bobstay sizing

[osteoderm]

From The Apprentice I get the general procedure to estimate bobstay loads, but there's also the mention of an additional safety factor given the bobstay's vunerable (both to corrosion and impact) location.
Is the 2.5x (or thereabouts) safety factor supposed to be above and beyond the calculated load on the bobstay, or instead above and beyond the sizing of the jibstay (with its own inherant safety factor)? Going with the latter makes for a 14mm bobstay on my 32' cutter; seems a little excessive, but then again...
My dual boomkin shrouds have a healthier staying angle, but I'll make them the same size as the bobstay for more straightforward stocking of spare bits.

[Brion Toss]

Hello,
We are talking about two things here: relative load; and varying safety factors. The diagram in the Apprentice will give you the relative load. Let's say it showed that your bobstay should be 50% stronger than your jibstay, and that the jibstay was 5/16" wire, with a breaking strength of 12,500lbs. The bobstay, however, would not see a strain 50% greater than 12,500lbs, but a strain 50% greater than the load on the jibstay. Again, hypothetically, let's say that the actual maximum load on the jibstay was 4,600lbs. We would put a safety factor of at least 2.5 on that for cruising, which would get us up in the neighborhood of the break for 5/16". And 50% over that load, 6,900lbs., would be the bobstay load, but we'd probably put at least a 2.75% SF on that, landing us somewhere between the breaks for 3/8" and 7/16". At this point we'd stop and think a bit: is that jibstay load realistic? If it is high, then maybe 3/8" would be fine for the bobstay. But if all the numbers make sense, there'd really be no appropriate choice other than 7/16".
This is the kind of thing we go through, in much greater detail, when spec'ing every rig component, for clients or for consultations. Lots of wrinkles and variables to consider, but it's part of how you get the right rig.
Fair leads,
Brion Toss

[osteoderm]

Thanks Brion! That clears it up nicely. I already have some loads estimated relative to righting moment, and will work from those numbers, rather than "rules of thumb".
My bowsprit is a new addition, so i have a blank canvas to work with, and at least am not being confronted with fitting the right rigging to the wrong tangs; I'll fabricate the headgear bits to fit the loads.
Quite unlike the rest of the old swaged rig; all 9/32" wire, but with a mix of tang and clevis sizes down to 7/16"... Just going ahead and making new tangs and chainplates properly sized for 1/2" pins all round; enough evidence of corrosion on some of them to warrant replacing all of them anyways.