Darryl, do they also make it a bit more difficult to lift a hull in marginal conditions because of the down force they generate on the windward hull?

There are scaling problems with the following anecdote but...I have built and raced model trimarans (mini40) for awhile and have found that T-foils haven't been faster in most conditions. Upwind, the extra drag from them and extra drag from not being able fly the hulls was slow. They made it harder to sail downwind, which was when they were supposed to work, because the boat wouldn't accelerate as fast in a gust, which would load up the rig making it want to nose-dive.

As I said, there are scaling problems with the anecdote but the main problem I see with T-foils on multihulls in general is making sure you can still lift a hull, probably only a problem in marginal conditions.