As has been stated hundreds of times now on this and other Boards, there are lots of effective ways to implement a good RF ground.
Gord may well be correct re: coupling differences in cored hulls but, happily, it really doesn't matter. You DO NOT have to couple to seawater, or even connect directly to it.
However, for static bleedoff and for reducing noise
it is generally good practice to at least run a short ground strap from the tuner ground lug to the nearest bronze thru-hull. If you don't have any, what about s/s rudder
S/S rubrails, toerails, pushpit/lifeline/pulpit complexes, bit radar
arches, etc., etc., all work well.
Radials will work just fine. Elevated radials work even better than burying them in the bilge
. Basically, just run 'em as best you can and, wherever possible, use 1/4 wavelengths of insulated wire for the bands of interest.
There's even a commercial
product being sold on eBay which is a shortened RF ground; just lay it around the bilge
. Haven't tried it myself, but there's no reason it shouldn't work. I've done something similar as an experiment
and thought about a marketable product, but just haven't got around to it :-) My experimental ground worked just fine, though.
strap to a thruhull will work OK all by itself. Radials will likely improve both tuning ease and radiated power.