Updated:
Original:

AIS Anxiety

William Solberg of Los Angeles, California, asks:"You have done a great job keeping us up to date on the new AIS technology, but I’m wondering whether it is better to use a masthead antenna with a splitter or a dedicated antenna mounted aft on the rail. Your suggestions regarding the installation of a secondary dedicated AIS antenna seem to put it on the aft rail or on

William Solberg of Los Angeles, California, asks:

"You have done a great job keeping us up to date on the new AIS technology, but I’m wondering whether it is better to use a masthead antenna with a splitter or a dedicated antenna mounted aft on the rail. Your suggestions regarding the installation of a secondary dedicated AIS antenna seem to put it on the aft rail or on some other structure there. Isn’t there a higher risk of clutter when the antenna is mounted low and aft?

On balance it seems to me that when one is dealing with terrestrial VHF signals, a horizon gain with a splitter trumps coax loss, and therefore a masthead antenna in combination with a dual channel AIS receiver with a built-in splitter, like the AIS-Multi by Comar for example, makes a lot of sense. If that is correct, what do you think about using a general-purpose marine VHF masthead antenna that is designed to work reasonably well over the whole range of frequencies in the VHF spectrum?"

Tim Bartlett replies:

Whatever way you go you have to make a compromise. The reason I prefer to have a dedicated antenna is that since AIS B is relatively low-power, just 2 watts, no matter how high up you mount your antenna you are never going have much more than a 10-mile range before the transmission runs out of power. You are correct in saying range depends on the antenna’s height. If two boats have antennas 10 feet above the water, each one’s radio horizon is going to be limited to about 10 miles.

But a drawback to mounting an antenna up high is that unless you have a two-masted rig, there will only be room for one antenna, meaning you can’t send or receive AIS messages when transmitting on VHF. You might be transmitting on VHF to resolve a potential collision risk, which is just when you want to be able to get constant data flowing to and from your AIS unit.

Related

ed3b8ae9-b65d-2941-47ec-cd0277bfcbe8

Mirabaud Voting Open to the Public

Photos from the industry's top photographers are in, and the 12th annual Mirabaud Yacht Racing Image competition is underway. An international panel of judges has selected this year's 80 finalists, which have been published online. The panel will also select the winner of the ...read more

P1320232-copy

Annapolis’ Boat Show is Back

After a year off in 2020, the United States Boat Show in Annapolis is back. From the diminutive Areys Pond Cat 14 XFC to the massive Lagoon Sixty 5, many of the SAIL’s 2022 Best Boats Nominees are on display for the public to get a firsthand look at, and SAIL’s Best Boats panel ...read more

05-Squall-in-the-ITCZ

Close-Hauled to Hawaii

The saying “Nothing goes to windward like a 747,” is one of my favorites. I actually once took a 747 upwind, retracing my earlier downwind sailing route across the Pacific. I’ve also done a fair bit of ocean sailing to windward. The 747 was a lot more comfortable. But then ...read more

01-LEAD-IMG-2106

Refurbishing Shirley Rose: Part 3

If you missed the first installment, click here. The hull and deck of Shirley Rose had been repaired, but what kind of sailboat would she be without a sturdy rig? I was told she was ready to sail, and that the owner replaced the standing rigging a few years before. Shirley Rose ...read more

211007MINI_1208-2400x1600

Mini Transat: Bouroullec and Fink Win Leg One

The Mini Transat is a roughly 4000-mile course that comprises two legs— Les Sables D’Olonne, France to Santa Cruz de La Palma in the Canaries, and Santa Cruz de La Palma to the French Caribbean island Guadeloupe. Two fleets of Mini 6.50s compete—the Production class in ...read more

01-LEAD-7-1-Rhiannon-loaded-on-the-truck-with-Clark,-Andre,-and-Louis

Book Excerpt: Taken By The Wind

In 1975, as a senior at Harvard, the question for Chicago-area sailor Mike Jacker became what to do next. The answer, as related in his new book Taken by the Wind, was to make a small-boat voyage to Tahiti with his grade-school friend Louis Gordon and Harvard classmate Clark ...read more

Maserati _Arthur Daniel

The RORC Caribbean 600 is Back

With a start planned for February 21 in Antigua, the famed 600-mile Caribbean race is back. The course circumnavigates 11 Caribbean islands starting from English Harbour, Antigua, and heading north to St Maarten and south to Guadeloupe, passing Barbuda, Nevis, St Kitts, Saba and ...read more

01-LEAD-14_00_210613_TORE03_JRE_4266_16961-3000x3000

The Ocean Race Europe

The fully crewed, round-the-world Ocean Race has experienced tremendous change over the years. From the 1993 transition to a one-design fleet to an ever-shifting route, what began as the amateur Whitbread Round the World Yacht Regatta in 1972 is a very different race today. The ...read more