could lowered foils turn a fast boat into heavy weather boat?

anyone explored using a fast (sail or motor) boat's hydrofoils to increase seaworthiness at low/no speed?

 

I guess you are effectively talking about something akin to stabiliser wings. They are reasonably well proven.

There used to be Ferry here in NZ that operated in the Cook Strait (hideous piece of water). She had big hydraulic stabiliser wings and was able to sail comfortably in conditions that saw the bigger Cook Strait ferries tied up. She was a beast.

 

That's the kicker...at slow/no speed = no lift force.

Foils require fwd speed to generate lift.

There is of course Seakeeper: Seakeeper https://www.seakeeper.com/

And Island Engineer Inc.: Home Island Engineering, Inc. http://www.islandengineering.com/
they have a unique zero speed mode on their fins....