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Old 01-12-2012, 10:33 AM   #21
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RE: Locating one's radar antenna

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Marin wrote:markpierce wrote:Marin wrote:
Conversely, the higher a radar antenna is mounted the less it will see items close to the boat.**
*My antenna is maybe 24 feet above the water, and it shows close objects in the immediate area, such as boats on the opposite side of the pier.

The issue isn't the distance to the target, it's the height and size of the target.* A radar beam*fans out both in width and depth from the antenna.* Close to the antenna it is narrower and not very "thick."* Even so, next-door boats are easy because they are as large as yours*if not more so.* Great big target that sticks up quite a ways above the water.

*But*a lot of the berths are empty (note earlier picture)*and the radar shows the piers.* The only significant "blank" spaces is the water.
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Old 01-12-2012, 11:27 AM   #22
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RE: Locating one's radar antenna

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*But*a lot of the berths are empty (note earlier picture)*and the radar shows the piers.* The only significant "blank" spaces is the water.

*If it didn't I would say you had a really crappy radar.* Anything that sticks up with any significance will be seen.* Throw a crab pot float into the water about 30 feet from your boat and see if your radar sees that.* That's what I'm talking about.
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Old 01-12-2012, 01:23 PM   #23
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RE: Locating one's radar antenna

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markpierce wrote:Marin wrote:
Conversely, the higher a radar antenna is mounted the less it will see items close to the boat.**
*My antenna is maybe 24 feet above the water, and it shows close objects in the immediate area, such as boats on the opposite side of the pier.

*You sure it's safe? Looks like it has desolved a lot of the other boats in your marina.
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Old 01-12-2012, 01:43 PM   #24
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RE: Locating one's radar antenna

Where ever you mount your radar the man say's use it.

It will last longer.

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Old 01-13-2012, 12:32 AM   #25
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RE: Locating one's radar antenna

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GonzoF1 wrote:*
*You sure it's safe? Looks like it has desolved a lot of the other boats in your marina.
*I sent them to Mexico.
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Old 01-13-2012, 12:42 AM   #26
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RE: Locating one's radar antenna

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Marin wrote:markpierce wrote:
*But*a lot of the berths are empty (note earlier picture)*and the radar shows the piers.* The only significant "blank" spaces is the water.

*If it didn't I would say you had a really crappy radar.* Anything that sticks up with any significance will be seen.* Throw a crab pot float into the water about 30 feet from your boat and see if your radar sees that.* That's what I'm talking about.

Think it all depends on the float. Doubt any recreational-boat radar will pick up an empty bleach-bottle float, for instance. *I never had expectation of seeing on radar any marker for a crab/lobster pot marker. Why don't crab/lobster men have floats with a radar reflector at least three feet above their floats? (Because they don't want anyone to know where their traps are?)
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Old 01-13-2012, 01:07 AM   #27
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Locating one's radar antenna

Most of the commercial crab pot floats I've seen have a big metal fender washer on the line next to the float. That would help with the radar return assuming one's radar beam swept that low. But we've gotten returns in calm water from floats with no washers on them. We get returns from birds on the water, too.

The floats are solid foam with a hole drilled up the middle for the line that goes down to the crab trap. I don't know if we'd get a return from an empty plastic jug. Bu those are illegal for use as pot floats, at least in this state (don't know about BC).

But the point is that the higher one's antenna is, the farther away from the boat the transmission beam will travel before it hits the water. That's the one advantage of a lower antenna-- the sweep will hit the water closer in so one will see the small stuff closer to the boat. This can be handy when one is picking one's way through a field of commercial floats. If one doesn't boat where this kind of crabbing, shrimping, etc. occurs, it's not any advantage.

I suspect that the commercial fishermen don't use poles or anything on their floats because it would make them very hard to retrieve with the fast spinning pot pullers they use. And the poles would get in the way on the boat*and generally be a pain in the ass. The lobster fishermen we watched and talked to on Prince Edward Island use the same basic type of float that the crabbers use out here.

The net fishermen--- and the lobstermen that lay out a long row of pots connected*by the same line that lies on the bottom--- have to have a a*pole on the float that supports each end of the net or pot line*with a radar reflector on it. And I think a light, too.


