Clevis Pins

[caiman]

Why do we use clevis pins instead of nuts and bolts to attatch standing rigging?Are Clevis pins a different grade to A2 /A4 stainless steel?If so why are they not marked?How do you know what grade of SS a Clevis pin is made from?
I apologise if this subject has been covered previously.
This is my first new post on this forum.I have also just posted my first reply!!
Cheers
Caiman

 

[Avocet]

Welcome!

And I don't know!

I don't imagine clevis pins are made from anything different to A2 bolts, but that's just a guess. If you used a bolt, you'd probably have to either bear the loads at least partly on the threads (generally poor practice from a fatigue point of view) or you'd have to suffer a great deal of spare thread poking out beyond the nyloc nut. This would be likely to tangle with jib sheets as you tack. (in fact, I am constantly amazed at how one can tangle job seets in shroud attachments when tacking. If you tried to do it deliberately with a piece of rope, I bet you'd only manage it 1 in 100 times)! Alternatively, you could get a "special" bolt made with an unusually long length of plain shank and an unusually short length of thread. That would cost more than a clevis pin though.

 

[alahol2]

Probably cost, neatness, ease of fitting/removal? I did use a bolt at the bottom of my forestay fitting on the last boat. That was used for about 10 years quite successfully. Before anyone castigates me, the load bearing portion was all unthreaded and the nyloc nut was replaced every year.

 

[Evadne]

The only engineering reasons I can think of are that for strength, a plain bar is of greater strength than a threaded rod going through the same hole. I'd be worried, though, if the actual loads came anywhere near the breaking strain of an 8mm(?) bolt in shear.

As an aside, when I've worked on German research ships, their favoured shackle design uses a nut and bolt instead of a shackle pin, which has the advantage it can go into the shackle from either side.

 

[Boathook]

Agree that there's nothing wrong with nuts and bolts, but I would not be happy with the thread taking the load.

 

[caiman]

Hi guys thanks for the replies
I appreciate that the plain area of the bolt should be the load bearing area,but for length,any excess could be cut off just on the edge of the nyloc nut.
I well remember the leeward jib sheet dragging the split pin out of the leeward shroud on my old GP14.The clevis promptly fell out ,leaving me with only the windward shroud.I've never been able to make a boat sail upwind as well before or since!I had to because I could'nt tack !
Can anyone tell me if the breaking strain of 5mm standing rigging is more or less than putting a 10mm bolt(size of my current clevis pins) in shear?
Cheers

 

[PabloPicasso]

Using nuts and bolts to retain riging is just plain bad practice! Clevis pins cannot rattle themselves undone if they are properly retained with a (bent) split pin. Nuts and bolts can, and do!!

 

[Avocet]

Hi guys thanks for the replies
I appreciate that the plain area of the bolt should be the load bearing area,but for length,any excess could be cut off just on the edge of the nyloc nut.
I well remember the leeward jib sheet dragging the split pin out of the leeward shroud on my old GP14.The clevis promptly fell out ,leaving me with only the windward shroud.I've never been able to make a boat sail upwind as well before or since!I had to because I could'nt tack !
Can anyone tell me if the breaking strain of 5mm standing rigging is more or less than putting a 10mm bolt(size of my current clevis pins) in shear?
Cheers

It's not really a case of "breaking strain" because the shroud will be loaded in pure tension, but the bolt will be loaded in "double shear", maybe with a bit of bending. The stress in the bolt would be dependent on the geometry of the toggle and clevis. At a guess, if it was OK with a 10mm clevis pin, you'll be fine with a 10mm bolt though. I'd caution against cutting the thread off flush with the nyloc though - maybe leave at least 1 complete thread clear.

 

[caiman]

Thanks for the replies
I must correct myself.In the story of the GP,the clevis pins were held in by split rings as often seen on dinghys,not fully bent split pins.Why would using bolts be bad practise?I reckon that any excess play can be taken out by snugging the nut down so that the 'rattle'is removed ,but the wire end fitting can still swivel to align itself.I have never seen a marking on a clevis pin saying what grade it is constucted from.Even on the packets of clevis pins hanging on the stands in the chandlerys there is no indication of the grade of steel used.Wheras on bolts the grade is usualy on the bolt head.If we ever replace a clevis pin,how do we know that the replacement pin is of the same grade as the original?
I agree that leaving one thread proud of the nut is good practise.I agree that clevis pins secured with fully bent split pins are less likely to come adrift.But with my own experiance,sheets,ropes etc catching split pins (not rings this time)can and do straighten them.This would be rectified as we do our next pre sail check,but then so would a loose nut be re-tightened.Has anyone had a good condition nyloc nut ever undo itself?Would the geometry of a nut/bolt nipped up so that there is barely any play, be better than a clevis with loads of slack?Are there specific marine grade clevis pins?How do we recognise them?
Questions Questions.
Cheers

 

[Avocet]

Can't answer the question on material grade for clevis pins. to be honest, have never really thoguht about it! They'd have to be pretty awful stuff to fail because they're much bigger than the cross sectional area of the rigging wire or the tangs that they pass through!

