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Catalina/Capri 25/250 Sailor's Forums

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VHF with integrated AIS receiver

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Ryan L
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USA
230 Posts

Initially Posted - 01/29/2012 : 03:19:11

Since I'm selling my boat (she's in the swap meet section) I thought I'd post a few things from her that I thought might interest other people in this forum. In this case, our VHF with integrated AIS receiver.

AIS is a system that uses VHF radio to transmit position data (on channel 70). The position data comes primarily from the ship's GPS. All commercial ships are now required to have a transmitting AIS (including small fishing charters all the way up to supertankers). Many recreational yachts are starting to carry AIS transmitters and receivers as well.

Our radio is just a receiver. In other words, we can "see" them but they can't see us. AIS is not radar, nor is it a substitute for radar. Plenty of boats, especially recreational boats, are not yet transmitting AIS. BUT in many ways an AIS receiver gives you much the same info that a radar would in terms of relative position to other ships.

For example- the image below shows one of the screens you can select. Here's what the various info is showing:

• The number at top is the DSC "address" of the ship in question. With this radio you can push one button and that ship will hear a loud tone "alarm" on their bridge indicating an incoming call. When they key their mic their VHF will automatically switch to whatever channel you pre-selected prior to hailing them.

• The "radar" screen to the left shows range rings with you in the center. They can oriented north up or heading up. The various small circles represent ships. They are positioned on the screen relative to their bearing to you. The small lines coming off the small circles indicates the direction those ships are traveling.

• DST = distance to the selected ship

• BRG = bearing to the selected ship

• CPA = "closest point of approach" or how close the ship will come to you

• TCPA = "time to closest point of approach" or how long until the CPA happens

• SOG = "speed over ground" this is the vessel's current speed via GPS

There is a lot more info if I were to scroll down but these are the key ones for helping prevent collisions, especially in limited visibility. The reason TCPA is blank is because neither the selected ship nor my vessel was moving when I took the pic (we're in a marina) so we are not getting any closer. In this case CPA is also the actual distance of the ship at that moment.

You can set alarms for TCPA and CPA at whatever range or time interval you specify. For example, you can set an alarm to let you know if a commercial ship will pass within a specified distance of you or will come close to you within a specified amount of time.

If you see a close call or collision is a possibility you can then directly contact the ship (via DSC explained above) and ask what are their intentions and/or inform them of your position (IF APPROPRIATE!)

Another useful thing about this radio is that it displays GPS info. This lets us keep our primary GPS on deck (for the watch person) while someone else can still enter the log data while below (we do it hourly offshore or sooner if in restricted visibility). Very useful in wet or cold weather...

For all this to work the VHF must be integrated into you GPS via NEMA. If you haven't done this before don't get intimated, it's easier than it looks once you understand a few basics. We integrated the VHF, GPS, and tillerpilot so the boat can now steer herself to waypoints as well as hold a heading. This is useful especially if there is a cross current (the boat will adjust her heading into the current so her COG is rhumb line to the way point even though her magnetic heading will be above or below).

So there you go, a relatively inexpensive way to add a nice safety feature if you sail in waters around commercial traffic.

"Naoma"
1988 Ericson 38-200
San Diego, CA

Formerly of:
"Maria T"
1987 C25 SR WK 5695
San Diego, CA
L DOCK ARMADA

Edited by - on

TakeFive
Master Marine Consultant

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2272 Posts

Response Posted - 01/29/2012 : 10:00:45

Great summary, written in the way that the original documentation should be. Thanks for posting it! And good luck selling your outstanding vessel.

