[Public-list] Chainplate covers?
Mike Lehman
sail_505 at hotmail.com
Wed Dec 15 14:51:01 PST 2004
Forgive me, Roger, but it seems like a lot of time [and expense] for
something that only takes a few minutes each year [re-caulking the
chainplates]. Hell, in the time we spent sending a replying to these emails,
we could have caulked our chainplates. This is not a weak point in the A30
construction; it is a proven method for attaching shrouds; it has withstood
the test of time and severe stress and it only becomes vulnerable through
owner neglect [because the owner let water saturate and damage the bulkhead
because they did not maintain the boat properly].
Mike Lehman
><((((º>¸.·´¯`·...¸><((((º>
----- Original Message -----
From: "Roger L Kingsland" <rkingsland101 at ksba.com>
To: "Alberg 30 Public List -- open to all" <public-list at alberg30.org>
Sent: Wednesday, December 15, 2004 5:11 PM
Subject: Re: [Public-list] Chainplate covers?
Mike,
Thanks for your reply. I understand all the flexibility stuff relative to
building structural design where the connections are rigid but the remainder
of the structure is flexible. Without springs, shock absorbers or other
gizmos that I haven't seen on stay connections, I would argue it is not
possible to make a "flexible" connection with a point load such as a stay.
To me the flexibility issue is how the load is distributed through flexible
materials "downstream" of the rigid point load connection. That's where the
flexibility of the diaphragms (hull, deck, bulkheads) comes into play. I
hope everyone agrees the factory connection must be rigid by the time it
reaches the upper bulkhead bolt; otherwise the bolts would work causing
eventual failure. I am assuming (I hope, correctly) that my detail simply
moves the point where everything is rigid up about 2".
With my detail, once the rigid connection to the bulkhead is achieved, there
will be no load on the deck unless A), the bulkhead connection fails; or B),
there is flex in the 90 degree bend at the top of the chain plate. The
latter is prevented through a simple structural calculation to confirm
sufficient thickness (that I hope to cajole one of our structural
consultants into doing). Basically, if the chain plate can't slide up the
bulkhead and the bulkhead does not move vertically, the portion against the
bottom of the deck will not apply any upward force.
To me the issue is weather adding a 3" length of the deck to the rigid
portion of the connection will cause cracking or will the remaining 30+ feet
be able to take up the flex lost under the new deck plate. If the former
were the case, other areas with rigid plates (mast step, stanchion bases,
bow bracket, mainsheet traveler) would have similar problems.
One other consideration is that the "free" portion of the plate (area
between top bulkhead bolt and turnbuckle connection) on the factory detail
might function as some form of shock absorber necessary to absorb the slight
(probably under 1,000 pounds) eccentric load caused by the inward angle of
the stays which pulls the whole mess toward the mast. If this is the case,
extending the vertical tab welded to the deck plate a few inches will have
the same effect.
Relative to Alberg/Whitby compromises (IE, design intent), I am sure
economics of a production boat in competition with Pearson came into play.
I am willing to invest the time to make improvements to those compromises
but have been careful not to change anything made an effort not to change
the basic structural flexibility. For reasons stated above, I don't think
the detail is a "significant structural modification;" however, Mike
Lehman's comment that he has never seen it done this way certainly argues
for additional research.
Thanks everyone for the valued feedback. Off I go to ponder further.
Roger Kingsland
----- Original Message -----
From: "Meinhold, Michael J" <MICHAEL.J.MEINHOLD at saic.com>
To: "Alberg 30 Public List -- open to all" <public-list at alberg30.org>
Sent: Wednesday, December 15, 2004 2:56 PM
Subject: RE: [Public-list] Chainplate covers?
> Roger -
> I hope that before you make a significant structural modification you
> understand why Alberg/Whitby chose the system and made the compromises
> they
> made (I can't say that I can identify all the reasons). I agree with Mike
> Lehman in that a good general principle in ship design is flexibility, not
> rigidity. What flexibility implies is distribution of load and both over
> time and space.
>
> You need to carefully consider the path of the load is being carried . In
> your new joint, the load is carried by the threads of your acorn nuts. It
> then transfers to the vertical bolts and your L-Bracket. From there it's
> partly transferred to the bulkhead and partly to the deck, depending on
> how
> the whole arrangement is tightened up.
>
> In the directly connected chainplates the chain plates transfer the load
> to
> the bulkhead partly through shear between themselves and the bulkhead, and
> partly to the bolts and then the bulkhead. No load is carried by the deck.
> I believe it would be a mistake to use the deck to carry any large
> vertical
> load.
>
> As Mike says, most of the time it wouldn't matter, but under trying
> conditions the loads are going to approach the breaking strength of the
> wire. I would say you want the wire to fail first!
>
>
> Mike Meinhold
> Rinn Duin #272
>
>
> -----Original Message-----
> From: public-list-bounces at alberg30.org
> [mailto:public-list-bounces at alberg30.org]On Behalf Of Roger L Kingsland
> Sent: Wednesday, December 15, 2004 10:50 AM
> To: Alberg 30 Public List -- open to all
> Subject: Re: [Public-list] Chainplate covers?
>
>
>
> There seems to be an inherent problem with any detail where the chainplate
> passes through an "open" hole in the deck that must be filled with
> sealant.
