chain plate design change

[blue-max]

I have seen the posts regarding the weakness of the cup and ball detail of the below deck  shroud support. Rather than replace like for like I wonder if anyone has made a modification to strengthen  the support. The rod linking the deck plate to  the bracket on the hull looks very slim - I guess about 12 mm. Perhaps 16 mm would be better? Is there a way to do  away with the "link"  in the original design and have a rod from the deck plate run through the hole in hull bracket and held with a nut/nuts on the underside?     

[Yngmar]

The rod has a ball head, allowing it to rotate to ensure correct alignment. Without any articulation, you're creating sheer loads that can lead to rapid failure. So if you want to replace it all, you need to have articulated fittings on the inside, same as outside. You could use a toggle and swaged eye just like outside, on either rod or wire rope to achieve this. Rod is generally neater and will last indefinitely inside (unless you leave it leaking for a long time). However, rod riggers with the right tools are hard to find and more so now that synthetic is replacing rod.

If you go with wire rope, you also need a turnbuckle to tension it correctly. The rod has simply a thread cut into one end and is tensioned with nuts against the bulkhead fitting, at least on our boat it was.

You do not need to oversize things, rod rigging is used in yachts above deck and has well documented working load limits, typically about 30% higher than 1x19 A4 wire rope of the same diameter. Bavaria has already sized them accordingly (although I think it's Selden that did the rig calculations for them).

[blue-max]

Thanks for your comment which  I take to  heart. I have been keeping an eye on these below deck  fittings . There is some evidence of deck  leakage in the past (previous owner) but I have had nothing there (plenty  elsewhere!) I can't see anything on the metal that would make me anxious  but I wonder if I should replace anyway. No way to  strip  and reassemble as the threads distort. Its not just the expense but also  finding the expertise and having confidence in the outcome.

[Yngmar]

I've had the shroud chainplates out twice, first time to rebed them as they were leaking and second time to replace the bolts, as one had a small crack in the head.

You will not see crevice corrosion from the outside, only if you remove the deck fittings. It's no big deal and you don't have to unstep the mast, you can support it with halyards and do one side at a time, won't even lose your rig tuning if you count the turnbuckle turns.

Once the outer part is off the inner part can be slid down for inspection/cleaning. The rods itself I didn't remove as they were dry and unaffected.

The failures I've heard of didn't occur at the rod ballhead, but at the deck fitting or bolts. One 38 Ocean owner lost his mast this way in Turkey and had quite a story to tell.

[blue-max]

On FB there are more accounts of rig failure from this component. Keeps me thinking a better design is needed.

[blue-max]

I have done some further research but have some further questions . It looks like the underdeck fittings cannot be disassembled for re-use. The crimped cup at the base destroys the threads as its unscrewed; the 24mm nuts on the rod within the lower bracket can't be undone because there is insufficient space to  get a spanner on them. Perhaps not, maybe someone has achieved this with a socket and wrench? If so it might be possible to extract  the assembly minus nuts by taking it through the top of the deck. The weak spot it appears is the lip at the top of the rod which  is held between  the deck plate and its backing plate. If I understand Ingmar correctly I should be able to  see the lip when taking out the plates holding it and then decide from there what to  do.

For peace of mind I think I will  end up replacing the tie rod ( I have rust stains at the base of the tie rod on the painted heel) But I am thinking to  change the design. My guess is the top lipping is copied from rod rigging - which  would require regular inspection and re-welding. So  I am thinking to  replace with a spherical or semi spherical threaded rod end joined to  a new rod (threaded at each  end) From memory I think this  rod is only 14mm diameter ( the shrouds are 12mm wire) so  perhaps the rod should be 16mm diameter. I don't see the point of the 24mm threaded rod coming up  through the bracket. Its always the weakest link which  breaks. The 16mm rod could run through to  the inside of the bracket and held by double nuts. The spherical threaded rod end could be fully threaded or half bore. The join could be sealed by welding. To get semi spherical rod end I could I could cut  a full bore one in half and then weld the top  connection. Should last my lifetime! But I have not been ale to  source these rod ends in 316 only in 304 stainless ( the existing is  304 ) The advantage of this design is that there is much greater surface area for contact  of the components and it allows for articulation but it may be necessary to  have a spacer between the deck  plates to accommodate for the greater depth of the rod end .

