Can the radar see through the flybridge?

[MikeP]

I have noticed that many vintage 53 MY Hatts have the radar mounted on the eyebrow over the windshield. Several in our marina have that configuration and the 53MY brochures from back in the day show that as a common setup.

So in that case, is there radar coverage in the quadrant behind the radar - where the flybridge sits - or is the radar coverage restricted to the sides/front of the boat?

 

[av8torrich]

To answer the your question, you will incur a loss depending on the composition of the material obstructing the RADAR. The additional loss over free space path loss is probably negligible, and not worth worrying about.

 

[Boatsb]

To answer the your question, you will incur a loss depending on the composition of the material obstructing the RADAR. The additional loss over free space path loss is probably negligible, and not worth worrying about.

The loss will be your testicles. You do not want to be in the direct path of the radar. You need to blank the area behind where people will be.

 

[av8torrich]

The loss will be your testicles. You do not want to be in the direct path of the radar. You need to blank the area behind where people will be.

Not only testicles, but any liquid filled body part (eye balls are a good example), could be impacted. I know Furuno used to publish the safety distances in their manuals. If this is not the case any longer, follow the recommendation which shows distance the array should be placed in reference to other antennas (i.e. VHF/MF/HF/GPS Antenna), and make sure you are further than the most stringent distance requirement.

Due to the narrow beam width emitted from the array of these RADAR systems, if you are a couple feet above or below, odds are you will be fine.

 

[rsmith]

Before hard tops became popular in the 80's most of the convertibles had this setup also. I have thousands of hours of standing behind Decca 101's and super 101's. As a birth control method it wasn't too effective, I have 3kids. Range losses are more a factor of the installer failing to set the tilt angle of the scanner to the boats running angle. If it's set level when the boat is at rest it will be shooting the sky when the boat is at cruise.

 

[MikeP]

Thanks! My radar is on a 12-15 foot Marquipt mast, hinged at the FB deck but I have been thinking about removing the mast for several reasons and TEMPORARILY mourning the radar on the eyebrow while I decide whether to have a FB hardtop or a radar arch installed...or come up with some other method.

I understand the concern re the radar/body parts and figure that if we needed the radar we would be operating from the lower helm anyway.

 

[thoward]

The radar does not pick up through the fiberglass. You will see 180* forward.

 

[Boatsb]

The dome is usually fiberglass. The microwaves will go through fiberglass. You must blank the aft area or you can get burns and or worse.

Anyone who "knows better" is encouraged to personally try it.

 

[doc g]

Go broadband (simrad) and mount the 12 " dome where ever you want and yes you will have a blind spot where the radar can't see. These put out no more radiation than a cell phone and the close in image is incredible .......Pat

 

[jim rosenthal]

Agreed. I think he already has a radar and wants to put in temporarily up front on the bridge until he decides what to do permanently. Like arch versus radar mast, or shorter mast, or whatever. I think if he were doing it from scratch, he'd use broadband as you said.

Just curious, does BB radar come in open array, or just domes? Idle curiosity.

 

[av8torrich]

I just wanted to note, most commercial RADOMES, and military ones for that matter are constructed from fiberglass mixed with other non reflective materials. I can tell you from personal experience, fiberglass boats can be difficult to see when attempting target acquisition because they have such a low RADAR cross section (RCS). Typically the primary return comes from other metallic structures (i.e. Engines, T-Top Support, Antennas, Metallic Paint Etc). Drug smugglers have gotten keen to this fact, and have gone to great lengths to reduce the RCS, that we are now often forced to track them by observing the wake of the vessel. This of course requires fancy processing, which is another topic in its entirety.

For this reason, RADAR can typically "See" through fiberglass. What becomes problematic is if there are other metallic or reflective material inside of the fiberglass structure which your are trying to "See" through. I can also imagine a scenario where moisture trapped in fiberglass could cause issues too.

With regards to safe distances from the RADAR, there are many variables which delineate this. These typically include EIRP (I would go with Worse Case), Beam width, Free space Path Loss, and Frequency. Using some pretty straight forward equations, one can calculate what the minimum safe distance should be from the array. That being said, virtually all the manuals from RADAR manufacturers address what is acceptable and safe.

Another item I would be cautious about is the term "blanking". Typically blanking takes place in processing (i.e. video blanking). Just because you see no returns in the video does not mean the transmitter is not longer turned on when the array is pointed towards you, or to the aft of the vessel. The term I typically use is sector scan, which typically works as follows; Transmitter is turned on from 271 through 089 degree, and then is off from 090 through 270 degrees. It is entirely possible consumer RADAR manufacturers consider these two terms as synonymous, but I would double check to make sure you are not getting a false impression the RADAR is in fact not transmitting in your general direction.

The radar does not pick up through the fiberglass. You will see 180* forward.

 

[Boatsb]

From a furuno installation manual.


1.38 Sector Blanking
Administrations may require the radar to stop
transmitting toward the bridge when it is installed
on the foremast. Two blanking areas can be set at
installation. No echoes appear in the blanking
areas.

Area of no transmission
(no echoes appear)
Figure 1-29 Blank areas where
transmission is suspended


Raymarine, garmin and others have the same warnings and setting.

 

[av8torrich]

Agreed "Sector Blanking" is the same as what I call Sector Scan.

From a furuno installation manual.


1.38 Sector Blanking
Administrations may require the radar to stop
transmitting toward the bridge when it is installed
on the foremast. Two blanking areas can be set at
installation. No echoes appear in the blanking
areas.

Area of no transmission
(no echoes appear)
Figure 1-29 Blank areas where
transmission is suspended


Raymarine, garmin and others have the same warnings and setting.

 

[Boatsb]

Agreed "Sector Blanking" is the same as what I call Sector Scan.