Yes, Avocet's split rings sometimes catch the job sheets. I just tape them up. The amount of projection of a clevis and split pin (or ring) is usually less than a nyloc nut and an extra thread, so for this reason, I think they'd be worse.

Definitely NOT a fan of tightening up the nut to take out the play in the tongue. Stainless is awful stuff for fatigue and tightening them in this way would be likely to (a) bend the tangs so that they were no longer purely axially loaded, (b) posibly even start a fatigue crack and (c) reduce another means of ensuring that the whole system "self-aligns". I can see that they OUGHT to self-align on the other parts of the system but can't see the point of removing one degree of freedom.

Finally, a cautionary tale about nylocs and A2 stainless. I nearly lost Avocet's rudder many years ago. Now admittedly, this was an underwater application where A2 should not have been used anyway, whereas I accept a rigging screw would be different, but these bolts and nuts appeared perfect. When I took them off, to invesigate the play that had developed, I found that under the nut, the bolt threads had wasted away to almost nothing as a result of crevice corrosion. The nylon of the nyloc had provided an excellent seal at one end of the nut, and the nut bearing on its washer had provided an excellent seal at the other. The result was that between the two, there was insufficient oxygen to maintain the oxide layer and it nearly cost me a rudder! Now I use A4 with plain nuts and spring washers AND I change them each season (or at least I would do if the boat was in the water)! OK, I accept that the rigging is NOT under water, but I still have a slight mistrust of nylocs on A2 stainless!

 

[prv]

Finally, a cautionary tale about nylocs and A2 stainless. I nearly lost Avocet's rudder many years ago. Now admittedly, this was an underwater application where A2 should not have been used anyway, whereas I accept a rigging screw would be different, but these bolts and nuts appeared perfect. When I took them off, to invesigate the play that had developed, I found that under the nut, the bolt threads had wasted away to almost nothing as a result of crevice corrosion.

I saw precisely the same with Kindred Spirit's rudder, except that the wasting, while worst on the threads, also extended to most of the bolt. Fortunately I found this while taking off the rudder to extract the propshaft, not after having lost it. Having seen those bolts I also removed the ones on the hull side of the pivot, with similar results.

The new ones are A4, but I think I'll still take them out for inspection in a couple of years' time.

Pete

 

[lw395]

Can't answer the question on material grade for clevis pins. to be honest, have never really thoguht about it! They'd have to be pretty awful stuff to fail because they're much bigger than the cross sectional area of the rigging wire or the tangs that they pass through!

Yes, Avocet's split rings sometimes catch the job sheets. I just tape them up. The amount of projection of a clevis and split pin (or ring) is usually less than a nyloc nut and an extra thread, so for this reason, I think they'd be worse.

Definitely NOT a fan of tightening up the nut to take out the play in the tongue. Stainless is awful stuff for fatigue and tightening them in this way would be likely to (a) bend the tangs so that they were no longer purely axially loaded, (b) posibly even start a fatigue crack and (c) reduce another means of ensuring that the whole system "self-aligns". I can see that they OUGHT to self-align on the other parts of the system but can't see the point of removing one degree of freedom.

Finally, a cautionary tale about nylocs and A2 stainless. I nearly lost Avocet's rudder many years ago. Now admittedly, this was an underwater application where A2 should not have been used anyway, whereas I accept a rigging screw would be different, but these bolts and nuts appeared perfect. When I took them off, to invesigate the play that had developed, I found that under the nut, the bolt threads had wasted away to almost nothing as a result of crevice corrosion. The nylon of the nyloc had provided an excellent seal at one end of the nut, and the nut bearing on its washer had provided an excellent seal at the other. The result was that between the two, there was insufficient oxygen to maintain the oxide layer and it nearly cost me a rudder! Now I use A4 with plain nuts and spring washers AND I change them each season (or at least I would do if the boat was in the water)! OK, I accept that the rigging is NOT under water, but I still have a slight mistrust of nylocs on A2 stainless!

Even on dinghies, I prefer loctite to nylocs, or as well as.
There was a phase in some dinghies when shrouds were commonly held on with bolts, because bolted-on parts counted as part of the hull weight. I don't think there are any real strength issues, but the ability of such things to work loose has to be seen to be believed.

 

[prv]

As an aside, when I've worked on German research ships, their favoured shackle design uses a nut and bolt instead of a shackle pin, which has the advantage it can go into the shackle from either side.

It's not restricted to German research ships - the square-rig sailing ships I've been on use them as well. "Normal" shackles on the running rigging where they need to come on and off, but mostly nut&bolt ones on the standing rigging.

Pete