satellite compass

[AKFish]

I'm just getting to the installation of a Furuno SC30 GPS compass. My Maretron SSC200 is effected by the steel hull, to the extent that when heeled to port, there is a 20 deg swing in heading as the mass of the hull moves out of the way. I should mention that I had to install that compass on the mast away from the hull.

I hated to have to bite the bullet, but it was getting hard to nav via auto pilot due to course recovery upon heeling. Probably the best ancillary feature is the heave compensation while plotting on my personal bathemetry generator. It should smooth out the sawtooth from swells and paint a more accurate bottom profile.

Anyone else make the jump to this instrument?

 

[twistedtree]

I'm installing the Simrad equivalent - an HS70. They are pricey, but I've heard nothing but good things about their performance.

One thing to note with the SC30 - there is an internal battery that needs to be replaced at some interval. I know a number of people who have discovered this at inopportune times. You might want to put it on your regular maintenance list to avoid surprises.

 

[twistedtree]

Can you tell us more about your "personal bathemetry generator"?

 

[AKFish]

One thing to note with the SC30 - there is an internal battery that needs to be replaced at some interval. I know a number of people who have discovered this at inopportune times. You might want to put it on your regular maintenance list to avoid surprises.

OK...good to know. I couldn't find anything in the manual that says this. Only a reference to fuses if not powered through the bus. I might give Furuno a call to verify what kind of battery.

On the bathymetry, I got in "cheap" with a recreational version of MaxSea plus PBG. Here is what it is starting to look like...It think it's awesome for what it does. There are better systems, like WASSP, but they are $$$$. This works for what I do, I just have to go around the area a couple of times to get a good idea of what's really down there.

I chose this type of system because of the saltwater limitations on other "photo realistic" type sonar units. The higher frequencies used for the great detail cannot penetrate deep enough for what I want to "see". This graphic representation is about the best I can do for the money, but it's way better than the 3D bathy data set that is the basis for this type of display. Best part about it though is that I don't loose the information like a sonar unit. It's recorded to the disk.

I'm hoping that the heave compensation from the satellite compass will help to eliminate the saw pattern on some of the soundings. The software is already smart enough to compensate for the tide, which can be as high as 20ft swing. So, when I get a PING back, the database is updated with a corrected depth that doesn't include the wave height.

I suppose the reason they work so well together is because I am sticking with Furuno and Maretron primarily. I used to have a multi-vendor system and it worked OK. I do like the N2K bus for adding other boat sensors too. Weather station next primarily for wind info.

I would like to post some more "interesting" views, but I'm afraid KSanders will start trying to decode my fishing spots...

 

[twistedtree]

Very cool!

 

[AKFish]

Here's another one, where you can see the structure after passing over it, where a chart would not show much at all. It's neat to go back to where you've been and check out the bottom. I find that I change my course a bit just to capture some new data when chugging along.

 

[MYTraveler]

I hated to have to bite the bullet, but it was getting hard to nav via auto pilot due to course recovery upon heeling. Probably the best ancillary feature is the heave compensation while plotting on my personal bathemetry generator. It should smooth out the sawtooth from swells and paint a more accurate bottom profile.

Anyone else make the jump to this instrument?

I have the SC50, which I purchased because of its amazing heading accuracy (something under 1 degree) and heading consistency (something like 10% of the heading accuracy), which I wanted for my autopilot. At the time I was aware of its heave compensation capabilities, but didn't expect to make use of that. It was installed wrong as part of my boat's original commissioning, but the factory said tough luck. (The mistake was to not give it a clear view of the sky; it is positioned below the top of the tower so the tower, a radar and satellite domes occasionally block a GPS signal and I get an annoying abort error and the system switches over to a different, and less accurate, heading source.) I have since bought the MaxSea Explorer software with PBG -- that is pretty cool, but I don't really think the heave control is all that important to getting a good bottom picture, and least not in the conditions in which I fish.

 

[Boydski]

Anyone else make the jump to this instrument?

I have a Furuno SC-502 Satellite Compass with the SC-303 Antenna at the top of the mast. It is incredibly accurate and keeps the autopilot super accurate. When I switch over to the backup autopilot (using the fluxgate compass), the boat starts to wander like a drunken sailor.

You will like the sat compass. I have not had any issues with it, even passing under bridges.

 

[AKFish]

Thanks for the good input. I just finished the install and kept clear of all. I made an adapter plate in the shop then through bolted that to a platform on top of the mast.

I fired up the nav system and it worked right away. Very sensitive while blowing around in the slip. Can't wait to see how it works in different sea states. Looks like my opportunity for that is coming up with forecast 9 ft swell and 20 kts

 

[cafesport]

One thing to note with the SC30 - there is an internal battery that needs to be replaced at some interval. I know a number of people who have discovered this at inopportune times. You might want to put it on your regular maintenance list to avoid surprises.

