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Author Topic:   Modern Small Boat Electronics
jimh posted 08-13-2012 07:28 AM ET (US)   Profile for jimh   Send Email to jimh  
We just finished an eight-day cruise with a group of fellow boaters whose small boats are nicely equipped with modern electronics. Modern marine electronics are quite amazing.

First of all, all the boats in our fleet had digital selective calling (DSC) radios, and the DSC radios were integrated with GPS receivers and chart plotters. We could all request a position report from the other boats, or we could send a position report to the other boats. This proved to be very handy. For example, one evening one of the boats split from our group and headed to a different overnight stop. When they arrived, they sent a position report. We knew they had made it to their destination. And, of course, we could selectively call the other boats to initiate a conversation.

In addition, two of the boats had AIS receivers. When we were in the St. Mary's River, a very busy commercial shipping channel, the AIS receivers let us know when freighters would be passing our anchorage. We even found another recreational boat with a Class-B AIS transponder.

One of the boats had a satellite radio receiver and a subscription to a weather data service. We could get near-real-time weather RADAR images, wave height information, and wind speed and direction information. One evening we planned to cook out on a shore, but we waited about an hour to let some rain pass by us. We could see the rain cell on RADAR.

PeteB88 posted 08-14-2012 01:05 PM ET (US)     Profile for PeteB88  Send Email to PeteB88     
I am thinking about adding weather module to my Raymarine A57D and radio set up. Would like to know more about this technology. Jim - Do a webinar - now that would be cool. I'd even loan you my new pro- HD video gear to produce it.
jimh posted 08-16-2012 08:12 AM ET (US)     Profile for jimh  Send Email to jimh     
Our fleet consisted of six boats. As I mentioned, all the boats had Class-D DSC VHF Marine Band radios, GPS receivers, and chart plotters. Two of six had AIS receivers. One of the boats had dual fixed-mount VHF Marine Band radios, RADAR, and satellite weather information delivery. Three boats carried hand-held VHF Marine Band radios in addition to their main fixed-mount radio.

All the boats had modern SONAR units.

Two of the six boats had electronically operated engine throttle and shift controls.

I believe most of the boats had a NMEA-2000 network. One boat had a SmartCraft network.

That is a lot of small boat electronics in the fleet of six boats.

The outboard engines were also quite electronic and modern. Five of the six boats had low-emission engines. Two of the boats had four-cycle outboard engines with sophisticated electronic fuel injection. The other four boats had two-cycle outboard engines, but three of those four were modern, direct-injection, low-emission, computer controlled two-cycle engines. There was only one boat with conventional carburetor two-cycle engines.

The age of the hulls was as follows: 1987, 1990, 1992, 1992, 2005, 2010. The three oldest boats had been re-powered with newer engines.

jimh posted 08-18-2012 04:37 PM ET (US)     Profile for jimh  Send Email to jimh     
Pete--The weather satellite receiver was very cool, but you have to temper enthusiasm for it with the subscription price. For the level of data being received I think the cost was $40/month.
Mambo Minnow posted 08-19-2012 10:31 AM ET (US)     Profile for Mambo Minnow  Send Email to Mambo Minnow     
The new Garmin GDL40 is less expensive at $299 than the $699 GXM51 and provides weather subscription on a pay as you go basis. Much more cost effective for the weekend or seasonal boater.
PeteB88 posted 08-19-2012 10:59 PM ET (US)     Profile for PeteB88  Send Email to PeteB88     
Forty Bucks! whoa. My price pain threshold is modulated by the fact that as much as I would like to spend lots of money, all my available cash is tied up in bills. Well not all but when we were scrimpin and savin years back that was our favorite line when someone, especially an obnoxious salesman, would try to convince us to spend money on something. Interestingly it shut up most of them. Ten bucks and a ~$300 module, maybe or if I/we were cruising like you guys. Thanks and best to you.
6992WHALER posted 08-20-2012 01:35 AM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
The GDL40 needs cell towers. In Canada my cell phone costs $2.00 per minute when we can find a cell tower. So the GDL40 at $5.00 a day plus what ever the fee is for international service might be more expensive than the satellite system. The XM satellite is $10 per month for a US basic package or $30 per month for a US and Canada comprehensive package.

XM lets you change packages at will, and lets you turn the system on and off for the season with no activation charges.
I have mine scheduled to turn on June 1st and off September 1st. I changed the package to the $30 one just before we went to Canada on August 1st.

In the past they would let you add XM radio for $10 per month if you had the weather package. I recently installed a XM satellite compatible stereo so someday I might add that.

