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Opinions on Radars
I had a JRC 1000 on my first boat and now I am restoring a 43 Endeavour
ketch and it is time to think about radars. The JRC was a nice unit but woefully underpowered. I would like to see out 8 to 10 miles with the radome mounted 20-30' up the mizzen. I know that the 4kw will give more power out and thus burn thru in foggy conditions but most of the 4kw units have the big displays. Everyone on this group knows the drill...what will give me the biggest bang for the buck with the best reliability amd a thin small display. Thanks Bruce -- Shield Finishes and Nauticoat Marine Finish Systems www.shieldfinishes.com |
Bruce on horizon wrote:
I had a JRC 1000 on my first boat and now I am restoring a 43 Endeavour ketch and it is time to think about radars. The JRC was a nice unit but woefully underpowered. I would like to see out 8 to 10 miles with the radome mounted 20-30' up the mizzen. I know that the 4kw will give more power out and thus burn thru in foggy conditions but most of the 4kw units have the big displays. Everyone on this group knows the drill...what will give me the biggest bang for the buck with the best reliability amd a thin small display. The RayMarine equipment lets you mix and match the displays and the domes so you get what you need now, and upgrade later. BTW, the radar horizon is about 7 miles from a transmitter 30 feet up. Large targets will of course be seen at a larger distance, but I can't say that I've had any problem with my low power Raytheon, and I cruise in Maine and Cape Cod. |
I would like to see out 8 to 10 miles with the
radome mounted 20-30' up the mizzen. Hi Bruce, As Jeff says, your radar will not be able to pick up small targets past your visible horizon (about 6.3 nm according to Bowditch). You will be able to pick up big, tall contacts further out, but that's about it. I'd stick to a 1.5 to 2 kw radar if I were you. Higher power doesn't "burn" through anything, including fog, and I think 4 kw is over kill for what you'll be doing. In fact at the short ranges you'll be operating at, the higher power will probably be a disadvantage. The RayMarine stuff looks pretty nice and has alot of nice features (like color and MARPA (their adaptation of ARPA)). But I'd go with a small Furuno if you can afford it or another JRC if you're on the cheap. Just my biased opinion though. Walk around the docks and see what the smaller commercial fisherman in your area use. They tend to only get stuff that works, why not do the same? Just remember, if you get too fancy a radar, chances are your attention will be fixated on that fancy screen and not your main navigation tool: your "Mark I Mod II Eyeballs" ;-) Hope this helps, Paul =----------------------= Renewontime A FREE email reminder service for licensed mariners http://www.renewontime.com =----------------------= |
On Sun, 13 Feb 2005 17:20:53 -0500, "Bruce on horizon"
wrote: I would like to see out 8 to 10 miles with the radome mounted 20-30' up the mizzen. I Sidebar question: Am I woefully ignorant on radar implementation or am I correct in assuming that a target heading directly for one's bow would be invisible to a mizzen mounted radar due to the three-to-four degree "screen" of the main mast directly ahead? Or am I missing something? Why the mizzen (aside from its convenience and the fact few people use a mizzen stays'l, so nothing to hook the radome or mount). R. |
rhys wrote:
On Sun, 13 Feb 2005 17:20:53 -0500, "Bruce on horizon" wrote: I would like to see out 8 to 10 miles with the radome mounted 20-30' up the mizzen. I Sidebar question: Am I woefully ignorant on radar implementation or am I correct in assuming that a target heading directly for one's bow would be invisible to a mizzen mounted radar due to the three-to-four degree "screen" of the main mast directly ahead? Or am I missing something? Why the mizzen (aside from its convenience and the fact few people use a mizzen stays'l, so nothing to hook the radome or mount). R. Quite possibly, IF you where an expert helmsman at all times. otn BTW I hate small displays. I'd get the biggest one possible. Also, don't get hung up on the "height of eye" distance capabilities of your radar ..... your "HE" may only say 6ish miles, but you'll be able to see a whole bunch of stuff beyond that. otn |
rhys wrote:
Sidebar question: Am I woefully ignorant on radar implementation or am I correct in assuming that a target heading directly for one's bow would be invisible to a mizzen mounted radar due to the three-to-four degree "screen" of the main mast directly ahead? A common misconception. If you think about it, you will realize that the radio energy of flowing off of and being received along the entire width of the antenna which is much wider than your mast. A healthy percentage of it is reflected back and to the sides, but most of the energy just flows right on past the mast. It works the same in reverse for the reflected energy coming back from a target. Thus, the strength of the reteurn is reduced, but you are still able to see it. Othereise, all those boats with mast mounted radars would have a fairly wide cone to their rear where they pick up nothing. In answer to Bruce's original question, overall, I like the Raymarine units. The one I put on my last boat worked so well for me, I put one on this boat too and like it just as well. I find the JVC screens harder to see and focus on than the others, but this may just be a personal thing. Whatever you do, mount the display so that it can be seen at the helm, not just at the nav station. A friend of mine's radar is just visible at the nav station and having played radar operator calling instructions up to him at the helm while dodging freighters in dense fog on SF Bay, I'm here to say that this arrangement sucks. Fair winds - Dan |
I am not a schill for Practical Sailor (subscription newsletter), nor
