I am going to be installing a 23' whip antenna for a new SSB radio installation on my boat. My vessel is all-aluminum construction with a center pilot house. How would you suggest mounting this antenna on this vessel? 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 didn't mention how large the vessel is or whether she is power or
sail. I assume she is power the pilot house is on the order of seven
feet above deck.

If you are able to keep the antenna at least two feet from the pilot
house, you shouldn't experience too much signal loss. The proximity of
the pilot house is likely to cause some directivity in the antenna's
radiation pattern, but with two-thirds of the antenna above the pilot
house, it will probably be ok. I have seen cases where the antenna is
insulated to just above the height where it is supported so the antenna
actually starts seven feet above the deck. It is only 16 feet long in
that case but the entire 16 feet would radiate efficiently. Most auto
tuners should handle that on all but the lowest frequencies, and there
are workarounds available.

Your alternatives to the above are to mount the antenna farther from the
pilot house (e.g., at the stern), giving up the support attachment, or
mounting it atop the pilot house (ugh) and guying it. Of course,
depending upon your frequencies of interest, a much shorter whip could
be the solution, maybe obviating the need for guys.

On a calm day, you should be able to do some experimentation before
actually installing the antenna.

Good luck,

Chuck

bradleyj wrote:
I am going to be installing a 23' whip antenna for a new SSB radio
installation on my boat. My vessel is all-aluminum construction with a
center pilot house. How would you suggest mounting this antenna on this
vessel? 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.

I am going to be installing a 23' whip antenna for a new SSB radio
installation on my boat. My vessel is all-aluminum construction with a
center pilot house. How would you suggest mounting this antenna on this
vessel? 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.

Well, I don't know if you are talking about something like a metal
Morad WH-23 or a fiberglass 23' Shakespeare or equivalent, but both need a
two piece mount. Probably some swivel bottom mount so it can be laid down at
times, and an upper support mount at least two feet up from the bottom.
Placing these two mounts as high as possible on the metal side of the pilot
house is fairly common. If you really want to gain all that length above the
pilot house, a fabricated aluminum tripod or sturdy welded post about three
feet high is cool.
The lead-in from the antenna to the tuner should be almost all outside
the aluminum pilothouse. Lots of boats (and ships) put the tuner outside the
pilothouse, near the antenna base to avoid any lead-in inside the
pilothouse. If you do the latter, very careful attention to sealing of the
coupler, and if you elect to vent it (Usually a plus), be sure the vent hole
is where the manufacturer recommends (at the very bottom, of course).
It would make suggestions a lot easier if you could post a picture or
drawing of your boat.
Tell us when you test so we can listen and report!
Old Chief Lynn

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.

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

Gary Schafer wrote in
:

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

regards
Gary



Shrouds?....(c;

The discussion was about where to mount the antenna for best radiation.
There are many antennas and mounts that require no cheap little plastic
support like Shakespeare uses on their antennas.

What I'd like to see mounted on top of his pilot house is an antenna like
the Moonraker 18B, with a proper, supportive deck mounting:
http://www.moonraker.com.au/marine.htm#MFHF
Click on 18B for the PDF file. Get the untuned version.

I'd mount this antenna THROUGH the cabin roof so it comes out in the
overhead panel or a cabinet with the tuner mounted out of the weather
inside the pilot house inside the panel. We have no pictures of his
pilot house so we can't see where that might happen. With the tuner
inside the boat, it'd take a direct lightning hit to destroy it, not
seawater. No cables, connectors, wires only the whip would be in the
weather, solving the big corrosion problems completely. This antenna
mount is designed to do just that, feeding the RF through the roof into
the dry tuner inside.

No extra "support" for the bassboat swingdown is necessary....

All this depends on other data we don't have. Where does he go
boating?....Is he going to be going to sea, or is he going up and down
the ditch with all the drawbridges? (If he's not going to sea, there's no
point in HF comms, anyway, so I assume he's going to sea.)....How high is
his mast over the pilothouse?....Does he need a swingdown mount, really,
or are we doing this just because that's the way it's always been done?

We don't have all the data. I was just responding to where the antenna
would be best mounted for best radiation. That's not necessarily the
best for his situation....

Boy, I never expected to get so much great advice so fast!! I'm digesting it all now. I've known since I started looking in to this that I'd have an awesome ground plane, but I never gave much thought to problems I'd have mounting the antenna. I'll let you know how I decide to go. By the way, I tried to post photos of the boat, but this server kept giving me errors. Here's a web site with a pictu

http://www.specmar.com/boatpics/boatpic55.jpg

Larry makes some good points, although they are couched a little too
heavily in absolutes. I don't agree that the losses with a two-foot
separation would necessarily be unacceptable.