I believe the sc 30 is different as it's is an all in one and does not have a separate processor with a battery backup like the 50 does.

 

[Capt Kangeroo]

I have the Comnav Vector G2 satellite compass, it has built in auto pitch and roll compensation along with truly remarkable accuracy. The G2 is fully self contained (no display required) and can be connected to any PC for adjustment and monitoring. I believe Comnav also makes and brand-names them for Furuno & Simrad. I don't think they are catching on real well in the recreational market due to the hefty price tag but I am seeing quite a few now on freighters & commercial ships.

 

[Ski in NC]

How does the sat compass work? Does it figure out heading by determining the direction of various sat signals? Or does it get a gps position fix, then another fix, and calc course off those two. The latter would require boat being in motion. I guess it must be the former. So is signal coming from gps sats or some other sat?

Curious about this. I guess I could read up on my own!!

Never liked my fluxgate feeding the AP. Works ok but sloppy. Dreamed about using a gyro heading sensor. Then looked at the prices...WOW!!! Nevermind!!

So this sat compass makes a good AP heading sensor???

 

[Aquabelle]

Eric: I think the WHOLE purpose of a sat compass is that it gives the very best heading data to an autopilot. Gyro compensated fluxgate compasses are a big improvement over a standard fluxgate......much cheaper than a SC, but certainly not as accurate, but good enough for most recreational boaters I would think.

 

[Capt Kangeroo]

Ski, all of the above. I'm no expert but a grossly simplified explanation of the way they work, as described in my manual, is that inside the antenna there are two sophisticated military grade GPS's about 1ft apart. These things are so deadly accurate they can sense the minute distance deviation between each other, this information is then fed to an internal computer and the pitch and roll sensors to come up with a heading which is accurate to mere inches. I'm sure the signals must go through a ridiculous amount of processing but I can confirm they work. Another great advantage is you can be standing dead still and still get a heading. At anchor or docked, there is near zero wander.

 

[Alaskan Sea-Duction]

I would like to post some more "interesting" views, but I'm afraid KSanders will start trying to decode my fishing spots...

Then give them to me!!! Secret hole, hidden mountain thing! K and I could team up!!

 

[Wxx3]

...When I switch over to the backup autopilot (using the fluxgate compass), the boat starts to wander like a drunken sailor.
.

And all this time I thought it was just me

 

[Boydski]

And all this time I thought it was just me

That's my story, and I'm sticking to it!

 

[twistedtree]

If i recall correctly, it's three GPS receivers in a triangular arrangement. Its essentially a differential gps base station and mobile station in one unit. The differences in position between the three receivers, and their known physical positions relative to each other lets you calculate a precise heading even when you are not moving. It really pretty clever. Pricey, but 1 deg or better accuracy.

 

[AKFish]

BIG improvement

Just back from a week long trip using the new antenna. WOW. Very accurate heading that was so fast on the update that it made overnight steering in the slop much easier. Now, the only thing left is to repeat the heading over the 0183 bus to my old ComNav AP head.

All of my expectations for heave compensation were met. Amazingly flat bottom profile while riding up to 12' swells. The accuracy of the PBG is sort of cheating when it comes to finding structure. It is not a shallow water, photo-realistic side scan picture, but this works at depths that those higher frequencies will not penetrate.

The whole satellite receiver should not be so expensive, so I suspect it will come down in price over time as more options hit the market. Glad I made the move though.

 

[AKFish]

I didn't think that selective availability would effect me but it looks like my biggest concern with this tech has appeared.

After a couple of weeks using GPS satellites to determine my heading with great precision, all of a sudden I am all over the place. At anchor my depth alarm goes off and I know we are fine in 10 fathoms. The depth was jumping, the heading was swinging and the sensor thought up to 37 deg list at one point. I removed the heave compensation option and the sounder was fine. Boat was at anchor and the numbers were showing rolling and pitching back and forth swing, so it was not a corrupt bus type thing.

Next day things were back to normal and just fine. This was my worst case reason to be skeptical of this instrument, but I don't have another choice within reach due to the steel hull. The hardest part is not being able to trust the instruments.

Funny how GPS has made it easy for more "mariners" to leave the dock, but there's no guarantee they have the skills to make it back. I still keep a paper chart and know how to use it...

 

[twistedtree]

Were you near a bridge or other obstruction? I was at a marina in Charleston right near a bridge and my GPS was going totally wacky. It turned out it was continually losing and reacquiring the satellites. As soon as I moved away from teh bridge it became stable again. I guess they mean it when they say you need a clear view of the sky.....

 

[MYTraveler]

Probably not SA

I didn't think that selective availability would effect me but it looks like my biggest concern with this tech has appeared.

I believe that SA has been turned off, but would no doubt be reactivated in time of emergency. And it is probably tested periodically, although I leave my plotter running 24/7 and my boat's position is very stable, so the signal can't be degraded very often.

Moreover, the SC doesn't depend on absolute accuracy to determine heading.