multi point connection."

If you check the catalogue, Croby, you will see that they do not state that only Bow can be loaded at angles, they do qualify that only certain pin types can be loaded at angles. Indeed, the pictures of both the dee and bow show the 45 degree indicator cast on the shackle. The only one that they state which is not to be loaded at an angle is the shackle with the pin that is retained by spilt pins/R clips. This is because the pin eyes are forced apart and can sheer out the split pins. Threaded pins prevent this.

If you care to resolve the forces on the pin from either a D or Bow loaded at say, 45 degrees, where the pin is secured through a padeye, it will be noticed that the resultant direction(s) on the pin is the same for both types (angled loads have to be downrated below the WLL). Also, if both types are free to articulate they will hang across their diagonal dimension if the connection point width allows (this is common on slinging only arrangements). Note that D shackles are used on padeyes where sheaves may pull in any direction but the downrating must be taken into account.

http://www.thecrosbygroup.com/html/default.htm#/en/89 Perhaps you can ask the Crosby representative why the D shackle has the 45 degree markings?

 

[GHA]

If you check the catalogue, Croby, you will see that they do not state that only Bow can be loaded at angles, they do qualify that only certain pin types can be loaded at angles. Indeed, the pictures of both the dee and bow show the 45 degree indicator cast on the shackle. The only one that they state which is not to be loaded at an angle is the shackle with the pin that is retained by spilt pins/R clips. This is because the pin eyes are forced apart and can sheer out the split pins. Threaded pins prevent this.

If you care to resolve the forces on the pin from either a D or Bow loaded at say, 45 degrees, where the pin is secured through a padeye, it will be noticed that the resultant direction(s) on the pin is the same for both types (angled loads have to be downrated below the WLL). Also, if both types are free to articulate they will hang across their diagonal dimension if the connection point width allows (this is common on slinging only arrangements). Note that D shackles are used on padeyes where sheaves may pull in any direction but the downrating must be taken into account.

http://www.thecrosbygroup.com/html/default.htm#/en/89 Perhaps you can ask the Crosby representative why the D shackle has the 45 degree markings?

Must admit, despite buying thousands of shackles when working as a rigger I never noticed the 45° markings on the Dee's. Though no one really uses them for bridling, 2 steel wire rope eyes won't fit and even soft sling spansets sit awkwardly on top of each other.

 

[afterpegassus]

Must admit, despite buying thousands of shackles when working as a rigger I never noticed the 45° markings on the Dee's. Though no one really uses them for bridling, 2 steel wire rope eyes won't fit and even soft sling spansets sit awkwardly on top of each other.

There are indeed 45 indicators on the Crosby D's (or two part shackles as we sometimes describe them) though other makes do not. Where they are used in a correctly fitting padeye, there is very limited lateral articulation at the pin end so they can be a reminder as to their limits (say) when a block is attached.

 

[Andrew G]

Cutting Bow Pin Head Off

Am I correct then in thinking that shackles have been designed and manufactured more for their rigging (ie lifting) uses rather than for marine anchoring? That would explain why some Dee shackles have such a long pin which tends to nullify their otherwise better passage between bow roller cheeks.
Some have mentioned cutting off and slotting the pin head - is this what you had in mind? The idea is to leave enough of the head to tighten/loosen it with a spanner and to be able to mouse it through a slot.

Cheers, Andrew

 

[noelex]

Some have mentioned cutting off and slotting the pin head - is this what you had in mind? The idea is to leave enough of the head to tighten/loosen it with a spanner and to be able to mouse it through a slot.

Almost, there is just enough material to drill a small hole in the remaining metal above or below where the hole was.
This enables you to mouse the shackle with the wire going through a hole instead of just a slot.
The head of the pin can still be cut so that it projects out very little.
You can also use some Locktight for "belt and braces"

Surprising it can usually still be undone, although there is not much to grip on with the spanner, so consider it may need to be cut off and destroyed if left for a while, with a bit of corrosion.

 

[Andrew G]

Thanks for all your contributions. Cheers, Andrew

 

[vyv_cox]

I have not moused a shackle for years. Loctite 242 is a perfect substitute.

 

[RAI]

I have not moused a shackle for years. Loctite 242 is a perfect substitute.

Plumber's PTFE tape works quite well too and reduces thread lock due to corrosion on galvanized shackle screws.
Cable ties work well for mousing.