I'm sure this has been asked a thousand times but where can I get some good unbiased guidelines on mounting a radar dome? Is modern radar a health hazard if the dome is mounted too low?
Radar dome mounts
- Thread starter Kuntrymann
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I have heard many theories on the safety issue. I erred on the side of caution and mounted it high on my backstay. Building your own backstay mount is fairly simple. See the link:
http://treilley.myphotoalbum.com/view_album.php?set_albumName=album12
http://treilley.myphotoalbum.com/view_album.php?set_albumName=album12
I would always play safe. The theory is that the ammount of energy transmitted is very very low. However, on the basis that its relativley easy to avoid being in the direct beam of the radar, its best out of the way. Remember the beam shape, typically 2-5deg in azimuth, and 25-30deg horizontal. So from the height on the back stay extend an angle down 15deg and you are still in the beam, but not the main beam. Hope this helps.
Kuntryman, there was an article this month in Sail,
and the author had a specific recommendation, which was lower on the mast than i would have expected. Because the energy is somewhat focused in about a 25 degree cone, he suggested it be high enough to keep the boats occupants out of the beam, but no higher (maybe 12-15 feet up). His reasoning was that if placed too high, close low objects (bouys, etc)would disappear just when you need to know where they are! Yes, the range is reduced, but should still be several miles, and less weight aloft is another benefit. FWIW< I agree with him.
cup
and the author had a specific recommendation, which was lower on the mast than i would have expected. Because the energy is somewhat focused in about a 25 degree cone, he suggested it be high enough to keep the boats occupants out of the beam, but no higher (maybe 12-15 feet up). His reasoning was that if placed too high, close low objects (bouys, etc)would disappear just when you need to know where they are! Yes, the range is reduced, but should still be several miles, and less weight aloft is another benefit. FWIW< I agree with him.
cup
When I installed our radar, I went back and forth over how to mount it. I asked a lot of people about the radiation. Most "experts" said it's nothing to worry about as long as you're not standing right by it. I, personally, think that those who are most exposed to different types of radiation (and this a type of radiation) tend to be the ones who most underestimate the dangers. I believe in ten or twenty years from now, we will be seeing conclusive evidence that the electromagnetic rays from cell phones are damaging to the brain. In fact, several studies already seem to show that. So I opted for safety and put mine up on the back stay. I got a self leveling mount for $500. I'm glad I put it up there - one less health hazard to worry about.
Microwaves, what comes out of a radome, can be hazardous if the intensity and concentration is high enough. With marine radars, and their typical locations, it's generally not an issue.
Long-term exposure to low levels of microwave radiation, as has been demonstrated in laboratory experiments, can induce a variety of unwanted effects in lab animals. Radomes should be operated when needed for navigation or safety but in standby or off when the radar is not needed.
OSHA has determined that a maximum safe level of exposure to microwaves is 0.2 milliwatts per centimeter squared. Radiation levels in small marine radar units will vary slightly according to brand make or model so exact numbers would need to be taken for your specific dome. If you got close, perhaps 3-4 feet from a typical 2kw dome, and in direct line of sight, not off vertical axis, you could potentially see microwave exposure exceeding the OSHA guidelines. By the time you move 8 to 10 feet away the levels on a typical 2kw could not likely exceed the OSHA max exposure standard.
When you move off the horizontal plane of the radars beam the exposure levels are even lower than a direct line of sight. With a dome 10 feet over head you have little worry of direct levels higher than the OSHA max exposure.
It's still a good idea to mount a radome as high as possible especially when using a pole/stern mount if for no other reason than better performance. I prefer a spar mounted for the added level of performance.
One thing people don't often consider though is that a marine radar spins, though some can TX while stationary, so the person in front of a radar will only see approximately 20% of what they would see with a stationary, non-rotating beam. If I am recalling the article I read years ago correctly it stated that even at positions as close as three to four feet, with a rotating scanner, you can see levels that don't exceed the OSHA guidelines.
