This year (my 50th) has been a year of getting everything I want for Peapod (my cd 28). A windlass...200' of chain...a garmin chartplotter...a ST2000 tillerpilot...a mastmate mast ladder...and last but not least a furuno radar unit. I will mount it on the mast and here is my question...where should it go? I assume it should be below the spreaders...anyone have a 28 with radar on the mast?
By the way, my boat is one of those 1976 no-frills models that came with plastic ports. Last year I replaced them all with bronze ports from NewFoundMetals....they look great!....after a season of sailing with them in all kinds of weather not a single drop has come in...and they look real nice...I will get a picture and post it soon for anyone considering this kind of upgrade.
Paul Grecay
Peapod
1976 cd 28
pagrecay@aol.com
radar placement
Moderator: Jim Walsh
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Ken Cave
Re: radar placement
Are you sure you want to mount a radar on the mast? I have a CD 28, and the former owner mounted the unit on a pole that is attached on the back stay with a swivel mount. The pole and swivel do costs some bucks, but, hey! anything we do to our boats costs bucks!!
Ken Cave
Dragon Tale
CD 28 #227
bcave@whidbey.net
Ken Cave
Dragon Tale
CD 28 #227
bcave@whidbey.net
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Paul Grecay
Re: radar placement
Yes - it is going on the mast...I have the mast mount and I am not crazy about a pole on the stern...the swivel leveling mount on the backstay is definitely out - new sails come first and for me, it's one or the other. No doubt the self leveling mounts are better, but I have found that the mast mount is sufficient for most purposes.
Paul
pagrecay@aol.com
Paul
Ken Cave wrote: Are you sure you want to mount a radar on the mast? I have a CD 28, and the former owner mounted the unit on a pole that is attached on the back stay with a swivel mount. The pole and swivel do costs some bucks, but, hey! anything we do to our boats costs bucks!!
Ken Cave
Dragon Tale
CD 28 #227
pagrecay@aol.com
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kerrydeare
Re: radar placement
I mounted the Furuno radome on the backstay on my 28, but that's not your choice. On other CD's (ranging from a 25D to several 28's to 33 and 36 footers), I have seen radomes usually mounted just above the spreaders. I am not at all sure that the exact location is critical, although considerations such as fouling sails and rigging, radar horizon, etc., probably came into play.Paul Grecay wrote: a furuno radar unit. I will mount it on the mast ... [but] ... where should it go? I assume it should be below the spreaders...anyone have a 28 with radar on the mast?
kerrydeare@yahoo.com
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Tom
Re: radar placement
Paul, This is a judgment call. I just did this on my 31. You want the dome as high as possible for the best range, but you have to take into consideration that the staysail is going to rub on the dome when you tack, so you want to minimize that chafe point. I ran the staysail up and then stood back to see where I had the most sail clearance. On my 31 this turned out to be about 3 feet down from the spreaders because of the way the staysail is cut. Too high and you get into too little space where the staysail stay gets near the mast at the top. You have to be low enough to give the top of the staysail room to tack when you come about. You have to think about blocking the steaming and deck light too. Another thing you have to consider is whether the cable will reach to the place where you plan to put the display unit. I had to buy the extra long cable to reach as there's no splicing into the cable with an extension unless you're an expert with courage.
One thing I forgot and now have to change is that the topping lift for the staysail boom is now just above my dome. I have to climb the mast and move the eyestrap down below the dome so I can use the topping lift. When everything is off the mast so you can pull it, it's easy to forget that the topping lift is going to be there.
I installed a pvc pipe inside the mast to keep the radar cable from banging inside and then ran the other wires inside it also. Brought the radar cable out at the base of the mast in the mast step well and ran it under the cabin sole in a plastic pipe over to the display unit. It's easier to drill this hole in the mast step when the mast is out. A clean installation, but it takes some time to do it. You'll discover that they put the big plug on the wrong end of the cable so that you can't install the cable before you fit the mast and then set the mast in place. You have to step the mast and then snake the cable up to the dome inless you're willing to cut huge holes in the bulkheads etc. to pass the plug through. You'd think the manufacturer had never installed one of these or they'd know better. So it's good to fit a "pull wire" inside the mast before you step it to facilitate pulling the cable up to the dome after the mast is stepped. I bought a Raytheon rather than the Furuno so yours may be different, but it's something to consider before starting. Think about lights, topping lift, and how you're going to run the cable before jumping in.
