On Sun, 29 Jan 2006 22:41:06 -0500, Larry wrote:

bradleyj wrote in
:

I understand that it is important to keep the whip from coming
too close to any metal. This is an obvious problem, since this boat is
all aluminum. Any suggestions or references would be appreciated.



You're very lucky, as HF operators go. The metal boat will make an
excellent "ground plane", the counterpoise plastic boat owners dream of.

What kills HF is any PARALLEL metal which the RF waves intercept on their
way out of the boat. This actually creates a capacitor, its two plates
being the mast at boat ground and the whip, with the air as its
insulator, thus shunting the RF energy off to ground. Two feet is not
enough, infinity is. The further you can get the whip away from any
metal rising over it, the better. The best place is atop the mast with
the whip sticking way up above it, but this isn't very practical as
you'll be going under overhead obstructions. So, let's mount the whip as
far away from the mast as we can get, including its guy wires and other
metal/wire/conductive things going aloft.

Let's put the base for the whip on TOP of the nice metal pilot house
ground plane (which ends up perpendicular to the whip). This makes USE
of the excellent ground plane effect of the horizontal pilot house roof,
while keeping the E-field from intersecting it.

PLEASE DO NOT MOUNT THE WHIP ON THE SIDE OF ANY METAL HOUSE if you can at
all help it. The shunt capacitance of the whip near the wall of the
pilot house exterior mounted for convenience on the side somewhere is
just awful...sucking your signal off to that metal along side the whip.
Signals suck like that.

You didn't mention a flybridge atop the pilot house so I'll assume you
don't have one. So, let's mount the whip dead centerline of the pilot
house roof, about a foot from the forward edge of it, with the
weatherproof tuner right next to it. The tuner's output wire to the whip
should be as short as you can possibly make it as that becomes part of
the antenna (and part of the shunt signal off to metal problem).

The ideal mount would be a hole in the pilot house roof with an insulator
mounted THROUGH the roof with the tuner mounted safely INSIDE the pilot
house right next to where the feed-thru mount's "hot" bolt protrudes
inside. Of course, though I'd be proud as hell of it, myself, the
yachties would scowl, seeing the tuner overhead of the pilothouse...(c;

Be sure, wherever you mount the whip/tuner to put a heavy metal stainless
strap from the tuner's ground bolt to the BARE METAL under the closest
leg of the tuner where it's bolted to the pilot house roof, a fantastic
ground.

I'm green with envy. Lionheart has a long strap ground to the engine
block...the only metal mass of any consequence in the plastic ketch....
(sigh).

Larry W4CSC
Lionheart WDB-6254
Icom M802, Icom AT-130, 55' long insulated backstay....poorly
grounded...dammit.

And just how would you recommend supporting that 23 foot whip mounted
on top of the pilot house?

regards
Gary