do I play one on TV, but I do find their articles generally useful, educational and informative. They did a piece on 'Entry Level LCD Radar' in September '04, the preamble to which you can see he http://www.practical-sailor.com/pub/...es/5003-1.html MW |
I ditto your comment about the radar in the cockpit. That is the reason I
want a smaller LCD at the helm. I will be right on top of the display, not trying to look at it from 10' away. Bruce -- Shield Finishes and Nauticoat Marine Finish Systems www.shieldfinishes.com "Dan Best" wrote in message ... rhys wrote: Sidebar question: Am I woefully ignorant on radar implementation or am I correct in assuming that a target heading directly for one's bow would be invisible to a mizzen mounted radar due to the three-to-four degree "screen" of the main mast directly ahead? A common misconception. If you think about it, you will realize that the radio energy of flowing off of and being received along the entire width of the antenna which is much wider than your mast. A healthy percentage of it is reflected back and to the sides, but most of the energy just flows right on past the mast. It works the same in reverse for the reflected energy coming back from a target. Thus, the strength of the reteurn is reduced, but you are still able to see it. Othereise, all those boats with mast mounted radars would have a fairly wide cone to their rear where they pick up nothing. In answer to Bruce's original question, overall, I like the Raymarine units. The one I put on my last boat worked so well for me, I put one on this boat too and like it just as well. I find the JVC screens harder to see and focus on than the others, but this may just be a personal thing. Whatever you do, mount the display so that it can be seen at the helm, not just at the nav station. A friend of mine's radar is just visible at the nav station and having played radar operator calling instructions up to him at the helm while dodging freighters in dense fog on SF Bay, I'm here to say that this arrangement sucks. Fair winds - Dan |
Jeff Morris wrote:
Bruce on horizon wrote: I had a JRC 1000 on my first boat and now I am restoring a 43 Endeavour ketch and it is time to think about radars. The JRC was a nice unit but woefully underpowered. I would like to see out 8 to 10 miles with the radome mounted 20-30' up the mizzen. I know that the 4kw will give more power out and thus burn thru in foggy conditions but most of the 4kw units have the big displays. Everyone on this group knows the drill...what will give me the biggest bang for the buck with the best reliability amd a thin small display. The RayMarine equipment lets you mix and match the displays and the domes so you get what you need now, and upgrade later. BTW, the radar horizon is about 7 miles from a transmitter 30 feet up. Large targets will of course be seen at a larger distance, but I can't say that I've had any problem with my low power Raytheon, and I cruise in Maine and Cape Cod. I've had minor second thoughts on this after checking the specs. In the "old days" more powerful domes were heavier and used more power - that is not the case now - the 4kW Raymarine dome only weighs a few pounds more and uses 1 or 2 Watts more juice. I'm still not sure of the value for long distance viewing, but the high power dome will have finer resolution, so that a pair of channel buoys will be resolved as two targets further away with the more powerful unit. Navigation is easier, since coastlines will more closely resemble the chart. However, this takes a lot of practice and you're better off relying on a good gps. The downsides of the large unit is almost double the cost (a $1000 premium on the RayMarine list) and a much larger dome (an issue for those trying to hide the dome from the jib). |
Stay away from Raymarine! Since they separated from Raytheon, they're
turning into cheap junk. Stick with Furuno. -- Keith __ "Usually, terrible things that are done with the excuse that progress requires them are not really progress at all, but just terrible things." - Russell Baker "Bruce on horizon" wrote in message ... I had a JRC 1000 on my first boat and now I am restoring a 43 Endeavour ketch and it is time to think about radars. The JRC was a nice unit but woefully underpowered. I would like to see out 8 to 10 miles with the radome mounted 20-30' up the mizzen. I know that the 4kw will give more power out and thus burn thru in foggy conditions but most of the 4kw units have the big displays. Everyone on this group knows the drill...what will give me the biggest bang for the buck with the best reliability amd a thin small display. Thanks Bruce -- Shield Finishes and Nauticoat Marine Finish Systems www.shieldfinishes.com |
On Mon, 14 Feb 2005 04:22:24 GMT, otnmbrd
wrote: rhys wrote: Sidebar question: Am I woefully ignorant on radar implementation or am I correct in assuming that a target heading directly for one's bow would be invisible to a mizzen mounted radar due to the three-to-four degree "screen" of the main mast directly ahead? R. Quite possibly, IF you where an expert helmsman at all times. Agreed, and I know what you are getting at. But if seas are flat, wind is calm, and you are on a misty seaway at dusk/dawn motoring at five knots under autopilot, I can see where a trawler or small frieghter doing the same on a reciprocal course would be nearly invisible to you simply due to the fact that your radar's proximity alarm or "range guard" or whatever they call it would not go off until the ship on the collision course was on top of you...solely due to the mizzen placement. A person on watch on a calm, foggy night (say a 75 foot high bank of fog, giving the impression it's clear "enough" overhead, but miserable all around) *might( hear engine noise or see a dim glow. But with the terrible watch-keeping on commercial traffic these days, I wouldn't count on being seen, either. I suppose the other side of the equation is that a mainmast mounted radome on a ketch has poor coverage aft, meaning that a ship overtaking you from dead astern would also be hard to notice in such conditions, particularly over your own exhaust note. But such conditions are exactly when one would use radar, no? R. |
