[Public-List] Bulkheads

Thu Feb 4 19:14:52 PST 2016

Hi All,

You know, I just got done reading the West System company's involvement in building wind turbine blades and their use of hardware bonding in a wood/epoxy system....interesting stuff.

Wes

> On Feb 4, 2016, at 1:44 PM, Jim Mennucci via Public-List <public-list at lists.alberg30.org> wrote:
> 
> Here's a caution  regarding using thickened epoxy filled holes to improve
> bearing area stress distribution for the chain plate joints.
>   - the chain plate connection to the boat is an important structural
> connection.  Here's a little tutorial on strength of materials: There's a
> property of materials called the modulus of elasticity, for steel its
> 30,000,000, aluminum: 10,000,000, plywood 1,000,000 and unreinforced epoxy:
> 15,000 psi.  Using epoxy as a structural component actually makes the
> connection less strong.  Making plugs out of G10 which is a glass
> reinforced epoxy would be a different story.  I don't have any
> data detailing what the modulus of elasticity is for G10 but I expect that
> its at least as good as plywood.  Using steel, aluminum would improve the
> bearing capacity.  G10 would be as good as plywood and maybe better.  But I
> wonder if all of this is needed.  Here's a couple thoughts:
>    - the only time we've seen chain plate failures is when the wood has
> been damaged by water.  Insuring structurally sound wood is the key.  If
> you got water damage and your doing a serious restoration then the
> bulkheads can be replaced which Towney talked about.  If you just want to
> go sailing knowing the chain plates are solid then local replacement of the
> damaged area with appropriate backing plates tying everything together is
> reasonable.
>    - we found years ago that the 1/4-20 fully threaded fasteners were
> marginal and have recommended for years to replace them with 5/16 bolts
> which has be described previously in this thread.
>    - backing plates that capture all three bolts is easy to implement  and
> vastly increases bearing area to distribute bolt tension loading which
> becomes significant as the wood softens...backing plates better accommodate
> wood deterioration than washers.
>    - the knees in the v-birth have to be structurally sound, a reasonable
> improvement was also discussed in this thread.  On my Alberg the fiberglass
> tabbing was separating from the hull so I redid them while also doubling
> the length of the knees and glassing them in.  Lengthening the
> knees spreads the load out over a larger area reducing stress.
> 
> With everything structurally sound go sailing BUT pay careful attention
> to the keeping the water from leaking in around the chain plates.  They
> require constant attention.   I don't know of a fix that can be done with
> out requiring periodic maintenance.  Does anyone know a way?
> 
> Jim Mennucci
> 
> 
> On Tue, Feb 2, 2016 at 10:15 PM, Hernán Scarnichia <
> public-list at lists.alberg30.org> wrote:
> 
>> 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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