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-   -   How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ? (https://www.cruisersforum.com/forums/f134/how-does-opencpn-compare-to-b-and-g-raymarine-and-garmin-new-boat-install-264798.html)

AboutTime1 23-05-2022 20:58

How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
I'm looking at price lists on new boats. The "electronics package" on dual helm cruisers is typically $12-15K on a new boat for a pretty standard B&G package. Not including anything at the chart plotter table.

Would you order a new boat without an electronics package and install OpenCPN on it ? What could you build for $5K ?

Where would one get some nice sunlight readible waterproof touchscreen displays for the helms ?

Thanks

goboatingnow 23-05-2022 21:23

How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
Good quality branded 10” optically bonded sunlight readable IP67 or greater lcd screens are running at $1000 plus you have to build a decent reliable computer on top of that.

This is often more or close to the price of a branded marine MFD.

Dockhead 23-05-2022 21:32

Re: How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
You want the electronics package. $15k is very reasonable. I spent about double that on my electronics when I replaced them some years ago, and I did all the installation myself. You do really want good instruments, and you do want proper marine chart plotters/MFD's. Don't cheap out here. OpenCPN is fabulous, but use that in addition to, not instead of, normal electronics. Minicomputer at the chart table with large display, running OpenCPN and connected to the boat network, for passage planning. You could skip the marine chart plotter/MFD at the chart table if you really want to (I didn't), but don't skip at the helm.


Other things to pay attention to:


1. Good compass. Essential for autopilot performance, radar overlay, etc. Good satellite compasses are now in reach with the Furuno SCX20 selling for around a grand.


2. Good wind instrument.


3. Good speed transducer. Accurate boat speed essential for valid true wind calculation.



4. Good radar set.

AboutTime1 23-05-2022 21:59

Re: How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
Quote:

Originally Posted by goboatingnow (Post 3628004)
Good quality branded 10” optically bonded sunlight readable IP67 or greater lcd screens are running at $1000 plus you have to build a decent reliable computer on top of that.

This is often more or close to the price of a branded marine MFD.


You haven't priced MFDs recently, especially the larger ones.

AboutTime1 23-05-2022 22:02

Re: How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
Quote:

Originally Posted by Dockhead (Post 3628010)
You want the electronics package. $15k is very reasonable. I spent about double that on my electronics when I replaced them some years ago, and I did all the installation myself. You do really want good instruments, and you do want proper marine chart plotters/MFD's. Don't cheap out here.

So what does a B&G or RayMarine chart plotter do that OpenCPN doesn't ?

Or better yet, I'm a software developer. What couldn't I make OpenCPN do if I wrote some code ?

Quote:

OpenCPN is fabulous, but use that in addition to, not instead of, normal electronics. Minicomputer at the chart table with large display, running OpenCPN and connected to the boat network, for passage planning. You could skip the marine chart plotter/MFD at the chart table if you really want to (I didn't), but don't skip at the helm.
Why ?

Quote:

Other things to pay attention to:


1. Good compass. Essential for autopilot performance, radar overlay, etc. Good satellite compasses are now in reach with the Furuno SCX20 selling for around a grand.

I'm not sure what is so great about that compass. RC flight controllers sell for a few hundred $$ and have inertial compensation in all axes with Kaufmann filtering.



Quote:

2. Good wind instrument.

One can use the very same transducers with OpenCPN. No need to skimp here.



Quote:

3. Good speed transducer. Accurate boat speed essential for valid true wind calculation.

Nothing will beat an inertial navigation system used in a flight controller for this.



Quote:

4. Good radar set.

Radar is an extra on top of the price I mentioned above.

Dockhead 23-05-2022 23:00

Re: How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
Quote:

Originally Posted by AboutTime1 (Post 3628021)
So what does a B&G or RayMarine chart plotter do that OpenCPN doesn't ?

Or better yet, I'm a software developer. What couldn't I make OpenCPN do if I wrote some code ?

Why ?

A real marine plotter/mfd is a rugged, waterproof, self contained device which is devoted to purpose, with a much better developed interface for use for pilotage. They almost never crash, they have bright daylight visible waterproof screens, they have waterproof connectors for network and power. They have integrated controls which you can use even with gloves on. To recreate this yourself would cost multiples of what the plotter costs, and would never be as good -- what kind of pointing device are you going to use at the helm? If you want to save money, you can do a single Vulcan plotter (the Vulcan is much cheaper, but won't network with other plotters).

I'm a big fan of OpenCPN, and use it at the nav table for all my passage planning and navigation, but it is not well suited for pilotage. It is also far less stable than commercial plotters.

Quote:

Originally Posted by AboutTime1 (Post 3628021)
. . .I'm not sure what is so great about that compass. RC flight controllers sell for a few hundred $$ and have inertial compensation in all axes with Kaufmann filtering.

