[C320-list] Backstay blocks... question for you engineering types

[Tony Murphy]

Lou,

I have not used one of the backstay adjuster’s you’re referring to (I believe you’re talking about the one made by CS Johnson… here… http://www.defender.com/product.jsp?path=-1%7C118%7C2358491%7C2358500&id=76471)

The notes say that there should be a 1.5:1 ratio between the backstay base width and car height.  But I believe it should say something along  the lines of “The car won’t release if it’s higher than 1.5 times the width of the base (distance between two backstay turnbuckles).

Because of this, I decided to go with the 3 Harken wire blocks… which Jon Vez indicated in his writeup.  I am modifying Jon’s installation a bit and will post comments in a couple weeks after I have it installed. 

Tony
Bella Sol #886


On May 22, 2014, at 8:18 AM, aronella at gmail.com wrote:

> I recently installed a four sheave adjuster; it tightens very well, but does not go back up when released. It has to be forced up (with a LOT of force by the boathook).  Any suggestions greatly appreciated.
> Thanks,
> Lou Spitz
> 
> Sent from my iPad
> 
>> On May 19, 2014, at 2:46 PM, Jon Vez <jonvez at comcast.net> wrote:
>> 
>> Hi Tony,
>> 
>> Still a lurker here...the SWL for the ratchet is for the cam portion and is
>> more than enough to handle any load you can put on it. If it were anywhere
>> near the 300 lb breaking strength there is no way you would be able to
>> release it. I use the same SWL on the ratchet/cam for my jib furler on my
>> 355.
>> 
>> -----Original Message-----
>> From: C320-list [mailto:c320-list-bounces at lists.catalina320.com] On Behalf
>> Of Tony Murphy
>> Sent: Monday, May 19, 2014 12:11 PM
>> To: C320-List at Catalina320.com
>> Subject: [C320-list] Backstay blocks... question for you engineering types
>> 
>> I'm working on pulling together the parts to assemble the backstay adjuster
>> as described on the C320 website.  Thanks to Jon Vez for the wonderful
>> writeup and illustrations.
>> 
>> I am wondering about one thing. the triple blocks that Jon described on the
>> starboard side all seem to be rated for a SWL of at least 1800 lbs.
>> Likewise, the single wire blocks (3 of them) are all rated for SWL of about
>> 2000 lbs.  The 5/16" lines all seem to have well over 3000 avg tensile
>> strength.  However, when I'm looking for a single racketing block with cam
>> for the port side, all I seem to be able to find online are ones with a SWL
>> in the 300-600lb range (if I stick with the matching 57mm Harken carbo
>> blocks). I realize this block isn't absolutely necessary if you don't want
>> "coarse" adjustment as Jon mentioned in his writeup.
>> 
>> Am I missing something? Maybe I'm making it too complicated.  Does anyone
>> know the typical loads that will be placed on these components?  If I could
>> reduce the SWL requirement for the triple blocks, I could definitely shave
>> off a hundred or more of the total cost, but I'm afraid to do that without a
>> better working knowledge of what loads I should expect to see.
>> 
>> Tony Murphy
>> Bella Sol #886
>>