On Mon, 14 Feb 2005 05:16:13 GMT, Dan Best
wrote: A common misconception. If you think about it, you will realize that the radio energy of flowing off of and being received along the entire width of the antenna which is much wider than your mast. A healthy percentage of it is reflected back and to the sides, but most of the energy just flows right on past the mast. It works the same in reverse for the reflected energy coming back from a target. Thus, the strength of the reteurn is reduced, but you are still able to see it. Othereise, all those boats with mast mounted radars would have a fairly wide cone to their rear where they pick up nothing. OK, so it's a function of radome width and radar wavelength then. Is it fair to say that there is a weaker area of coverage dead ahead and dead astern, then? The masts must absorb SOME of the signal. I am thinking that a "watch strategy" for using radar under unfavourable conditions might be to alter course five degrees or so every three miles (depending on radar range) or so to confirm the absence of traffic in such "weak spots", if they exist. My experience in this is limited (obviously), but many years ago I did use directional antennas for base-station CB radio of all things and noticed how signal strengths would fluctuate at various points. I figure radar is similar. R. |
rhys wrote:
On Mon, 14 Feb 2005 04:22:24 GMT, otnmbrd wrote: rhys wrote: Sidebar question: Am I woefully ignorant on radar implementation or am I correct in assuming that a target heading directly for one's bow would be invisible to a mizzen mounted radar due to the three-to-four degree "screen" of the main mast directly ahead? R. Quite possibly, IF you where an expert helmsman at all times. Agreed, and I know what you are getting at. But if seas are flat, wind is calm, and you are on a misty seaway at dusk/dawn motoring at five knots under autopilot, I can see where a trawler or small frieghter doing the same on a reciprocal course would be nearly invisible to you simply due to the fact that your radar's proximity alarm or "range guard" or whatever they call it would not go off until the ship on the collision course was on top of you...solely due to the mizzen placement. Doing some geometry, the mast blocks about a 1 degree angle from the mizzen. The horizontal beam width of the low power units is about 5 degrees, so most of the energy will get past the mast. The higher power units have a tighter beam and thus would loose a bit more, though the Ray 4kW dome is still at 4 degrees. The high power, open arrays tend to get down below 2 degrees, so they may get blocked more. Frankly, I doubt this is really a problem. On the other hand, a jib that fouls the radar on every tack is a major pain! .... I suppose the other side of the equation is that a mainmast mounted radome on a ketch has poor coverage aft, meaning that a ship overtaking you from dead astern would also be hard to notice in such conditions, particularly over your own exhaust note. My radar doesn't seem to have a problem seeing "around" the mast. I suppose the close proximity of the mast might absorb some energy, but I haven't noticed it. But such conditions are exactly when one would use radar, no? This is why I avoid going in a straight line :-) |
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On Mon, 14 Feb 2005 09:43:06 -0500, rhys wrote:
On Mon, 14 Feb 2005 04:22:24 GMT, otnmbrd wrote: rhys wrote: Sidebar question: Am I woefully ignorant on radar implementation or am I correct in assuming that a target heading directly for one's bow would be invisible to a mizzen mounted radar due to the three-to-four degree "screen" of the main mast directly ahead? R. Quite possibly, IF you where an expert helmsman at all times. Agreed, and I know what you are getting at. But if seas are flat, wind is calm, and you are on a misty seaway at dusk/dawn motoring at five knots under autopilot, I can see where a trawler or small frieghter doing the same on a reciprocal course would be nearly invisible to you simply due to the fact that your radar's proximity alarm or "range guard" or whatever they call it would not go off until the ship on the collision course was on top of you...solely due to the mizzen placement. A person on watch on a calm, foggy night (say a 75 foot high bank of fog, giving the impression it's clear "enough" overhead, but miserable all around) *might( hear engine noise or see a dim glow. But with the terrible watch-keeping on commercial traffic these days, I wouldn't count on being seen, either. I suppose the other side of the equation is that a mainmast mounted radome on a ketch has poor coverage aft, meaning that a ship overtaking you from dead astern would also be hard to notice in such conditions, particularly over your own exhaust note. But such conditions are exactly when one would use radar, no? R. The mast is not nearly wide enough to block the smallest radar antenna. I had a Furuno 1720 mounted on a stern tower for 11 years without seeing a blind spot, and a Ray SR70 for the last 3 seasons. The Raytheon is much better than the old Furuno, but mainly because it is a 20-year later design, making use of digital computer techology. I expect a new Furuno would be fine also. My only complaint with the Ray is that its dimmest back-light setting is too bright. The garmin GPS maounted beside the display at the helm dims down much lower. I have bought red gel filters from a theater lighting place which keep the display from swamping my eyesight on watch. HTH Rodney Myrvaagnes J36 Gjo/a "We have achieved the inversion of the single note." __ Peter Ustinov as Karlheinz Stckhausen |
rhys wrote:
