Lower Shroud Under deck mounting broken

[Screen Saver]

Hi. Does anyone know how the stainless strut shown in the picture is attached to the underside of the Baby Stay Deck fitting. After a very scary large bang I found mine would seem to have broken lose from the underside of the deck fitting that holds the topside baby stay.

If anyone knows how to remove this on Hunter 49 that would be better, but if not any ideas drawings of how it connects to the top underside deck fitting would be great news.

Thanks
Alan

 

[dlochner]

It is (was) probably one piece. Also it is the port lower shroud. A baby stay goes is between the forestay and the mast and is used to prevent the mast from pumping.

 

[Screen Saver]

Hi Dave
Yes your right about the name, my mistake.
So given this is a Hunter with selden B&R rig, is this a standard part that selden would supply perhaps in different sizes or do you think it would be a custom part made by Hunter in production ?
Any idea what its right name for it would be ?

 

[SG]

Hi. Does anyone know how the stainless strut shown in the picture is attached to the underside of the Baby Stay Deck fitting. After a very scary large bang I found mine would seem to have broken lose from the underside of the deck fitting that holds the topside baby stay.

If anyone knows how to remove this on Hunter 49 that would be better, but if not any ideas drawings of how it connects to the top underside deck fitting would be great news.

Was the deck damaged or did the connection pull through the deck? Do you have picture where the stay goes through the deck? Did you look behind the settee to see what the fitting connection looks like at the stringer and/or hull? Is the rod loose from there?

 

[jssailem]

From a Basic approach (have not seen this part of Hunter rig) Baby stays are in pairs, one port and one starboard. Do they look the same? If not can you see the differences? Pictures?

 

[dlochner]

Hi Dave
Yes your right about the name, my mistake.
So given this is a Hunter with selden B&R rig, is this a standard part that selden would supply perhaps in different sizes or do you think it would be a custom part made by Hunter in production ?
Any idea what its right name for it would be ?

It is a chainplate. It is probably a continuous from the anchor point below decks to the shroud. There may be a separate cover on deck where the chainplate exits or the cover is integral to the chainplate. Some where behind or below the settee it should be attached to something substantial with several bolts. The plastic cover on the interior is decorative. A photo of the connection between the chainplate and shroud would be helpful.

To remove the chainplate the shroud will need to be disconnected and the chainplate unbolted from wherever it connected. It should lift out. There should be a sealant around the chainplate and that will need some persuasion to give up its grip.

Contact a rigging supply company, like Rigrite or Rigging Only (US companies) about replacements.

The bigger issue is why did it break? The simple answer is the tension on it was too great. The actual reason may involve crevice corrosion. Stagnant water surrounds the SS chainplate which causes it to pit, corrode, and form cracks. Eventually, it is too weak to withstand the loads and it cracks. It would be prudent to remove the starboard chainplate and inspect and perhaps replace it.

 

[Terry Cox]

Different model boat here, but our stays are secured to the hull via a large bracket imbedded into the FRP during layup. Saw a picture of one once, but no idea where, probably on this site. The bottom of the SS rod shown in your picture likely is attached to this wide bracket, which is designed to spread the load placed upon it. Might need a yard tech look into it for you , or perhaps Marlow Hunter can shed some light.

 

[LeeandRick]

From a Basic approach (have not seen this part of Hunter rig) Baby stays are in pairs, one port and one starboard. Do they look the same? If not can you see the differences? Pictures?

Wrong A baby-stay is typically a wire attached to the mast near the lower spreaders and the deck approximately 25% forward for the mast step. The baby-stay, unlike an inner forestay, does not carry a sail. The stay is the forward counterpart to the aft lower shrouds.

 

[Screen Saver]

Well its off and will attach some pictures. The design I believe is strong and sound. From the round fitting on the deck a 14mm solid rod is inserted into the flat round deck fitting. It protrudes well into the top plate at least an inch and is welded well all the way around. The 14mm rod broke just off at the base of the deck mounted plate, and it would seem to have been broken for some time based on the colour, with only a small amount of fresh metal holding it. When this broke all that was holding it was the deck fitting and fortunately imbedded within the fiberglass deck is another plate onto which the deck fitting is bolted. I am assuming the bang was as the long rod letting go, the deck took up the load and I guess I was lucky it did not tare the deck fitting out and the mast come down.

