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Choosing an antenna for your boat
A boat can have many types of antennas for
communications, and others for navigation and entertainment. In each
category so there are many types of antennas to choose from. To
complicate matters even more, there are combination antennas that do
multiple jobs in one package. However, the only way to get to the
end is to start... somewhere... so let's take a look at the most common
antenna need, VHF, first.
A VHF antenna normally broadcasts and
receives within the VHF band. VHF is a method of encoding
transmitted signals, but by world accord (isn't that amazing!) certain
frequencies and "bands" of frequencies are reserved for maritime
VHF communication. Connected to a transceiver, like Shakespeare's SE
2001-EX, SE 2010, or the unmatched SE 6000TM nav-com, a VHF
antenna puts you in touch with your fellow boaters, with drawbridge
operators, and if needed with the Coast Guard (or other maritime authority
in your country). VHF systems let you call for help, receive weather
information, and exchange necessary communication with fellow boaters.
The range for VHF is not very far - line of sight from the antenna,
actually. For longer range communication other choices abound.
In a VHF system, the antenna is the most
important link. A poor antenna will give poor system performance
from even the finest transceiver, and a great antenna will help you get
the absolute best out of a marginal transceiver.
- What boat?
In choosing an antenna for your boat, the first consideration is the
boat itself, as well as what type of boating you do with it. If
yours is a simple fishing boat that would be dwarfed by a 23-foot
antenna, then of course the longer, better, higher-gain antennas are
out of the question. If yours is one of the luxurious boats with
the multiple decks and the hot and cold running champagne, then that
23-footer might not even do - you might need the longer range
communications of SSB and Shakespeare's 35-foot Styles 222 and 229-F
antennas. Or check into Shakespeare's other large VHF Commercial
Antennas, instead. Remember, though, that the important
consideration is not just the size of the boat, but what you do with
it. If you never take your 90-footer out of Lake Fishbitten,
then you don't need a huge antenna, after all. And it's not
likely that you'll take your bassboat Pacific island hopping.
If that small fishing boat at the
fishing boat store got you hooked, look into Shakespeare's three-foot
antennas like the Style 5240-R. It's a half-wave, Low Profile,
end-fed antenna with a 36" stainless steel whip and chrome plated
brass ferrule. The Style 5241-R is the same design as the
5240-R, but with a heavy-duty stainless steel whip for stability at
high speeds. The 5247 is basically the same thing, but its heavy
duty whip Lifts and Lays down out of the way while you cast around the
boat in search of the elusive bass creature. If you need to
remove your antenna for storage of your boat, the Style 5242, has a
quick-disconnect fitting for easy attachment and removal of its
stainless steel whip.
VHF antennas can be mounted on a flat
surface, or attached to a rail. For sailboats, you can mount
low-profile antennas like these or the 5215 series on a mast, and the
extra height of the mast will give them superior performance.
The Style 5215-C-X even comes with a 60-foot coax for just such
mounting. We'll come to a more thorough treatment of antennas
for sailing vessels later on.
These low-profile antennas are three
feet long. One size larger would be the five-foot Style 396-1.
Remember, with VHF, longer and higher is better. The smaller
antennas might all you need for close-in, however, or your boat might
not accommodate a longer antenna. Can you see one of those
23-footers on a bassboat? The bass would laugh themselves silly.
- Consider the available space for
mounting an antenna (and a radio), and how the antenna will have to be
mounted.
- Rail mounting. Antennas attach
easily to a variety of sizes of rails with handy rail mounts.
The ratchets on them make lowering the antenna quite easy - for
fishing or trailering, whatever. The rails can be horizontal
or vertical, slanted or not. The simplest rail mount is
Shakespeare's Style 4720 Economy Rail Mount. It's a simple
clamp and a simple 1"-14-thread bracket that holds the
antenna to the clamp.
- Surface (deck or bulkhead) mounting,
flat or vertical. Mounting an an antenna to a flat surface
requires either a flange mount, or a ratchet mount. Larger
antennas have their own special needs - discussed shortly.
On most boats, it's a safe bet that most of the available flat
surfaces aren't exactly vertical or horizontal. They slope.
The easiest way is with a ratchet mount that handily adjusts for
the sloping surface and still permits quickly raising or lowering
the antenna in the direction you want.
- Mounting Kits. Even if your
boat is large enough so you don't have to take down your antennas
to fish, many longer antennas probably have to be lowered to clear
bridges, boat houses or other overhead obstructions. The
two-part antenna mounting kit provides that option. The
upper bracket snaps open, so you can lay down the antenna when you
need to, and raise it again quickly when clear of the obstacle.
- Mast mounting (for sailboats, or
attached to some mast-like structure on your boat). Antennas
can be strapped to a mast quite easily. Some antennas are
intended for this mounting method, having an elongated sleeve at
the bottom for the purpose.
- Where will it be on the boat?
Your antenna should definitely be mounted as high as possible.