On Mon, 14 Feb 2005 15:54:04 GMT, wrote: This is why I avoid going in a straight line :-) The only way the mast would make for a problematic blank or shadow would be if the boat and the target were both completely still. Thanks for the clarifications, guys. So, to sum up, if you have a mizzen, it's a great spot for a radar with little downside unless you think you need the height of the mainmast, but then you may foul an overlapping genoa. Does that sum it up? Yup. After sailing a sistership with the radar mounted high on the mast, I mounted mine below the baby stay, and never regretted it. Reason I'm asking is that steel ketches look good to me on a number of levels. Now, if I can just figure out how to put a windvane AND davits behind a mizzen mast....G The windvane should go high on the mizzen, as on my friends boat: http://www.sv-loki.com/Moonshadow/Pg22.jpg Note that the davits are behind, and also serve as a good place for solar panels. R. |
Thanks for the clarifications, guys. So, to sum up, if you have a
mizzen, it's a great spot for a radar with little downside unless you think you need the height of the mainmast, but then you may foul an overlapping genoa. Does that sum it up? Just remember that a radar sends out radio waves, and any metal in front of it will cause part of your radar signal to be bounced back to your radar. The metal mast and rigging may not obscure your radar display (an empty "shadow area"), but some of that energy will be bounced right back and can either cause interference or even damage to your radar's receiver. All the more reason not to use a 4 kw system. Admittedly, any installation an a sailboat would be a compromise, just as long as you're aware of whatever the limitations/consequences might be. Now, if I can just figure out how to put a windvane AND davits behind a mizzen mast....G The windvane should go high on the mizzen, as on my friends boat: http://www.sv-loki.com/Moonshadow/Pg22.jpg Note that the davits are behind, and also serve as a good place for solar panels. Wind -vane- or wind -generator-? The pictures show what I'd call a "wind generator". Mounting a wind vane self steering system is a whole different kind of animal. Which is it you need help with? Paul =---------------------------= Renewontime A FREE email reminder service for licensed mariners http://www.renewontime.com =---------------------------= |
rhys wrote:
Agreed, and I know what you are getting at. But if seas are flat, wind is calm, and you are on a misty seaway at dusk/dawn motoring at five knots under autopilot, I can see where a trawler or small frieghter doing the same on a reciprocal course would be nearly invisible to you simply due to the fact that your radar's proximity alarm or "range guard" or whatever they call it would not go off until the ship on the collision course was on top of you...solely due to the mizzen placement. A person on watch on a calm, foggy night (say a 75 foot high bank of fog, giving the impression it's clear "enough" overhead, but miserable all around) *might( hear engine noise or see a dim glow. But with the terrible watch-keeping on commercial traffic these days, I wouldn't count on being seen, either. G I'll avoid comment on commercial watchkeeping nowadays, as I've been out of that loop for @15 years. However, since I "do" get involved with a lot of recreational boaters, I'd call their average ..... not the best. I.E., you don't rely on anyone but yourself to maintain a good watch. I suppose the other side of the equation is that a mainmast mounted radome on a ketch has poor coverage aft, meaning that a ship overtaking you from dead astern would also be hard to notice in such conditions, particularly over your own exhaust note. But such conditions are exactly when one would use radar, no? R. You'll find that many vessels of many types and sizes have "blind spots" associated with their particular scanner installation. As part of your good watchkeeping, you should be aware of these "blind spots" for your particular vessel, and act accordingly. otn |
renewontime dot com wrote:
Thanks for the clarifications, guys. So, to sum up, if you have a mizzen, it's a great spot for a radar with little downside unless you think you need the height of the mainmast, but then you may foul an overlapping genoa. Does that sum it up? Just remember that a radar sends out radio waves, and any metal in front of it will cause part of your radar signal to be bounced back to your radar. The metal mast and rigging may not obscure your radar display (an empty "shadow area"), but some of that energy will be bounced right back and can either cause interference or even damage to your radar's receiver. All the more reason not to use a 4 kw system. What??? Are you claiming its dangerous to mount a radar on the mast? Actually, most masts will reflect the energy away. RayMarine advises to put a block of wood between the mast and dome if there's interference on the screen, but I've had several (including a large Nonsuch mast) and never seen a problem. I don't see how there would be a problem with the main mast interfering with a mizzen mounted dome. |
In article ,
renewontime dot com wrote: Higher power doesn't "burn" through anything, including fog, Bzzzzt, wrong answer Dude, would you like to try for what is behind Door #3?????? When was the last time, you measured Water Adsorption at 10Ghz? Obviously, not in the last 50 years, since Xband has come into Marine Radar use. Water Adsoption is a Significant cause of loss of Targets, when the humidity of the air between the transmitter and target is high. 4Kw PPP wil certainly "Burn thru" more humid air than 2Kw PPP. One must also consider, that heavy rain, like in squalls, will also tend to drop the siganl level of received targets in the Xband, due to defraction of the RF by the rain droplets. These, and other KNOWN, physical elements all play a part in Maximum Detection Distance of a target in Marine Radar Systems. Me one who deals with this stuff every day...... |
In article ,