As to the cause; The possibility of being over tight seems unlikely, both because a rigger had suggested just recently I should tighten the rig and because I had in the last 12 months adjusted the rig based on Seldens white paper for this rig. In very basic terms, it gave a very rough method and stated you could not over tighten it with a 12 inch spanner and do not under any circumstance place an extension on the spanner. It went on to say how to measure the stretch in each stay from standing free to tensioned. Both if these I followed and if anything, the passing rigger was a little right as my stretch measurements were not quite as far as selden suggested they could be. These were also measured under a 30 knot load. However I believe the correct tool to measure this is a lose ( or something like that) I will see if I can buy one to more accurately measure the tension

So there is some suggestion water could have caused this possibly due to lack of sealant, or simply age of sealant. from my limited knowledge this also is not applicable. a) there was no sealant other than those around the actual bolt wholes to stop water coming inside the boat. The plate itself as shown in the photo has not be cleaned, it had no sealant and lifted off the deck very easily. I also don't believe any should be there. b) my understanding of stainless is that stainless in water 24x7 never seeing air is far worse than stainless which is in and out of the water. Stainless requires water and air in and out to form a coating oxidizing to prevent corrosion and coat in what we call or see as tea staining which is in fact protecting the stainless. So by sealing it and trapping water in there for long periods would add to the problem.

My believe is this just ware and tare and it broke at the weakest point just below the weld probably due to heat from the weld. In terms of age and ware the boat has done nearly 3 circumnavigations in terms of NM, more than many others would do in 25 plus years. It has seen 70+ knots and sailed 75% to 85% of its NM, so perhaps this is reasonable.

I have contemplated increasing the rod from 14mm to 18mm, but at this point I dont know if I could get the same grade of rod, nor am I confident of stainless welders in Philippines, so I might just have to buy a new one. I will probably buy two and do the other side before I do lose the mast.

The end of the Rod is colored coded what looks to be Azure Blue ( 309 Stainless ) until today I never new it existed.
The chance of me getting that here I would estimate as zero.

Time for a beer and think through the next step.

 

[dLj]

You’ll have a bit of a time getting 309 just about anywhere. But it’s not impossible. That being said, if you can get cold finished 316L it has the same mechanical properties as 309 and is quite corrosion resistant. If you can find standard 316, it has identical mechanical properties to 309. However, that may be more difficult to get than either 316L or 309. Modern mills producing these stainless alloys produce what’s called dual certifiable 316 family alloys so really just about all 316 today is 316L.
The so called “tea” you mention I disagree with. It is an indicator of corrosion processes that I would not want present.
Your photos are a bit blurry so I can’t really see the fracture surface so can’t really tell you what was going on there but general appearances do indicate a not unlikely stress corrosion cracking scenario. But really I’d have to be able to examine the fracture surface to know for sure.

cold finished 316L should not be difficult to find.

dj

 

[dlochner]

One factor in its failure is crevice corrosion. Another factor may well be age and experience. You didn't mention what you were doing when it broke. A sudden high load from a wind gust or a gybe could have been the fatal blow.

On the attached photos I've indicated where I think there is corrosion. You might try contacting the a company that produces rod rigging for help.

 

[Noodat Lady]

When I bought my little boat, the seller walked me through the rigging. Mostly new terms to me, I made an effort at memorising them. He taught me the term "baby stay" among others. A week later I paid a sailing instructor to come and give me a lesson on rigging, mast stepping etc. When I proudly used the term baby stay he slapped me down hard. This was a shroud, not a stay. Stays run fore and aft. He made the point that nomenclature on a boat can be a matter of life and death, since things can happen so quickly and giving or understanding the wrong name in a crisis may be fatal.

