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Old 10-08-2015, 08:03   #106
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Re: Radar Arch Fail - Cautionary Tale

He says he is going to do it again WITH IMPROVEMENTS TO FASTENERS AND PADS.

He didn't say he was going to hide anything from the buyer, in fact by posting here it's pretty clear he can't hide anything to a determined buyer.

Sheesh.

I really dislike when folks get self righteous. Maybe it's just human nature?
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Old 10-08-2015, 08:06   #107
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Re: Radar Arch Fail - Cautionary Tale

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Originally Posted by Kenomac View Post
You and the OP are not understanding the recommendations make by the engineers in prior posts. Read them again. Most likely the cause of the sheared bolts was due to accelerated loads bearing down and essentially cutting through the undersized bolts. It's unlikely the wind was the cause of the failure.

Another issue, and in some ways more of a concern ethically.....Now the OP intends to remount the same failed rig and sell it to an unknowing buyer.
You should re-read your posts checking for acceptable tone before posting.

Several possibilities have been explored in previous posts.
Another possibility is damage from hurricane ODILE.
You don't have to agree for it to be true.
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Old 10-08-2015, 08:11   #108
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Re: Radar Arch Fail - Cautionary Tale

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Originally Posted by hamburking View Post
You should re-read your posts checking for acceptable tone before posting. .
Acceptable tone=political correctness=B.S.

Sorry, I apologize if I twisted any panties.
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Old 10-08-2015, 08:13   #109
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Re: Radar Arch Fail - Cautionary Tale

I think the op is best off patching the holes in the side of the hull and sell the boat without an arch that's destined to fail again.




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Old 10-08-2015, 08:22   #110
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Re: Radar Arch Fail - Cautionary Tale

Quote:
Originally Posted by Kenomac View Post
Acceptable tone=political correctness=B.S.



Sorry, I apologize if I twisted any panties.

This apparently doesn't apply to you, given your sensitivities in other threads.

Walk the talk.

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Old 10-08-2015, 09:45   #111
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Re: Radar Arch Fail - Cautionary Tale

What a pile of irresponsible horse pucky!

Atlantic Towers has sold tens of thousands of arches over the last 20-years. This is the only documented failure I can find.

YES - something failed but I seriously doubt it was due to the strength of the mounting bolts (shear tension compression - who cares?). Thousands of other towers have stayed up in far more stressful conditions.

The OP really needs to determine what was different in his application and experience. If you just blame it on "weak bolts" then you will never understand why those particular bolts failed when they have tens of thousands of years of successful experience in the identical application on other boats.

WHY did the OP bolts fail when others don't?
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Old 10-08-2015, 09:53   #112
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Re: Radar Arch Fail - Cautionary Tale

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What a pile of irresponsible horse pucky!

Atlantic Towers has sold tens of thousands of arches over the last 20-years. This is the only documented failure I can find.

YES - something failed but I seriously doubt it was due to the strength of the mounting bolts (shear tension compression - who cares?). Thousands of other towers have stayed up in far more stressful conditions.

The OP really needs to determine what was different in his application and experience. If you just blame it on "weak bolts" then you will never understand why those particular bolts failed when they have tens of thousands of years of successful experience in the identical application on other boats.

WHY did the OP bolts fail when others don't?
Most arches are probably mounted with the forward poles on the deck and the rear on the deck or a sloping transom. In those cases the bolts will be under a fraction if the tension that they would be when the arch is mounted on the vertical hull.
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Old 10-08-2015, 09:58   #113
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Re: Radar Arch Fail - Cautionary Tale

Quote:
Originally Posted by hoppy View Post
Most arches are probably mounted with the forward poles on the deck and the rear on the deck or a sloping transom. In those cases the bolts will be under a fraction if the tension that they would be when the arch is mounted on the vertical hull.
Not really, those would mostly be in bearing instead of shear.
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Old 10-08-2015, 10:17   #114
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Re: Radar Arch Fail - Cautionary Tale

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Not really, those would mostly be in bearing instead of shear.
If the rear poles were mounted on the deck or a moderately sloping deck, then a lot of weight would be supported by the deck/transom rather than the bolts.

The tensile strength of bolts is much higher than the sheer strength (sheer is approx 60% of tensile from what I've found)
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Old 10-08-2015, 10:22   #115
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Re: Radar Arch Fail - Cautionary Tale

Quote:
Originally Posted by TacomaSailor View Post
What a pile of irresponsible horse pucky!

Atlantic Towers has sold tens of thousands of arches over the last 20-years. This is the only documented failure I can find.

YES - something failed but I seriously doubt it was due to the strength of the mounting bolts (shear tension compression - who cares?). Thousands of other towers have stayed up in far more stressful conditions.

The OP really needs to determine what was different in his application and experience. If you just blame it on "weak bolts" then you will never understand why those particular bolts failed when they have tens of thousands of years of successful experience in the identical application on other boats.

