That is only correct, for the most part, if you consider strength of signal and projection over flat plane ONLY (in other words - over short distance); however, if considering the Earth's curvature - a longer antenna will always give you MORE RANGE. For various reasons it is difficult to exceed 20-25 mile effective range radius but you will not get even close to that maximum possible distance/range with a short antenna mounted low.The difference in range between a 4ft and 8ft antenna is negligible. Per the VHF antenna range calculators, you might get an additional 1-3miles of additional range with an 8ft antenna when 40-60 miles offshore. I typically use the 4ft antenna because they are easier to fold down and I am vain and down like 8ft, flimsy antenna flopping all over the place in a 2ft sea.
Additionally, I like the Digital (brand) antenna simply because their barrelled-end (the end that attaches to the back of the VHF radio) detaches very easily and screws back on. This is a nice feature when trying to "fish" the VHF antenna cable through your t-top pipework. You can do the same thing with a Shakespeare antenna but their barrel-end is much harder to install/uninstall
Agree with 'the higher the antenna the better', especially on a non-rocking/rolling boat. Our previous boat had two VHF radios. One attached to an 8', 6 db antenna, mounted on the flybridge with the base of the antenna 11' above the water. (effective height, 19' tall). The other radio was hooked to a Shakespeare (4018) two-piece 19' tall 9db antenna where the base was also mounted 11' above the water (effective height, 30' tall/above the water). I could communicate between the Pungo Creek area of NC to Silver Lake on Ocracoke Island to a friends boat that had a similar 9 db set up on his boat. (We could NOT with the 8' 6db). The distance, (the way the crow flies) between Pungo Creek and Ocracoke is about 46 miles. Under certain conditions VHF can 'skip' and give a longer range than even the direct line of sight antenna-to- antenna graphics depict.; especially with the 9 db that concentrates the signal to the horizon. 9 db is a great way to go, but on rocking/rolling smaller boats, the 9 db signal is often just lost/directed into the water, and/or directed into outer space! On our Parker-Sized boats, the 8' 6db is a good compromise. We could use a 9 db, but it would work best, only on calm days.That is only correct, for the most part, if you consider strength of signal and projection over flat plane ONLY (in other words - over short distance); however, if considering the Earth's curvature - a longer antenna will always give you MORE RANGE. For various reasons it is difficult to exceed 20-25 mile effective range radius but you will not get even close to that maximum possible distance/range with a short antenna mounted low.
View attachment 27835
Your not talking one of those 3ft sailboat antennas......are you?I think to go with small whip style antenna.
I'm with Warthog! I have many friends over the years that wasted time and $$ with a short, 3db whip antenna. They can sometimes RECEIVE signals from a great distance (say, from another boat or USCG base-station, and who are NOT using a 3db!), but your 'sending/broadcast' signal will fall short. I've been told many times, "Hey, I heard you calling me, why did you (meaning me!) not respond?!" The simple answer is, I didn't respond because it was impossible to receive their weak, short-range, 3db signal. I didn't hear them. A 3db will do a little better mounted 60 feet in the air on top of a sailboat mast, but that's just because of the height; the signal is still a weak 3db. (Sailboats use them because if they had higher db antennas, most of the signal would be shot into the water or into outer space when healed over).Your not talking one of those 3ft sailboat antennas......are you?
A 18ft boat with no T top is always hard to figure out......But do NOT waste time and $ on a Lil 3ft whip.....Been there done that.....You want a ratchet mount on console and lay it forward when not in use.
I’ve got the 8’ Shakespeare Mariner with their ratchet mount mounted to my fiberglass tee top. As Warthog said, use the correct bolts (I put a dab of 4200 under the mount) and you won’t have any problems.My boat has hardtop t top. I am worried about extra dynamic loads on a skinny sandwich of the top. I will be using it for emergency coast guard communication. Athe there any light/short antennas better than others?
Another vote for the bigger antenna. You should absolutely not be looking at anything less than a 4' aerial, preferably 8'. Look at the underside of your T-top; very likely you have mounting plates designed specifically for the mounting of antenna bases. If not, use a backing plate made from starboard or fiberglass and thru-bolt the mount. If you're really worried about it, you can fashion a mount that spans one of the T-top tubes, or install a product like this: Universal Mounting BracketMy boat has hardtop t top. I am worried about extra dynamic loads on a skinny sandwich of the top. I will be using it for emergency coast guard communication. Athe there any light/short antennas better than others?
Of note, most 4' antennas are 3 - 4.5db antennas, compared to the 8' antenna's 6db rating. Andy's chart above illustrates what the effect of a lower decibel rating is in terms of radiated energy. Both the energy and the height of your antenna will affect the range of your transmission.VHF radio transmission distance is based upon 1) curvature of the Earth, 2) height of the receiving antenna, and 3) height of the transmission antenna.
The additional range offered by an 8ft antenna is about 1mile (or less) than a 4ft antenna) assuming both are mounted to a cabin or T-Top 8ft above the water.
Here is the calculator ...... CEPD Tools - Transmission Calculators