Jeff Morris wrote: I'm still not sure of the value for long distance viewing, but the high power dome will have finer resolution, so that a pair of channel buoys will be resolved as two targets further away with the more powerful unit. Navigation is easier, since coastlines will more closely resemble the chart. However, this takes a lot of practice and you're better off relying on a good gps. The above is due to a narrower Horizontal Beamwidth, and not the PPP (Peak Pukse Power) of the transmitter. Radar OEM's tend to put the bigger antennas (narrower Horizontal Beamwidth) on their Larger PPP transmitters as a rule, but the two are mutually exclusive specifications. Third and fourth Generation Marine Radars, all have Log Recivers, SolidState Frontends, and that is why they preform as well as the older Second Generation Radars that had twice the PPP in the transmitters. Where it used to take 10Kw and a 6 Ft SlotLine antenna to pickup 48 mile targets in second genertion Marine Radars, the 4Kw 4Ft Slotline antennas of the Fourth Generation work just fine on the same paths. Like wise the 2Kw 3Ft Slotline Radars of the Third Generation will compare very nicely with a 2Kw flatpanel antennas of todays small boat radars, with the exception of the very wide Horozontal Beamwidths of those flat panel antennas, that can't differentiate between two targets at the same distance, but closer than 6 or 7 degrees in bearing. Bruce in alaska -- add a 2 before @ |
"renewontime dot com" wrote in message
... Just remember that a radar sends out radio waves, and any metal in front of it will cause part of your radar signal to be bounced back to your radar. The metal mast and rigging may not obscure your radar display (an empty "shadow area"), but some of that energy will be bounced right back and can either cause interference or even damage to your radar's receiver. All the more reason not to use a 4 kw system. No it won't. When the radar is transmitting, the receiver is shut off or the path from the antenna to the receiver is blocked. When the tranmission stops, the receiver is switched on again but not immediately. So the first strong echos from very nearby objects will not reach the received. Apart from that, the receivers' sensitivity is increased from almost nothing to full gradually to compensate for the weaker echos from longer distances. Meindert |
On Mon, 14 Feb 2005 10:11:18 -1000, renewontime dot com
wrote: Just remember that a radar sends out radio waves, and any metal in front of it will cause part of your radar signal to be bounced back to your radar. The metal mast and rigging may not obscure your radar display (an empty "shadow area"), but some of that energy will be bounced right back and can either cause interference or even damage to your radar's receiver. All the more reason not to use a 4 kw system. Unless his ketch is very long indeed, any echo energy from the mast will arrive and depart while the antenna is closed. Rodney Myrvaagnes J36 Gjo/a Does one child rape really change Strom Thurmond's lifetime record? For better or worse? |
On Mon, 14 Feb 2005 21:22:32 GMT, Me wrote:
In article , renewontime dot com wrote: Higher power doesn't "burn" through anything, including fog, Bzzzzt, wrong answer Dude, would you like to try for what is behind Door #3?????? When was the last time, you measured Water Adsorption at 10Ghz? Obviously, not in the last 50 years, since Xband has come into Marine Radar use. Water Adsoption is a Significant cause of loss of Targets, when the humidity of the air between the transmitter Perhaps you mean 'absorption?' 'Adsorption is hardly possible for rf. and target is high. 4Kw PPP wil certainly "Burn thru" more humid air than 2Kw PPP. One must also consider, that heavy rain, like in squalls, will also tend to drop the siganl level of received targets in the Xband, due to defraction of the RF by the rain droplets. These, and other KNOWN, physical elements all play a part in Maximum Detection Distance of a target in Marine Radar Systems. Me one who deals with this stuff every day...... Rodney Myrvaagnes J36 Gjo/a Does one child rape really change Strom Thurmond's lifetime record? For better or worse? |
Jeff Morris wrote in
: I've had minor second thoughts on this after checking the specs. In the "old days" more powerful domes were heavier and used more power - that is not the case now - the 4kW Raymarine dome only weighs a few pounds more and uses 1 or 2 Watts more juice. Pot metal and plastic is much lighter, which is what the Raymarine is made from. They'll replace it when the pot metal consumes itself from the condensation of breathing in and out through the drain tube makes it rain inside the dome, though. We're on our third...(sigh) The communications on the RL70CRC also failed, which explains why we couldn't get the Seatalk Gyro/Compass to ever calibrate properly, no matter how many times we turned it slowly. They fixed that, too, but I don't think it was ever working right in the first place. Isn't it amazing how 2,000 watts of peak RF power just appears from thin air for only 1-2 watts more DC? Magic? Divine intervention? Maybe its the printer stepper motor that turns the rubber band that drives the PC board antenna array...?? I'm still not sure of the value for long distance viewing, but the high power dome will have finer resolution, so that a pair of channel buoys will be resolved as two targets further away with the more powerful unit. Navigation is easier, since coastlines will more closely resemble the chart. However, this takes a lot of practice and you're better off relying on a good gps. Ah, but you have another problem in the fog. The higher the antenna, the further away the target will disappear as the target approaches the boat! You won't see the bouy 8 miles away with the antenna down low, but you WILL see the bouy in the fog a LOT closer to the boat as you, hopefully, pass it. Traveling at Mach 1, I'd understand having more range. But, traveling at 6 knots I'd rather see that target two boatlengths off the port bow with a lower-down antenna....wouldn't you? The downsides of the large unit is almost double the cost (a $1000 premium on the RayMarine list) and a much larger dome (an issue for those trying to hide the dome from the jib). I'm tired of changing out pot metal Raymarine antenna pods. There's gotta be a way to build a $2000 radar transceiver that isn't made out of the same materials as the window winder in a '97 Ford pickup. The damned chassis it's all mounted in is made of ZINC!! Idiots.... Look inside for yourselves! Don't trust me. Unscrew the 4 little flathead screws and take the top of the dome off. Do it on that boat down the dock and see if it's wet inside! Furuno? Anyone had water destroy a Furuno radar dome?? |
