My 8 foot extension mast was looking pretty bad and would get your hand full of fiberglass splinters if you touched it ☹ I got a new one with the nice gelcoat finish and when I went to take the AIS antenna off, it broke the base. Since I had to buy a new antenna anyway, I decided to get an AIS version (https://www.amazon.com/Shakespeare-5250-AIS-Classic-Skinny-Antenna/dp/B0029WVMBS/ref=sr_1_3?keywords=shakespeare+AIS&qid=1551801317&s=gateway&sr=8-3-spell ). The old antenna was a plain old VHF antenna and the AIS unit measured the SWR at 1.4 to 1. The new antenna measures at 1.1 to 1, which is better. (For SWR, lower is good) The actual real world difference in range will probably not be great enough to measure. I ran the coax calculator and the difference in loss between 1.1:1 and 1.4:1 is about 2% for 20 feet of coax at 162 MHz. So the conclusion IMHO is if you are buying a new antenna for AIS work, for even money the AIS version is a tiny bit better, but I wouldn’t go spending much extra on it. Conversely you will lose a percent or two if you use an AIS antenna for a comm antenna. Note this whole discussion is based on 3dB gain antennas. Higher gain narrows bandwidth considerably as well as radiation angle. I would not use a 6 or 9 dB gain antenna on a sailboat in any case.
Joe Della Barba Coquina C&C 35 MK I
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