Leaving aside whether the near-field losses will arise from electric
(displacement currents as Larry suggests) or magnetic fields, almost all
metal structures above the deck will alter the near-field properties of
a deck-mounted antenna.

Regarding the sufficiency of a two-foot separation, I would point out
that most HF mobile antennas are mounted well within two feet of the
vehicle's vertical metal components for something like two feet of
vertical rise. There is ample evidence that these installations "work",
or if they do not, it is usually not because of proximity to the
vehicle's vertical surfaces. HF antennas on aircraft have been run
entirely along the metal fuselage with separations on the order of two
feet. These "work" also.

So before rejecting the customary deck-mounting of a 23-foot whip with a
horizontal support, it would be useful to provide the OP with some
concrete indication of how well the antenna is likely to perform
compared to the next best alternative. While I can't do that
quantitatively, (I did suggest an experiment, which a competent tech
could do fairly quickly) it is my experience that such an installation
could be satisfactory.

With only the top 16 feet as a radiator, near-field losses become
negligible but tuner losses predominate. At higher frequencies (above 8
MHz, for example) 16 feet in the clear will probably outperform 23 feet
mounted next to the pilothouse. At lower frequencies it is more
difficult to say which would be better.

Lacking further information from the OP, that is probably the best we
can offer. The antenna, tuner, and SSB manufacturers should be contacted
to mine their experience.

For the strong of heart, center- and/or top-loading could even be
employed in some circumstances to shape the current distribution on the
whip in such a way as to reduce losses near the pilothouse.

Out of curiosity, did the boat's designer/naval architect not address
this design detail? Surely it is not an out-of-the-ordinary design question.

Chuck

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.

bradleyj wrote:
Boy, I never expected to get so much great advice so fast!! I'm
digesting it all now. I've known since I started looking in to this
that I'd have an awesome ground plane, but I never gave much thought to
problems I'd have mounting the antenna. I'll let you know how I decide
to go. By the way, I tried to post photos of the boat, but this server
kept giving me errors. Here's a web site with a pictu

http://www.specmar.com/boatpics/boatpic55.jpg


Nice boat, but I would not use a deck-mounted whip since it would be
surrounded by metal: not only by the pilothouse, but by the sides as
well! Instead, consider a 16-foot whip mounted on an insulated support
at the level of the gunwhales and supported at the pilothouse roof. With
all the windows in the pilothouse, I wouldn't give losses a second thought.

Good luck.

Chuck

In article ,
"Lynn Coffelt" wrote:

I am going to be installing a 23' whip antenna for a new SSB radio
installation on my boat. My vessel is all-aluminum construction with a
center pilot house. How would you suggest mounting this antenna on this
vessel? 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.

Well, I don't know if you are talking about something like a metal
Morad WH-23 or a fiberglass 23' Shakespeare or equivalent, but both need a
two piece mount. Probably some swivel bottom mount so it can be laid down at
times, and an upper support mount at least two feet up from the bottom.
Placing these two mounts as high as possible on the metal side of the pilot
house is fairly common. If you really want to gain all that length above the
pilot house, a fabricated aluminum tripod or sturdy welded post about three
feet high is cool.
The lead-in from the antenna to the tuner should be almost all outside
the aluminum pilothouse. Lots of boats (and ships) put the tuner outside the
pilothouse, near the antenna base to avoid any lead-in inside the
pilothouse. If you do the latter, very careful attention to sealing of the
coupler, and if you elect to vent it (Usually a plus), be sure the vent hole
is where the manufacturer recommends (at the very bottom, of course).
It would make suggestions a lot easier if you could post a picture or
drawing of your boat.
Tell us when you test so we can listen and report!
Old Chief Lynn



After looking at the Jpeg of the boat in question, I would like to ask
only one question. What would be the purpose of a MF/HF Marine Radio
Installation aboard this vessel? It hardly looks big enough to do any
High Seas operations, but if one could come up with a reasonable answer,
then Old Chief Lynn, makes a good case for the best MF/HF Antenna
installation for this vessel. All the above not withstanding, understand
that any 23Ft unloaded antenna isn't really long enough to provide
quality communications below about 6 Mhz. Also understand that in order
to fit a MF/HF Marine Radio System, you MUST apply for, and be granted,
a Vessel Radio Station License, by the FCC, as this type of radio is
NOT covered by the Blanket Station License granted to all non-commercial
vessels of US flag. All Radio Operators who use this radio, MUST also
apply for, and be Granted, a Restricted Marine Radiotelephone Operators
Permit. (unless you are operating the vessel in alaska)


Bruce in alaska
--
add a 2 before @