[Public-List] Bulkheads

Michael Connolly via Public-List public-list at lists.alberg30.org
Fri Feb 5 17:01:37 PST 2016



----- Original Message -----

From: "Michael Connolly" <crufone at comcast.net> 
To: "Hernán Scarnichia" <hernanscar at gmail.com> 
Sent: Friday, February 5, 2016 9:28:39 AM 
Subject: Re: [Public-List] Bulkheads 

Hernan, 
Thanks for the very analytical response. My chain plates are original and need to be removed and inspected/most likely replaced. 
  
All the documented A-30 rig/mast failures to date in normal sailing conditions have been from four components, 1) rotten bulkheads which in turn cause the chain plates to rip out and bolts to fail. 2) the threads in the bronze turnbuckle bodies failing,  3) failures of the original copper Nicropress swages or other terminals on the wire and 4) broken spreaders.  George and Mike L if there are others please chime in.  It would be good for all of us to know all the known examples of how A-30 rigs have failed. To my knowledge rigs have not failed because of broken chain plates, stem head fittings, back stay fittings or masthead/tang fittings. Even though there is a need to inspect chain plates for SS crevice corrosion cracking, I have not heard of a rig failure on an A-30 due to strictly chain plate failure. 
  
A-30's which have been rolled have, for the most part, lost their rigs. In this most extreme sailing adventure that is to be expected. 
  
I always felt the Epoxy "donuts" around fitting fasteners was to seal the end grain of coring materials, not to increase bearing strength? Very interesting comment about West System G-Flex Epoxy from Don C. 
  
With that in mind, I believe that the original size of the SS chain plates is adequate, even though others have increased the size (probably thickness) when replacing them. 
  
I have always liked Don Campbell's solution of fashioning "curbs" around his chain plate deck slots. I have observed this tactic on more expensive finely finished boats. 
  
Lots of great discussion here.  Concerning caulking for chain plate deck slots. Why not consider the type of tarred hemp which is used for carvel planked wooden boats?  Gord can comment on this I assume.  Use this with the concept of renewing it each and every year.  Or perhaps the type of "Clam" fitting used on decks where wiring or co/ax cable penetrate the deck? These have a replaceable gasket/seal which can be inspected and renewed as needed. Because of the stress and movement in this situation I believe that it is not a repair it and forget it exercise. Life Caulk is a wonderful product for this purpose, but perhaps hard to remove and renew and still get the best adhesion, in successive applications. That is why my hair brained idea of tarred hemp.  This can be picked out with a packing tool and replaced with new with perhaps the same adhesion as the first application? Schaeffer SS covers over the tarred hemp on top of Don's "curbs"would compress and hide the tarred mess from view.  
  
The thoughtful input from this list is "First Rate". Thank you all. 
Michael #133 
  

----- Original Message -----

From: "Hernán Scarnichia" <hernanscar at gmail.com> 
To: "Michael Connolly" <crufone at comcast.net>, "Alberg 30 Public List -- open to all" <public-list at lists.alberg30.org> 
Sent: Tuesday, February 2, 2016 10:15:23 PM 
Subject: Re: [Public-List] Bulkheads 


Michael, 
I thought about adding bushings. There is an article on wooden boat #206 from 2009 that describes using G10 tubes and plates to reinforce bulkheads this way. https://goo.gl/photos/vCozrEUgKh3GdGNH8 

On my boat the knees for the forward lower shrouds were too rotten and the tabbing was de-laminating from the hull so I rebuilt them using 3/4" G10 and made them longer (below the shelf) and better tabbed to the hull. No bushings needed here as G10 is hard enough. 
I will probably replace the plywood on the aft lower knees with G10 too. 
For the upper shrouds the bulkhead is not rotten but the bolt heads have pulled a little bit because of the small washers used. I'm planning on using a 6"x12"x1/2" G10 backing plate on each side of the bulkhead and adding some extra bolts to better distribute the load on the wood and through bolt it to the hull tabbing too. Increasing the bolt size to 1/2 should take care of the slightly deformed holes on the bulkhead. 

What size of chain plate will you use? What do most Albergers use when replacing chain plates? 

>From my calculations my current chain plates (3/16x1-1/4) will start deforming at 4200 lbs. I've read it is recommended to have chain plates 30% - 50% stronger than the wire so that would be 3/8 x 1-1/2 with 4 1/2" bolts each. 


On Tue, Feb 2, 2016 at 5:44 PM, Michael Connolly via Public-List < public-list at lists.alberg30.org > wrote: 


Thanks to all who responded to my request.  There is one question still unanswered. Has anyone used bushings around the chain plate bolts to increase the bearing surface area of the bolts as they pass through the plywood bulkhead? Thoughts about making an even larger hole in the plywood. 
Michael #133 
. 
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