If I could easily switch to a mast mount dome instead my current stern pole I'd do it in a heart beat.
A dome 10' off the water will see a 10' tall target at about 7.6 miles.
A dome 20' off the water will see a 10' tall target at roughly 9.2 miles.
Most mast mounts are roughly 25-30 feet high or more. This means much better range.
Never under estimate the distance you'll need. I have on many occasions. It is common place in fog for folks to really zoom in on range but it is better to fight the urge to do so. We have a ferry up here called the "Cat" that runs at over 50 knots. A 6nm dome visibility is just not enough in pea soup for one vessel traveling 50+ knots and the other 6knots trust me. A 56 knot closing speed happens fast. If you sail in shipping lanes you want distance if you don't it's not a big deal.
I have found NO USEFUL loss with a dome mounted on the spar. If you need to see targets at less than 25 yards (for those with say a 36 foot boat that is roughly 50 feet off your bow), and have not already acquired the target long before, you're going to be in trouble either way.
The need for radar vis at 45 feet from your vessel is about as rare as it gets which on a stern pole on a 36 foot vessel is needing 9' of vis beyond your bow..
We get very thick fog up here and even with the thickness I usually still have about 90-150 feet on a thick day to where I can make out a vessel. Perhaps two to three times per year the vis drops to less than a boat length. Still get the 8' pole and not the 6' pole and you'll be better off.
I still think folks clamoring for the "close range" have not really spent enough time in thick fog to see a need, or lack there of, for seeing a 4' high target at 45' from the dome or 9' off the bow of a 36 footer with the pole mounted at the stern. As I said above if you have not yet acquired the target before its 50 feet off the bow you have MUCH bigger issues..
Again, where you sail, and how you sail, night / day /fog determines more about your requirement than anything. At night you want long range, in shipping lanes at night or with fog you want long range. If your bay sailing a low dome is fine.
Keep in mind that in the troughs of ten foot rollers and eight foot radar pole will be barely level with the tops of the waves every few seconds. A dome 25-30 feet off the water will still be higher (15'-20' above the wave tops when in the trough) than that of a pole mount in flat water..
Long-term exposure to low levels of microwave radiation, as has been demonstrated in laboratory experiments, can induce a variety of unwanted effects in lab animals. Radomes should be operated when needed for navigation or safety but in standby or off when the radar is not needed.
OSHA has determined that a maximum safe level of exposure to microwaves is 0.2 milliwatts per centimeter squared. Radiation levels in small marine radar units will vary slightly according to brand make or model so exact numbers would need to be taken for your specific dome. If you got close, perhaps 3-4 feet from a typical 2kw dome, and in direct line of sight, not off vertical axis, you could potentially see microwave exposure exceeding the OSHA guidelines. By the time you move 8 to 10 feet away the levels on a typical 2kw could not likely exceed the OSHA max exposure standard.
When you move off the horizontal plane of the radars beam the exposure levels are even lower than a direct line of sight. With a dome 10 feet over head you have little worry of direct levels higher than the OSHA max exposure.
It's still a good idea to mount a radome as high as possible especially when using a pole/stern mount if for no other reason than better performance. I prefer a spar mounted for the added level of performance.
One thing people don't often consider though is that a marine radar spins, though some can TX while stationary, so the person in front of a radar will only see approximately 20% of what they would see with a stationary, non-rotating beam. If I am recalling the article I read years ago correctly it stated that even at positions as close as three to four feet, with a rotating scanner, you can see levels that don't exceed the OSHA guidelines.
As for mounting the dome it all depends on your typical use. If you are a bay sailor who does not see much fog or do much at night then a stern pole should provide plenty of performance & range. On the other hand if you sail in the open ocean, near shipping lanes, in steep seas or areas with fast sport fishing type yachts there is no substitute for height and the resulting range.
If I could easily switch to a mast mount dome instead my current stern pole I'd do it in a heart beat.
A dome 10' off the water will see a 10' tall target at about 7.6 miles.
A dome 20' off the water will see a 10' tall target at roughly 9.2 miles.
