Standing Rigging Extensions

RichH · Jun 4, 2009

Again you are totally totally WRONG.
You are basing your 'theory' solely on tensile strengths that are for ductile failure only, completely ignoring the fatigue endurance limit values. Ignoring the fatigue values (by published values, adding adequate safety factors, or by values derived by actual destructive testing) is foolhardy and omits one of the MOST IMPORTANT factors pertaining to cyclically loaded structures such as boat rigging. One who sizes such solely on tensile values alone is totally omitting these important selection factors.
A chain link is a complex beam and is much beyond simple tensile values to ensure that it will 'work' over long term service. Recommending such is totally irresponsible.

Ross · Jun 4, 2009

If we accept your premise that chains under cyclic tensile loads are subject to fatigue failure, what are we to do about those chains that we attach to our anchors?

tsmwebb · Jun 4, 2009

RichH said:
Again you are totally totally WRONG.
You are basing your 'theory' solely on tensile strengths that are for ductile failure only...

A quick google search suggests the SWL for proof coil in SS or galvanized >= SWL for SS rigging wire of the same nominal wire size. If the OP has marine forks then he can probably fit a size larger chain than he has wire. I have done no research here, but my suspicion is that we're talking about giga cycles before failure within the SWL... No? I'd worry more about chafe than cycling.

--Tom.

Ron20324 · Jun 4, 2009

MacMikey said:
My shroud lines have turnbuckles and if I were to add addjuster plate (ss bar with holes) and another turnbuckle to attach to the chain plate do any of you see a problem with having to turnbuckles on the same shroud line?

As I said before, Beneteaus come with two turnbuckles connected back-to-back by the threaded rods. I guess they do this to make a quick hookup when stepping the mast, then have enough travel to tighten the mast to it's proper bend.

Ross · Jun 4, 2009

And I was catching flack for suggesting something strange?

RichH · Jun 4, 2009

Ross said:
If we accept your premise that chains under cyclic tensile loads are subject to fatigue failure, what are we to do about those chains that we attach to our anchors?

Simple answer, just like the other segments of the rigging system .... when the accumulated cycle time at load (≥1/3 UTS) exceeds approximately 1 million cycles, we watch them break.

RichH · Jun 4, 2009

tsmwebb said:
A quick google search suggests the SWL for proof coil in SS or galvanized >= SWL for SS rigging wire of the same nominal wire size. If the OP has marine forks then he can probably fit a size larger chain than he has wire. I have done no research here, but my suspicion is that we're talking about giga cycles before failure within the SWL... No? I'd worry more about chafe than cycling.

--Tom.

Actually its only about 1 million cycles needed for fatigue fracture when loaded above the published "fatigue endurance limit" of the material. You dont design for only tensile values when cyclical loads are involved, especially with 300 series stainless. The Fatigue Endurance Limits of most 300 series stainless is approx. 1/3 of Ultimate tensile strength or 30ksi. Of course the "geometry" of the structure may affect further 'de-ratings' of the strength values .... such as in structure involving various 'flexure' modes such as beams ... and this case a toroidal beam in the form of a chain link. IF you stay under the applied stress as defined as the 'fatigue endurance limit' then the service life can approach infinite cycles.

Ross · Jun 4, 2009

Is UTS ultimate tensile strength? If so that represents a loading in excess of the usual 1/5 load to breaking strength safety factor, rendering this entire discussion moot.

tsmwebb · Jun 4, 2009

RichH said:
... IF you stay under the applied stress as defined as the 'fatigue endurance limit' then the service life can approach infinite cycles.

Yes. I think that's the "if ... then" that we're looking at all things being equal.

--Tom.

RichH · Jun 4, 2009

I respectfully suggest that you get your medications changed.
Blue water boats usually are designed at FS=4; coastal @ 3; inshore @ 2.
FS=6 would represent cranes, etc. in lethal service, etc.

Ross · Jun 4, 2009

RichH, You are beginning the sound like a young robin. Most of the time I find your posts to be reliable but on this one you have been quibbling.

Maine Sail · Jun 4, 2009

Ok ..

OK guy lets tone it down just a tad please.

This discussion is great, and we welcome more of it, but when we start taking it to a personal level... well that is not within forum guidelines or acceptable. You guys can butt heads all day long UNTIL you begin throwing personal jabs, even mild ones, as they are ALWAYS intended to get under anothers skin..!

We can still have this discussion without bringing it to a personal level...

Acceptable strong or bold statements would include:

"Again you are totally totally WRONG."

"Recommending such is totally irresponsible."

Unacceptable & unnecessary personal jabs would include:

"I respectfully suggest that you get your medications changed."

"Therefore inspite of your effort to baffle with BS"

Good evidence based discussions, heated or not are great but please leave the other stuff out it adds nothing to the conversation other than feeding a fire..

Thanks!

I really do like this thread, lots of good info!

Ross · Jun 4, 2009

Re: Ok ..

Mainesail, While we have your attention, I have a question. The other day when we were talking about anchor lights You made a post and I determined that our forum program doesn't recognize subscripts and superscripts. Is there a low cost way to correct this?
It will make life much more fun if we can post location as D>M>S with the proper superscripts or with temperature as 76degrees F instead of 760 F.

Maine Sail · Jun 4, 2009

Ross said:
Mainesail, While we have your attention, I have a question. The other day when we were talking about anchor lights You made a post and I determined that our forum program doesn't recognize subscripts and superscripts. Is there a low cost way to correct this?
It will make life much more fun if we can post location as D>M>S with the proper superscripts or with temperature as 76degrees F instead of 760 F.

That is a good question for the big guy. Believe it or not but I am about the most computer illiterate guy you'll find on here..

I tried to look and see if I could figure it out the other day but could not so reverted to a link. My guess is Phil would know how to do that.

Sorry for the hijack! Now back to our regular scheduled programming..

Steve Dion · Jun 4, 2009

I can't wait until the surveyor sees this!

I bet the insurance company is looking forward to insuring this vessel too!

Ross · Jun 4, 2009

All hands on deck! Clear the decks, prepare to repel boarders!!

tsmwebb · Jun 4, 2009

Steve Dion said:
I can't wait until the surveyor sees this!

I bet the insurance company is looking forward to insuring this vessel too!

Is that re: chain as a rigging element or a home modified boat not built to plan? Many "classic" and classically styled boats use chain as rigging elements. You see it a lot on bowsprits which are much more highly loaded than shrouds. I presume some insurance company is covering them. RH is right that it has to be done correctly, but it is not an insane or unprecedented thing.

PS. Just as a data point NBS safety factors for upper shrouds ~3.0 to 3.2 and about 15 for fore/back stays. But in practice rigging is "next size up" so factors are usually a little bigger. Nobody really expects rigs to spend a lot of time at max righting moment though.

--Tom.

Manny · Jun 4, 2009

What's the base of the mast like?

Is there any reason you just couldn't cut the base of the mast down the amount that the cabin top was raised? Are there sheaves or anything at the base? This way the mast ands sails would still be at the designed height keeping the center of effort (is that the correct term?) as designed. A cheap hacksaw or a dremel and a few minutes of careful measuring would do the job.

Manny