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<DIV><FONT face=Arial size=2>Hi Michael,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>As someone who has been aboard the Rankin/Lehman/et
al type repairs, and being a 37 guy, I perhaps can add a note of
objectivity. I found the work done to be first rate and not looking like an add
on - in fact most would think they came from the factory that way.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Being a free country, do as you see fit, but for my
2 cents the Aluminium job as done by the Chesapeake gang works great. Taking a
another look as to whether it is best is the whole concept of progress. But
their method works and looks good.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Cheers,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>John</FONT></DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=Crufone@aol.com href="mailto:Crufone@aol.com">Crufone@aol.com</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=public-list@alberg30.org
href="mailto:public-list@alberg30.org">public-list@alberg30.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Saturday, February 23, 2002 3:02
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [Alberg30] Mastbeam Repair
Revisited</DIV>
<DIV><BR></DIV><FONT face=arial,helvetica><FONT lang=0 face=Arial size=2
FAMILY="SANSSERIF">George D, Michael L, Dan S, et al,<BR><BR>My original
concern with using Aluminum for this repair was that owners were using SS
bolts in contact with the Aluminum. I see now that Al 6061 alloy is
being used. This is pretty good stuff, aircraft wing ribs are made from
6061. While 6061 is reasonably corrosion resistant, I have seem some
very nasty SS / AL dissimilar metal corrosion. In the presence of water
vapor it increases and add the Chloride ion and you have the chemistry for
active, runaway corrosion, i.e., a battery.<BR><BR>I didn't think that
Aluminum fasteners would be tuff enough, so I gravitated toward using SS for
both the stiffeners and the fasteners.<BR><BR>I also felt that the SS
stiffeners would be thinner and less obtrusive. Originally I guessed
that the Al plates would be 1/4" thick, but I have now seen references to both
3/8" and 1/2" thicknesses.<BR><BR>I did some measurements on my boat #133 from
the center of the beam and from both the port and starboard door jamb down to
the sole. I took measurements before and after tuning the rig and then
again before and after the 80 mile maiden voyage down to Lake Erie. In
all cases the mast beam was lowering about twice as much in the center of the
beam as at each of the door jambs, only 12" distant.<BR><BR>My hypothesis was
that the boat wasn't getting noticeably wider as the mastbeam collapsed and
that the center of the beam was flattening more than the entire beam was
falling.<BR><BR>I then thought that I didn't like the conventional fix by
drilling 5/16" holes for bolts through the wood laminations, in some cases
severing the laminations in half.<BR><BR>It came to me that if one could
prevent the laminations from slipping relative to one another that would solve
the majority of the problem. The idea then came to install bolts or
dowels of some material vertically through the stack of laminations to prevent
horizontal slip. The difficulty would be to install the fasteners
without penetrating the cabin roof.<BR><BR>About this time an Engineer friend
of mine pointed out that if the beam was prevented from flattening then it
could not collapse. He suggested that if a stiff enough piece of
material were laminated to the bottom side of the lamination stack then the
beam would not be able to flatten in the center. This guy mentioned that the
"sistered" Al plates would not even be needed! This played into my idea of
vertical fasteners but against the known fact that the strength of an I Beam
is mainly in the web and not the flanges. <BR><BR>So... I wanted to do both
and came up with the idea of a SS weldment. SS would allow the material
to be thinner and the weldment would have far more strength due to it's
channel cross-section. Hummm......now to address the fastener
issue.<BR><BR>I have not taken the mast base off from the outside of the cabin
roof so I don't know if there is an opportunity to use vertical fasteners
through the mastbeam at that location. Someone mentioned in one article
that the counterbores for the mast base attachment went down about half way
into the mastbeam. This seams excessive, but could present a location
for through fastening the original wooden laminates and repair channel
together. <BR><BR>My thought would be to investigate adhesive bonding the
channel to the original wooden mastbeam. Perhaps not as the sole method
of attachment but as a way to limit the number of mechanical fasteners.
I would consider the location of the mechanical fasteners carefully, avoiding
severing the wooden laminates and staying clear of the center of the beam and
the web area of the beam.<BR><BR>My thoughts on installation would be to use a
router to reduce the thickness of the lower wooden laminate to receive the
channel without any loss of headroom. I am also considering the use of
recessed fasteners so that a thin lamination of teak could be applied over the
SS channel to conceal the metal and give the appearance of the original wooden
beam.<BR><BR>Hope that this clears up my thought process on the mastbeam
repair. I just thought that I would attempt to combine an effective
repair with the original beauty of the boat. To make the boat sound
again without altering her original looks.<BR><BR>Michael #133</FONT>
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