Most mast mounts are roughly 25-30 feet high or more. This means much better range.
Never under estimate the distance you'll need. I have on many occasions. It is common place in fog for folks to really zoom in on range but it is better to fight the urge to do so. We have a ferry up here called the "Cat" that runs at over 50 knots. A 6nm dome visibility is just not enough in pea soup for one vessel traveling 50+ knots and the other 6knots trust me. A 56 knot closing speed happens fast. If you sail in shipping lanes you want distance if you don't it's not a big deal.
I have found NO USEFUL loss with a dome mounted on the spar. If you need to see targets at less than 25 yards (for those with say a 36 foot boat that is roughly 50 feet off your bow), and have not already acquired the target long before, you're going to be in trouble either way.
The need for radar vis at 45 feet from your vessel is about as rare as it gets which on a stern pole on a 36 foot vessel is needing 9' of vis beyond your bow..
We get very thick fog up here and even with the thickness I usually still have about 90-150 feet on a thick day to where I can make out a vessel. Perhaps two to three times per year the vis drops to less than a boat length. Still get the 8' pole and not the 6' pole and you'll be better off.
I still think folks clamoring for the "close range" have not really spent enough time in thick fog to see a need, or lack there of, for seeing a 4' high target at 45' from the dome or 9' off the bow of a 36 footer with the pole mounted at the stern. As I said above if you have not yet acquired the target before its 50 feet off the bow you have MUCH bigger issues..
Again, where you sail, and how you sail, night / day /fog determines more about your requirement than anything. At night you want long range, in shipping lanes at night or with fog you want long range. If your bay sailing a low dome is fine.
Keep in mind that in the troughs of ten foot rollers and eight foot radar pole will be barely level with the tops of the waves every few seconds. A dome 25-30 feet off the water will still be higher (15'-20' above the wave tops when in the trough) than that of a pole mount in flat water..
I got it from radaronthelevel.com. It's a lot cheaper than others because instead of using hydraulics, he simply has a nylon collet and a bolt that tightens down on it to control the swing.
Incidentally, in reply to Maine Sail's comments aboute what OSHA says, but I think they don't take one factor into account: Just like chemical toxins, all these things are cumulative. Also, when they set their levels for what is "safe", they merely mean that at such-and-such a level, your chances of getting cancer (or suffering some other sort of damage) are X% - in other words, a certain number out of a thousand will get cancer (or something else) from it.
In the case of cell phones, there are other effects that aren't measured, including memory loss, evidently. If this is so for cell phones, then it is probably true for other forms of radiation, including radar. For me, part of the pleasure of sailing is to get away from as much of modern society's pollution (including noise pollution) as possible. That's why I prefer zero exposure if that's possible.
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John
With an 8-10 foot above deck dome height you will not be out of the line of sight while on deck and parts of your body will be in the way. I still believe the exposure is so low as not to worry but you make reference to "zero exposure if possible". If that is what you are after then when ever someone is on deck you should press stby or move the dome to the spar and get it up high enough so that when on deck there is no chance of being within sight of the TX beam..
Image courtesy Raymarine
With an 8-10 foot above deck dome height you will not be out of the line of sight while on deck and parts of your body will be in the way. I still believe the exposure is so low as not to worry but you make reference to "zero exposure if possible". If that is what you are after then when ever someone is on deck you should press stby or move the dome to the spar and get it up high enough so that when on deck there is no chance of being within sight of the TX beam..
Image courtesy Raymarine
The radiation safety issue was discussed in detail a while back. It should be in the archives if you are interested; a search with my name should get to it.
Allan
Allan
Nope, the pressure has the same dampening effect. It takes a little bit to get the pressure right so that it will swing but not wildly, but it works.
As for zero exposure: I did some calculations based on the spread of the radar (I think it goes at a 30 degree angle, no?). My radome is mounted where the back stay splits into two, and based on my calculations some body sitting up by the mast would be out of the rays. All the way forward, and you would be exposed.
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