There in lies the problem. The rigging was specified in rod by my designer,
John Fox but budget constraints require that I drop back to 1x19. What I
got back from the companies bidding on it in 1x19 is considerably beefier.
Almost 50% higher minimum load.
Using an RM@30 of 60K and Larsson & Eliasson I get close to John's numbers.
Gerr's rule of thumb comes out a little lighter. Haven't quite finished
working up Toss's method but what I have so far is a little heavier.
To throw a kink in the mix, I also got some figures from Colingo for Dynex
Dux 75. Their strength figures at 20% of breaking strength come out about
the same as Rod. The up weight is about 1/5 as much and with all the
fittings the total price is about 20% less than 1x19. Even better I can
splice 12 strand braided blindfolded. If they can convince me there will
not be a problem with abrasion at the spreaders I may seriously look at
synthetic rigging.
--
Glenn Ashmore
I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at:
http://www.rutuonline.com
Shameless Commercial Division:
http://www.spade-anchor-us.com
"Wayne.B" wrote in message
...
On Fri, 8 Aug 2008 21:21:12 -0400, "Glenn Ashmore"
wrote:
Just verifying my standing rigging specs before approving my order and
need
someone to confirm my calculations. All the formulas I have found for
standing rigging loads are based on RM@30 but all I have is RM@1. The
formula for RM is RM=Displacement*GM* SIN but I don't have the metacenter
height (GM) either so working backwards;
RM/GM=Displacement*SIN
therefore (I hated that word in 10 grade algebra)
GM= RM/Displacement*SIN
Substituting:
GM=1952/24,400*.01745
GM=4.58
Now, to get RM@30:
RM@30=55,931 (Say 60K lb.)
Am I on the right track?
Probably but I would strongly encourage you to work with professional
rigging specialists such as Hall Spars or Navtec. It is important
that the calculations be backed up with a "reasonability check" based
on what similar boats are successfully using.
Another good resource would be Tom Anderson at Hathaway, Reiser and
Raymond in Stamford, CT. Tom and Ben Hall both gave me a great deal
of help when I re-rigged my old Cal-34.
http://www.navtec.net/home/index.cfm
http://www.hallspars.com/
http://www.hathaways.com/