Are Hydrofoils legal?

[Bear Islander]

I would like to get one but how can this be legal. I have seen them on the lake several times without registration.

A few years ago I put a small electric motor on a pedal-boat and was told I must register it and display bow numbers and sticker. I don't see how to do that on a foil.

The size of the motor does not matter. If it is mechanically powered it must be registered.