Well, give it a try and let us know how it works, but I rather doubt that this is better than any given run of the mill fluxgate, which are all inertia compensated by now. Satellite compasses have a lot of advantages, and the new Furuno one has sub one degree dynamic heading accuracy and outputs high frequency high accuracy 3D motion (all Six Degrees of Freedom) and attitude data. The attitude data likewise has sub one degree dynamic accuracy. The quality of this data is crucially important to autopilot and radar performance. Even the best fluxgate compasses leave something to be desired.

Quote:

Originally Posted by AboutTime1 (Post 3628021)
. . .Nothing will beat an inertial navigation system used in a flight controller for this.

On what basis do you say this? If this is true, then that's interesting, but I'd like to see the facts. I would be quite surprised if the application is more demanding than for a yacht autopilot, which requires very complex calculations as the vehicle is interacting with moving sea. The motion of a yacht sailing in a moving sea is much more complex than the motion of an aircraft.

Or did you mean for calculating true wind? Your inertial guidance system is useless for this -- you don't need heading at all, you need speed through the water. This is hard to measure and is one of the main challenges in yacht instrumentation.

Speed through water is measured on big ships with doppler speed logs. These have not so far been miniaturized sufficiently to use on our boats. We have paddlewheel transducers which are not very good -- influenced very much by the boundary layer and requiring a lot of compensation to give decent data. Or ultrasonic and electromagnetic logs which all have their own weaknesses. Cruisers don't usually bother too much with this and consequently don't have really good true wind data. For racing, good true wind data is extremely important, so a lot of trouble is gone to to get decent speed through water data, mostly a lot of calibration to work out the non-linearity, compensation for heel, etc.

wholybee 23-05-2022 23:05

Re: How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
The only advantage of a "real" chart plotter over opencpn is the waterproof works when wet daylight readable screen. You can get that for opencpn, but it's isn't cheap.

But opencpn does not replace the entire electroncs package, only the chart plotter. You still need all the transducers, the nmea2000 network gear, VHF, converters, etc. Even without a chart plotter that's many thousands of dollars.

The speed transducer is speed through water, not speed over ground. So your inertial gizmo won't work. You only need an electronic compass if you have an autopilot, and they come with one. No need for the $1000 thing.

Alot is your preference. More and more sailors are using exclusively an iPad and a backup iPad. I'm not approving of that, only pointing out that what you need is a lot less than what some will tell you.

AboutTime1 24-05-2022 00:10

Re: How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
Quote:

Originally Posted by Dockhead (Post 3628030)
A real marine plotter/mfd is a rugged, waterproof, self contained device which is devoted to purpose, with a much better developed interface for use for pilotage. They almost never crash, they have bright daylight visible waterproof screens, they have waterproof connectors for network and power. They have integrated controls which you can use even with gloves on. To recreate this yourself would cost multiples of what the plotter costs, and would never be as good

LOL.

Quote:

I'm a big fan of OpenCPN, and use it at the nav table for all my passage planning and navigation, but it is not well suited for pilotage. It is also far less stable than commercial plotters.
That can be easily fixed.

Quote:

Well, give it a try and let us know how it works, but I rather doubt that this is better than any given run of the mill fluxgate, which are all inertia compensated by now. Satellite compasses have a lot of advantages, and the new Furuno one has sub one degree dynamic heading accuracy and outputs high frequency high accuracy 3D motion (all Six Degrees of Freedom) and attitude data. The attitude data likewise has sub one degree dynamic accuracy. The quality of this data is crucially important to autopilot and radar performance. Even the best fluxgate compasses leave something to be desired.
A GPS based compass is just 2 GPS receivers placed some distance apart. You can get the heading of the boat by calculating the heading vector between the two receivers. They'll be operating in differential mode, so the distance error between them will be small.

Quote:

On what basis do you say this? If this is true, then that's interesting, but I'd like to see the facts. I would be quite surprised if the application is more demanding than for a yacht autopilot, which requires very complex calculations as the vehicle is interacting with moving sea. The motion of a yacht sailing in a moving sea is much more complex than the motion of an aircraft.
Drones fly at 60 MPH and pull 10Gs in their 3D maneuvers. The IMU system updates at 100Hz. A boat in waves is standing still compared to this application.

Quote:

Or did you mean for calculating true wind? Your inertial guidance system is useless for this -- you don't need heading at all, you need speed through the water. This is hard to measure and is one of the main challenges in yacht instrumentation.
Actually, you need speed over ground. True wind = Apparent wind - boat velocity over ground. Velocity needs magnitude and direction.

Quote:

Speed through water is measured on big ships with doppler speed logs. These have not so far been miniaturized sufficiently to use on our boats. We have paddlewheel transducers which are not very good -- influenced very much by the boundary layer and requiring a lot of compensation to give decent data. Or ultrasonic and electromagnetic logs which all have their own weaknesses. Cruisers don't usually bother too much with this and consequently don't have really good true wind data. For racing, good true wind data is extremely important, so a lot of trouble is gone to to get decent speed through water data, mostly a lot of calibration to work out the non-linearity, compensation for heel, etc.

Boat speed through water only really matters as far as tides are concerned. If there are no tides then speed over ground is the same as speed over water.

goboatingnow 24-05-2022 00:15

How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
Quote:

Originally Posted by AboutTime1 (Post 3628018)
You haven't priced MFDs recently, especially the larger ones.



