Reflection is pretty pointless.
Here's an experiment. Have someone point their card headlights on full beam at you at nighttime, somewhere reasonably dark. You probably won't be able to see very much.
Now, take a small mirror, and reflect the light back at them. It wil. be annoying, but hardly blinding
Sure, a suitably big parabolic might be able to collect, reflect and focus enough of the beam to distress people on the boat, but:
- That's a big, fragile thing to carry on a speedboat
- That's a non-trivial and non-cheap bit of optics to manufacture
- That's a tricky thing to aim and focus from a little boat in open water.
- Good luck aiming at something that is dazzling you with a vomit ray
And that's even before you consider it has a fixed focal length... too close or too far away and it won't be much good...
So, no. You can't defend yourself this way.