TomCambria@mindspring.com
One thing I forgot and now have to change is that the topping lift for the staysail boom is now just above my dome. I have to climb the mast and move the eyestrap down below the dome so I can use the topping lift. When everything is off the mast so you can pull it, it's easy to forget that the topping lift is going to be there.
I installed a pvc pipe inside the mast to keep the radar cable from banging inside and then ran the other wires inside it also. Brought the radar cable out at the base of the mast in the mast step well and ran it under the cabin sole in a plastic pipe over to the display unit. It's easier to drill this hole in the mast step when the mast is out. A clean installation, but it takes some time to do it. You'll discover that they put the big plug on the wrong end of the cable so that you can't install the cable before you fit the mast and then set the mast in place. You have to step the mast and then snake the cable up to the dome inless you're willing to cut huge holes in the bulkheads etc. to pass the plug through. You'd think the manufacturer had never installed one of these or they'd know better. So it's good to fit a "pull wire" inside the mast before you step it to facilitate pulling the cable up to the dome after the mast is stepped. I bought a Raytheon rather than the Furuno so yours may be different, but it's something to consider before starting. Think about lights, topping lift, and how you're going to run the cable before jumping in.
Paul Grecay wrote: This year (my 50th) has been a year of getting everything I want for Peapod (my cd 28). A windlass...200' of chain...a garmin chartplotter...a ST2000 tillerpilot...a mastmate mast ladder...and last but not least a furuno radar unit. I will mount it on the mast and here is my question...where should it go? I assume it should be below the spreaders...anyone have a 28 with radar on the mast?
By the way, my boat is one of those 1976 no-frills models that came with plastic ports. Last year I replaced them all with bronze ports from NewFoundMetals....they look great!....after a season of sailing with them in all kinds of weather not a single drop has come in...and they look real nice...I will get a picture and post it soon for anyone considering this kind of upgrade.
Paul Grecay
Peapod
1976 cd 28
TomCambria@mindspring.com
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John R.
Re: radar placement
Just above the spreaders by about a foot or so. Steaming light and or foredeck light should be just below the dome.
Paul Grecay wrote: This year (my 50th) has been a year of getting everything I want for Peapod (my cd 28). A windlass...200' of chain...a garmin chartplotter...a ST2000 tillerpilot...a mastmate mast ladder...and last but not least a furuno radar unit. I will mount it on the mast and here is my question...where should it go? I assume it should be below the spreaders...anyone have a 28 with radar on the mast?
By the way, my boat is one of those 1976 no-frills models that came with plastic ports. Last year I replaced them all with bronze ports from NewFoundMetals....they look great!....after a season of sailing with them in all kinds of weather not a single drop has come in...and they look real nice...I will get a picture and post it soon for anyone considering this kind of upgrade.
Paul Grecay
Peapod
1976 cd 28
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Larry DeMers
Re: radar placement
The mast location is fine if that is what you prefer..but realize that height is not the only critical factor here. The problem at hand is not the same as installing a VHF antenna for instance, where the higher the antenna, the longer the range.
In reality, the critical factor with radar installation for most sailors is that they primarily want to see the objects that they may hit ahead of them in the fog, more than an awfully large object 14 miles away, but that same object would be nice to know about too.
The ability to use radar to see your way into a channel that is hidden in fog or at night is a critical function for sailors that explore new areas. Radar, with a vertical angle of projection of about 6 degress, will paint what it reflects off of. If the dome is mounted quite high..like say 3/4 of the ways to the masthead (I have seen this on several larger boats), then the vertical beam width will cause the radars beam to hit the water hundreds of feet in front of the boat, missing altogether anything inside of this range. Not a very useful installation in my opinioin, since all the operator will see is traffic way out in front (interesting perhaps..useful..not really).
Mounting the antenna further down the mast..*or on a stern mounted pole or on the backstay*, will cause the beam to intersect the water at a much closer distance to the boat, with the distance decreasing as the antenna is lowered. At about 12-15 ft. above deck, you get about the best range/close up visibility trade off. At that height, objects within probably 50 ft. in front of the bow will paint on the screen, and this then can be used to guide yourself thru a buoyed channel or into a rock enshrouded opening in the shoreline, whereas with that higher mounted antenna, this detail would be literally be 'under the radar' beam.