-- Edited by Marin on Friday 13th of January 2012 02:11:35 AM
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Old 01-13-2012, 01:33 AM   #28
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RE: Locating one's radar antenna

Thanks for the info, Marin.* Seen crabpots on*dock and on boats only.* On the TV program "Lobstermen," I always wonder why trawlers keep pciking up the lobster pots.* Either there is a "war" out there or the radar reflectors are ineffective?
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Old 01-13-2012, 08:40 AM   #29
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RE: Locating one's radar antenna

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Most of the commercial crab pot floats I've seen have a big metal fender washer on the line next to the float. That would help with the radar return assuming one's radar beam swept that low. But we've gotten returns in calm water from floats with no washers on them. We get returns from birds on the water, too.

The floats are solid foam with a hole drilled up the middle for the line that goes down to the crab trap. I don't know if we'd get a return from an empty plastic jug. Bu those are illegal for use as pot floats, at least in this state (don't know about BC).

But the point is that the higher one's antenna is, the farther away from the boat the transmission beam will travel before it hits the water. That's the one advantage of a lower antenna-- the sweep will hit the water closer in so one will see the small stuff closer to the boat. This can be handy when one is picking one's way through a field of commercial floats. If one doesn't boat where this kind of crabbing, shrimping, etc. occurs, it's not any advantage.

I suspect that the commercial fishermen don't use poles or anything on their floats because it would make them very hard to retrieve with the fast spinning pot pullers they use. And the poles would get in the way on the boat*and generally be a pain in the ass. The lobster fishermen we watched and talked to on Prince Edward Island use the same basic type of float that the crabbers use out here.

The net fishermen--- and the lobstermen that lay out a long row of pots connected*by the same line that lies on the bottom--- have to have a a*pole on the float that supports each end of the net or pot line*with a radar reflector on it. And I think a light, too.



-- Edited by Marin on Friday 13th of January 2012 02:11:35 AM
*I have thought about adding the broadband radar for the sole purpose of spotting crab pots and debris.* Now that the reviews of the 4G stuff is saying that the long distance performance is good, I would feel no need to have both or worry about it.

My new to me boat has very servicable equipment.* The inner geek in me wants the latest and greatest.
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Old 01-13-2012, 09:25 AM   #30
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RE: Locating one's radar antenna

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markpierce wrote:
I always wonder why trawlers keep pciking up the lobster pots.* Either there is a "war" out there or the radar reflectors are ineffective?
*Around my neck of the water, Long Island Sound, the current will often drag the float under water. Get a long piece of seaweed or some growth on the line and it goes under even farther. Waves, sun relfection, etc sometimes hide what is visible. Even a careful boater can run over one of the trap lines and snag it with their prop or rudder. (That is why I have a line cutter)

*

*

*
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Old 01-13-2012, 10:08 AM   #31
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RE: Locating one's radar antenna

I wouldn't worry too much about the little stuff on the water. Use your radar to find and avoid big stuff, that is, anything big enough to damage your prop or shaft, should you hit it. My bow will push little stuff outboard enough to miss the running gear. You should experiment with little stuff, to see how big it has to be before there is any danger that it will actually hit your running gear.

Also, radar dialed in to the closest range, if you are trying to see deadheads close aboard, in say a night crossing of any body of water, will miss everything that is just off screen, including that big fishboat that is closing at 25 knots (combined speeds) and not watching for you. (those fishboats are not required to have AIS until they reach the legislated minimum size, so your only sure way to avoid them is to find them before they find you)

Your Radar is of much greater value set on a 3 mile range than a 1/4 mile range. On anything outside of the 1/4 mile range, the circle of noise surrounding the transmitter, and the area of unswept water close to the boat, roughly the same size, are insignificant.