One of the electronics Jim forgot is the heading sensor that is connected to my GPS/Radar. It allows the radar and chart plotter to work much better together and MARPA is now functional. I will need more time to play with this feature before I really have a handle on what it can do.

He also left the Auto Pilot on board the Holly Marie off the list, but I do have it disconnected for some repairs so it was not functional during the cruise.

jimh posted 08-21-2012 08:27 AM ET (US)     Profile for jimh  Send Email to jimh     
John's fine boat HOLLY MARIE was certainly the most electronic-equipped in the fleet. Thanks for the further details.
jimh posted 08-21-2012 08:41 AM ET (US)     Profile for jimh  Send Email to jimh     
John's mention of XM Satellite weather data brings to attention the distinction from Sirius Satellite weather data. I did not realize the two companies, although now joined, continue to offer different weather data packages.

XM Marine Weather service via satellite is available with GARMIN's GXM 51 receiver with MSRP $700. See

Sirius Marine Weather service via satellite is available with a LOWRANCE LWX-1 receiver with MRSP $99. See

The LWX-1 was just recently on a promotion with a $99 rebate if one activated the receiver with Sirius for a qualifying data service subscription.

jimh posted 08-21-2012 08:54 AM ET (US)     Profile for jimh  Send Email to jimh     
The compass on HOLLY MARIE is also electronic. It is a KVH Azimuth 1000, I believe. See Azimuth-1000.aspx

This also provides a heading output on NMEA-0183, and this tells the auto-pilot the boat's current heading.

There are a lot of electronics and interconnections on small boats these days.

6992WHALER posted 08-21-2012 09:46 AM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
The KVH Azimuth 1000 is talking to the Garmin GPS 3206.

Unfortunately the Simrad AP 11 Auto pilot's flux gate compass will not share data with the rest of the electronics on board.

The information shared between the Garmin GPS and the Simrad Auto pilot only goes one way, location information is sent to the Auto Pilot from the Garmin.

I have the Garmin GDL 30A weather data receiver. This unit can receive XM audio as well as weather. It has a black box and an antenna while the new receivers have eliminated the back box.

I have no NMAE-2000 on board all the electronics are either connected by the Garmin Network or NMAE-0083. NMAE-2000 would be very nice as I have a rat's nest of wires behind my dash.

jimh posted 08-21-2012 10:27 AM ET (US)     Profile for jimh  Send Email to jimh     
To paraphrase an old saying about watches: A man who owns two electronic compasses never knows what his heading is.
6992WHALER posted 08-21-2012 11:59 AM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
Jim, that is so true.

Life sure was a lot easier when the magnetic compass was always correct, and the VHF radio only had 12 channels.

swist posted 08-21-2012 07:01 PM ET (US)     Profile for swist  Send Email to swist     
My GPS always agrees with my Ritchie compass - to the degree. Always makes me feel confident that the GPS is not picking up some cosmic alpha-rays or interference from some iPad on a plane flying overhead.
jimh posted 08-21-2012 08:26 PM ET (US)     Profile for jimh  Send Email to jimh     
A GPS receiver cannot measure heading.
newt posted 08-21-2012 09:29 PM ET (US)     Profile for newt  Send Email to newt     
True, but a gps can calculate heading based on change of position.
newt posted 08-21-2012 09:32 PM ET (US)     Profile for newt  Send Email to newt     
Or is it bearing? Either way, If you are moving, your gps will tell you which direction you are moving and therefore which way your boat is headed which may or may not agree with your Ritchie compass.
jimh posted 08-22-2012 08:10 AM ET (US)     Profile for jimh  Send Email to jimh     
A GPS receiver cannot calculate heading. A GPS receiver can only deduce course over ground by the track point method. A GPS receiver computes the current position. It compares the current position with a previous position. It assumes the course between them was a straight line. It calculates the course over ground based on those assumptions. The GPS receiver has no idea in what direction the bow of the boat is pointed. You could be moving the boat in reverse and going stern-first, or you could be drifting in the waves while laying abeam. The GPS has no idea of the heading. There is no mechanism in a GPS to know the heading.

There are GPS heading sensors, but they are based on having two GPS receivers. The GPS receivers are usually located several feet apart and oriented so they lay on a line that is 90-degrees to the keel. The two GPS receivers independently compute their position. Then the heading is deduced by knowing the location of the GPS receivers relative to the bow. This is the only way you can deduce heading from GPS--you need two receivers and a sophisticated algorithm. Such a sensor can also calculate roll angle by comparing the elevation of the two receivers.