So once your goal is understood, then you can proceed to choose an installation location and height.
On DeLaMer, we mounted the radome on a 9ft. deck mounted pole on the boats port quarter, and have found that it works in all conditions and heel angles likely to be experienced while in fog, heavy rain, or at night. We have used this radar to guide ourselves thru rock shoals marked with small islands that had to be skirted, and that put us within 5 ft. of the shoreline, then thru a 2 mile long fjord-like channel to locate a hidden break in a rocky shoreline 15 ft. wide, that led to two of the most beautiful land locked/hurricane hole type anchorages on Lake Superior. In fog, this would be tough to navigate without prior experience. But the close in readings from the radar showed the details very well, and made the job very easy.
Another use of the close-in visibility of the lower mounted radome is when we return to the marina in fog or limited visibility conditions. We have a narrow 12 ft. deep channel to follow for 3/4 mile, marked with a steel gate at the marina entrance, and a set of smaller nun buoys 100 ft. in front of this metal gate. We can see these two buoys as individual buoys, set about 25 ft. apart, as well as the steel gate mass ahead of the buoys..and the buoys stay visible until they are probably 20 ft. in front of the boat.
This ability has guided us home at night or in fog several times, and is of such value to us that I would not trade it for being able to see something at the far extreme of our radars visibility (16 miles nominally). We can see 1000ft. freighters at 12 miles out, so that is still sufficiently far enough away to be of good use to us.
Your ability to see further to the horizon will not increase all that much by raising the antenna from the 12 ft. above deck mark, to say the 18 ft. above deck mark. But you will loose the critical close-in visibility by raising the antenna to that height.
Given the difficulty of running the cable, mounting the antenna, interfering with the staysail topping lift block and fall, interfering with the deck light and/or steaming light etc., we found the stern mounted pole to be far easier to install and use. It has proven very satisfactory to us, and is not even what I consider a compromise..as some things are on the boat.
Hope some of this helps,
Larry DeMers
s/v DeLaMer
Cape Dory 30 Lake Superior
demers@sgi.com
In reality, the critical factor with radar installation for most sailors is that they primarily want to see the objects that they may hit ahead of them in the fog, more than an awfully large object 14 miles away, but that same object would be nice to know about too.
The ability to use radar to see your way into a channel that is hidden in fog or at night is a critical function for sailors that explore new areas. Radar, with a vertical angle of projection of about 6 degress, will paint what it reflects off of. If the dome is mounted quite high..like say 3/4 of the ways to the masthead (I have seen this on several larger boats), then the vertical beam width will cause the radars beam to hit the water hundreds of feet in front of the boat, missing altogether anything inside of this range. Not a very useful installation in my opinioin, since all the operator will see is traffic way out in front (interesting perhaps..useful..not really).
Mounting the antenna further down the mast..*or on a stern mounted pole or on the backstay*, will cause the beam to intersect the water at a much closer distance to the boat, with the distance decreasing as the antenna is lowered. At about 12-15 ft. above deck, you get about the best range/close up visibility trade off. At that height, objects within probably 50 ft. in front of the bow will paint on the screen, and this then can be used to guide yourself thru a buoyed channel or into a rock enshrouded opening in the shoreline, whereas with that higher mounted antenna, this detail would be literally be 'under the radar' beam.
So once your goal is understood, then you can proceed to choose an installation location and height.
On DeLaMer, we mounted the radome on a 9ft. deck mounted pole on the boats port quarter, and have found that it works in all conditions and heel angles likely to be experienced while in fog, heavy rain, or at night. We have used this radar to guide ourselves thru rock shoals marked with small islands that had to be skirted, and that put us within 5 ft. of the shoreline, then thru a 2 mile long fjord-like channel to locate a hidden break in a rocky shoreline 15 ft. wide, that led to two of the most beautiful land locked/hurricane hole type anchorages on Lake Superior. In fog, this would be tough to navigate without prior experience. But the close in readings from the radar showed the details very well, and made the job very easy.
Another use of the close-in visibility of the lower mounted radome is when we return to the marina in fog or limited visibility conditions. We have a narrow 12 ft. deep channel to follow for 3/4 mile, marked with a steel gate at the marina entrance, and a set of smaller nun buoys 100 ft. in front of this metal gate. We can see these two buoys as individual buoys, set about 25 ft. apart, as well as the steel gate mass ahead of the buoys..and the buoys stay visible until they are probably 20 ft. in front of the boat.
