Offshore capable rig and correctly interpreting the rigger's apprentice

[Brion Toss]

Hi,
Good questions all.First, flimsy: some monohulls are stiffer than others; the solid line in the chart is a reliable average resistance to heel, and in my experience is good for most boats. You might try running the formula for the higher an lower values, and see if you get much if any difference in wire size.
The variance is definitely not about safety factor; that is added later. It is about the vessel's inherent stiffness. An incline test is always a good idea, if only to check the data from that formula.
When Beth talks about "working load," it could mean whatever you want, but the load at 30 degrees of heel is generally used. Ultimate load is usually about 1.5 times that (more on this number later), and you add a safety factor onto that. Do the math, and you will see that a safety factor of about 2.7 gives you a break strength of 4 times the working load. This is an important bit of math.
Finally, that 2.78 number has nothing at all to do with high latitudes; it is a component of mast design, wherein the jibstay, forestay, and backstay add compression to that imposed by the shrouds. So righting moment at 30 degrees, times 1.5 is total shroud load, and the same moment, times 2.78 is total mast compression.
Fair leads,
Brion Toss

[Ole1291]

Originally Posted by Brion Toss

Hi,
Good questions all.First, flimsy: some monohulls are stiffer than others; the solid line in the chart is a reliable average resistance to heel, and in my experience is good for most boats. You might try running the formula for the higher an lower values, and see if you get much if any difference in wire size.
The variance is definitely not about safety factor; that is added later. It is about the vessel's inherent stiffness. An incline test is always a good idea, if only to check the data from that formula.
When Beth talks about "working load," it could mean whatever you want, but the load at 30 degrees of heel is generally used. Ultimate load is usually about 1.5 times that (more on this number later), and you add a safety factor onto that. Do the math, and you will see that a safety factor of about 2.7 gives you a break strength of 4 times the working load. This is an important bit of math.
Finally, that 2.78 number has nothing at all to do with high latitudes; it is a component of mast design, wherein the jibstay, forestay, and backstay add compression to that imposed by the shrouds. So righting moment at 30 degrees, times 1.5 is total shroud load, and the same moment, times 2.78 is total mast compression.
Fair leads,
Brion Toss

Now it's all much clearer to me.
Yes, I forgot the 1.5 factor was for ultimate load , my mistake. With your explanation it makes perfect sense.
It looked weird that Casey used the precise same number (2.78) that was in your book for the mast compression calculation, so I half suspected a misunderstanding.

Thanks for having taken the time to answer my questions, it actually helped me a lot.

George