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

Wed Jul 16 11:09:48 PDT 2008

Randy,

The point load from the mast puts the top of the beam in compression and the
bottom in tension with very little force in the middle of the vertical
dimension of the beam where the bolt holes are.  The aluminum "gusset
plates" add considerable strength by transferring the load laterally.  I
suppose the original wood helps but acts mostly as a spacer separating the
new beams and keeping them from twisting.  We use a similar technique when
reinforcing old, wood structures in buildings including the heavy timber
wood trusses in our architectural office which was built in 1888.

I don't know to what extent the original construction transferred beam loads
down the door jambs but your addition of the knees is definitely the "bees
knees" because you have probably reduced the span of the beam.  I recall
from structures class that doubling the span of a beam increases the load on
a beam by more than four times; so, by cutting the span in half or more, you
have probably increased the strength of the beam considerably.  If fact, go
ahead and put that new 65' main mast on her, add a mizzen and go like the
wind with your new yawl.  One serious note, the loads at the bottom of the
new knees need to be adequately transferred/distributed to the hull and/or
keel but, given the quality of your work, I suspect that is already the
case.

Roger Kingsland, Managing Partner
Kingsland Scott Bauer Associates

KSBA 
________________________________

Architects/Planners/InteriorDesigners/ProjectManagers

3441 Butler Street
Pittsburgh, PA 15201
N 40° 27.8344'  W79° 57.9831'

412-252-1500 ext.101 
412-779-5101 cell 
412-252-1510 fax
r.kingsland at ksba.com
www.ksba.com

-----Original Message-----
From: public-list-bounces at lists.alberg30.org
[mailto:public-list-bounces at lists.alberg30.org] On Behalf Of Randy Katz
Sent: Wednesday, July 16, 2008 12:47 PM
To: public-list at lists.alberg30.org
Subject: [Public-List] RESENT: Mast Beam Variation --what's best?

(The text I wrote is easier to actually find in this version!)

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.> > ______ 

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