Power goes on and off-flickers

That is most likely because the radio is drawing more power than the wire can provide. First make sure you have good connections, especially a good clean ground. Next make sure the power wire from the boat is at least the same size or thickness as the power wire on the radio. If that doesnt work, you may want to wire the radio directly to the battery, using an aftermarket inline fuse and wire available at any car audio store.