Which Type of VHF Radio Antenna Is Suitable for a 18-Ft Fiberglass Center Console?

- Books and people in this newsgroup recommend 6dB 8-ft antenna for a small powered boat. This sounds good. But I am wondering whether a 8-ft antenna is too large for my 18-ft boat. Will this make the boat "look" very top-heavy? Do people really use a 8-ft antenna in a small boat like mine?

- The other alternative is a 3dB 3-ft antenna and accepting the reduced range. Does a 3dB antenna provide a good enough range given the fact that I won't go too far away from the shore (because the boat is considered as a "bay boat")?

- According to post in this newsgroup, we need a metal plate for grounding if we use a 3dB antenna, and a fiberglass boat doesn't have it. My boat is a fiberglass boat. What's the alternative? Does this mean that I cannot use 3dB antenna?

Thanks for any info in advance.

Jay Chan

I've got an 8' antenna and a 14' boat. I figure that I need every inch of range I can get...

http://home.comcast.net/~galmgren/glastron/2000s/Blue-Boat_7-04_004.jpg

$999.99, plus shipping and handling.

Besides, if he's out in an 18' boat more than 15 miles from shore, he better be carrying an EPIRB...and filing a float plan. Should he fail to return as planned, a CG aircraft will pick his radio up from nearly 30 miles or more...no matter how big his antenna is.

Keep in mind that the antenna on passing ships/shrimp boats/etc. are at least 30-50' above the water...meaning that his 3' antenna will reach them almost as well as the 8' antenna.

As I said before, the height of the receiving antenna on most vessels that are going to render assistance has a greater influence on your radio's effective range than the height of your own antenna.

I regularly hear CG broadcasts coming out of St. Pete...and I'm 160 miles from them. Granted, they're using higher power equipment and very tall broadcast towers (perhaps broadcasting from aircraft), but I hear them on my boat with the 3' antenna just as well as the Grady with an 8' antenna on top of the hardtop.

I often do a simple cost/benefit analysis when trying to make a decision like this, and in Jay's case it is a no brainer.

It's not about the cost. I'd go with the 3' on top of the railing of the center console, because it's out of the way when fighting a fish...and the height above the water line is only a couple of feet less than my 8'.

I go home and check the possible location for a 8-ft antenna in my 18-ft boat. I have a feeling that a 8-ft antenna is just too long. If I mount it in the front rail of the T-top and set the antenna at a 45-degree angle toward the stern, the 8-ft antenna will still stick out covering the entire deck in the stern of my boat. This is going to be a problem if I want to cast from the deck in the stern of my boat because my fishing rod "may" hit the antenna. A 3-ft antenna that is pointing straight up will not have this problem.

A 3-ft antenna mounted on the T-top will be as much as 9-ft above the water level. According to this formula: range-in-miles = square-root-of-height-above-water-in-feet x 1.42 I should expect to get the range of up to 4.26 miles. This seems to be more than enough because I will be boating and fishing near the shore (not more than a couple miles from the shore), and the coast guard with their very tall antenna should be able to reach me.

OK, seem like I should get a 3-ft 3dB antenna.

Jay Chan

I have a feeling that if mine is a 21-ft boat with a taller T-top (like the Mako center console that I see in ad), I would have chosen a 8-ft antenna. But mine is a small 18-ft boat, and I have a feeling that it just doesn't make the cut for a 8-ft antenna.

Jay Chan

Jay Chan

There is no need for a ground with a VHF antenna.

Either the 3 db or 6 db antenna will be adequate for near shore coastal operation.

The dB rating plays a relatively minor role in the distance the signal travels. The height of the transmitting antenna plays a larger role. But the height of the receiving antenna is the most important element.

Example: A 3' antenna mounted on the top of the gunwale of a small boat might be 5' above the water line. It can travel only 5 miles to another antenna that is only 5' off the water...but can travel 15 miles to an antenna that is 100' high (like at a Coast Guard station).

An 8' antenna mounted on the same gunnel can travel 9 miles to another antenna that is only 5' off the water (big difference!), but only travels 18 miles to that 100' antenna (a not so big difference from the 3' antenna).

If the CG antenna is 250' above sea level (mounted on a tower on a mountain for example), the 3' antenna can travel 23 miles...and the 8' travels 25 miles.

So the question is... Who do you want to call with that radio?

Another boat within 5 miles? Then either antenna is fine.

The Coast Guard when you're 10-15 miles from shore? Then either antenna is fine once again.

Here's a good link to explain this further: http://www.yachtworks.net/Store/antennas.htm

I see no downside with going with the 8 foot antenna.