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
Author:
Publish date:
Updated 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

TOTW_PromoSite

SAIL's Tip of the Week

Presented by Vetus-Maxwell. Got a tip? Send it to sailmail@sailmagazine.com No chafe, safe stay  If you’re leaving the boat unattended for a longish period, there’s a lot to be said for cow-hitching the shorelines, as this sailor did. They’ll never let go, and so long as the ...read more

belize600x

Charter Special: Belize

It would be hard to imagine a more secure spot than the Sunsail base on the outskirts of the beachside community of Placencia, Belize. The entire marina is protected by a robust seawall with a channel scarcely a few boatlengths across. It’s also located far enough up Placencia ...read more

DSC00247

DIY: a Top-to-Bottom Refit

I found my sailing “dream boat” in the spring of 1979 while racing on Lake St. Clair in Michigan. Everyone had heard about the hot new boat in town, and we were anxiously awaiting the appearance of this new Pearson 40. She made it to the starting line just before the race ...read more

01-oysteryachts-regattas-loropiana2016_063

Light-air Sails and How to Handle Them

In the second of a two-part series on light-air sails, Rupert Holmes looks at how today’s furling gear has revolutionized sail handling off the wind. Read part 1 here. It’s easy to look at long-distance racing yachts of 60ft and above with multiple downwind sails set on roller ...read more

HanseCharles

Video Tour: Hanse 348

“It’s a smaller-size Hanse cruiser, but with some big-boat features,” says SAIL’s Cruising Editor, Charles J. Doane. At last fall’s Annapolis Boat Show, Doane had a chance to take a close look at the new Hanse 348. Some of the boat’s highlights include under-deck galleries for ...read more

amalfitown

Charter Destination: Amalfi Coast

Prego! Weeks after returning from our Italian flotilla trip last summer, I was still feeling the relaxed atmosphere of the Amalfi Coast. It’s a Mediterranean paradise, with crystal-clear waters, charming hillside towns and cliffside villages, plenty of delicious food and wine, ...read more

image005

Inside or Outside When Sailing the ICW

Last April, my wife, Marjorie, and I decided to take our Tartan 4100, Meri, north to Maryland from her winter home in Hobe Sound, Florida. This, in turn, meant deciding whether to stay in the “Ditch” for the duration or go offshore part of the way. Although we had both been ...read more

MK1_30542

SailGP: There’s a New Sailing Series in Town

San Francisco was the venue of the biggest come-from-behind victory in the history of the America’s Cup when Oracle Team USA beat Emirates Team New Zealand in 2013, so it seems only fitting that the first American round of Larry Ellison’s new SailGP pro sailing series will be ...read more