[Rhodes22-list] My Centerboard delamination
Lou Rosenberg
lsr3 at MAIL.nyu.edu
Thu Dec 9 19:33:06 EST 2004
>Lou, Roger,
Todd,
That is exactly what I have also there is no gelcoat on my board or
my rudder I believe.
Lou
> My c/b from the 1974 didn't (appear to) have any gelcoat on it
>either, but I am not sure. When I sanded the c/b with a palm sander
>using fine grit (150?) paper to remove the the this layer of old
>powdery bottom paint, the board looked like amber epoxy with large
>fibers embedded just below the surface.
>
>Todd
>
>
>----- Original Message -----
>From: "Lou Rosenberg" <lsr3 at MAIL.nyu.edu>
>To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
>Subject: Re: [Rhodes22-list] My Centerboard delamination
>Date: Thu, 9 Dec 2004 16:34:31 -0500
>
>>
>> > 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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>>
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>
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