I wonder how many experts here are wondering if they've been nuking themselves?

This is a perfect example of why DIY is not always the best way.

I don't give myself stitches (very often anymore) because a Dr. Does it better. I don't do my own taxes either. I pay a professional and don't worry about the cost. They're worth it.

 

[av8torrich]

To be honest, you would be surprised how close you can safely get to an array. I am not recommending going out of your way to do so, but typically its feet not tens of feet. I have been working in RF and Electromagnetic's virtually all of my career. Most of us know, you get more unwanted radiation from the sun than reasonable exposure to surface search consumer RADAR.

Installations are amazingly pretty straight forward, with a little attention to detail. While I agree it should be treated with a healthy amount of respect, I do not think it is something that needs to be feared. I think because folks cannot see this particular type of electromagnetic phenomena, people treat it like voodoo.

I wonder how many experts here are wondering if they've been nuking themselves?

This is a perfect example of why DIY is not always the best way.

I don't give myself stitches (very often anymore) because a Dr. Does it better. I don't do my own taxes either. I pay a professional and don't worry about the cost. They're worth it.

 

[Boatsb]

Agreed "Sector Blanking" is the same as what I call Sector Scan.

I wonder how many experts here are wondering if they've been nuking themselves?

This is a perfect example of why DIY is not always the best way.

I don't give myself stitches (very often anymore) because a Dr. Does it better. I don't do my own taxes either. I pay a professional and don't worry about the cost. They're worth it.

 

[Boatsb]

To be honest, you would be surprised how close you can safely get to an array. I am not recommending going out of your way to do so, but typically its feet not tens of feet. I have been working in RF and Electromagnetic's virtually all of my career. Most of us know, you get more unwanted radiation from the sun than reasonable exposure to surface search consumer RADAR.

Installations are amazingly pretty straight forward, with a little attention to detail. While I agree it should be treated with a healthy amount of respect, I do not think it is something that needs to be feared. I think because folks cannot see this particular type of electromagnetic phenomena, people treat it like voodoo.

My example would be a simple 4K open array.

100w/meter squared RF is measured at 55 inches or almost 6 feet.
10W/meter squared RF is measured at 178 inches or almost 15 feet.

If I had to run for a few hours with a RADAR mounted right in front of the bridge 4 feet away Id be concerned.

The point is the manufacturers have added a blanking area that you can set to not radiate humans. Every installation manual I have seen from RADARs has the warning to not shoot through people so I figure they know something about it.

Its the same with SSB. There is a suggested distance from people to the antenna.

When you get radiated all the time your on your boat it makes the outdoors less healthy.

 

[av8torrich]

Those are, or have to be main beam power density measurements. This mean you are in the main beam. If you go back, you will note I told said a couple feet above and a couple feet below and you will be out of the main beam of RADAR. You will note there are many Raymarine 4KW HD RADAR installs on very small center console boats. In most of those cases you are not getting 6' - 15' away ever. That is because when you look at the antenna beam pattern, you will note that the power is attenuated pretty heavily a couple of degrees from main beam (-3dBm Point). It is not uncommon to see >45dBm of attenuation in less than five degree in some applications.

With regards to SSB, I find a requirement which requires someone to stay 15' away at 2182 KHZ LSB suspect. While the output of the transceiver may be 100W (low duty cycle), the antennas which are used for this application have less that unity gain! Not only are the antennas incredibly inefficient at these frequencies but the are omni directional in nature. For most people, you would have the install the vertical array dead center of your 30' boat and walk to the bow or stern to your make a call on your radio? I don't think that makes much sense,

Look at how the USCG installs not only RADAR, but MF GMDSS on their smaller RIB's. You will note, at all time their personal are much closer than 15' and most of the time closer than 6' to the two antennas in question.

 

[Boatsb]

Those are, or have to be main beam power density measurements. This mean you are in the main beam. If you go back, you will note I told said a couple feet above and a couple feet below and you will be out of the main beam of RADAR. You will note there are many Raymarine 4KW HD RADAR installs on very small center console boats. In most of those cases you are not getting 6' - 15' away ever. That is because when you look at the antenna beam pattern, you will note that the power is attenuated pretty heavily a couple of degrees from main beam (-3dBm Point). It is not uncommon to see >45dBm of attenuation in less than five degree in some applications.

With regards to SSB, I find a requirement which requires someone to stay 15' away at 2182 KHZ LSB suspect. While the output of the transceiver may be 100W (low duty cycle), the antennas which are used for this application have less that unity gain! Not only are the antennas incredibly inefficient at these frequencies but the are omni directional in nature. For most people, you would have the install the vertical array dead center of your 30' boat and walk to the bow or stern to your make a call on your radio? I don't think that makes much sense,

Look at how the USCG installs not only RADAR, but MF GMDSS on their smaller RIB's. You will note, at all time their personal are much closer than 15' and most of the time closer than 6' to the two antennas in question.

SS IS A PITA. We can usually get 6 to 10 foot from the antenna but not much more. The RADAR is usually above the people on the navy and coast guards boats that I've worked on.

Blanking is only important if your in line with the scanner. If it's a foot or two above you it's pattern will go over hour head for the first 15 feet. After that the RF power drops enough to be safe.

 

[av8torrich]

I found this link which I thought was pretty good:


http://www.ybw.com/forums/showthread.php?325793-Radar-emmissions-and-Health-and-Safety

I thought the author was able to describe the topic in a fairly straight forward manner. May be worth a review.

SS IS A PITA. We can usually get 6 to 10 foot from the antenna but not much more. The RADAR is usually above the people on the navy and coast guards boats that I've worked on.

Blanking is only important if your in line with the scanner. If it's a foot or two above you it's pattern will go over hour head for the first 15 feet. After that the RF power drops enough to be safe.