This ability has guided us home at night or in fog several times, and is of such value to us that I would not trade it for being able to see something at the far extreme of our radars visibility (16 miles nominally). We can see 1000ft. freighters at 12 miles out, so that is still sufficiently far enough away to be of good use to us.
Your ability to see further to the horizon will not increase all that much by raising the antenna from the 12 ft. above deck mark, to say the 18 ft. above deck mark. But you will loose the critical close-in visibility by raising the antenna to that height.
Given the difficulty of running the cable, mounting the antenna, interfering with the staysail topping lift block and fall, interfering with the deck light and/or steaming light etc., we found the stern mounted pole to be far easier to install and use. It has proven very satisfactory to us, and is not even what I consider a compromise..as some things are on the boat.
Hope some of this helps,
Larry DeMers
s/v DeLaMer
Cape Dory 30 Lake Superior
Paul Grecay wrote: This year (my 50th) has been a year of getting everything I want for Peapod (my cd 28). A windlass...200' of chain...a garmin chartplotter...a ST2000 tillerpilot...a mastmate mast ladder...and last but not least a furuno radar unit. I will mount it on the mast and here is my question...where should it go? I assume it should be below the spreaders...anyone have a 28 with radar on the mast?
By the way, my boat is one of those 1976 no-frills models that came with plastic ports. Last year I replaced them all with bronze ports from NewFoundMetals....they look great!....after a season of sailing with them in all kinds of weather not a single drop has come in...and they look real nice...I will get a picture and post it soon for anyone considering this kind of upgrade.
Paul Grecay
Peapod
1976 cd 28
demers@sgi.com
-
John Sill
Re: radar placement
You definitely want to mount the radar above or below the spreaders. Keep them out of the plane of the antenna by > 8". I mounted mine above the spreaders, mast light and staysail topping lift, but below the staysail forestay. it is a little higher than I wanted (ref. minimum range discussion; swing is also amplified) but pretty much out of harm's way. The staysail is pretty small up there so there's very little rubbing force. This did require an optional 20 meter cable for my CD31 with the radar display mounted at the helm. So far all seems to be working well. Installation with the mast up was made practical by a very helpful neighbor.
Good Luck,
John
Beholder's Eye, CD31
Good Luck,
John
Beholder's Eye, CD31
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Warren Stringer
Re: radar placement
(Snipped)
If you go with a pole mount at the stern I would make sure that the heads of all persons in the cockpit are below the lower divergence boundary of the beam. While there is no indication or proof of potential harm that I am aware of, (I have not researched this !), it seems to be sensible to avoid direct exposure to the beam.
Warren
s/v Eendracht
CD 36 #54
wstringer@aristotle.net
My Raytheon RL72 unit has a vertical beam divergence of 12.5 degrees above and below the horizontal; I believe most small boat radars will be similar. Any radar will also have a minimum distance below which it will not detect an echo; this distance is usually given in the information which comes with the unit. On the Raytheon it is about 65 feet. Knowing the beam divergence and the minimum echo distance, straightforward trigonometry will allow you to determine the maximum height of the mount on the mast which will still allow you to pick up an object at water level at the minimum distance FROM THE RADAR. In Larry's case, with the radar mounted on a pole at the stern, he will be able to follow an object closer in to the bow than you would with a mast mount, regardless of the height of mount.Larry DeMers wrote: The ability to use radar to see your way into a channel that is hidden in fog or at night is a critical function for sailors that explore new areas. Radar, with a vertical angle of projection of about 6 degress, will paint what it reflects off of. If the dome is mounted quite high..like say 3/4 of the ways to the masthead (I have seen this on several larger boats), then the vertical beam width will cause the radars beam to hit the water hundreds of feet in front of the boat, missing altogether anything inside of this range. Not a very useful installation in my opinioin, since all the operator will see is traffic way out in front (interesting perhaps..useful..not really).
Mounting the antenna further down the mast..*or on a stern mounted pole or on the backstay*, will cause the beam to intersect the water at a much closer distance to the boat, with the distance decreasing as the antenna is lowered. At about 12-15 ft. above deck, you get about the best range/close up visibility trade off. At that height, objects within probably 50 ft. in front of the bow will paint on the screen, and this then can be used to guide yourself thru a buoyed channel or into a rock enshrouded opening in the shoreline, whereas with that higher mounted antenna, this detail would be literally be 'under the radar' beam.