WHY did the OP bolts fail when others don't?
I agree with you that I suspect something else is going on.
Although I maintain that mounting the bracket on the side is not a good way IMHO... as the bolts are in direct shear. If mounted on deck , the shear is far less as the force component is either tensile or on the deck surface (mostly depending on angle to the deck)
I suspect some bolts loosened up allowing things to work a bit. Hard to say. But with the bracket at 90 degree angle I could see the leverage on the bracket working them loose for sure. I've seen a lot of towers on power boats, none were side mounted that I remember.
With the 350# or so up that high, there is pretty good leverage going on.
The OP is selling the boat, If I were him I would just put quality bolts in and sell it.
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Old 10-08-2015, 10:25   #116
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Re: Radar Arch Fail - Cautionary Tale

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Originally Posted by hoppy View Post
Most arches are probably mounted with the forward poles on the deck and the rear on the deck or a sloping transom. In those cases the bolts will be under a fraction if the tension that they would be when the arch is mounted on the vertical hull.
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Old 10-08-2015, 16:49   #117
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Re: Radar Arch Fail - Cautionary Tale

It wasn't a normal shear failure. If the bolts had sheared at normal steel stresses there would be deformations around the bolt holes.
It was fatigue (or possibly crevice corrosion) !!!!
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Old 10-08-2015, 22:55   #118
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Re: Radar Arch Fail - Cautionary Tale

Quote:
Originally Posted by hamburking
You should re-read your posts checking for acceptable tone before posting. .
Acceptable tone=political correctness=B.S.

Sorry, I apologize if I twisted any panties.
Quote:
Originally Posted by colemj View Post
This apparently doesn't apply to you, given your sensitivities in other threads.

Walk the talk.

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Old 11-08-2015, 06:21   #119
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Re: Radar Arch Fail - Cautionary Tale

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Originally Posted by Kenomac View Post
Acceptable tone=political correctness=B.S.
Actually, Acceptable = agreeable; tolerable; allowable; suitable; adequate; satisfactory.

Whereas, Political correctness a isterm used to criticize language, actions, or policies seen as being excessively calculated to not offend or disadvantage any particular group of people in society.
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Old 11-08-2015, 11:09   #120
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Re: Radar Arch Fail - Cautionary Tale

Allow me to introduce some fundamental principals of failure analysis used by engineers as I recall from my younger life as a mechanical engineer. The bolts in question as mounted on the hull are subjected to multiple stresses. First, the bolts are stressed by the tension introduced by tightening the nuts. Second, the bolts and mounting flanges/backing plates are subjected to the forces necessary to resist the torque of the load on the end of the arch -- this bending moment expressed in units of torque (ft. lbs.) is transferred to the several mounts and met with a combined counter torque by the bolts in shear once the friction between flanges/backing plates is overcome (if it is overcome). Third, the dynamic force of the load (dinghy) acting through the cantilevered arch as measured by the Mass x acceleration as the arch load cycles in a seaway. The vectorial sum of these forces acting on the cross-section of the bolts is the principal stress vector, which will be oblique to the cross section of bolt as it combines lateral and axial stress components. Interestingly, at the time of installation or maintenance of the bolts, an additional torsional stress is introduced by the act of tightening the nuts, and is often the time that fasteners will fail if that torsional component of the principal stress exceeds ultimate tensile strength in combination with other loads then acting on the fastener.

The principal stress, once determined is then compared to the yield stress of the material, discounted to accommodate stress concentrators such as cut threads and other abrupt changes in geometry, and deformation of the bolt shank if any, should the mounting flanges/plates have shifted. Cut threads are a severe stress concentrator as compared to rolled threads. The cyclic stress (such as the dink suspended on a bobbing boat) introduces the doctrine of fatigue, which can be quantified using empirically derived curves showing number of cycles at given stress levels. As I recall, carbon steel has an infinite life when subjected to cyclic stress less than 30% of the yield strength -- unlike all others such as aluminum and stainless which have finite cycle life at any level of stress. Cyclic stress militates changing fasteners from time to time in order to avoid fatigue failure.

Corrosion cracking, among other sources of introducing significant stress concentration, drastically affects the cyclic life of a fastener, and will lead to failure as the crack propagates toward the center of the fastener from its outside surface. Far less stress is required to propagate a crack to failure than would defeat a smooth surface. Torsional stress and bending moment related stress are transferred to the outside surface of the fastener, the center of the bolt being its neutral axis. Tension force stresses the entire diameter uniformly, but surface cracking or sharp deformations will diminish the useful loading of any fastener.

Fatigue failures generally show concentric rings across the diameter of the bolt working their from the point of highest stress inwards, and leaving a portion of the bolt that shows either a shear or tension failure when its ultimate strength across the diminished cross sectional area is reached.

I won't pretend to analyse the failure at hand here, but perhaps the foregoing principals will be useful as you consider how the deck arch mounting hardware is loaded statically and dynamically. Consideration of one or another of the stress components is inadequate as a basis of analysis. It is the vectorial sum of all stresses acting on the fasteners that must underlie any investigation of a failure -- and should govern design and installation means and methods.

With Best Regards,
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