So, this thread is about a shroud, not a stay, and I think OP or Mods need to rename it.

Bob

 

[LeeandRick]

Looking at a picture of A Hunter 49 this assembly appears to be the chainplate for the lower shroud that attaches just below the lower spreader. In a picture it looks like the shroud angle changes a few degrees at the rigging screw (turnbuckle) attachment. Was there any deck damage under the fitting that may have caused a bending moment at the break point? Definitely check the other side.

 

[SG]

Is this a picture of deck configuration? I trust that the fitting in question is connected to the one with the red-arrow?

I'm guessing from your information that the "rod" goes into the base plate which is above deck? As noted above, if the above deck fitting really took that uplift, then I'd check that carefully to see if there was any damage to the deck below or whatever is reinforcing the connection.

Is the fitting threaded into the base plate? or, Is there a nut on the end of the fitting above deck (which would hidden by the turnbuckle covers in the picture above)? or, Was the fitting all welded together? (which I doubt, but...)

(On our boat, the chain plates slide through a fitting which is sealed. If the chain plate breaks or the shroud (s/k/a side stay, etc.) parts, then the deck is not taking a load).

 

[Brian D]

@Noodat Lady, one of the mods took care of the name for you.

 

[Screen Saver]

So I will try to answer all the questions;

Yes 309 is impossible to get here without ordering internationally. 316 is also very much a challenged both need to be imported. I’m no expert in metals or strengths but based on my general understanding over the years and this link AISI 309 Stainless Steel vs. Annealed AISI 304 :: MakeItFrom.com
I have decided to go for 304 and increase the size to around 19mm almost 30% and do both sides.
I will have to agree to disagree with the tea staining sorry about that.Its a bit like saying all 4 legged animals are dogs in my view. So yes if there is a fracture or crack then you agree you will get tea staining in all probability ( all dogs have 4 legs) but because there is tea staining does not mean its bad or a fracture, but simply oxidization protection ( another words not all for legged animals are dogs). Just my view and I could well be wrrrrrrrrrong.

Yes crevice corrosion could play a part, although clearly the shaft had been machined down from the threaded end at around 16mm on the thread, to the nice polished shaft to around 14mm. So where did the crevice come from initially if not stress crack. So yep the thread at the bottom is bigger than the shaft, which seemed very odd to me. So how did the crevice get there, possibly simply from age and stress.

At the time there was about 14-18knts of true steady beam wind and around 1m sea’s So nothing big and as I was in no hurry I was reefed on the main a little, full overlapping job out.

The gear is produced by Selden.

Yes the post heading probably should be changed, yep I’m told it is actually called D1. Im not sure how to change the heading.

Yes the pictures provided by Annapolis are in fact correct. I looked for any angle issues and yes there is a difference. As this is a production boat to actually correct that would be significant. My guess is the strut would need to tilt probably 4 degrees inward at the top to align perfectly with the stay line from deck to just below cross tree. However un like the J boat issues of past for example, this miss alignment is not transferred to the turnbuckle and the design allows the turnbuckle to move a good 40’ before any pressure would be put on it. There would be some horizontal inward pressure on the deck fitting itself as a result of the angle mismatch. While I agree its not ideal, its not something I will attempt to change. Clearly the deck is reinforced and strong as it took the full load and nothing is visibly wrong.

Yes the rod goes from the bottom of that heavy inverted U bracket, where there are two nuts on 16mm rod, up through a couple of shelves, through a plate set in the deck that the chain plate is bolted too and it goes through the chain plate by about 25mm. The top is not threaded its welded 25mm up each side and 14mm across the top and bottom. Looks good. It broke as it comes out of the chain plate base, and its not welded on the bottom of the chain plate.

With hind sight I have now attributed the blame 50% to ware & tear and 50% to Waisai–To be dis masted or not–Part 1

 

[DArcy]

It looks like the chain plate is long past its best before date. I would assume all of the chainplates on the boat would be in similar condition and should be pulled for inspection before being trusted.
I'm more than a little surprised there is no sealant where the deck is penetrated. Your discussion about standing water on stainless is not wrong but properly applied sealant will keep water away from the stainless, not trap it against it. The lack of sealant may have contributed to the corrosion. If the bolts had sealant, compare them to the condition of the rod which didn't have sealant to give yourself an idea of what is the right way to go.
And staining is a sign of corrosion, it is not desirable.