rhys wrote in
: Agreed, and I know what you are getting at. But if seas are flat, wind is calm, and you are on a misty seaway at dusk/dawn motoring at five knots under autopilot, I can see where a trawler or small frieghter doing the same on a reciprocal course would be nearly invisible to you simply due to the fact that your radar's proximity alarm or "range guard" or whatever they call it would not go off until the ship on the collision course was on top of you...solely due to the mizzen placement. If the radar antenna were a point source of RF out and back, this might be true. But, it's not a flashlight. The flat panel PC board planar array of the 2KW Raymarine dome is about 2' wide. The whole panel radiates and receives RF, so it's like having a set of "eyes" on the mizzen that are 2' apart. Could you see around the mainmast to all targets, the mainmast being 20' away from you with this "eye" arrangement? Yes, it works, even on small bouys 3 miles away. I've swung the boat through each degree very slowly to see if the bouy I could see off to the side had a blind spot dead ahead. It didn't. The panel isn't a point source like a flashlight. It's more like a 2' diameter floodlight shining past the mast, illuminating the target dead ahead, but probably with some loss of efficiency. |
rhys wrote in
: Now, if I can just figure out how to put a windvane AND davits behind a mizzen mast....G R. B&G Pilot has "wind mode" to track the wind with the autopilot. Works great in that mode, too. No cure for the davits if your mizzen boom is too low..... |
"Larry W4CSC" wrote in message Ah, but you have another problem in the fog. The higher the antenna, the further away the target will disappear as the target approaches the boat! You won't see the bouy 8 miles away with the antenna down low, but you WILL see the bouy in the fog a LOT closer to the boat as you, hopefully, pass it. Traveling at Mach 1, I'd understand having more range. But, traveling at 6 knots I'd rather see that target two boatlengths off the port bow with a lower-down antenna....wouldn't you? I have to wonder how serious a problem this really is. For instance, if I can run between two buoys spaced 300' with a scanner that's over 100' in the air and watch them pass down my side, how much difference can there be with a small boat and a scanner placed 30' up, unless you are totally crowding the buoy to one side (not good). Also, by that point, if you lose sight of the buoy, you should have all ready changed your concentration to some new point or reference, ahead. otn |
On Tue, 15 Feb 2005 04:44:49 GMT, Larry W4CSC wrote:
Furuno? Anyone had water destroy a Furuno radar dome?? OK, crap construction drives me nuts, particularly when it's something (like a radar) which MUST spend its working life out in the elements. Assuming the radar itself isn't absolute crap...like that "Mars Bar" radar the Brits made 25 years ago, say...what is *your* radar of choice for durability? 'Cause once I go up the mast, I don't want anything short of a hurricane to cause damage to that radome... My buddy swears by his old Kodan CRT unit, but he's got a big ketch and more room and power than most people to play with. The thing is a toaster-sized box bolted to his coaming, and it takes skill to use it, but if you can learn that skill, it's accurate as hell. R. |
On Mon, 14 Feb 2005 14:38:03 -0500, Jeff Morris
wrote: Does that sum it up? Yup. After sailing a sistership with the radar mounted high on the mast, I mounted mine below the baby stay, and never regretted it. Good. Thanks. One day I hope to use this information wisely. Reason I'm asking is that steel ketches look good to me on a number of levels. Now, if I can just figure out how to put a windvane AND davits behind a mizzen mast....G The windvane should go high on the mizzen, as on my friends boat: http://www.sv-loki.com/Moonshadow/Pg22.jpg Note that the davits are behind, and also serve as a good place for solar panels. Agreed, but I didn't mean windvane as in wind generator, but as in "mechanical self-steering" like this: http://www.voyagerwindvanes.com/ I can't determine how THAT would work on a ketch, with or without davits. R. |
On Mon, 14 Feb 2005 21:07:37 GMT, Dan Best
wrote: I dissagree. The antenna that the energy is radiating off of is much wider than the mast, so while some of the energy is reflected and scattered, most of it just flows right on past. The reverse happens with the reflected energy. As a result, the targets are weaker, but should still be there. If this were not the case, then whenever you had a mast mounted radar, everything in a fairly wide cone behind you would be invisible and this is obviously not the case. Thanks to you and Otnmbrd for these answers. On a related topic, make sure that you mount the display where it can be seen by the helmsman. A friend of mine has it mounted where it can only be seen at the nav station and having played radar officer calling up instructions to the helm on a foggy night in SF Bay while dodging freighters, I'm here to say that that's not how you want to set it up. It would tend to "compound errors", certainly. I've installed something on my current boat, however, that I haven't seen before. I got a gooseneck armature from an old draftsman's flourescent