[Public-list] Chainplate covers?

Wed Dec 15 11:56:09 PST 2004

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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