Great picture Wes...
You posted everything I remember from my "Strength of Materials" class.
You posted everything I remember from my "Strength of Materials" class.
3126 CAT needs replacement!
- Thread starter searaycruisn
- Start date
- Nov 26, 2006
- 7,628
- Boat Info
- 2008 44 Sedan Bridge
- Engines
- Cummins QSC-500's
Straight Drives
If you look at the inside of the rounded, broken metal part, you see numerous concentric rings. If I'm understanding this correctly, that shows that a small layer failed at a time, then the piece kept functioning for quite a long time until the remaining metal could not support the load and the rest tore away all at once (no more concentric rings).
Alex D
Active Member
I would assume that beach marks refer to marks left on the hull from beaching the boat.
Yours truly,
Mr. Obvious
Yours truly,
Mr. Obvious
OK... where are the red balls?
Alex D
Active Member
Look down, Gary, look down !:grin:
very good.... I like a person that is quick like that. You must be from VA.
Alex D
Active Member
No points Gary ... sorry ... I boat in Southern VA and live in NC, but look at the flag in my avatar. Do you know what it stands for?
I am not familiar with the flag... The colors are German but I don't know the crest....
Alex D
Active Member
techmitch
Well-Known Member
- May 1, 2008
- 8,323
- Boat Info
- 1999 270 DA
- Engines
- Twin 4.3s W/Alpa I Gen II's
wes where did you get this pic? it looks exactly like the crank i took out of my 84 wellcraft 260 with a 350 eng. it lasted about 850 hrs. i think it was around 1992 when i did that job.
Jim240
Member
Years as a grad student running multiple projects in a fatigue research lab... then too many years as a structural analyst for an aerospace company I won't name... I've seen more beach marks than I care to.
Most of what is written here is correct. But basically a crack starts and has a sharp notch/tip, the stress concentration factor of which is really, really high. Load comes up, the crack grows a bit and localized deformation of the metal causes arrest of the crack growth. The load comes down, residual stresses reverse and do some funky things and the cycle starts all over. Every cycle can make a little mark, like the sand. Sooner or later, you reach the critical crack length and the load is enough that the crack doesn't stop, but suddenly fails the entire section.
Now the failure above of the crankshaft, the visible marks are indicative of a very high stress field for them to be that noticeable. Away from the journal you can see where the steel failed in a half cycle. What went wrong here is in the smooth part by the journal. Most likely an electron microscope would let you see how the metal was failing and allow you to see if an initial manufacturing defect was the actual problem, or a pit or a riding condition or a...
What I'm trying to point out is that you can have indications of fatigue without it being the root cause of the failure. I can't imagine how anyone would be able to just look at a shaft with the naked eye and know for certain what the root cause was. If you're really good, you can get a good idea with a loupe (magnifying glass), but even then it's an educated guess with a fair amount error... and what I was trying to point out in a previous post, it's probably about the same price to just pay the claim then to have a good lab do a full failure analysis.
My advice, push them on why they think the root cause was fatigue and ask them what lab they sent it to and that you'd like a chance to review the specimens (to do a full analysis they'd have to section off and polish specimens from the failure site). I have a strange feeling they had Joe in back look at it and check the fatigue box on the form.
As for what happened to the rest of the engine, I'm still waiting to hear what people think if they could be related... I learn a lot from here... love it!
Most of what is written here is correct. But basically a crack starts and has a sharp notch/tip, the stress concentration factor of which is really, really high. Load comes up, the crack grows a bit and localized deformation of the metal causes arrest of the crack growth. The load comes down, residual stresses reverse and do some funky things and the cycle starts all over. Every cycle can make a little mark, like the sand. Sooner or later, you reach the critical crack length and the load is enough that the crack doesn't stop, but suddenly fails the entire section.
Now the failure above of the crankshaft, the visible marks are indicative of a very high stress field for them to be that noticeable. Away from the journal you can see where the steel failed in a half cycle. What went wrong here is in the smooth part by the journal. Most likely an electron microscope would let you see how the metal was failing and allow you to see if an initial manufacturing defect was the actual problem, or a pit or a riding condition or a...