If you are trying to avoid the crab floats, in say Ganges Harbour, you will see them on 1/2 mile range, you will see them better on 1/4 mile range, and you will always see them long before they enter the circle of noise/unswept area close to the boat. Also, the commercial crabbers here always use sinking line and never use big fender washers or anything that would help radar visibility. They sometimes even use two gallon plastic jugs, ( I am looking at one right now) or anything that will float. The regulations here require them to be identified with the crabber's license numbers but don't prohibit any old cheap floating object from being used.
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Old 01-13-2012, 11:22 AM   #32
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RE: Locating one's radar antenna

I had a Californian 42LRC on which the PO had put the radar directly in front of the fly bridge such that it was waist high if you were seated at the helm. Everyone I talked to said no problem but it took me about 30 seconds to have someone move it to the mast.
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Old 01-13-2012, 11:40 AM   #33
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RE: Locating one's radar antenna

We upgraded from 2.2 KW to 4 KW radar last year after being advised (from a number of sources) that it will make a world of difference in the detail we would see, particularly close in. I would have to say that the difference is huge. Don't know about crab/prawn trap floats, but small jetsam & flotsam stuff shows up well - as does our wake at 7.5 knots.

Not taking any health chances, we installed a 7' aluminum mast at the aft end of our bridgedeck, which is about 10' back from the helm seat. Our previous 2.2 KW unit had a 4' mast but also*presumably less radiation.*We calculated the required height by using my 6'4" son in law standing at the helm seat as the reference. Since the verticle beam of the radar is 20 degrees, a 10 degree slope down from the radar unit would just skim over his head. (We had also taken into account the extra height gained by the antenna apparatus itself.) Plus, all indications are that the risk is neglible at 10', but who wants to*chance having grandchildren*with unusual characteristics?

Since I always prefer to run the boat from the upper helm I can now always have the radar on, and if we ever do any night running I would definitely only do it from the upper helm with the radar on.
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Old 01-13-2012, 12:03 PM   #34
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RE: Locating one's radar antenna

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markpierce wrote:
On the TV program "Lobstermen," I always wonder why trawlers keep pciking up the lobster pots.* Either there is a "war" out there or the radar reflectors are ineffective?
Because the lobsterpot lines are very long so the distance between the floats and reflectors is very far.* The otter doors of a trawl net plow along the bottom.* So if a trawler crosses a lobster pot line the doors will snag it and pull it along, and when the trawl net is retrieved the whole mess comes up.* The trawlermen can probably tell if their gear has snagged something and is pulling it along as the resistance will be very high and this will be reflected in the strain on their equipment and the way the trawl rig "behaves."* But by then the damage is done and all the trawlermen can do is recover their gear and clear what's left of the lobsterpot line.

Also wind and waves can conspire to break the radar refectors or their mounts, or the line can break and the float drift off.* All kinds of things happen on the ocean.
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Old 01-13-2012, 12:12 PM   #35
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RE: Locating one's radar antenna

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koliver wrote:
I wouldn't worry too much about the little stuff on the water.
*The "little stuff" can have long lines hanging from it in the case of crab or shrimp floats, and if you've ever gotton one around your prop or rudder (we*got a totally invisible-from-the surface, unattached pot line around one of our rudders once)*you will know it is indeed something to worry about.

Even sinking line doesn't guarantee anything because with the currents we can get*and depending on how long*the pot line is,*the line often goes out at quite an angle from the float.* Which is why in a crowded field of pot floats if you have to*pass them closely*it is always wise to pass them on the down-current side because the line will be slanting away on the up-current side.

The fender washers I've seen on a lot of floats are not there for radar reflection.* I dont' think the crabbers care about that.* They are used on the line between a knot and the float itself, I assume as part of the way they keep the float on the line.
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Old 01-15-2012, 07:54 PM   #36
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RE: Locating one's radar antenna

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Marin wrote:JAT wrote:
I'm sure there will be rebuttals....but in this case I would be sure to err on the side of caution.
*Yes.* Big difference between the radar units you are talking about and today's recreational boating radar units.* ATC radar puts major*interference into a* professional video camera from quite a*distance away.* Up to a mile.**That same*video camera held right next to the Furuno radome on our boat sees no interference at all.

*

I understand what you are saying....but the ATC radar I am speaking about is a truly portable unit made to set up on LZ's in combat zones. *It was not a really high powered radar in comparison with general air field radars that would probably fry a pigeon flying by.

I think though that some of the difference would be that milspec radars have a more finely tuned transmitter, and use fairly heavy duty magnetrons, which I would assume would push a much higher Kw rating, as opposed to recreational marine radars that are probably at the lower end of the power ranges. *Furunos tend to run between 1Kw and 60Kw.