That's super important, so here it is again: Your antenna should
definitely be mounted as high as possible. VHF signals are
line-of-sight only. so, the higher you can mount your antenna, the
farther it can "see" to the horizon, and the more boats or
other radios it can reach.
In this respect, sailboats have it
made. Installation of a small antenna on top of a sailboat's
high mast can give performance equal to or better than a long antenna
on a small boat.
Choosing a location for your antenna is
an extremely important part of choosing the antenna itself.
Remember to keep the antenna away from large metal objects, and
especially away from other radiating devices (like other antennas).
The antenna should not be mounted closer than three feet from the
radio, but it shouldn't be so far away that the radio's signal is
depleted before it gets to the antenna.
Don't forget to consider where you have
to put the boat when it's not in use. If the antenna will have
to be lowered when you come in to port, you'll have to be able to get
to it to do so.
- What kind of boating do you do?
The real question is: How much range do you really need from
your radio? The farther you venture from shore the longer reach
you'll need from your radio - and thus from your antenna - to
communicate with base stations like the Coast Guard. The farther
out you go, the farther you have to reach to communicate with other
boats, too. It can get pretty sparsely populated out there.
If yours is a fishing vessel, and you need to communicate with others
in your fleet who are some distance away, you'll need a large antenna,
high up. For VHF, output power is limited to 25 watts. So,
the antenna has to "reach" with its antenna gain, a function
of antenna height, length, and quality.
- Safety first
The main reason people have VHF radios on board is to call for help,
if help is ever needed. So, make sure the system you choose will
have enough reach and power to be of service in an emergency.
Simply rapping with the other boaters around your dock is fine, but if
you need help, you want to be able to call for help and be heard.
Don't shortchange yourself into a small antenna that won't get your
signal across the water when you need it most. When it comes to
safety, err on the side of caution.
| Here is a formula for
calculating the range of an antenna:
Calculation for Range of an
Antenna:
Square Root of Height (in feet)
above water x 1.42 = Range in miles
Remember to perform the
calculation for BOTH vessels, then add the results to get the
range between two vessels.
|
- Antenna Gain
Shakespeare's VHF antennas come in gain categories, like 3dB, 9dB,
etc. This is a measure of how efficient the antenna is with the
signal you feed it, but it depends a great deal on the length of the
antenna. The gain of an antenna is stated in deciBels (dB) of
effective radiated power. Gain is an increase (or even a
decrease) in ERP. You do not get antenna gain from any so-called
amplifiers built into the antenna, and it does not mean you can put
more than the maximum legal 25 watts into a VHF antenna. You
only get dB gain from longer, more efficient antennas. High gain
factors are 6dB, 9dB, and thereabouts. Unity means no antenna
gain - a multiplier of "one."
Shakespeare Marine TV Antennas
The world of boating is a wonderful world, indeed, but it only has the
comforts of home if you take the comforts along with you. Take
television, for example. TV signals are, like VHF radio,
line-of-sight. Commercial broadcast stations go to great lengths -
up to 2000 feet - to get their antennas as high as possible for the widest
coverage, but if you're way down at "sea" level on your boat,
you might need a decent TV antenna to pull them in, and get all those
wonderful television shows coming in clear on your boat.
Shakespeare's marine TV antennas come in two main types: omnidirectional
and directional. Generally, if you're going to do most of your
marine TV watching anchored someplace (there are lots of other
considerations, too, naturally), you'd go for a directional TV antenna.
These have the same benefits as the ones on top of your house - they can
be rotated for best reception of various stations. That is, you can
point them toward a station, and easily re-aim them for a different
station if you need to.
On the other hand, if you're going to do a lot of TV watching out on the
water, where rolling seas and oft-changing course would keep a couple of
galley slaves busy re-aiming a directional antenna, you can keep life
simpler with an omnidirectional antenna. It doesn't have to be aimed
to pick up the stations.
Shakespeare's directional TV antennas are
the SeaWatch® 2040 and the SeaWatch® 2050. The latter goes the
extra mile by adding an infrared remote control with which to aim the
antenna. The 2040 has a cable-tethered remote.
Adjusting for Signal strengths
Another thing about Marine TV is you don't know whether you're going to be
watching from dock side, where the stations come in strong, or from after
a day of fishing at your favorite spot, where the signals are far from
optimal. Shakespeare's SeaWatch® 2025 Marine TV Antenna, an
omnidirectional one, offers a solution: adjustable signal
amplification. The sleek looking antenna comes with dual amplifiers
that let you boost or attenuate the signal as needed, using a knob on the
controller panel. The 2025 also steps out of the way when it's off,
switching in its auxiliary input (for cable or satellite TV reception, if
you provide the appropriate hardware and program service).
A little tip from the Technical Support department here: marine TV
antennas should not be mounted in your vessel's spreaders. It's
better to mount the antenna above or below the spreaders. |
