I concur. My reasoning in my previous message is due to the height factor mostly. Mounting a lower gain antenna on a sport boat really is not that great. A 6-db 8-ft antenna is far better, but doesn't look that great. Most VHF radios are putting out around 25-watts. They vary from manufacturer to manufacturer, but all advertise 25-watts (or 1-watt for close-in comms). As for antenna gain, the higher the gain, the smaller the angle of use is.
There are many factors. The general-use antenna for boating has been 8-ft with 6-db gain for a long time. It is a great all around size. 4-ft is good for light coastal use (within clear sight of land) or lake use. Otherwise buy the 8-footer and raise/lower it as you use it. (I had a 16-ft extension with a 8-ft antenna on my old Roamer. I could see quite a distance).
I now have 2 14-ft 8-db antenni mounted on the upper half of the 3/4 tower on my flybridge. Not sure what the effective range is yet, but it's up there. If comms are important to you (and they should be), don't skimp on this. It could save your life or someone elses someday.
There are many factors. The general-use antenna for boating has been 8-ft with 6-db gain for a long time. It is a great all around size. 4-ft is good for light coastal use (within clear sight of land) or lake use. Otherwise buy the 8-footer and raise/lower it as you use it. (I had a 16-ft extension with a 8-ft antenna on my old Roamer. I could see quite a distance).
I now have 2 14-ft 8-db antenni mounted on the upper half of the 3/4 tower on my flybridge. Not sure what the effective range is yet, but it's up there. If comms are important to you (and they should be), don't skimp on this. It could save your life or someone elses someday.
There are actually three (3) variables that come into play that determine the transmission distance of your VHF. They are:
1. Power
2. Antenna gain
3. Height
It seems that all the textbook discussions focus on the "height" part and from experience, the power and antenna gain play a bigger role for boaters. As an example, you can stand on the highest mountain with a 5 watt radio with a 2 dB gain built-in antenna and you are only going to be able to transmit a few miles.
If you look at this fancy diagram, you can see the effect of antenna gain on the radiation patterns from the antenna:
Take that cross section shown and the radiation patterns are essentially rotated around the antenna and look like a donut. A small SS whip has a gain of about 3 dB and looks like a fat donut and a 16' fiberglass antenna can push up to 10 dB gain created a stretched out donut. However, the smaller gain antenna is not as sensitive to having the antenna straight up and down like a smaller gain antenna is... Add more power to the antenna, and the distance increases subject to the height.
My experience with a 6 dB antenna is that it'll transmit about 10-12 miles with a 20 watt radio. That is far less than what a height calculator will show... You need a higher gain antenna (9-10 dB) and some serious power to transmit the full "line of sight" that textbooks discuss. My 4 dB antenna on my dinghy is good for about 3-4 miles.
My 2 cents.