[Rhodes22-list] My Centerboard delamination

[Lou Rosenberg]

>Lou,


  Roger,
  Trust me -there is not an inch of gelcoat on that board or  my 
rudder for that matter!
   I have seen Catalina CBs and rudders and they do have gelcoat.  But 
this baby was really neglected and she might have once had some but 
someone stripped it off years ago.   That is paint caked on.. When I 
took my sander to it , it came off easily and will finish soon .  Btw;
  I  will try to post my mounts next to the mounts I found when I 
pulled off the cap.. two worlds apart! In fact I cannot see how the 
previous owner sailed the boat with the board blocks as dysfunctional 
as they were when I found it.
  Still working on the mounts almost done but this is not  a game of 
horse shoes so almost is "not ready yet!'

and..
  When this boat goes back into the water I am going to hire a good 
jazz band to play , and surprise all the marina folks!  i played 
trombone for a living and still have some brass fiends who can swing!
Lou
>
>No gelcoat on your centerboard you say?  Quack?
>
>I took another look at your photos.  Man, if that's not gelcoat; then, it's
>some of the thickest bottom paint I've ever seen!  It's hard to believe that
>any boat builder would build an underwater part like a centerboard & just
>paint over the raw FRP laminate.  However it got that way, assuming you are
>correct & that delaminating layer is really old bottom paint; then, I would
>strip all the bottom paint off your centerboard down to the raw FRP
>laminate.  Fix any cracks or delaminations in the FRP laminate.  Then, I
>would put down an unthickened epoxy tie layer, 20 mils of epoxy with West
>422 Barrier Coat additive, and a couple coats of bottom paint.
>
>By the way, if you really don't have any gelcoat on your centerboard; then,
>you should consider doing some dimensional comparisons with your rudder
>blade.  With no gelcoat, the FRP laminate in the centerboard may be swollen
>due to water absorbsion &/or freeze/thaw cycles.  This could be another
>reason for the interference fit in your centerboard well.
>
>Roger Pihlaja
>S/V Dynamic Equilibrium
>
>----- Original Message -----
>From: "Lou Rosenberg" <lsr3 at MAIL.nyu.edu>
>To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
>Sent: Thursday, December 09, 2004 2:27 PM
>Subject: Re: [Rhodes22-list] My Centerboard delamination
>
>
>>  >  Roger,
>>
>>    I may be missing something here but my CB does not have any gelcoat
>>  on it at all.
>>    It was obvious to me that if it was there originally, it came off or
>>  was removed and the board was sanded down to the glass mat and
>>  painted with bottom paint.  I was referring to sanding this cracked
>>  and heavily layered section down to the glass and then painting it
>>  with bottom paint.
>>    Indeed , an new board would most likely have been gelcoated but I am
>>  not planning on doing that to this board at this time.
>>    Lou
>>
>>
>>
>>
>>
>>
>>
>>
>>http://www.rhodes22.org/pipermail/rhodes22-list/attch/200412/07/CB_flaking_
>n
>>  >ear_pivot__st_1.jpg
>>  >
>>  >looks like a brittle compression failure of the gel coat to me.  This
>damage
>>  >was probably done over a relatively short period of time.  I would guess,
>as
>>  >the centerboard was starting to jam, you &/or the previous owner tried to
>>  >force the centerboard into & out of the centerboard well.  Does the
>location
>>  >of this damage correspond to a location in the centerboard well where
>there
>>  >is a lot of bulging?  You will have to remove the failed gel coat back
>from
>>  >the failure site to where the bond with the FRP laminate is sound.  The
>gel
>>  >coat will have to be faired out.  Then, you will build the gel coat back
>up
>>  >to the original level with thickened epoxy.  Don't forget to use an
>>  >unthickened epoxy "tie layer" as I've previously described.  One of the
>nice
>>  >MOC properties of epoxy is that it is a much more ductile material & has
>a
>>  >higher bulk modulus vs. the polyester gel coat on the centerboard now.
>The
>>  >epoxy repair will be MUCH less likely to suffer the same sort of brittle
>  > >compression failure.  In fact, I'll make a fearless prediction & tell you
>>  >that, as long as you properly prep the surface & use a "tie layer", the
>>  >centerboard gel coat will fail somewhere else before the epoxy repair
>fails.
>>  >
>>  >I see at least 3 kinds of damage in:
>>  >
>>
>>http://www.rhodes22.org/pipermail/rhodes22-list/attch/200412/07/CB_lower_le
>a
>>  >ding_edge.jpg
>>  >
>>  >There is long term abrasive wear on the flanks of the centerboard.  The
>>  >elliptically shaped dent on the leading edge looks like a ductile
>failure,
>>  >"impact crater".  I also see what looks like a delamination crack
>emanating
>>  >from the elliptical dent. (i.e. the elliptical dent was probably the
>crack
>>  >initiation site)  Interestingly, although the elliptical dent is a
>ductile
>>  >failure, the crack is a type of brittle failure, so you have a mixed mode
>>  >failure at this site.  I would guess the elliptical dent & delamination
>>  >crack involved something on your trailer, perhaps the frame on one of the
>
>>  >centerboard rollers.  The irregular shaped gel coat failure near the
>>  >elliptical dent looks like another brittle compression failure.  The
>>  >compression failure may have been another result of the extreme
>compression
>>  >loading involving the tight centerboard/centerboard well fit.  It looks
>like
>>  >you may also have a delamination crack on the leading edge at the very
>>  >bottom of the centerboard.  The abrasive wear pattern on the flanks of
>the
>>  >centerboard suggests that this delamination crack occurred because the
>sides
>>  >of the centerboard were getting squeezed.  This compression loading on
>the
>>  >flanks of the centerboard would have resulted in a high tensile stress
>>  >(pulling apart) on the centerline of the leading edge radius.  This
>tensile
>>  >stress was relieved when the leading edge delaminated & cracked.  I would
>>  >guess this crack is not very deep, probably not much below the gel coat.
>>  >Previous posts have talked about how to repair delamination cracks with
>slow
>>  >curing epoxy.
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>>
>
>
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