[Public-List] Bulkheads

Sat Feb 6 16:26:33 PST 2016

I think someone, earlier in this thread, mentioned the knees supporting the
deck (or something along those lines). I'm curious about this. on #456 it
appears as though there was a liner around the knees that was cut out by a
PO, but from what I can tell, the knees don't appear to ever have been in
contact with the deck, or even the liner. Can anyone shed some light on
this for me?
Since I will be rebuilding the knees, is there any concern with tabbing the
knees to the underside of the deck? Is flexibility between the deck & the
hull a necessity?

The link below shows a photo of what I'm talking about.

https://www.dropbox.com/s/erhr89fwfju6ikm/SAM_0896.JPG?dl=0

Thoughts?

Chip
#456

On Sat, Feb 6, 2016 at 12:23 PM, via Public-List <
public-list at lists.alberg30.org> wrote:

> Don
>
> You're right about the epoxy modulus...I asked google what the modulus was
> and it gave me the value in pascals and I missed a digit when converting to
> psi...but nonetheless the strength of unreinforced epoxy is still too low
> to be used structurally.
>
> You bought up a very good point about the aft stay knee.  I'm a little
> surprised but I don't think there's any collected knowledge that The
> association can fall back on.  There's been no failures that I'm aware of,
> hence no knowledge.  There's enough fiberglass covering the wooden knee
> that its conceivable to me that the connection in some cases is working
> without the wood playing a role, my hunch.  There's a lot of boats out
> there that don't maintain the deck seal and no reported problems.  Can
> anyone add any experience to this?
>
> The mast pumping that occurs when the boat falls off a wave and the load
> release that occurs when tacking does subject the lower chain plates to
> cyclic loading.  If the lower chain plates arn't in line with the shrouds
> there will be moment loading which can work to enlarge bolt holes over
> time.  Seems like association members when refurbishing their chain plate
> seals should check for looseness and take action accordingly.  Wet wood in
> this situation would accelerate the wear.
>
> My two cents
> Jim Mennucci
>
> Sent from my iPhone
>
> > On Feb 4, 2016, at 3:45 PM, Don Campbell <dk.campbell at xplornet.ca>
> wrote:
> >
> >  There are a couple of other things that have not been discussed in this
> thread. One is the movement of chainplates under load and with a weakened
> deck this tends to be greater than designed or thought of.  There is
> possible sideways movement, fore and aft,  of the chainplate from the point
> of attachment of the wire to the top chainplate bolt. If there is any
> luffing of sails, backwinding, or shock loading from tacking, it can be
> more than one realizes. Any movement will cause added wear,  and the
> possibilities of working away at increasing deck wear and bolt hole size
> within bulkheads. I have used epoxy plates on top of the deck to reduce
> movement of chainplates and reduce the water inflow, while allowing
> sealants to be added under thread pressure. George has a couple of photos
> in the "maintenance, disorganized, chainplates" section of the website.
> These plates  considerably decrease the leverage from the pin holding the
> wire to the top bolt  that is possible with flex sealants and weak decks.
> This system also ends most periodic maintenance of rotten or waterlogged
> deck core, (provided the core is sound to begin with)  and extends the
> interval between replacing sealants in the space between chainplate and
> deck.
> >  As for Modulus of Elasticities of epoxies, Gougeon's "Gflex"
> (registered trade mark) is 150,000 p.s.i. unreinforced. This is a very easy
> epoxy to use and the testing of it comes very close to the specs for their
> 105 resin base for most of the other tests. Gflex is superior in adhering
> to several surfaces, including oily woods, when compared with or to other
> epoxies.
> >  The bonding of either the bulkhead or the knee is to the hull. This was
> originally done with polyester resins and the core of the knee was made of
> plywood. This was, in effect, a type of truss, similar to the deck
> composition. With water infiltration, the plywood (bulkhead or knee) has
> rotted in many, many hulls without the owner knowing it. It is not until
> the plywood rot gives way under load, and the tabbing then gives, that we
> realize the knee fails.  Thinking the rig is structurally sound is far
> different from knowing it is sound. It ought not be something that one
> finds when you are out on a race course, or out in 25 knot winds,  because
> even quick thinking to get on the opposite tack, head to wind or the sail
> down , may be too slow in practice. Test drilling of small holes or
> moisture meters may give some idea of troubles. In many cases the deck core
> will be weak as well and so it offers no strength to resist the chainplate
> pulling through the deck. I do not think that backing plates will make much
> difference if the core of the truss fails. The backstay chainplate offers a
> different problem. There is a moment of force there because of the design.
> The top bolt is aft of all the the others because the chainplate is angled
> aft at the top. Thus if the top bolt fails from a bad knee, then the
> leverage is increased on the lower bolts and shear is more likely. As the
> chainplate revolves around the bottom bolt as the others shear, and it
> holds because there is no longer a moment to shear it, once straight with
> the stay, there is a major overload in a straight pull to cause the shear
> then, and there is no deck that can hold that so the backstay flies free.
> One needs to be sure that structurally sound is based on fact not fancy.
> >  The differences between knee and bulkhead structurally are fairly
> simple.  The bulkhead holds a stay as well as supports the deck (which in
> the case of the AL30 supports the mast base)  and reduces torque on the
> hull. Any change to a bulkhead will change these three purposes. It is
> important to consider any fix by adding only a small amount of material to
> a bulkhead as to how it relates to all three. A knee only holds the stay.
> >  The one thing you do not want is to have a rig come down. It is very
> expensive to replace and probably more dollars than the boat is insured
> for, so the boat becomes a write off with the insurance company. Getting it
> back from them is one thing, having to pay for the rig replacement after
> that and getting insurance again can be frought with interest, (and lots of
> principle when it comes to money).
> > Don
> >
> > -----Original Message----- From: Jim Mennucci via Public-List
> > Sent: Thursday, February 04, 2016 1:44 PM
> > To: Hernán Scarnichia ; Alberg 30 Public List -- open to all
> > Subject: Re: [Public-List] Bulkheads
> >
> > 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
> >>> .
> >>> _______________________________________________
> >>> These businesses support your Association:
> >>> http://www.alberg30.org/store/A30supporters.html
> >>> Please support them.
> >>> _______________________________________________
> >>> Public-List mailing list
> >>> Public-List at lists.alberg30.org
> >>> http://lists.alberg30.org/listinfo.cgi/public-list-alberg30.org
> >> _______________________________________________
> >> These businesses support your Association:
> >> http://www.alberg30.org/store/A30supporters.html
> >> Please support them.
> >> _______________________________________________
> >> Public-List mailing list
> >> Public-List at lists.alberg30.org
> >> http://lists.alberg30.org/listinfo.cgi/public-list-alberg30.org
> > _______________________________________________
> > These businesses support your Association:
> > http://www.alberg30.org/store/A30supporters.html
> > Please support them.
> > _______________________________________________
> > Public-List mailing list
> > Public-List at lists.alberg30.org
> > http://lists.alberg30.org/listinfo.cgi/public-list-alberg30.org
> _______________________________________________
> These businesses support your Association:
> http://www.alberg30.org/store/A30supporters.html
> Please support them.
> _______________________________________________
> Public-List mailing list
> Public-List at lists.alberg30.org
> http://lists.alberg30.org/listinfo.cgi/public-list-alberg30.org
>