light and clamped it so that it swings into the companionway. It can be lashed in position with shock cord, if needed, but usually the friction knobs do the trick. On the armature I've secured a handheld GPS on "ship's power" (a 12 V cigarette lighter style adapter). This means I can reference the GPS quickly without using my hands, and without it being loose in the cockpit, without eating batteries (they go through AAs in 2-3 hours of continuous use), without losing "satellite lock" (because they are on all the time and in the companionway can "see" enough sky). Other advantages are (mostly) out of the weather (a ziplock bag will do the trick here as well). Of course, I have a tiller, which means I am standing most of the time by the companionway near the winches and aft of the traveller on the cabin-top. I wonder, however, if my "armature idea" would be useful for any similar devices, as opposed to a "hard-mount" at the wheel? If, for instance, you had a 15" LCD panel and a wireless mouse, the panel could be some distance away and still be readable. R. |
On Tue, 15 Feb 2005 04:54:14 GMT, Larry W4CSC wrote:
It's more like a 2' diameter floodlight shining past the mast, illuminating the target dead ahead, but probably with some loss of efficiency. Thanks, Larry. I understand this now. R. |
rhys wrote:
It would tend to "compound errors", certainly. I've installed something on my current boat, however, that I haven't seen before. I got a gooseneck armature from an old draftsman's flourescent light and clamped it so that it swings into the companionway. It can be lashed in position with shock cord, if needed, but usually the friction knobs do the trick. I've seen this type of mount on many boats, though not using the draftsman's armature. I think the catalogs have brackets intended to swing out in the companionway. On the armature I've secured a handheld GPS on "ship's power" (a 12 V cigarette lighter style adapter). This means I can reference the GPS quickly without using my hands, and without it being loose in the cockpit, without eating batteries (they go through AAs in 2-3 hours of continuous use), without losing "satellite lock" (because they are on all the time and in the companionway can "see" enough sky). Other advantages are (mostly) out of the weather (a ziplock bag will do the trick here as well). Of course, I have a tiller, which means I am standing most of the time by the companionway near the winches and aft of the traveller on the cabin-top. I wonder, however, if my "armature idea" would be useful for any similar devices, as opposed to a "hard-mount" at the wheel? If, for instance, you had a 15" LCD panel and a wireless mouse, the panel could be some distance away and still be readable. My current boat, being a catamaran, has a powerboat-like helm station with the radar mounted on a swinging arm to the side. My previous boat, had a clever idea that might be of use to some - A hatch was mounted in the bulkhead in the forward end of the cockpit, and the radar (a large crt) was mounted on a shelf inside. Its a nice solution for a display that is too large to mount on an arm. However, once you get used to have the controls at the helm, its hard to see how you can properly use a radar that isn't nearby. |
On Tue, 15 Feb 2005 04:44:49 GMT, Larry W4CSC wrote:
Isn't it amazing how 2,000 watts of peak RF power just appears from thin air for only 1-2 watts more DC? Magic? Divine intervention? Maybe its the printer stepper motor that turns the rubber band that drives the PC board antenna array...?? Not sure about the merits of this beef. A radar with a pulse repetition period of 1 millisecond, and a pulse width of 1 microsecond has a peak power about a thousand times greater than its mean power - and this is a standard feature of pulse radars.... Brian Whatcott Altus OK |
In article ,
rhys wrote: On Tue, 15 Feb 2005 04:44:49 GMT, Larry W4CSC wrote: Furuno? Anyone had water destroy a Furuno radar dome?? OK, crap construction drives me nuts, particularly when it's something (like a radar) which MUST spend its working life out in the elements. Assuming the radar itself isn't absolute crap...like that "Mars Bar" radar the Brits made 25 years ago, say...what is *your* radar of choice for durability? 'Cause once I go up the mast, I don't want anything short of a hurricane to cause damage to that radome... My buddy swears by his old Kodan CRT unit, but he's got a big ketch and more room and power than most people to play with. The thing is a toaster-sized box bolted to his coaming, and it takes skill to use it, but if you can learn that skill, it's accurate as hell. R. Give me a Furuno, over any other third and fourth generation Radar OEM and a Decca over any second generation Radar. First generation radars were all crap, and the fifth generation is just now coming out, so no one knows yet who has the best stuff....... Bruce in alaska -- add a 2 before @ |
In article . net,
"otnmbrd" wrote: I have to wonder how serious a problem this really is. For instance, if I can run between two buoys spaced 300' with a scanner that's over 100' in the air and watch them pass down my side, how much difference can there be with a small boat and a scanner placed 30' up, unless you are totally crowding the buoy to one side (not good). Also, by that point, if you lose sight of the buoy, you should have all ready changed your concentration to some new point or reference, ahead. otn OTN, the Horozontal Beamwidth of your Commercial Maritime Radar is significantly smaller than that of the units found on most Pleasure type vessels. That makes a HUGH difference in the Target Discrimination Ability between the two radars. Apples and Oranges, here....... Bruced in alaska -- add a 2 before @ |
I have two singout arms in my hatchway. The raday display is on one and