A GPS dual receiver system that can deduce heading is rather expensive, about $2,500 for the least expensive one I can locate. A magnetic compass based heading sensor is less expensive, about $500 to $600.

I don't know why marine heading sensors based on magnetic compasses are still so expensive. There is a nice magnetic compass sensor in an Apple iPhone. An iPhone also has a nice inclinometer and accelerometer, too.

The new iPhone 4S has a GNSS receiver that is better than most marine GPS receivers. The GNSS receiver in an iPhone can use the USA Air Force NAVSTASR Global Positioning System, and also use the Russian GLONASS system. And it can also use precision fix augmentation systems from the FAA (WAAS) and the European Geo-stationary Navigation Overlay System (EGNOS). I have not seen any marine GNSS receiver that matches that.

swist posted 08-22-2012 08:14 AM ET (US)     Profile for swist  Send Email to swist     
Yeah, it calculates the heading from movement. The only time it's wrong is when the boat is stopped, at which point it reads some random heading which has no relationship to the way the boat is pointing.

I would improve the Garmin software to read **INV** or something like that when the position fixes are too close together to get a valid heading. Maybe some GPS units already do that.

jimh posted 08-22-2012 08:15 AM ET (US)     Profile for jimh  Send Email to jimh     
A GPS receiver can compute the bearing from its current position to another position. The bearing from your present position to another place is not the same as your boat's present heading. The boat's heading is not the same as the boat's course over ground.
jimh posted 08-22-2012 08:20 AM ET (US)     Profile for jimh  Send Email to jimh     
Swist says:

"Yeah, it calculates the heading from movement. The only time it's wrong is when the boat is stopped, at which point it reads some random heading which has no relationship to the way the boat is pointing."

No, this is wrong. The heading is often quite different from the direction the boat is moving. I already gave you two examples of this:

--the boat is making sternway. The heading is roughly 180-degrees from the direction of movement;

--the boat is drifting in current, wind, or waves and laying abeam; the heading is 90-degrees from the direction of movement.

Even when making forward propulsion the heading is often different from the direction of movement due to the influence of current or wind.

Again, a single GPS receiver cannot know anything about heading. There is no method for a GPS receiver to measure heading.

tmann45 posted 08-22-2012 10:10 AM ET (US)     Profile for tmann45  Send Email to tmann45     
The new definition of "heading" as used in the Garmin and Lowrance manuals is "direction of travel" as opposed to the traditional "direction the bow is pointing".
jimh posted 08-22-2012 11:56 AM ET (US)     Profile for jimh  Send Email to jimh     
Emphasis on "new definition."

M-W.COM says:


--the compass direction in which the longitudinal axis of a ship or aircraft points; broadly : direction

Richard Quinlivan posted 08-22-2012 12:20 PM ET (US)     Profile for Richard Quinlivan  Send Email to Richard Quinlivan     
The direction the vehicle is pointing is heading. The direction the vehicle is going i.e the direction the velocity vector is pointing is Track or Ground Track. Your GPS is really clueless about heading. Heading is what the compass displays.I am sure that Garmin doesn't redefine heading in their aviation products.
newt posted 08-22-2012 12:50 PM ET (US)     Profile for newt  Send Email to newt     
Swist says "My GPS always agrees with my Ritchie compass - to the degree. Always makes me feel confident that the GPS is not picking up some cosmic alpha-rays or interference from some iPad on a plane flying overhead."

Jim responds "A GPS receiver cannot measure heading."

Both statements are correct.

jimh posted 08-22-2012 02:31 PM ET (US)     Profile for jimh  Send Email to jimh     
"Both statements are correct."--If so, there are a lot of guys who wasted $600 on a heading sensor when they already had a GPS.

The inference I get is that swist's boat is always moving forward, there is never any leeway due to wind or current, there is no magnetic variation from true, his compass has no deviation, and his GPS position fix is always extremely accurate. That's when heading and course over ground might agree. But it's not otherwise likely to occur.

jimh posted 08-22-2012 03:05 PM ET (US)     Profile for jimh  Send Email to jimh     
The GPS signal that marine GPS receivers use is the L1 carrier, transmitted at 1575.42-MHz. Cosmic rays are not actually electro-magnetic radiation as might be implied by the term ray; they're charged sub-atomic particles.

In aircraft the radio-frequency transmitters in iPads--if they have that option--are required to be switched off by regulations. They're not likely to be a source of interference when off. Let's see if they could interfere when switched on.