I do have a few additional comments:
<ul><li>Registering the MMSI is critical for all of these safety features to work properly. This is also true for all DSC radios (basically every fixed mount radio manufactured over the last 10+ years), whether with or without AIS.</li>
<li>Interfacing a chart plotter or GPS to the radio is also very important for DSC radios without AIS. It enables automatic transmission of your GPS coordinates with any DSC call, and when you press the "Distress" button. In an emergency, this frees you up to tend to business instead of reading off your coordinates to the USCG manually. This could save your life. This is so important that I purchased a dedicated GPS puck to connect directly to the radio. I didn't want this feature to be dependent on my computer-based chartplotter or handheld GPS running continuously.</li>
<li>I put a review of this same radio into Mainsheet last summer, however I used OpenCPN to display the AIS output. Your summary describes getting the maximum use out of the radio's display, which is very helpful to the non-geeks who don't want to interface a chartplotter (which is probably the majority of people).</li>
<li>The collision alarm features can be a mixed bag. If you sail offshore or in a wide expanse of water, false alarms are rare. However, if you sail in busy areas, you may get a lot of false alarms. On my river, the potential for a false alarm exists every time a ship comes around the bend. Often the CPA is on land, which is rather humorous. I have tweaked the settings to minimize the false alarms, but cannot eliminate them. And if you interface the AIS with a chartplotter, you'll get duplicate false (and true) alarms on it and the radio - you may want to disable the alarm feature on one of them.</li>
<li>The radio also has automated weather alarms which make an earsplitting noise, and require you to acknowledge and switch to a weather channel. Sometimes these alarms are for distant locations that are not relevant to your sailing area. Overall, it's a net plus.</li>
<li>Anyone who purchases this radio should seriously consider the [url="http://www.defender.com/product.jsp?path=-1|344|301236|320907&id=1133628"]SH RAM3 remote mic[/url]. This will provide full control of the radio in the cockpit, including the same display that the radio has down below. This is more than just a convenience, because it enables you to silence an alarm from the cockpit. The alarms can be very noisy, and you don't want to have to leave the cockpit every time one goes off. This is true of the false alarms, and is especially true if a collision is actually imminent.</li></ul>
Some of my posts on this topic can be found [url="http://www.catalina-capri-25s.org/forum/topic.asp?TOPIC_ID=22845"]elsewhere in this forum[/url] and on [url="http://www.sailnet.com/forums/electronics/71615-sending-gx2150-ais-nmea-data-chart-plotter-over-bluetooth.html"]Sailnet[/url].

Edited by - TakeFive on 01/29/2012 10:04:20

Ryan L
Navigator

Members Avatar

USA
230 Posts

Response Posted - 01/29/2012 : 19:16:00

Thank you. You too actually... I remember reading about your work and being impressed with the engineering. Thanks for the additional points you added to this thread. Good info.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by RhythmDoctor
 Great summary, written in the way that the original documentation should be. Thanks for posting it! And good luck selling your outstanding vessel.

I do have a few additional comments:
<ul><li>Registering the MMSI is critical for all of these safety features to work properly. This is also true for all DSC radios (basically every fixed mount radio manufactured over the last 10+ years), whether with or without AIS.</li>
<li>Interfacing a chart plotter or GPS to the radio is also very important for DSC radios without AIS. It enables automatic transmission of your GPS coordinates with any DSC call, and when you press the "Distress" button. In an emergency, this frees you up to tend to business instead of reading off your coordinates to the USCG manually. This could save your life. This is so important that I purchased a dedicated GPS puck to connect directly to the radio. I didn't want this feature to be dependent on my computer-based chartplotter or handheld GPS running continuously.</li>
<li>I put a review of this same radio into Mainsheet last summer, however I used OpenCPN to display the AIS output. Your summary describes getting the maximum use out of the radio's display, which is very helpful to the non-geeks who don't want to interface a chartplotter (which is probably the majority of people).</li>
<li>The collision alarm features can be a mixed bag. If you sail offshore or in a wide expanse of water, false alarms are rare. However, if you sail in busy areas, you may get a lot of false alarms. On my river, the potential for a false alarm exists every time a ship comes around the bend. Often the CPA is on land, which is rather humorous. I have tweaked the settings to minimize the false alarms, but cannot eliminate them. And if you interface the AIS with a chartplotter, you'll get duplicate false (and true) alarms on it and the radio - you may want to disable the alarm feature on one of them.</li>
<li>The radio also has automated weather alarms which make an earsplitting noise, and require you to acknowledge and switch to a weather channel. Sometimes these alarms are for distant locations that are not relevant to your sailing area. Overall, it's a net plus.</li>
<li>Anyone who purchases this radio should seriously consider the [url="http://www.defender.com/product.jsp?path=-1|344|301236|320907&id=1133628"]SH RAM3 remote mic[/url]. This will provide full control of the radio in the cockpit, including the same display that the radio has down below. This is more than just a convenience, because it enables you to silence an alarm from the cockpit. The alarms can be very noisy, and you don't want to have to leave the cockpit every time one goes off. This is true of the false alarms, and is especially true if a collision is actually imminent.</li></ul>
Some of my posts on this topic can be found [url="http://www.catalina-capri-25s.org/forum/topic.asp?TOPIC_ID=22845"]elsewhere in this forum[/url] and on [url="http://www.sailnet.com/forums/electronics/71615-sending-gx2150-ais-nmea-data-chart-plotter-over-bluetooth.html"]Sailnet[/url].
<hr height="1" noshade id="quote"></blockquote id="quote">

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