sizing rope for boom preventer?

[rdykiel]

Hello,
how should I size the breaking strength of a rope used as a boom preventer on a Dana 24? Standing rigging is 3/16 SS with breaking @4,700lbs, main sail area is 152 sqft. What are the rules to apply?

Boom preventer rope goes thru block forward and back to cockpit.

Also looking for recommendations between standard sta-set, endurabraid, or dyneema.

Thanks

[Brion Toss]

Hi,
Think of the preventer as a mainsheet, led from the end of the boom. The loads are lower than even an end-boom mainsheet, however, as you only use the preventer in low apparent windspeeds, so you might run calculations for, say, 10 knots for your boat, instead of 20. Further factor in that the preventer almost exclusively deals with lateral loads, while the mainsheet must handle the vertical component as well. At least when paired with a vang, a preventer can be handled with little effort, even on much larger boats.
For your boat, try 3/16" Spectra, at the most, for the boom pieces, and 3/8" VPC for the deck pieces.
Fair leads,
Brion Toss