Having owned both cats and tris, I feel at least somewhat qualified to make useful comparisons and to discuss some of the issues raised in previous posts. The "twitchy bobble" is, imho, mostly a catamaran
phenomenon and has its roots in two separate but sometimes interactive sets of forces. The first is obvious and well recognized, this being the result of simple geometry: in some conditions with the sea beam on (mostly), one hull will be up on the crest of the swell and the other in the trough and this condition can occillate rather rapidly. A slight change of course will substantially diminish this and the boat will be much happier but the crew will still feel the "twitchy bobble" in most near beam-on conditions. The second phenomenon is the tendency for the driven hull to switch from leeward to windward in some sea states and on various points of sail. This action can occur in a greater variety of conditions and is more subtle. Of course, the two phenomenon are not mutually exclusive.
The sea-keeping of the cruising trimaran
is more like a very svelte monohull
with training wheels. Any "twitchy bobble" is more likely the result of the monohull
sailor experiencing a lighter, more lively and better performing vessel after having been more used to sailing at anchor
. The space given up in the trimaran
main hull versus the monohull can be balanced against the tri's ability to carry lighter, bulky items like sails
in the amas (which should never be used for heavy stowage). As the trimaran becomes more performance oriented, the tendency is to carry one ama un-immersed at anchor
, thus leading to weeble wobble (as distinct from twitchy bobble.) One can deliberately violate the prohibition against carrying heavy objects in one ama to attenuate this effect.
I hope this clears things up.
Happy New Year!