Your thoughts appreciated       

[Yngmar]

Rod rigging is not welded (that'd be disastrous), nor are there threaded on cups. The mushroom shaped end is cold formed out of the rod itself in a hydraulic press. Like this one for example: https://www.talurit.com/products/powerful-swagers/special-machines/rod-presses/rp-60t/

Do you have a photo of yours to ensure we're even talking about the same thing?

Rods are typically made of Nitronic 50 or similar, not 316 stainless like wire rigging.

[blue-max]

Thanks for the information Yngmar - I was only repeating what a rigger told me many years ago, Glad I did not take his advice (My rod forestay was still good after 40 years) I doubt this method of forming the rod ends would be available in Turkey - perhaps in Istanbul where super yachts are made. Can you answer my question about being able to  inspect the rod end from the top with the deck plates removed.
Its also obvious from the photo that its impossible to undo the bottom nuts with a socket.

I am also wondering about the deck structure at the place of the deck  plates - is it solid fiberglass or sandwich? It surely must be solid to  avoid compression weakness

PS photo file too large to attach  will try  later to  add

[blue-max]

 I'll try and post another photo  which shows the vulnerability of the standard design for tie rods . The forged/extruded end rests in a semi spherical spacer which is contained in a shaped plate welded to the base of the back plate. This is a vulnerability. I think I will replace the back  plate with a thicker one machined to  take a threaded semi-spherical end. Sorry won't let me attach

[blue-max]

see attached photo

[Yngmar]

Those look the same as ours at the top, different at the bottom - our bottom was simply a thread cut into the rod and bolted into the massive stainless steel brackets attaching it to ~50mm plywood laminated to the keel matrix. This was done with jam nuts, so tension could be adjusted there, although never had to and it might be to turn the nuts in place.

The backing plates don't look too bad, I'd try polishing them and see if there's any more than just a few pits. Check the outer half too and definitely use new bolts and nuts when refitting it (buy from an industrial supplier online, not the chandlery stainless bin). Rod rigging typically fails at the cold formed mushroom head bottom where it bears the load, so that needs to be inspected thoroughly, or get new rods made since you have it all out anyways and the cost for such short pieces shouldn't be astronomical if you find a company doing it.

Then keep it all nicely sealed and dry and it'll last forever!

[blue-max]

That's not mine but from a sister boat. I'm in the preparation stage for the Spring. I'll post some more pics (one of the cup  and the other from my boat) now that I found away to reduce size.
I would still like to know if the deck  is solid where the deck plate and its backing plate make contact. If not it would need spacers to  protect it from deformation due to compression when torqueing the screws. Can you recall the diameter and length of the screws. Is the backing plate threaded or are there nuts at the end of the screws? From the photo it looks like the screws are fitted by nuts 

[blue-max]

 2 was too many!

[Yngmar]

Yes, our deck was solid, the bolts therefore not very long. My order from wegertseder.com is below. Your much larger boat would probably use larger bolts, or perhaps ours were massively oversized

There are nuts on there, washers and spring washers, I've also added threadlocker when refitting.

Code: [Select]

Pos. Art.-Nr. Bezeichnung Werkstoff Abmessung Menge Preis
1 2610-278 DIN 7991 Senkschrauben mit Innensechskant ROSTFREI A4 M 12 x 50 10 St. 12,56 €
2 2900-244 DIN 934 Sechskantmuttern ROSTFREI A4 M 12 20 St. 6,15 €
3 1500-380 DIN 125 Unterlegscheiben Form A ROSTFREI A4 A 13 25 St. 4,03 €
4 1710-934 DIN 127 Federringe Form B = glatt (=Standard) ROSTFREI A4 B 12 50 St. 4,06 €


[blue-max]

many thanks