When reading about small boats, I often find myself at Michael Storer’s website. It’s always fun and always informative (even though the formatting on it needs to be fixed!)
Here is a great article by Michael on outriggers, which includes double outriggers for trimarans. He has got a few nice pics too, including the ones I’ve linked to on this page.
Michael is a small boat guy who designs sailing craft for budget conscious self-builders. The article makes some foundational points about amas; I really enjoy the way he answers the straightforward questions of readers.