Diodes for sailboat lighting circuit?
The arrangement you have drawn will work, subject to you choosing appropriate diodes. But there is probably a better way:

You can use switches which switch more than one light at once. Specifically Double Pole Single Throw (DPST) switches.  One each for Motor and Sail, and a normal SPST switch for anchor. Of if you want three identical switches, use three DPST ones and leave the other two terminals on the anchor switch unused.







simulate this circuit &ndash; Schematic created using CircuitLab

I'm not entirely sure what you mean by preventing "Flowbacks".  If you were to try to set up a similar circuit using just SPST switches it wouldn't work, because closing the anchor switch would allow current to flow down and back to the motor switch, then on to the red/green lamp. If that is what you meant, then using the DPST switches prevents that.

Note that neither your design or mine prevent you from putting all of the lights on at once by closing more than one switch. If that is something you want, you could use one 4-position switch. Either DP4T (which might be harder to find suitably waterproof) or a SP4T with diodes.