So once your goal is understood, then you can proceed to choose an installation location and height.
Another use of the close-in visibility of the lower mounted radome is when we return to the marina in fog or limited visibility conditions. We have a narrow 12 ft. deep channel to follow for 3/4 mile, marked with a steel gate at the marina entrance, and a set of smaller nun buoys 100 ft. in front of this metal gate. We can see these two buoys as individual buoys, set about 25 ft. apart, as well as the steel gate mass ahead of the buoys..and the buoys stay visible until they are probably 20 ft. in front of the boat.
Your ability to see further to the horizon will not increase all that much by raising the antenna from the 12 ft. above deck mark, to say the 18 ft. above deck mark. But you will loose the critical close-in visibility by raising the antenna to that height.
Larry DeMers
s/v DeLaMer
Cape Dory 30 Lake Superior
If you go with a pole mount at the stern I would make sure that the heads of all persons in the cockpit are below the lower divergence boundary of the beam. While there is no indication or proof of potential harm that I am aware of, (I have not researched this !), it seems to be sensible to avoid direct exposure to the beam.
Warren
s/v Eendracht
CD 36 #54
wstringer@aristotle.net
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Larry DeMers
Re: radar placement
Warren,
Good points!~ There are some health effects associated with (but not actually warned against) exposure to radar..cataracts among them. So your warning of making sure that nobody is getting a dose of the rf is important. On our installation, the mast is 9 ft. up from the stern counter on our CD30, or about 12 ft. above cockpit level. We are safe there..but deck work would not be a good idea while the radar was running. Usually these two functions do not occur simultaneously though.
Cheers,
Larry DeMers
demers@sgi.com
Good points!~ There are some health effects associated with (but not actually warned against) exposure to radar..cataracts among them. So your warning of making sure that nobody is getting a dose of the rf is important. On our installation, the mast is 9 ft. up from the stern counter on our CD30, or about 12 ft. above cockpit level. We are safe there..but deck work would not be a good idea while the radar was running. Usually these two functions do not occur simultaneously though.
Cheers,
Larry DeMers
Warren Stringer wrote: (Snipped)
Larry DeMers wrote: The ability to use radar to see your way into a channel that is hidden in fog or at night is a critical function for sailors that explore new areas. Radar, with a vertical angle of projection of about 6 degress, will paint what it reflects off of. If the dome is mounted quite high..like say 3/4 of the ways to the masthead (I have seen this on several larger boats), then the vertical beam width will cause the radars beam to hit the water hundreds of feet in front of the boat, missing altogether anything inside of this range. Not a very useful installation in my opinioin, since all the operator will see is traffic way out in front (interesting perhaps..useful..not really).
Mounting the antenna further down the mast..*or on a stern mounted pole or on the backstay*, will cause the beam to intersect the water at a much closer distance to the boat, with the distance decreasing as the antenna is lowered. At about 12-15 ft. above deck, you get about the best range/close up visibility trade off. At that height, objects within probably 50 ft. in front of the bow will paint on the screen, and this then can be used to guide yourself thru a buoyed channel or into a rock enshrouded opening in the shoreline, whereas with that higher mounted antenna, this detail would be literally be 'under the radar' beam.
So once your goal is understood, then you can proceed to choose an installation location and height.
Another use of the close-in visibility of the lower mounted radome is when we return to the marina in fog or limited visibility conditions. We have a narrow 12 ft. deep channel to follow for 3/4 mile, marked with a steel gate at the marina entrance, and a set of smaller nun buoys 100 ft. in front of this metal gate. We can see these two buoys as individual buoys, set about 25 ft. apart, as well as the steel gate mass ahead of the buoys..and the buoys stay visible until they are probably 20 ft. in front of the boat.
Larry DeMers wrote: Your ability to see further to the horizon will not increase all that much by raising the antenna from the 12 ft. above deck mark, to say the 18 ft. above deck mark. But you will loose the critical close-in visibility by raising the antenna to that height.
