Posted by Alan Kusinitz (akusinitz@…>)
Well, what’s really important here
is that the spartite use on my F-33 should be fine! J
Alan
From: FreedomOwnersGroup@yahoogroups.com [mailto:FreedomOwnersGroup@yahoogroups.com] On Behalf Of sailorvela
Sent: Tuesday, November 13, 2007
8:21 AM
To: FreedomOwnersGroup@yahoogroups.com
Subject: [FreedomOwnersGroup] Re:
Spartite
OK, while Shore hardness is an important measure in
plastics and
related to the compressive modulus. I think displacements in the
elastic region should be determined by the compressive modulus. I
would relate the shore hardness more to the ability of the material
to distribute the load evenly.
Spartite compressive modulus: 55KSI.
So, in a typical Freedom 40 CK 6000# ballast. Draft 4.5’. Give it a
conservative moment arm of 7 ft with the boat knocked over flat.
Then the righting moment (I know, it really should be the
displacement of 22,0000# over the distance between the CG and the
center of flotation when knocked flat, but this is just a coarse
approximation). Then max moment ~ 42,000 ft/lb.
Guessing a collar width of 1 in and a diameter of 1 ft. with a
bearing area of 1/3 of the circumference: bearing area: 62ð *1/3 ~
37.7 in. sq.
Also guess an arm between the mast collar and foot of ~ 6 ft.
Stress to react to the 42,000 ft lb moment : 7,000/37.7~ 185 psi
Then the displacement due to compression of the spartite collar
would be in the order of
Displacement: 185/55000: ~0.003 in. (about 0.002 if the collar
width is 1.5 in.)
About 0.003 in(rough guestimate) this also includes a de-facto
factor of safety of 2 since there are two masts sharing the load.
I don’t think displacement or mast movement would be an issue with
spartite stepped masts under normal conditions.
Am I correct?
And yes, Nani/Bright Star masts were re-stepped using spartite as
recommended by rigging experts.
Cheers
Alex,
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