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:

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

MHS-GMR_3549

New Multihulls 2018

Farrier F-22 New Zealander Ian Farrier ushered in a new genre of sailing with his folding-ama trailerable trimarans, the best-known of which are the Corsair designs. Farrier’s last project before he passed away last year was this sweet little tri. Available in three versions, ...read more

shutterstock_373701682

Cruising: Island Comeback

The U.S. Virgins Islands have surged back from the devastation of the 2017 hurricanes, with new infrastructure plans that will benefit charterers and cruisers alike. After hurricanes Irma and Maria roared through the Leeward Islands in September 2017, it was impossible to ...read more

albintoilet

Gear: Albin Pump Marine Toilet

Head Start Is there room for a new marine toilet? Albin Pump Marine thinks so, having just introduced its line of Swedish-built heads—ranging from compact to full-size models—to the American market. The toilets feature vitreous porcelain bowls and either wooden or thermoplastic ...read more

07n_45R2699

Multihull Sailor: Classic Cats

If you’re looking for a decent sub-40ft cruising cat, you have few choices when it comes to new-boat offerings. It is a well-known fact that the multihull market has taken off in a way very few could have predicted. Despite Hurricane Irma’s recent destruction of a large part of ...read more

TOTW_PromoSite

SAIL's Tip of the Week

Presented by Vetus-Maxwell. Got a tip? Send it to sailmail@sailmagazine.com Thanks a bunch  This scene is very calm and seamanlike. No frantic rope throwing or shouting. As he passes the line to the gent on the dock, the crew on the boat says, quietly and clearly, “Would you ...read more

mcarthy-and-mouse

Experience: McCarthy and the Mouse

Sitting at the helm in a light breeze, my arms crusted with a fine rime of salt, my skin so dry I’d lost my fingerprints, I heard a clatter and a curse from below. There were only three of us a thousand miles from shore and only one on watch at a time. Usually, the off watch lay ...read more