My Raytheon RL72 unit has a vertical beam divergence of 12.5 degrees above and below the horizontal; I believe most small boat radars will be similar. Any radar will also have a minimum distance below which it will not detect an echo; this distance is usually given in the information which comes with the unit. On the Raytheon it is about 65 feet. Knowing the beam divergence and the minimum echo distance, straightforward trigonometry will allow you to determine the maximum height of the mount on the mast which will still allow you to pick up an object at water level at the minimum distance FROM THE RADAR. In Larry's case, with the radar mounted on a pole at the stern, he will be able to follow an object closer in to the bow than you would with a mast mount, regardless of the height of mount.Larry DeMers wrote:
Larry DeMers
s/v DeLaMer
Cape Dory 30 Lake Superior
If you go with a pole mount at the stern I would make sure that the heads of all persons in the cockpit are below the lower divergence boundary of the beam. While there is no indication or proof of potential harm that I am aware of, (I have not researched this !), it seems to be sensible to avoid direct exposure to the beam.
Warren
s/v Eendracht
CD 36 #54
demers@sgi.com
-
Jerry
Health effects, maximum versus minimum range, long reply
Greetings from a former RADAR operator in the Navy. Yes, there are some health effects associated with RADAR energy. Think of it like a microwave oven. Would you put your head or hand in a microwave oven when it's on? I ask because it's essentially the same type of energy.
Cataracts problems and internal burns (remember a microwave oven cooks from the inside out)are some of the potential problems that you may encounter. I know there are some other effects that are possible but I cannot remember them off the top of my head.
Regarding minimum versus maximum range. There's going to be a major factor that will affect how close in you can see objects, sea clutter. Remember sea clutter or return extends out as a result of the bleeding of energy by the lobes of the RADAR wave. This can extend out to well over a mile depending on the RADAR.
Are you gaining a benefit when you decrease your RADAR's minimum range when you have the sea clutter overlapping that minimum range?
The biggest impact on the range of the RADAR is the height of the RADAR above the water. For a given height above sea level the RADAR if going to have a RADAR horizon. This RADAR horizon is a general idea of what kind of range you're going to have.
There are a lot of other factors that go into the range of a RADAR such as the power output of the antenna, the frequency (to some extent) of the RADAR, atmospheric conditions, the beam width and height, etc.... But, changing a lot of those factors isn't practical on a sailboat, or other vessles for that matter. If we look at increasing the power output of the antenna to increase range we have to use four times (it might be sixteen times I cannot remember off hand) as much power just to double the range. Cranking up the power output of the antenna increases battery consumption.
The cheapest way to gain detection range (this comes at the loss of minimum range) is to raise the height of the RADAR antenna. If we only look at the height of the antenna above water to determine range, or the RADAR horizon we can see a distinct difference is a small amount of height. Remember the RADAR horizon is just a general idea, it doesn't take into account factors like the pulse repition frequency, antenna rotation time, power output of the antenna, height of the target above the water etc....
At 10 feet above the water we have a range of 3.95 miles.
At 15 feet above the water we have a range of 4.84 miles.
At 20 feet above the water we have a range of 5.59 miles.
At 25 feet above the water we have a range of 6.25 miles.
At 30 feet above the water we have a range of 6.847 miles.
At 35 feet above the water we have a range of 7.40 miles.
At 40 feet above the water we have a range of 7.91 miles.
At 45 feet above the water we have a range of 8.39 miles.
At 50 feet above the water we have a range of 8.84 miles.
On average you gain almost 2/3rds of a mile of maximum range for every 5 feet higher you place the antenna. That's 2/3rds of a mile sooner that you will detect that freighter. In contrast how much do you gain in terms of a minimum range by lowering the height of you antenna?
Lest's say that you decide to drop the antenna from 30 feet to twenty feet in order to gain minimum detection. First you loose 1.25 miles of detection range to gain some minimum. I don't know what the minimum gain would be because I don't have enough information. However, let's say for the sake of argument that you gaing 100 feet in terms of minimum range. At an average speed of 6 knots you're travelling 10 feet per second ( I could be wrong on that my math isn't all that great).
That means that you have an additional 10 seconds of detection time. Now the question that needs to be asked is what's the RPM of the RADAR's antenna. Remember you only see an object when it's painted by the RADAR. Does the antenna rotate at 6 RPMS? If so then it's only going to paint that object once if you're lucky before it's inside the minimum range. At 10 RPM's you may be able to paint the object twice if you're lucky. Now remember sea clutter this is going to have an impact on what you can, and how much of it you can see close in.
