The details are a little sparse. Is this a steam launch with a live steam engine, or is it electric driven?
If live steam, can you both control engine speed and select forward/reverse with a single movement? If not, you will need an additional channel to change from forward to reverse, so 3 channels is the minimum you need (steering, speed and fwd/rev). If you have any other working features (a whistle for example) you will need another channel. Fortunately, there are some quite cheap multi-channel sets available, such as
this one.
If electric, then you will only need two channels, unless again you have other features (lights?) you want to control.
That's the best I can do without some more information.
Greg