I guess there are two parts to this question: (i) what do any Belgian rules say? (ii) what is sensible?
We are not exclusively UK based, but mostly, so make sure you get appropriate local advice. If like the UK there are no rules then I would suggest working out where to take your boat has to be your own decision based on experience and depends a lot on weather, number of other people around, your skills, what equipment you carry etc. Have you done any practical training? I'm not sure if Belgium has an equivalent to the RYA powerboat training scheme.