Another thing to remember is that boats heel to the side and bob up and down. THis will also have an impact on both minimum and maximum range. If it were me personally I would place the RADAR higher up in a effort to gain maximum detection range. But that's just me and my own personal prejudice on the matter.
If you have any questions feel free to e-mail me at pedal{nospam}@provide.net
Hope it helps
Jerry
nope@no.spam
Cataracts problems and internal burns (remember a microwave oven cooks from the inside out)are some of the potential problems that you may encounter. I know there are some other effects that are possible but I cannot remember them off the top of my head.
Regarding minimum versus maximum range. There's going to be a major factor that will affect how close in you can see objects, sea clutter. Remember sea clutter or return extends out as a result of the bleeding of energy by the lobes of the RADAR wave. This can extend out to well over a mile depending on the RADAR.
Are you gaining a benefit when you decrease your RADAR's minimum range when you have the sea clutter overlapping that minimum range?
The biggest impact on the range of the RADAR is the height of the RADAR above the water. For a given height above sea level the RADAR if going to have a RADAR horizon. This RADAR horizon is a general idea of what kind of range you're going to have.
There are a lot of other factors that go into the range of a RADAR such as the power output of the antenna, the frequency (to some extent) of the RADAR, atmospheric conditions, the beam width and height, etc.... But, changing a lot of those factors isn't practical on a sailboat, or other vessles for that matter. If we look at increasing the power output of the antenna to increase range we have to use four times (it might be sixteen times I cannot remember off hand) as much power just to double the range. Cranking up the power output of the antenna increases battery consumption.
The cheapest way to gain detection range (this comes at the loss of minimum range) is to raise the height of the RADAR antenna. If we only look at the height of the antenna above water to determine range, or the RADAR horizon we can see a distinct difference is a small amount of height. Remember the RADAR horizon is just a general idea, it doesn't take into account factors like the pulse repition frequency, antenna rotation time, power output of the antenna, height of the target above the water etc....
At 10 feet above the water we have a range of 3.95 miles.
At 15 feet above the water we have a range of 4.84 miles.
At 20 feet above the water we have a range of 5.59 miles.
At 25 feet above the water we have a range of 6.25 miles.
At 30 feet above the water we have a range of 6.847 miles.
At 35 feet above the water we have a range of 7.40 miles.
At 40 feet above the water we have a range of 7.91 miles.
At 45 feet above the water we have a range of 8.39 miles.
At 50 feet above the water we have a range of 8.84 miles.
On average you gain almost 2/3rds of a mile of maximum range for every 5 feet higher you place the antenna. That's 2/3rds of a mile sooner that you will detect that freighter. In contrast how much do you gain in terms of a minimum range by lowering the height of you antenna?
Lest's say that you decide to drop the antenna from 30 feet to twenty feet in order to gain minimum detection. First you loose 1.25 miles of detection range to gain some minimum. I don't know what the minimum gain would be because I don't have enough information. However, let's say for the sake of argument that you gaing 100 feet in terms of minimum range. At an average speed of 6 knots you're travelling 10 feet per second ( I could be wrong on that my math isn't all that great).
That means that you have an additional 10 seconds of detection time. Now the question that needs to be asked is what's the RPM of the RADAR's antenna. Remember you only see an object when it's painted by the RADAR. Does the antenna rotate at 6 RPMS? If so then it's only going to paint that object once if you're lucky before it's inside the minimum range. At 10 RPM's you may be able to paint the object twice if you're lucky. Now remember sea clutter this is going to have an impact on what you can, and how much of it you can see close in.
Another thing to remember is that boats heel to the side and bob up and down. THis will also have an impact on both minimum and maximum range. If it were me personally I would place the RADAR higher up in a effort to gain maximum detection range. But that's just me and my own personal prejudice on the matter.
If you have any questions feel free to e-mail me at pedal{nospam}@provide.net
Hope it helps
Jerry
nope@no.spam
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Mike Quinlan
Re: Health effects, maximum versus minimum range, long reply
I understand what you say, about height and max range Jerry, and can see why the Navy is concerned about it. However, I never have hit anything 16 miles away yet and am more worried about the rock jettie that I'm tring to find. My unit is ten feet above the water and can pick up a swimmer or crab-pot 20 feet away.
Mike.
mikieq@erols.com
Mike.
Jerry wrote:
mikieq@erols.com