My entire point is: *It would be smarter to err on the side of caution. *I knwo that during the entire 10 years I worked with the three different radars...the ground rule was "stay out of the beam" all the time.

*
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Old 01-15-2012, 08:02 PM   #37
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RE: Locating one's radar antenna

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Marin wrote:JAT wrote:
*Precisely. *The closer to the surface of the water it is mounted, the closer the effective horizon is and the shorter the range.
Conversely, the higher a radar antenna is mounted the less it will see items close to the boat.** This is the one advantage of a lower-mounted antenna like the one on our boat.* We have no need to see more than about 6-8 miles in the area we boat so a high antenna and the 36 mile rage of our radar would be of no value to us.*

But the water here*can be littered with crab pot buoys and other stuff.* In calm-ish water these things*will be painted*on our radar right up to*a boat length or*so from the bow.* Very handy when running in fog, which is usually accompanied by calm water.* In fog in areas where crab fishermen regularly work we'll run the radar at a range of 1/8 mile to spot the floats.* Many of them incorporate a big fender washer as part of their lashup so they show up on radar very well.

This is not a reason to mount a radar on the face of the flying bridge-- a mast or arch mount is better for several reasons.* But if one boats in an area with a lot of stuff in the water, particularly crab, shrimp, lobster or net floats, an antenna mounted lower rather than higher on the mast or arch can be very beneficial.



-- Edited by Marin on Wednesday 11th of January 2012 10:11:39 PM

*Your radar is, on that boat mounted about 3 or 4' lower than our on our arch.... *I think if I was concerned about items extremely close to the boat...I would place a slight wedge under the rear of the mount to tilt it slightly forward.

I am much like you...considering that we move along at the blistering speed of 7 to 7.5 kts....using the radar on 24 nm range is relatively pointless.*
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Old 01-15-2012, 08:49 PM   #38
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Locating one's radar antenna

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Conrad wrote:
...*Since the verticle beam of the radar is 20 degrees, a 10 degree slope down from the radar unit would just skim over his head. ...*
*Assuming a 10 degree slope for the bottom of the radar beam, an antenna mounted 24 feet above the water would "strike" the water about 136 feet away, while if mounted at 10 feet it would "strike" it about 64 feet away.* That's under 4 boat lengths and 2 boat lengths, respectively, for a 36-foot boat.

At 7 knots one would travel the 72-foot difference (136-64) in six seconds.* So, theoretically, one would have 6 more seconds to spot something on the water.* But then could one avoid the object within 2 boat lengths if the object was sighted at the last second?

With an antenna height of 10 feet above water level, the beam would be 8 feet high 16 feet away.* So, both eyes and brain would likely*be within the beam at the boat ends if standing on the deck.* With a 24-foot high antenna, the beam would be well overhead.

*


-- Edited by markpierce on Monday 16th of January 2012 12:46:26 PM
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Old 01-16-2012, 08:01 AM   #39
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RE: Locating one's radar antenna

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Old Stone wrote:
Jay - Trips up to Norwalk amaze me that boats aren't trapped in the lobster pot fields left and right. They are just barely visible and cover some pretty wide areas.

Don't want to get off thread TOO far here, but have you ever had to use or test your line cutter? Always been curious.
*Current one no, but previous boat (old 34 Mainship) I had spurs and they cut lines 3 times (In 14 seasons). You hear a "Thunk", look back, see buoy floating free. That quick.
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Old 01-16-2012, 11:44 AM   #40
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RE: Locating one's radar antenna

Our antenna is about nine or ten feet off the deck. The sweep is clear of anyone on deck unless, perhaps, a tall person were to stand on the end of the bow pulpit. Again, I'm not saying our antenna position is ideal. It's not for several reasons, none of which have anything to do with the transmission sweep hitting anyone on the boat (unless they are on the flying bridge). But the clarity and the size of the returns from very small targets like crab pot floats at close-in distances is very good, a "feature" that has served us well on several occasions. There is nothing special about the radar--- it's an off-the-shelf Furuno NavNet VX2. It's the lower mounting (I've been told by our electronics guy) that is helping us in this regard.
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