Regards, Bernie Johnson.
Rich Duffy wrote:
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> West Wight Potter Website at URL
> http://www.lesbois.com/wwpotter/
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> A note about filling old holes.
>
> Most of what I know about structures comes from the wonderful books
> of a British engineer, J. E. Gordon. In one of his books he writes
> about wooden masts and notes that putting in nails and screws seems
> to do little damage, but he warns against removing old ones,
> suggesting that doing so considerably weakens the structure. Instead,
> he suggests cutting them of flush.
>
> I've spent some time puzzling over this because, when I bought my old
> wood-spar P-14, it came with an bent old mast that had failed --
> right at the point where a previous owner had filled some old holes
> with some kind of wood putty.
>
> Gordon's description does not match his usual lucidity, but it seems
> that he's suggesting that the failure begins at the hole as a
> compression crease, stating that compression creases behave quite
> similarly to the more well-understood phenomenon of cracks in
> tension. He didn't go further into detail and I've never pursued the
> issue.
>
> I assume that Gordon's advice about not removing old screw was
> premised on the notion that a screw or nail that was forced into a
> spar would , logically, be a stronger compressive element than the
> surrounding material (demonstrably true since the fastener crushed
> the spar material as it was inserted). It's hard to imagine how you
> could fill the old hole with as effective a device as the screw you
> removed
>
> In the case of *my* mast, it's not simple to tell what happened. The
> failure seems to have been a tension failure. But it's likely that it
> could fail in tension after being weakened in compression. Masts are
> special-case beams in that they are subject to a routine flip-
> flopping of forces. In the case of my mast, the whole picture is very
> much complicated by the fact that the previous owner obviously
> flipped the mast fore-to-aft, moving all the fittings, undoubtedly in
> an attempt to counteract a very bad S-bend in the mast. Obviously the
> stays were improperly adjusted, so much so that the mast deformed.
>
> How applicable is this to aluminum? I dunno. Wood and metal are very
> different materials. But I'd expect that many of the issues are the
> same.
>
>
> Rich Duffy
> P-14 #362 Kula, HI
>
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> > West Wight Potter Website at URL
> > http://www.lesbois.com/wwpotter/
> > - - - - - - - - - - - - - - - - - - - - - - - - - - -
> > One problem with drilling holes in the mast for hardware, wires, etc is
> > that the holes create stress points in the mast when it bends. Depending
> > on the forces on the mast from the stays and the sail, parts of the mast
> > can be in compression or in tension or remain neutral. From the
> > standpoint of optimum mast strength would it be best to drill holes on the
> > front of the mast, on the back of the mast or on the side of the mast? Are
> > there anything like PEM nuts that I can insert into the holes to reduces
> > their effects as a stress point? Would filling the old holes with weld
> > material be beneficial? Jim Nolan P-19, P-15, L138T, LGYC #6
> >
> >
> >
> >