Judy,
Maybe a better way to interpret my "bend, bend..." remarks is to say that the
mast alloy (as described) will behave under stress more like a piece of wood
than like a piece of copper.
It is possible that some calculations could be done that would approximate the
behavior of the mast by using the equations for a round section (since you're
talking about bending back, right? - and the part of the mast under tension is
more or less round) but even if I were to do those calculations I wouldn't trust
them and wouldn't share the results for the following reasons:
1) The mast has holes drilled in it.
2) The mast is used and probably has scratches, corrosion and the beginnings of
cracks in it
3) My experience with aluminum heat treaters is that the process is arbitrary,
not well controlled and the results show tremendous variation.
4) The actual situation is much more complicated than the model - consider the
forestay tension, the support of the tabernacle, the shroud tension, the tension
of the mainsail luff, etc. etc.
The data published in the chart you posted yesterday is gathered by stretching
small bars of metal until they fail. The "bowing" of a hollow shape, with part
of the material in compression, and at risk of buckling, and the rest of the
material in varying degrees of tension is a big jump from the published data.
Even if you were to test a sample section of the same extrusion, I would still
suggest a generous safety factor since the variability in alloying, heat
treating, anodizing and environmental damage will have a profound effect on
performance.
Hope this helps,
Dave Kautz
P-15 #1632 "Tilly Lucy"
Palo Alto, CA
______________________________ Reply Separator _________________________________
Subject: Re: P19 Mast Specs ONLINE at Judy B's Website.
Author: Non-HP-JBlumhorst (JBlumhorst@aol.com) at hp-boise,mimegw7
Date: 2/9/99 11:58 PM
In a message dated 2/9/99 2:20:25 PM Pacific Standard Time, DAVID_KAUTZ@HP-
Sunnyvale-om5.om.hp.com writes:
> If I interpret this correctly, those of you worrying about causing a
> permanent
> bend in your mast need not worry much about that. These masts are going to
> bend,
> bend, bend a little more and SNAP!
>
> Bummer.
>
>
> Dave Kautz
> P-15 #1632 "Tilly Lucy"
Hi David,
I have a few sincere questions from reading your last email to the group.
How much "bend, bend, and bend some more" can the mast take before we get the
"SNAP" part?
Do you interpret the data to mean that snapping of the DM5 mast on the P19 is
likely to occur within the *relevant* range of 4 inches or so of constant
radius bending?
Or do you just mean to imply that if you bend it an enormous amount ("bend,
bend, bend some more") that you will get little warning before it snaps?
Regards,
Judy B.