[Alberg30] A30 mast support beam - Truisms

[George Dinwiddie]

Michael,

I don't think anyone is offended, but I think there is scepticism that
a stainless steel channel is better.

Some history:  When the mast beams of racing boats that were "rode
hard and put away wet" started delaminating, Bob Marshall came up 
with the "rolled aluminum bar" fix.  This was a heavy aluminum bar
that was curved to match the beam and sistered to it in the
forepeak.

Bruce Rankin was an engineer, and thought this fix was not optimal.
Indeed, at least one boat ended up using two of these beams, and
sistering both sides.  Bruce came up with the "two aluminum plates"
fix and I do not know of any failures.

I'm not a structural or mechanical engineer, and we've lost the
opportunity to ask Bruce for an analysis, but I think we can look
at this in simple terms.  The question is what advantages does a
stainless channel offer over the two aluminum plates.

First, let's look at the choice of materials.  Is stainless better
than aluminum?  I don't know the relative strengths of the alloys
involved, but the aluminum seems to be strong enough.  Even though
this is a hard aluminum alloy, I think it's probably easier to cut
than stainless.  Of course, if someone else is cutting it for you
this may not be important.  You'll still need to drill holes 'in
situ' though.

Second, is a channel better than two plates.  As I understand the
physics, the strength comes from the height of the vertical component.
Visualizing an I beam, it's the vertical part of that provides the
strength, and the top and bottom plates keep the vertical part in
column.  With the plates fastened to the wood beam, the beam itself
keeps the vertical part in column.  Therefore I think the addition
of a bottom plate is of little additional value.  It will, however,
slightly reduce the clearance (I bump my head often enough) and
will probably make the installation more difficult.

I guess you can see which approach I favor.  Peerhaps I'm missing 
something, though.  What advantages do you see for using a
stainless channel?

 - George

> Crufone at aol.com said:
> 
> Brian and all,
> Didn't mean to offend members of the group.  I did check out the mastbeam 
> repair photos on the Alberg30 site.  They are yet another version of this 
> repair.  Each of the seven Alberg 30 mastbeam repairs that I have seen to 
> date are different.  
> 
> Can I assume that the mastbeam repair photos on the web site are of the best 
> and preferred method to affect this repair?  If so then that would be helpful 
> information.
> 
> Would the Alberg 30 group be offended if "someone" designed a different and 
> perhaps better and easier to install repair and then shared that information 
> with the group?
> 
> I don't intend to sound like a pompous, stuff shirted jerk.  When I reviewed 
> all the available information on the repair and looked at several repairs, 
> with all the different materials people were using I felt that it could be 
> done better for perhaps not much if any more money.  
> 
> Thank you for all your comments.
> 
> Michael  #133 

-- 
 ----------------------------------------------------------------------
  George Dinwiddie                             gdinwiddie at alberg30.org
  The gods do not deduct from man's allotted span those hours spent in
  sailing.                                    http://www.Alberg30.org/
 ----------------------------------------------------------------------

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