The L1 carrier power on a GPS satellite is about 25-watts. The antenna is specified to have 13-dB gain, so the effective transmitter power is 500-watts. This is a power level in dBm of +57dBm. A GPS satellite is roughly 21,000-KM above the earth. The path loss is about 182-dB. The signal level on the ground should be about 57 -182 = -125dBm.

The transmitter in an iPad is specified with an output power of +15dBm. The transmitter in an iPad is not on the GPS frequency, but lets assume it might be malfunctioning and can interfere. An aircraft at 25,000 feet is 7.6-KM above the earth. The path loss is about 114-dB. The signal level on the ground, assuming no loss for passing through the metal fuselage of the airplane, would then be about 15 - 114 = -99 dBm.

Although the GPS satellite transmitter is more powerful than the iPad transmitter by 42-dB, or by a factor of about 15,000-times, the GPS transmitter is farther way from the Earth than an iPad in an airplane might be. The result is that the signal from an iPad at 25,000-feet might be stronger than the signal from a GPS satellite at 21,000-KM in orbit. The difference is about 25-dB in favor of the iPad, but, again, we are ignoring the effect of the iPad being inside an aircraft fuselage. I suspect that the attenuation of being inside a metal tube of the fuselage will significantly reduce the effective radiated power of an iPad toward the earth. However, you can see why you are required to shut off radio transmitters on airplanes. They could produce signal levels much greater than the GPS signals.

jimh posted 08-22-2012 03:07 PM ET (US)     Profile for jimh  Send Email to jimh     
The GPS on your boat is more likely to be affected by radio signals originating from equipment on your boat. For example, perhaps you are carrying an iPad on board. The iPad on board the boat will be a much more likely source of interference to your GPS than will be an iPad on a plane passing overhead at 25,000-feet or a charged sub-atomic particle (cosmic ray).
newt posted 08-22-2012 06:24 PM ET (US)     Profile for newt  Send Email to newt     
When my boat is moving, and my gps is set to display the compass, the gps compass reading is always very close to the Ritchie compass.
newt posted 08-22-2012 06:30 PM ET (US)     Profile for newt  Send Email to newt     
I feel bad for the people who wasted $600 on the purchase of heading sensors due to the statement above which is a true statement.
6992WHALER posted 08-22-2012 07:58 PM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
A heading sensor is a very nice thing to have when you have radar.
The radar and the chart plotter charts overlay better, and you can use the Radar MARPA features.

If you travel slow over long distances or you are swinging on an anchor your compass and GPS will disagree. If they do not something is wrong with your compass.

The heading sensor allows the chart plotter and the radar to line up. In other words the radar is always aiming at the bow, but the chart plotter aims at the direction of travel, not necessarily the bow.

If all you do is travel at high speeds in a little boat your compass and GPS will read close to the same when you are running.

The correct terms:

Heading is the direction you bow is aimed. (compass)

Course over Ground (or Track) is the direction the boat is traveling in relation to the bottom. (GPS)

If there is any wind or current it is doubtful that the heading and the Course over ground will be the same.

I did not spend $600 on a heading sensor but please do not feel sorry for me because I own one.

jimh posted 08-22-2012 10:23 PM ET (US)     Profile for jimh  Send Email to jimh     
A stopped watch is right twice a day, but no one thinks it keeps good time.
swist posted 08-23-2012 09:48 AM ET (US)     Profile for swist  Send Email to swist     
Jim - of course you are quite correct, and I probably overstated my original claim. I should have said "for the purposes of recreational boating, when the boat is moving more or less forward, and there is relatively little difference between the COG and the direction the bow is pointing, the GPS heading computation and the compass tend to be close to each other".

Also, the Ritchie compass which comes with a 170 Montauk moves around a lot when the boat is in motion over anything but 100% flat seas, and thus is pretty hard to read with one or two degree accuracy.

And I also will admit that it is good to be aware of those situations, that you list, in which the two devices could be far enough apart, that only the magnetic compass heading shild be trusted (and one should also be aware of situations/disturbances that affect the compass reading).

I am also sure that there is probably still something wrong with my corrected statement.

bluewaterpirate posted 08-23-2012 10:21 AM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
After reading all the above I mystified as to how my unit gets me to where I want to go and back safely.


jimh posted 08-23-2012 11:00 AM ET (US)     Profile for jimh  Send Email to jimh     
The GPS computed course over ground is quite useful, of course, and we all make use of it all the time. The heading sensor is needed for auto-pilots, its seems, and for overlaying radar plan-position-indicator echoes on a chart.
6992WHALER posted 08-23-2012 11:09 AM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
I agree, most people are mystified at how their GPS receiver gets them from one point to another.

