[Public-list] Backstay replacement...

[George Dinwiddie]

Well, Calypso has been sailing with 1/4 wire on all uppers, fore and aft 
since 1973 without incident. ;-)  I'm not saying the larger wire will 
cause your rig to fail.  I also hadn't noticed that you switched to 316 
stainless (which I deduce from your breaking strength of 9400 lbs).  I'm 
pretty sure the original wire is 304 stainless, which is stronger 
(approx. breaking strength of 8200 lbs for 1/4" and 10300 lbs for 9/32" 
1x19 wire).

BTW, Bruce Rankin calculated the strength of the chainplates at 9360 
pounds breaking strength.  All of this data is in the Maintenance Manual.

Did you check that the knees holding the chainplates are firmly butted 
to the deck?  And that the chainplates don't leak?  These are more 
frequent causes of rig failure than the wire.  At least, I've heard of 
these causes, but I've never heard of the wire, itself, failing.  If a 
strand breaks, of course, it's time to replace all the wire.  But you 
can see that pretty easy.

It's harder to see a cracked swage fitting, and these can bring down a 
rig.  In fact, Bruce Ranking said it was the most likely point of failure.

  - George

sousa, stephen (ENG) wrote:
> George,
> 
> Sorry for the delayed response, I have tied up building a new VW diesel
> engine over the past few days, almost done. With the price of fuel
> definitely worth the time and effort.
> 
> I checked the chain plate for the back stay she is held in place with 3 5/16
> bolts with stainless backing plates as all other chain plates are on 114. We
> have been sailing with 9/32 wire on all uppers, fore and aft since 97
> without incident.  When we ran the numbers with our rigger he and I felt it
> was a good choice and modifications made to #114 could support these
> changes. 
> 
> As you know we have made many changes to this boat over the years which made
> it stronger than she was originally and A30 members comments defiantly
> helped.
> 
> Also if anyone is looking at modifying the head area, we installed cherry
> with moldings in the spring, she looks nice down below.
> 
> Rich Hargraves sent me photos of his bow roller, the current project is
> going to be a stainless stem head fitting with integral bow roller. We a
> designing this modification currently not sure how I going to handle the off
> set with one piece. Our intension is to have integral chocks which removes
> the stress from the toe rail and also installing a windlass. When this
> project is complete, I will scan a few shots for the Alberg web site if you
> like to post them. 
> 
> Thanks for you concern and please if you feel items mentioned in the future
> do not play well for other I appreciate your response.
> 
> Best regards,
> Stephen
> 
>    
> 
> -----Original Message-----
> From: public-list-bounces at alberg30.org
> [mailto:public-list-bounces at alberg30.org] On Behalf Of George Dinwiddie
> Sent: Thursday, October 28, 2004 5:37 PM
> To: Alberg 30 Public List -- open to all
> Subject: Re: [Public-list] Backstay replacement...
> 
> 
> Stephen,
> 
> I don't think I've heard of a dismasting due to wire failure.  And I 
> think that to use the additional load capacity of the wire you'll have 
> to upgrade the attachment points.  As delivered, the bolts holding the 
> chainplates (including the backstay) are about half the strength of the 
> wire.  You'd have to do more than the 5/16" bolt upgrade to hold the 
> 9/32 wire down.
> 
> In other words, I think you may be optimizing in the wrong place.
> 
>   - George
> 
> sousa, stephen (ENG) wrote:
> 
>>Brian,
>>
>>I would recommend upgrading from 1/4 wire to 9/32 the safe working 
>>load of 1/4 is 6900 lbs and 9/32 is 9400 for a minimal increase in 
>>cost you gain a significant SWL.
> 
> 

-- 
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   When I remember bygone days                         George Dinwiddie
   I think how evening follows morn;            gdinwiddie at alberg30.org
   So many I loved were not yet dead,           http://www.Alberg30.org
   So many I love were not yet born.
                                             'The Middle' by Ogden Nash
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