> At best it is a critical maintenance issue; at worst, a means for water to
> degrade structural bulkheads. The chain plate must be flexible to the
> point
> where it first fastens to the bulkhead which is the top bolt. At that
> point
> it must be completely rigid or the chainplate will move and eventually
> loosen. Why not move that "point of rigidity" up so it is above the deck
> and a flexible connection through the deck is unnecessary?
>
> As part of the redo of the deck on #148, I have removed the chain plates
> and
> filled in the holes. One solution I thought about for the reinstall was
> to
> make 1/4" SS deck plates (roughly 2" x 3") with the a short piece of
> 1/4" welded vertically on the center to fasten the bottom of the
> turnbuckle
> (basically cutting off the top of the cahinplate and welding it onto the
> deck plate). Then make "L" shaped brackets to mount on either side of the
> bulkhead with the short leg of the "L" mounted against the underside of
> the
> hull to deck joint (one of the stronger areas of the boat). Vertical
> holes
> in the short leg drilled near the 90 degree bend would align
> with holes in the deck plate and two bolts through the deck would carry
> the
> load from the deck to the chainplates bolted to the bulkhead. All plates
> would be set in a 1/16" resin bed and bolts would be tightened
> sufficiently
> to get that good old friction connection (none of that squishy 5200
> stuff).
> It seems this solution would be strong, stiff, dry and fairly easy to
> install. I have posted a sketch on
> http://home.att.net/~jinnii/roger/perfect/pi_designs.html
> and would appreciate any feedback.
>
> Thanks,
>
> Roger Kingsland
>
>
> ----- Original Message -----
> From: "Alfredo" <alberg30sail497 at yahoo.com>
> To: "Alberg 30 Public List -- open to all" <public-list at alberg30.org>;
> <dk.campbell at sympatico.ca>
> Sent: Monday, December 13, 2004 3:29 PM
> Subject: RE: [Public-list] Chainplate covers?
>
>
> > Since we're on the topic, this is how I intend to someday do the
> > chainplates on Free Spirit.
> >
> > http://www.gizmology.com/V40/Upgrades/chainplateFix/index.html
> >
> >
> > --- "sousa, stephen (ENG)" <sousa_stephen at emc.com> wrote:
> >
> > > Don,
> > >
> > > If you could share the method used for the pattern it would be
> > > appreciated.
> > > This may be one of those items that would fall into the group
> > > purchase area.
> > > It would benefit all Alberg owners and could be very inexpensive it
> > > we
> > > purchase a large quantity. I would expect that all boats have the
> > > same
> > > installation for chainplates, so one pattern could be used on all
> > > boats?
> > >
> > > Thanks,
> > > Stephen
> > >
> > >
> > > -----Original Message-----
> > > From: public-list-bounces at alberg30.org
> > > [mailto:public-list-bounces at alberg30.org] On Behalf Of Don Campbell
> > > Sent: Sunday, December 12, 2004 7:48 PM
> > > To: Alberg 30 Public List -- open to all
> > > Subject: Re: [Public-list] Chainplate covers?
> > >
> > > Randy
> > > When I bought #528, I was taken to see a C & C deck which had a
> > > raised
> > > flat area around the chainplates with the SS plates of which you
> > > speak. I
> > > knew I needed to redo the deck on this boat so incorporated a raised
> > > flat
> > > area at the chainplates on my new deck. I then went to the scrap yard
> > > and
> > > found some 1/8th stainless plate that was food grade so probably 316
> > > (which
> > > is probaly not what is best for a marine environement, 304 is
> > > stronger and
> > > more durable, I gather, but strength is not that important here),
> > > cut it to
> > > size- about 1 1/2" x 2 1/2" and then took it to a machine shop to
> > > have the
> > > slot cut. I needed to file the edges a bit to get the chainplate
> > > angle
> > > correct in the slot but SS is relatively soft, so not difficult once
> > > in a
> > > vise. I have drilled 2 holes in the plates and drilled and tapped the
> > > epoxy,
> > > raised flat areas to match so I just tighten the 2 - 1/4 x 1/2 ss
> > > machine
> > > bolts to seal the caulking. Total cost about $25 Canadian when I did
> > > it 8
> > > years ago -$20 of that for the machinist. I need to redo that
> > > caulking job
> > > this winter. The raised part of the deck decreased the torque and
> > > twist on
> > > the chainpates at the deck level too. If you want to know how I did
> > > the
> > > pattern for the raised flat area let me know.
> > > Don
> > >
> > > Randy Katz wrote:
> > >
> > > > Speaking of chainplates (nice photos of the reinforcement straps,
> > > BTW)
> > > > has anyone found a source for chainplate covers? They are the oval
> > > SS
> > > > plates 2-2.5 inches long, slot in the middle, that fit over the
> > > > chainplate straps where they stick out of the deck. They get
> > > caulked and
> > > > sit over the deck opening, with the chain plate strap coming up
> > > through
> > > > their middle, and serve to help seal that deck opening.
> > > > I've checked West Marine and a few other stores-- they seem hard to
> > > find
> > > > at all but ones the size we need I never did come across.
> > > > Anyone know where to get them?
> > > >
> > > > Many Thanks,
> > > > Randy Katz
> > > > #249
> > > > Seattle, WA.
> > > >
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