Good suggestions guys, but I don't have any battery chargers, batterys or
converters on the boat.
Just plain old 120v wiring.
I have walked the marina and the noise on my portable radio gets loud
when I hold the radio close to each power pedastal.

That sounds, then, as if "hash" from other peoples' battery chargers,
switching power supplies, and perhaps the dock lighting systems is
getting back into the power mains. Not terribly unusual.

Corcom, Delta, and other manufacturers make modular RFI/EMI filters
which you might be able to use. They're usually built into a sealed
metal can; they usually have three leads or push-on tabs for
connection to the incoming power (and ground) and a pair of leads or
tabs for the filtered AC power. I've bought them at local
electronics-surplus stores, hamfest fleamarkets, etc. for a few
dollars each.

One such is http://sales.goldmine-elec.com/prodinfo.asp?prodid=6379 -
a 10-amp LC-type line filter, which they normally sell for $5 and have
on sale for $2.95 (plus shipping of course).

You could wire this (or a similar one) up in a metal or plastic box,
with a line cord, a duplex outlet, and a circuit breaker or fuse, and
have yourself a pretty nice little line-noise-reduction device.

It might not be a bad idea to add some ferrite beads around the wires,
as well, to help attenuate the higher-frequency RF noise which might
be present.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!