An interesting discussion. A couple of things to consider.

Another reader mentioned that VHF signals are essentially line of sight,
which means that the effective range of your radio is a function of,
among other things, the height of your antenna and the height of the
receiving antenna. Since you dont necessarily know the height of the
receiving antenna, it's hard to predict the range of the radio with any
precision. However, you can get a relative indication of the range of
an antenna mounted at 5' versus, say, 25'. At 5', the horizon is about
2 1/2 miles away. At 25' it's about 5 1/2 miles away. So, all other
things being equal, moving your antenna to the top of the mast should
roughly double your range. However, all other things are not equal, and
this should only be used as the roughest of estimates.

There are a couple other considerations. At 155mhz, there's a
reasonable amount of signal loss in the cable itself. For instance,
let's say that your marine radio is on high power, 25 watts. Let's say
also that you're using relatively low budget Radio Shack RG58, and that
the total cable length from the radio to the base of the antenna is 35'.
That's almost 2dB of signal loss, or roughly 16 watts of power at
the antenna. Obviously the shorter the feed line, the less loss.

The other obvious consideration is what happens if you lose your rig and
need to call for help? An antenna at the top of the mast performs
better, assuming the mast is still standing!

On my last boat, I solved this conundrum by having 2 separate VHF
radios, one with an antenna on the stern rail, and the other with the
antenna at the top of the mast. That way I was protected from a failure
of either of the antennas or the electronics themselves.

On the current boat, I have the luxury of having 2 masts. Each mast has
2 small high gain antennas at the top, offset by about 2'. The four
antennas are all interchangeable, so if one fails I can simply switch to
another. The four antennas are connected to a VHF marine radio, a dual
band VHF/UHF ham radio, an AIS receiver, and to the stereo system.



wrote:
I have a small sail boat (26') used for coastal cruising. It
would probably never be beyond 25 miles from the shore
line (maximum) and normally no more than 1 to 3 miles.

At present... it has a 1/2 wave Shakespeare mounted about
5 feet above the water line on a stern rail. The previous owner
has indicated that this arrangement has worked for him... and
I am assuming the standing wave ratio and that sort of thing is
ok... or must be... if his radio checks/contacts have been
satisfactory.

My question is...

Would I be *much* better off... moving the antenna to the top
of the mast... which would be 30 feet higher than where it is now
situated... based on the aforementioned cruising criteria?

Cause... if the gain won't be that *significant*... I don't want to
go through the hassle of remounting everything. Kind of like...
"...if it ain't broke why am I trying to fix it?" (smile)

Tnx for your help...

73

Bill
Southern California