What I'm trying to point out is that you can have indications of fatigue without it being the root cause of the failure. I can't imagine how anyone would be able to just look at a shaft with the naked eye and know for certain what the root cause was. If you're really good, you can get a good idea with a loupe (magnifying glass), but even then it's an educated guess with a fair amount error... and what I was trying to point out in a previous post, it's probably about the same price to just pay the claim then to have a good lab do a full failure analysis.
My advice, push them on why they think the root cause was fatigue and ask them what lab they sent it to and that you'd like a chance to review the specimens (to do a full analysis they'd have to section off and polish specimens from the failure site). I have a strange feeling they had Joe in back look at it and check the fatigue box on the form.
As for what happened to the rest of the engine, I'm still waiting to hear what people think if they could be related... I learn a lot from here... love it!
It was from a google search :huh:
Alex D
Active Member
Ohh ... and I thought it was a picture your "crank" :smt043
I agree... I wasn't trying to indicate otherwise. You obviously have more experience on the subject. It would seem on a shaft in a proven production boat that "fatigue" doesn't happen on it's own (unless there is a defect in the shaft) and something else happened to make the condition. It's the "something else happened" that needs to be found. Correct me if I'm wrong but doesn't a microscopic investigation determine approximately how many cycles may have passed? If this happened from a whack 10 hours ago versus an out-of-alignment condition from 400 hours ago would produce a different pattern I would think. Also, based on the material, isn't possible to actually determine the stresses that caused the failure (i.e. if the boat was being hot-rodded around)?
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Matt
Member
Your insurance policy should cover engine failures like the one you had even if the broken shaft caused it.
If the shaft cause the problem (which it shouldn't have) then it was because of a failure of a component and if it was just a failure of the engine due to a bad part then it is covered under latent defects.
A buddy of mine just was paied off for two blown engines in his formula 37 and the damage was HIS fault.
He was running at 40Mph his a wake and instead of pulling the throttles back he threw both engines into neutal. the engines have no rpm limiters and went to redline and way passed one blew up the other still ran but was rapping.
Several years back on a two year old Silverton I owned I blew up a engine running at 3400 rpm. the head gasket blew and water was sucked into the cylinder ended up splitting the block and shattering a piston. it was covered by insurance fully because of latent defects.
File a separate claim and see what happens.
Good luck.
Matt
If the shaft cause the problem (which it shouldn't have) then it was because of a failure of a component and if it was just a failure of the engine due to a bad part then it is covered under latent defects.
A buddy of mine just was paied off for two blown engines in his formula 37 and the damage was HIS fault.
He was running at 40Mph his a wake and instead of pulling the throttles back he threw both engines into neutal. the engines have no rpm limiters and went to redline and way passed one blew up the other still ran but was rapping.
Several years back on a two year old Silverton I owned I blew up a engine running at 3400 rpm. the head gasket blew and water was sucked into the cylinder ended up splitting the block and shattering a piston. it was covered by insurance fully because of latent defects.
File a separate claim and see what happens.
Good luck.
Matt
- Nov 12, 2006
- 5,334
- Boat Info
- 1999 Sea Ray 330DA
Twin 7.4 MPI (310 propshaft HP) V-drives
- Engines
- Twin Mercury Marine marinized 7.4L L-29 V8s
Cast iron block w 4-bolt mains
Why? They got their butts kicked. But at least unlike the rest of the german military, they didn't mass murder their own civilians. You get your butt kicked when you go out on the water?
Alex D
Active Member
I am glad you did not become a history teacher ...
- Nov 12, 2006
- 5,334
- Boat Info
- 1999 Sea Ray 330DA
Twin 7.4 MPI (310 propshaft HP) V-drives
- Engines
- Twin Mercury Marine marinized 7.4L L-29 V8s
Cast iron block w 4-bolt mains
You mean they were involved with the mass murder of several million men, women, and children?
Those colors are from the post-war West Germany and not the Nazi Germany... I assume this is the post-WWII Navy flag.... I don't know much about Germany other than from the exchange student that lived with us.
Woody
Well-Known Member
Your :smt101, you need :smt100 or at least this :smt021.
