Is 1/4 too big?

[StormJib]

Hello all,

Is 1/4" 316 ss far excessive for Bristol 27?
I am replacing chain plates and related hardware.

I have been aboard during 2 Mast failures, (different boats) I can't do that again.
1St due to soft bulkheads on deck stepped Mast.
2nd was result of improper Mast section according to Dywer spar.

Thoughts? Mike

[Stumble]

As a non-engineer I can't really make a suggestion about sizing, but if you are replacing them anyway I would highly recommend switching to titanium chainplates. I sell titanium chainplates and hardware, so it is defiantly a self-interest thing, but they can be stronger, smaller, lighter, and immune to corrosion for a relatively small premium.

Generally we recommend either having an engineer spec alloy and size, or replacing size for size with Grade 5. Grade 5 is massively stronger than 316, with roughly 5 times the yield strength, and about twice the tensile strength.

Some people have also used grade 2, which has Slightly higher yeild strength, but only 5/8 the tensile strength. They do this by going up in size to compensate for the lower tensile strength. Typically it doesn't take a massive increase, and not much more in cost, since the machining cost is the driver or purchase price, not the quantity of material (within reason of course).

[StormJib]

Do you have machinists you work closely with? Can you tell me any specific quote for a similar vessel? Or even a dis similar vessel so I can get a feel for pricing. How quick can you deliver? Web site?

Mike

[Brion Toss]

Hello,
Rigging is a matter of finding what the load is, and then dealing with that load. You suffered through a dismasting because of materials decay, which is to say someone wasn't dealing with the load through inspection and maintenance. You suffered through another dismasting because, apparently, the mast section was too small, which is to say someone wasn't dealing with the load through basic calculations. Making wire bigger won't necessarily deal with the load, as there are several other basic considerations besides scantlings, like staying angle, relative length, distribution of load, etc. You can make your chainplates out of titanium, or lead, or shitake mushrooms for all I care, but the choice of materials should happen way down the path. If you know the load, in magnitude and nature, and if you can assign an appropriate factor of safety, then wire diameter, and most everything else, will reveal itself.
Your rig is a system; treat it like one.
Fair leads,
Brion Toss

[Robbie.g]

+1
Start at RM @30 and get crunching.