A si-tex 10” gps chart plotter is around $1500 this would be similar functionality to open cpn

AboutTime1 24-05-2022 00:19

Re: How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
Quote:

Originally Posted by wholybee (Post 3628031)
The only advantage of a "real" chart plotter over opencpn is the waterproof works when wet daylight readable screen. You can get that for opencpn, but it's isn't cheap.

That was my impression as well.

Quote:

But opencpn does not replace the entire electroncs package, only the chart plotter. You still need all the transducers, the nmea2000 network gear, VHF, converters, etc. Even without a chart plotter that's many thousands of dollars.
Understood. We'll see.

Quote:

The speed transducer is speed through water, not speed over ground. So your inertial gizmo won't work. You only need an electronic compass if you have an autopilot, and they come with one. No need for the $1000 thing.
I'll be putting an autopilot on my boat.

Quote:

Alot is your preference. More and more sailors are using exclusively an iPad and a backup iPad. I'm not approving of that, only pointing out that what you need is a lot less than what some will tell you.

Interesting.

Dockhead 24-05-2022 00:34

Re: How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
1 Attachment(s)
Quote:

Originally Posted by AboutTime1 (Post 3628036)
. . . That can be easily fixed.


Really? I know the O development team. They are a very talented, dedicated team. They've been working on it for years. If you think you can easily fix it, then by all means get in touch and give them a hand. They hang out on this forum; see the OpenCPN section.


Quote:

Originally Posted by AboutTime1 (Post 3628036)
. . . A GPS based compass is just 2 GPS receivers placed some distance apart. You can get the heading of the boat by calculating the heading vector between the two receivers. They'll be operating in differential mode, so the distance error between them will be small.


In the case of the new Furuno compass, 4 GNSS (not just GPS) receivers, not 2. This gives 6 different baselines for calculating heading, attitude, and motion data:


Attachment 258276

AboutTime1 24-05-2022 00:42

Re: How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
A GNSS200L updates at 1 KHz and sells for $50.


Dockhead 24-05-2022 00:48

Re: How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
Quote:

Originally Posted by AboutTime1 (Post 3628036)
. . . Drones fly at 60 MPH and pull 10Gs in their 3D maneuvers. The IMU system updates at 100Hz. A boat in waves is standing still compared to this application.


The motion of a yacht sailing hard in a heavy sea is an order or two of magnitude more complex, than the motion of a drone pulling g's in a highly uniform medium like the air.


Quote:

Originally Posted by AboutTime1 (Post 3628036)
. . Actually, you need speed over ground. True wind = Apparent wind - boat velocity over ground. Velocity needs magnitude and direction.


False. You are new to sailing I guess? We sail in the sheer between air and water, so true wind for sailors is water-referenced, not ground-referenced. Ground-referenced wind we call "Ground Wind". Ground Wind is not useful for sailing except in totally still water, where ground wind and true wind are identical. Totally still water doesn't really exist in the ocean, almost ever.


Good explanation here, and why Ground Wind is not useful for sailing: https://raymarine.custhelp.com/app/a...calculate-them


Quote:

Originally Posted by AboutTime1 (Post 3628036)
. . . Boat speed through water only really matters as far as tides are concerned. If there are no tides then speed over ground is the same as speed over water.


Again, speed through water is THE most important data for sailing, and the hardest to measure. The water in the ocean is almost never completely still. There is almost always some kind of tide running or surface of the water affected by wind.


You use apparent wind for immediate, direct sailing tasks, but you need good true wind to find your laylines, for tactics, and for sailing downwind. Your pilot in wind mode switches from using apparent to using true wind when the wind is behind the beam. Sailing very close to DDW is quite dangerous without good true wind data.


You also need good speed through water data for sail trimming -- to understand the affect of adjustments. SOG is affected by the motion of the water, which is constantly changing.


If you don't race, and don't care that much about sailing (many cruisers don't, and that's fine), then you might not care much about it. But if you do care about sailing, good sail trim, good sailing tactics, even if you don't race, then you need good data, especially STW.

Dockhead 24-05-2022 00:49

Re: How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
Quote:

Originally Posted by AboutTime1 (Post 3628050)
A GNSS200L updates at 1 KHz and sells for $50.


It is not, however, a compass.

goboatingnow 24-05-2022 00:51

How does OpenCPN compare to B&G, Raymarine and Garmin ? New boat install ?
 
Quote:


A GPS based compass is just 2 GPS receivers placed some distance apart. You can get the heading of the boat by calculating the heading vector between the two receivers. They'll be operating in differential mode, so the distance error between them will be small
Heading is not computed in a sat compass that way as it’s too slow and subject to GNSS errors.

The system uses Real time kinematics and either a complex single receiver and two antenna of two receivers one slaved to the other

The phasing relationship of the gps signal received at the multiple antenna is then used to compute heading information the actual GNSS signal doesn’t actually need decoding per se to compute relative heading

I have a hemisphere sat compass.


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