a gps/fish finder is on the other. Unfortunately, there just wasn't quite enough room to attach both devices to just one arm, my hatch just isn't tall enough to have them one above the other. When both are deployed so the helmsman can see them, it's a little inconvienient since to in or out of the hatch, you have to either carefully step over them or swing one of them out of the way. In reality, this is not a big deal since the radar is only rarely used (but when we do use it, we are REALLY glad we have it). Fair winds - Dan Best rhys wrote: It would tend to "compound errors", certainly. I've installed something on my current boat, however, that I haven't seen before. I got a gooseneck armature from an old draftsman's flourescent light and clamped it so that it swings into the companionway. It can be lashed in position with shock cord, if needed, but usually the friction knobs do the trick. On the armature I've secured a handheld GPS on "ship's power" (a 12 V cigarette lighter style adapter). This means I can reference the GPS quickly without using my hands, and without it being loose in the cockpit, without eating batteries (they go through AAs in 2-3 hours of continuous use), without losing "satellite lock" (because they are on all the time and in the companionway can "see" enough sky). Other advantages are (mostly) out of the weather (a ziplock bag will do the trick here as well). Of course, I have a tiller, which means I am standing most of the time by the companionway near the winches and aft of the traveller on the cabin-top. I wonder, however, if my "armature idea" would be useful for any similar devices, as opposed to a "hard-mount" at the wheel? If, for instance, you had a 15" LCD panel and a wireless mouse, the panel could be some distance away and still be readable. R. |
In article ,
renewontime dot com wrote: The metal mast and rigging may not obscure your radar display (an empty "shadow area"), but some of that energy will be bounced right back and can either cause interference or even damage to your radar's receiver. All the more reason not to use a 4 kw system. Nope, not even close to being true. The radar receiver has a Range Gate built into the frontend that does not enable the receiver to see anything untill after the transmitted pulse has long since left the antenna. The Range Gate timing is what sets the Minimum Radar Range of the radar and is usually set so that the minimum range is on the order of 50 or 75 yards. Any reflected Transmitter Pulse will have long since traveled out to the mast or reflective surface aboard the same vessel and returned long before the Range Gate opened up the receiver frontend, looking for a return signal. Your thinking of the Second Generation Radars with RadioActive TR Cells, that when hear the end of their useful life just opened up and allowed the Transmitter Pulse to reach the Microwave Diode Crystals, and destroy them. All third generation and later radars, use a different Range Gate System, and are not subject to this type of problem. Any return signal from farther than 75 yards will be so attenuated in power density, that it can't hurt the receiver frontend. Inverse Square Law prevails in the RF World. Now the above is all well and good, but does not take in to account that when rafted up to another vessel which is operating it's Radar and your radar is operating as well, and the two antenna's point exactly at each other for a few cycles of their transmitters, that damage couldn't happen to the recivers from the others transmitter. the probubility of this is low, but still significant. Never allow a rafted vessel to operate a radar, when your antenna is pointed toward theirs. Bruce in alaska -- add a 2 before @ |
In article ,
Jeff Morris wrote: renewontime dot com wrote: Thanks for the clarifications, guys. So, to sum up, if you have a mizzen, it's a great spot for a radar with little downside unless you think you need the height of the mainmast, but then you may foul an overlapping genoa. Does that sum it up? Just remember that a radar sends out radio waves, and any metal in front of it will cause part of your radar signal to be bounced back to your radar. The metal mast and rigging may not obscure your radar display (an empty "shadow area"), but some of that energy will be bounced right back and can either cause interference or even damage to your radar's receiver. All the more reason not to use a 4 kw system. What??? Are you claiming its dangerous to mount a radar on the mast? Actually, most masts will reflect the energy away. RayMarine advises to put a block of wood between the mast and dome if there's interference on the screen, but I've had several (including a large Nonsuch mast) and never seen a problem. I don't see how there would be a problem with the main mast interfering with a mizzen mounted dome. Naw, don't worry about such stuff, it is not factual information anyway. Read Meinhert, and Bruce in alaska's posts for the FACTS....... Me |
"Bruce in Alaska" wrote in message news: OTN, the Horozontal Beamwidth of your Commercial Maritime Radar is significantly smaller than that of the units found on most Pleasure type vessels. That makes a HUGH difference in the Target Discrimination Ability between the two radars. Apples and Oranges, here....... Bruced in alaska This I understand. However, and here I need to be careful to note that my comments are not technical, rather, practical experience based, dating back to Decca 101's and KH 17's , on multiple size/type vessels ...... I've rarely experienced a serious problem with close aboard, lost targets that would negatively impact the navigational procedure I was using, including docking. Admittedly, some units were better than others, either due to the basic unit and/or it's condition and you needed to adjust some procedures, but, my point is that you don't want to consider a radar's use "drop dead useless" below a certain range, based on pure technical data, without first checking your particular unit under real conditions to see if they apply or are indeed a problem. MOFWIW otn |
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