[C320-list] Check your stem fitting - near catastrophic failure to C320

[Graeme Clark]

Further updates on this

The following photo (which you will need to copy the link and paste into your browser, to view) shows the fracture face of the stem head fitting.
You can quite clearly see where the cracks have started (one on each side) and how it has progressed, with a series of concentric semicircles. 
Obviously the darker rust marks are where the crack started, ie it has had longer to rust, and I believe this is essentially ‘crevice corrosion’

The ‘clean’ un-rusted part is all that was holding everything together before it gave way!

( Many if not most of you will hopefully already be aware of this , but for those that aren’t, basically, even stainless steel will rust if the water is de-oxygenated which happens wehre it stagnates in tiny little cracks and crevices)

http://i59.tinypic.com/9zoaqf.jpg
and
http://i58.tinypic.com/30c595i.jpg

My own boat http://i58.tinypic.com/2jcbqdk.jpg seems to have a hairline crack in the weld and will require further inspection.  The identical fitting from a Catalina 36 is shown for comparison in these other photos http://i62.tinypic.com/116tjyr.jpg

Strongly suggest that this is worth double checking on your own boat!

HGraeme
#366




On 4 Aug 2015, at 16:42, Marko Jamnik <markojamnik55 at gmail.com> wrote:

> Hello Graeme
> 
> Since my sail number is 304 and built in '95. I will check my situation and take a picture. Once again it could be just that one but worth while having  an overall inspection.
> Thanks for the heads up
> 
> MarkoJamnik
> Marquesas 304 Lake Ontario
> 
> 
> 
> On 2015-08-04, at 11:17 AM, Graeme Clark <cg at skyflyer.co.uk> wrote:
> 
>> Or try this link
>> 
>> http://oi58.tinypic.com/t8lwz9.jpg
>> 
>> G
>> 
>> Sent from mobile: please excuse typos etc.!
>> 
>> 
>>> On 4 Aug 2015, at 15:55, Daryl Hunt <drhunt at rochester.rr.com> wrote:
>>> 
>>> Hi Graeme,
>>>  FYI, when I click on the tinypic link I don't see the image.
>>> 
>>> /Best regards,
>>> /
>>> 
>>> /Daryl
>>> '99 C320 #660 Believe
>>> /
>>> 
>>> 
>>>> On 8/04/15 10:15 AM, Graeme Clark wrote:
>>>> 
>>>> Just to correct my own post!
>>>> 
>>>> The perspective of the picture I posted made me wrongly state there was a backing plate, I can now see that it is in fact looking at the entire broken cross-section of the vertical bar to which the forestay (headstay?) connects.
>>>> 
>>>> You can see a tiny rusty part, which someone with better engineering knowledge may confirm to be crevice corrosion -  almost certainly starting from a tiny pit where the  triangular gussets are welded in place?
>>>> 
>>>> Still very tricky to spot and worth a good look at your own boat to check for a similar issue maybe?
>>>> 
>>>> Graeme
>>>> 
>>>>> On 4 Aug 2015, at 13:12, Graeme Clark <cg at skyflyer.co.uk> wrote:
>>>>> 
>>>>> The C320 that I used to share before buying my own, suffered a near catastrophic failure of the stem fitting that attaches the forestay to the bow, last week;
>>>>> 
>>>>> How they didn't lose the mast I don't know
>>>>> 
>>>>> The boat is  serial no 303 built in 1996
>>>>> 
>>>>> This link, pasted into your browser, will show the failure, the red arrow is the fractured surface
>>>>> http://tinypic.com/r/t8lwz9/8
>>>>> (by the way, the halyard you see is the jury-rig to keep the mast up!)
>>>>> 
>>>>> For interest you may wish to see the current design of replacement offered by CD
>>>>> http://www.catalinadirect.com/index.cfm/product/2573_699/stem-fitting-c-320-c-34-c-36.cfm
>>>>> 
>>>>> Note that CD state they have removed the unnecessary and non structural triangular gussets that are clearly visible on the part that failed.
>>>>> 
>>>>> But you will also note that there is a ‘backing plate’ joining those two gussets that is located close to and to the rear of the part that failed.
>>>>> 
>>>>> My guess is that a small defect or other stress concentration was present on the rear of the vertical bar and over the years repeated flexing has caused a fatigue crack to develop and propagate.
>>>>> 
>>>>> The point is that it is very difficult to see this area, and I think any crack would be very unlikely to be spotted with a routine cursory inspection.
>>>>> 
>>>>> I have no idea if there’s any history of these parts failing, but If so I was not aware of it.
>>>>> 
>>>>> I would strongly recommend a careful  inspection of your own boat to make sure that no crack is developing in the same area.
>>>>> 
>>>>> I hope the above description is clear, but if I have confused you, please ask away and I will try and  explain further
>>>>> 
>>>>> Regards
>>>>> 
>>>>> Graeme
>>>>> #366, Jaskar
>>> 
>>> 
>>> 
>>> ---
>>> This email has been checked for viruses by Avast antivirus software.
>>> https://www.avast.com/antivirus
>