[Public-List] Mast Beam Variation --what's best?

[Randy Katz]

Message: 3 
Date: Wed, 16 Jul 2008 08:57:53 -0400 
From: "John S. Riley" <jriley at dsbscience.com> 
Subject: Re: [Public-List] Mast Beam Variation 
To: Alberg 30 Public List -- open to all 
<public-list at lists.alberg30.org> 
Message-ID: <487DF051.5090008 at dsbscience.com> 
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Jeffrey wrote: 
I don't think our mast beams are subjected 
to all that much stress. 


You might be surprised just how much stress is involved there. That's
a
heck of a compression load point loaded in one spot - and it's dynamic
in any kind of seaway. 

There are documented cases that these have failed at-sea, and it's a 
common problem with wooden supports of this kind (see for example the 
number of boats in Vigor's "Twenty Small Boats to Take You Anywhere" 
that have this as a maintenance issue). 

This is one structural issue that can affect the safety/seaworthiness
of
the vessel, and personally I would not do anything less than the 
absolute strongest support I could engineer if I had any lack of 
confidence in my installation at all. 

-- 
John 
s/v Gaelic Sea 
#521 



------------------------------ 

Message: 4 
Date: Wed, 16 Jul 2008 09:13:27 -0400 
From: Gordon Laco <mainstay at csolve.net> 
Subject: Re: [Public-List] Mast Beam Variation 
To: Alberg 30 Public List -- open to all 
<public-list at lists.alberg30.org> 
Message-ID: <C4A36C37.14A3E%mainstay at csolve.net> 
Content-Type: text/plain; charset="US-ASCII" 

I would totally agree - the mast beam is subjected to immense stress,
and as
John commented, dynamic loads in normal sailing let alone heavy
weather
multiply the load experienced while at the dock. 

The beam has to resist the combined loading of all the shrouds and
stays -
thousands of pounds. 

Gord #426 


Jeffrey wrote: 
I don't think our mast beams are subjected 
to all that much stress. 


You might be surprised just how much stress is involved there. That's
a
heck of a compression load point loaded in one spot - and it's dynamic
in any kind of seaway. 

There are documented cases that these have failed at-sea, and it's a 
common problem with wooden supports of this kind (see for example the 
number of boats in Vigor's "Twenty Small Boats to Take You Anywhere" 
that have this as a maintenance issue). 

This is one structural issue that can affect the safety/seaworthiness
of
the vessel, and personally I would not do anything less than the 
absolute strongest support I could engineer if I had any lack of 
confidence in my installation at all. 



------------------------------ 
Greetings,
I've always had a question about the alum. plate repair job for the
      mast beam. The problem force is a downward one. The beams that I
      know of are laminated wood, often with the 40 yr. old glue
      degraded to the point of no return. If one drills holes fore and
      aft through the beam, inserts plates and bolts, wouldn't the
      downward force still be, at least in part, unremedied?
I don't quite see how the sandwiching of the beam lends as much upward
     support as placing posts (or knees added to the existing door
     posts) under the whole thing, including under the alum. plates,
     would.
The only thing I can figure is that by sandwiching the laminated beam,
     by squeezing it really tight between those plates, it would tend
     to be solidified to some degree.
This is the reason that on my boat I did plates AND hefty knees, well
     bolted. (See our Alberg page at

http://alberg30.org/maintenance/HullDeck/MastBeam/SimpleGifts/

    Any comments or thoughts about this would be of interest!

Thank you,
Randy Katz
#249
Seattle/Bellingham, WA.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Message: 5 
Date: Wed, 16 Jul 2008 11:45:53 -0400 
From: Mike Lehman <sail_505 at hotmail.com> 
Subject: Re: [Public-List] Mast Beam Variation 
To: Alberg 30 Public List -- open to all 
<public-list at lists.alberg30.org> 
Message-ID: <BAY133-W567C2FCA6DCF29F9F2E9FB78F0 at phx.gbl> 
Content-Type: text/plain; charset="iso-8859-1" 


Althought the appearance of the aluminum sisters to the wooden beam in
the older boats may not be as attrative as the original beam, this fix
was engineered by Bruce Rankin who was a professor of engineering at
the US Naval Academy. The fix is permanent and there have not been any
failure is 20+ years with this fix.Mike Lehman
><((((?>`?.??.???`?.?><((((?>`?.??.???`?.?><((((?> > Date: Wed, 16 Jul
2008 09:13:27 -0400> From: mainstay at csolve.net> To:
public-list at lists.alberg30.org> Subject: Re: [Public-List] Mast Beam
Variation> > I would totally agree - the mast beam is subjected to
immense stress, and as> John commented, dynamic loads in normal
sailing let alone heavy weather> multiply the load experienced while
at the dock.> > The beam has to resist the combined loading of all the
shrouds and stays -> thousands of pounds.> > Gord #426> > > > Jeffrey
wrote:> >> I don't think our mast beams are subjected> >> to all that
much stress.> >> > > > > You might be surprised just how
much stress is involved there. That's a> > heck of a compression load
point loaded in one spot - and it's dynamic> > in any kind of seaway.>
> > > There are documented cases that these have failed at-sea, and
it's a> > common problem with wooden supports of this kind (see for
example the> > number of boats in Vigor's "Twenty Small Boats to Take
You Anywhere"> > that have this as a maintenance issue).> > > > This
is one structural issue that can affect the safety/seaworthiness of> >
the vessel, and personally I would not do anything less than the> >
absolute strongest support I could engineer if I had any lack of> >
confidence in my installation at all.> > ______