Re: Holes in mast

Rich Duffy (
Tue, 24 Aug 1999 19:32:46 -1000

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West Wight Potter Website at URL
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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

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

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

Rich Duffy
P-14 #362 Kula, HI

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> West Wight Potter Website at URL
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> 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