This is the best source for international frequencies that I know: http://www.rc-network.de/magazin/artikel_05/art_05-027/art_027-01eng.html
The French page is here - you will see that it is a bit complex... http://www.rc-network.de/magazin/artikel_05/art_05-027/laender/FRA.pdf
R/C has changed a bit since the old 27Mhz days. Your equipment is still legal, but, depending on where you operate your boat, you may find that you get a lot of interference from 27Mhz 'toys'.
A lot of modelling hobbyists in the UK moved to 35Mhz (for aircraft) or 40Mhz(for boats/cars) when these became available (in the 1980s, I think?). Buying a new one of these sets will be quite expensive. But recently 2.4Ghz became available for use.
2.4Ghz has a number of advantages:
1 - it uses the same band as 'wireless' computer communication. This means that it does not use a separate spot frequency for each model, but instead uses a more complicated command protocol, part of which involves 'binding' a particular transmitter and receiver together. Once you have done this, you do not need to worry about interference, and a practically unlimited number of models may fly together on what appears to be the same frequency...
2 - 2.4Ghz sets can be VERY cheap. Chinese-made Transmitter/Receiver imports range from £50 to £20! At the lower end the quality control may be poor, but they seem to work...!
I would keep your old Futaba as a vintage item, and consider a low-cost 2.4Ghz....