ratio

[tlar633]

any one know the best beam for a 20 foot tri( doesnt have to be a screamer but sparkling performer)

[bad dog]

For reference, some good performaing tris have the following BWL/LWL ratios:
Dragonfly 920: 0.8914
Corsair 750 Sprint: 0.7639
Grainger Essential 8: 0.8718 (approx).

Average of these samples: 0.8424

On that basis, a 20' or 6m tri would have a beam of around 5.05m, but could be as wide as 5.3m. But keep in mind that these three samples are bigger than 20', and that may change the dynamics slightly - this response may flush out some of the more experienced designers out there.

There is another recent thread somewhere on this forum which touches on the sweetest B/L ratio for tris - chasing the balance between longitudinal stability and driving power (righting lever) - search for it, there was some really good discussion (I think it was http://www.boatdesign.net/forums/multihulls/sink-swim-27250.html which is quite long - but well worth a skim).