I understand how it works and choose to add a heading sensor to my boat to make the system more accurate. I do not think it was a wast of my money.

I do not have a heading sensor on my 16 Sakonnet, I also understand that my GPS really does not know my heading. But in this boat I don't care if the GPS is a little confused.

I can say with complete honesty that my 1966 Richie compass, often agrees with my GPS receiver. All this tells me is that I have little deviation on the Sakonnet and I usually run it in calm water at high speed.

I can also say that my 2011 Richie compass on my 23 Walkaround hardly ever agrees with my GPS. This tells me that the 23 has more deviation, runs in rougher seas, travels more miles at slower speeds, and of course the compass might need adjustment.

I find it kind of funny that I am justifying my electronics in a post about small boat electronics.

The KVH Azimuth 1000 looks really cool on the dash, that alone should be a good enough reason to get one.

jimh posted 08-23-2012 11:13 AM ET (US)     Profile for jimh  Send Email to jimh     
The marvel of all these electronics is that they are now commonplace on small boats. When the EDMUND FITZGERALD sank in 1975 she did not have an electronic fathometer (echosounder) on board and there was no LORAN-C chain for the Great Lakes. She had a RADAR set, a Radio Direction Finder (RDF), and a marine radiotelephone set.

Here we are today with small boats typically having high-resolution color SONAR, precision-fix GPS receivers, extremely accurate digital cartography of practically every body of water in the USA and Canada, and sophisticated digital selective calling radios. Boats with RADAR probably have better sets than anything you could get in 1975. We've come a long way in marine electronics, especially in what can be reasonably installed on a small boat.

6992WHALER posted 08-23-2012 11:23 AM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
It is amazing how inexpensive, compact, and easy to use these electronic devices have become.
newt posted 08-23-2012 11:55 AM ET (US)     Profile for newt  Send Email to newt     
6992whaler, my apologies if you interpreted my comments on this thread in any way as a dig at you or your choices in electronics. That was not my intention.

I should also make a note to self not to spar with the moderator as he has the ability to rattle off long technical articles in very short time. I would pay handsomely to have his memory capacity.

newt posted 08-23-2012 11:58 AM ET (US)     Profile for newt  Send Email to newt     
Funny thing about some people and electronics though. I have a friend who has never bothered to learn how to use his GPS. When caught in fog, he navigates by compass, depth and sound. "Just head East until you hear the waves crashing on the beach. Then head South until you see the jetty. Follow the jetty around to the mouth..."
newt posted 08-23-2012 12:00 PM ET (US)     Profile for newt  Send Email to newt     
Oops. I am on the East Coast. Don't head east or you will end up in Europe. Head west until you hear the surf...
6992WHALER posted 08-23-2012 12:17 PM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
Nothing to worry about newt.

I like your friend, we all need to remember how to get home when the electronics fail.

jimh posted 08-24-2012 08:00 AM ET (US)     Profile for jimh  Send Email to jimh     
I learned to operate and navigate a boat without any navigation electronics. We used paper charts, the boat's compass, a hand bearing compass, and a carefully kept DR track. We had a sounder, but it just showed the depth in a digital display. We also had a knot meter. Of course, we were on a sailboat, and we moved much slower.

Today, if we are heading someplace new, into strange territory, we use GOOGLE EARTH for reconnaissance and pre-planning. It's really amazing how much has changed, and how the cost of modern electronics has become so low.

jimh posted 08-24-2012 08:11 AM ET (US)     Profile for jimh  Send Email to jimh     
Also, I should mention that we carry around a digital version of every NOAA chart for the USA, both in raster and vector format, on our laptop computer. The charts are available at no cost via download. We use a computer-based navigation program (Polar View NS) to pre-plan routes with those charts. We can also get a seven day weather forecast in three-hour increments from NOAA in GRIB format via a free download that takes typically only a moment of internet connection time. We have found these forecasts to be quite accurate and very useful in voyage planning. The wind direction, wind speed, and precipitation forecasts can be overlaid on our electronic chart. Again, amazing electronics and data.
swist posted 08-24-2012 11:59 AM ET (US)     Profile for swist  Send Email to swist     
My son took a friend out once when I wasn't here, got completely fogged in 5 miles from home. Got home no problem following the GPS. When he told me about this he announced "due to my superb navigational skills we got home safely". At which point I asked him how he would have returned with a paper chart and compass if the GPS went out. Of course he wouldn't have had a chance.

Dependence on electronics, as has been discussed here, is not a bad thing, unless it leads to arrogance like the above.

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