 

[dLj]

Oversized threaded ends is common for a loaded piece such as this one. There are several reasons. One reason is that allows for reducing a stress riser at the transition of the central bar to threaded end. You would do well to follow that geometry.

crevice corrosion/stress corrosion cracking are very similar mechanisms and in stainless steels have the same reasons for starting. Crevice corrosion starts at a small surface imperfection where a corrosion process starts and due to the limited access to oxygen the passive oxide layer is not reformed. The limited oxygen access is due to the crevice not allowing the oxygen the pass the the surface of the now unprotected stainless surface and the crevice along with its corrosion product grows into a crack and you are off to the races so to speak. Stress corrosion cracking is similar, without going into a deeper explanation, but the member where this process is happening is under stress. There are many reason that corrosin can start on the surface of this material but without the parts in my hands I can't tell you what your case is. Also, you can get a stress level that creates a small crack, initiating this process.

So what does this tell you? To avoid this you need to allow good access to air allowing maintenance of the passive oxide layer on the surface of the part. Using 304 in the marine environment increases your difficulties as it is also prone to chloride attack which can happen to that alloy. Both 309 and 316 are resistant to that form of degradation. It would be my suggestion to rebuild such that you can easily inspect every bit of that rod and be able to clean it if necessary.

With all due respect, rust colored weeping of any form is not acceptable for these alloys and demonstrate any number of corrosion problems that are not desirable. But you can believe whatever you wish.

dj

 

[Screen Saver]

DJ
You appear to be far more knowledgeable than I in this area and it makes me wonder for where did you gain this knowledge. I would be interested if there is a dummies explanation for "One reason is that allows for reducing a stress riser at the transition of the central bar to threaded end" I had assumed it was all just a simple matter of increasing the cross section in the low par of thread.

So I assume this "So what does this tell you? To avoid this you need to allow good access to air allowing maintenance of the passive oxide layer on the surface of the part" was the bases for hunter not sealing this, other than the bolts. So a) if it got water there it was not trapped and b) it could get air as well.

The link I provided above shows very little difference between 304 and 309 and I was hoping the increase in cross section would compensate for difference in strength and potential for stress related fatigue or cracks. However ultimately I have only a couple of choices, go now with 304 and a 30% increase in cross section or order the full thing from Selden which will take weeks.

I appreciate youre response. Can you tell me whether you agree that a constant changing mixture of air and water is far better for stainless than, either fully submersed 100% or never seeing water. In dummy terms my understanding is Stainless submersed ie no air is problem and the reverse while not as bad is equally a problem as it does not form the oxidizing layer which protects it.

Can you also tell me how this oxidizing layer that protects stainless might apper to the human eye, or are you saying it has no visible singns.

Thanks again for your sharing your thoughts.

 

[dlochner]

Can you tell me whether you agree that a constant changing mixture of air and water is far better for stainless than, either fully submersed 100% or never seeing water. In dummy terms my understanding is Stainless submersed ie no air is problem and the reverse while not as bad is equally a problem as it does not form the oxidizing layer which protects it.

All water contains some free oxygen molelcules and ions. When water flows past SS some of those molecules and ions attach to the SS and form the protective oxide layer. When water is not free flowing, say underneath a deck fitting, the oxygen is depleted and thus the oxide can't form. The metals then begin to corrode due to the chemistry of the metals.

The lack of sealant in your case, allowed water to get trapped and become stagnant near the chainplate which started the corrosion process. A SS prop shaft works and does not usually corrode because the water around it is free flowing. However, crevice corrosion can occur on the shaft in the cutlas bearing because the ribs of the bearing cause some water to become stagnant and oxygen depleted. Occasionally rotating the prop helps to avoid this.