Just like an Oil Rig.
The stability is better than a monohull by far.
The rolling effect will be the same as a monohull.
The wider the pontoons the greater the Stability.
http://en.wikipedia.org/wiki/Metacentric_height
ftp://ftp.fao.org/docrep/fao/011/i0625e/i0625e02b.pdf
http://titanic-model.com/articles/A_Matter_of_Stability_Trim/A%20Matter%20of%20Stability%20&%20Trim.pdf
http://www.gwpda.org/naval/gmdefn.htm
