Re-rig Cape Dory 25D

[Brion Toss]

Hi there,
We don't know what the loads on the wires are, so increasing or decreasing the diameters would be a shot in the dark at the moment. So before you address the clevis pin and wire diameter issues, let's see about those loads. Try the formula in the "Apprentice" or Skene's for standing rig sizes, based on waterline and half-beam at the chainplates, or have us do it. We'll go from there.
Fair leads,
Brion Toss

Originally Posted by Brion Toss

Hi there,
We don't know what the loads on the wires are, so increasing or decreasing the diameters would be a shot in the dark at the moment. So before you address the clevis pin and wire diameter issues, let's see about those loads. Try the formula in the "Apprentice" or Skene's for standing rig sizes, based on waterline and half-beam at the chainplates, or have us do it. We'll go from there.
Fair leads,
Brion Toss

I don't have a copy of "Apprentice" handy, and the nearest I can find by phone is about 8 miles by bicycle away (which I'll do when I'm done here), I'll have to make do with Skene's 8th edition (I have nothing newer.)

I don't think I have time to follow the short method, as it involves determining the GM via experiment, so I'm working through the long method, pg. 174.

area mainsail = 140 ft^2
area jib = 164 ft^2
I = 32'
wind pressure = 1lb
load per lineal foot (mast) = 4.375 lb.

Estimating the panels at 17' and 15'.

total athwartship load at:
masthead = 196.8125
spreader = 266.8125
deck = 304
[code]
load * shroud length
shroud tension = --------------------
spreader length (estimated 2.5 - 3.0')
[/code]upper shroud = (304 * 31.583)/2.5 - 3 = 3840.4928 lbs to 3200.4107 lbs

safety/stupidity factor = 4, so roughly 12,800 - 15,200 lbs. load, which by the tables in Skene's suggests stainless 1x19 sized 5/16" to 3/8". This seems a bit heavy, though that may be due to the safety factor (* 2 for error, * 2 for stupidity)

I'm trying to work from the Apprentice, pg 136, but the graph of course does not go down to 18.165' waterlines. I'm estimating again, but using a figure of 8,000 for the RM₃₀.

That would give a shroud load of 3,000 lbs. I'm not sure I understood the section regarding selecting wire, mostly the bit in which the load is broken out between uppers and lowers. The cap shrouds by a safety factor of 2.5 would be dealing with a load of 7,500, and the lowers 32.5% of this.

Going to the appendix for 1x19 ss 302/304 that suggests 7/32" or 1/4" wire for the cap, 1/8" or 5/32" for the lowers, probably the larger diameter for each.