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Old 26-08-2013, 20:43   #1
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Radar dome location??

In the next months I will install a Radar antenna in my boat, and I found two opinions, people who say that in the mast is better and others who say that in the stern arc is better..

So, I am not sure what to do..if you have some opininions are welcome !!

Thank you
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Old 26-08-2013, 20:59   #2
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Re: Radar dome location??

When I bought my boat, I found the radar mounted to a pole on the stern rail.

I hope to get a new one and mount it half way up the mast for larger view.
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Old 27-08-2013, 20:02   #3
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Re: Radar dome location??

I have mine moubted on the arch and typically pickup vessels 24-48 miles away.
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Old 27-08-2013, 20:19   #4
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Re: Radar dome location??

Sure it is non-Ionizing radiation, but I myself would prefer to have the Antenna as far from myself as possible. Also the higher elevation may give a few extra feet of range and a little bit less surface return closer in.

In reality it probably makes little difference as a lot of the effects of lower elevation are probably taken care of by the electronics of the radar.
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Old 27-08-2013, 20:50   #5
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Re: Radar dome location??

I'd mount it ON the mast rather than IN the mast.....
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Old 27-08-2013, 22:08   #6
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Re: Radar dome location??

It's a little hard if ya have a sloop or a cutter, if mounted on the mast some interfernce may accure between a large Genny and the radar mount, if this is not a problem then the mast is the way to go ! if your lucky enough to have ketch(lol) then the mizzen mast is the place. Ive really never cared for pole mounted radars, never had a problem, just looks feeble to me ! raised from a arch is good is ya have the room! But Ive always gone for a mast mount just for the extra hight and some extra range ! Just my 2 cents
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Old 28-08-2013, 05:14   #7
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Re: Radar dome location??

Ive had it both ways , pole and on mast. I found the pole mounting tended to cause more sea clutter and in bad weather, wave action interfered with acquisition .

As a result I prefer the higher mast mounting option

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Old 28-08-2013, 05:24   #8
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Re: Radar dome location??

The benefit to the arch is that you can put other stuff up there too.
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Old 28-08-2013, 05:29   #9
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Re: Radar dome location??

I have mine on the mast with a waltz self leveler. works well. they also offer a pole/arch mount and a backstay mount. The backstay mount is very popular.
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Old 28-08-2013, 05:38   #10
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Re: Radar dome location??

I just mounted mine on the mast last weekend and it was all pretty easy, much easier than buying a mount for the stern etc but if you already have a spot then would possibly be easier.

A few things to note that caught me out:

Although the new cables are you beaut and thinner - the bloody plugs are still large so you still have to drill larger holes in mast and through out your boat to route the cable.

I bought a basic scan strut mount which was over $500 which is almost a 1/4 the price of the radar.

other than that they are really easy. I prefer mount on the mast as it gives you a lot more flexibility with height etc.
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Old 28-08-2013, 06:47   #11
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Re: Radar dome location??

Quote:
Originally Posted by Mattyb View Post
...
A few things to note that caught me out:

Although the new cables are you beaut and thinner - the bloody plugs are still large so you still have to drill larger holes in mast and through out your boat to route the cable...
This is brand dependent. The Garmin radar cable is a simple 4 pair shielded cat 5 cable. it can easily be cut and fed through very small holes(1/2" with grommet) with a new connector crimped back on.

I have had backstay and mast mount. I prefer the mast mount. My boat is a cutter and the radome does not interfere with the staysail.
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Old 28-08-2013, 17:10   #12
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Re: Radar dome location??

Danny,
First off, learning how-to use the radar, and specifically how-to use it properly / optimally is going to be MUCH more important to almost all sailors/cruisers, than where the radar scanner is mounted....
But, since yo didn't ask about that, here are the answers to your actual questions...


In general a "mast mounted" radar scanner/radome is usually better....
There are reasons for this that are not opinion, but are factual and based on both physics/math, as well as real-world experience...

a) "mast mounted" radar scanners are more likely than "arch-mounted" / "stern-pole-mounted", to detect targets when in heavy seas....i.e. less likely to have their antenna beam blocked by wave tops than the "arch mounted" or 'stern-pole-mounted" scanners....
Simply because of their respective heights....

The "mast mounted" scanners are typically 20' - 30' above the waterline (mine is about 25' off the water), and "arch-mounted" / "stern-pole-mounted" scanners are typically only about 10' - 12' off the water, at most...
I personally sail in sea heights that would blanket the radar beam, if my radar was mounted much lower (say at the typical "arch" or "stern-pole" mounted heights of 10' - 12').....

This is a provable fact.....

Here are a couple photos showing my 24" / 4KW Raymarine radome mounted on the mast (approx. 25' above the water), and comparing to where it would be at if it were arch-mounted / stern-pole mounted (approx. height where my solar panels are)....









Higher res copies here:
4700105
4711201
4700403




b) "mast-mounted" radar scanners suffer little, if any, blanking from the stern (due to the mast), as some mention as a "negative" of mast-mounted scanners...
(not to mention, that with the normal "yawing" of our sailboats as they sail along, there is almost never going to be a target that is directly astern for more than a few scans...)



c) the increased scanner height (of "mast-mounted radars) can provide some advantage in target acquisition, especially when looking for smaller targets that are either low to the water and/or when in heavy seas....
But, do NOT believe that moving a radar scanner from 10' - 12' high to 25' high is going to significantly increase your radar's maximum range, as this is almost always going to be determined by the height (and size) of the target that you are trying to acquire/track!!!

Understand that looking for bouys or small channel markers isn't usually done from a dozen miles out, having your radar scanner up high enough to see these smaller targets (such as small boats, etc.) from more than 3 to 4 miles away is a good benefit from typical mast mounted radar scanners....



d) Typically lower mounted radar scanners (such as arch or pole mounted) suffer more close-in sea clutter problems when in bad weather / confused seas / etc., than those of higher mounted radar scanners....



e) If you elect to install an arch (not my idea of aesthetically pleasing, and not something I'd choose), mounting a radar scanner on it will shade/shadow any solar panels that you install on the arch....
And, since a large un-shaded solar array is usually the primary reason that some decide to install an arch, placing their radar on the arch is a VERY big mistake (although, unfortunately it is one that you see done often!!!)



f) Some boats that have poor stability or are just too "tender" for their owner's desire, might find that having additional weight aloft such as a radar scanner mounted up too high on a mast, etc. can add to stability issues / comfort issues....
BUT...
But, this is an unusual scenario, and in my opinion if your boat is so effected by such a small change in weight aloft, it is a questionable design vessel overall....

So, most sailors will find that a mast-mounted radar scanner to be better....



~~~~~

On a side note....
Radar range / radar horizon is just slightly beyond visual line-of-sight....
And understand that the maximum radar detection range, varies depending on the height of the antenna, the height of the target above the sea, the size, shape and material of the target, and the atmospheric conditions.

In order to dispel the myths of "maximum radar range"....
---- Here in the US ("British units" / non-metric country) we use "feet" and "statute miles" and a good rule-of-thumb....

Radar horizon (in statute miles) = The sq rt of double the height of the radar scanner (in feet).....

Ex #1: 10' high x 2 = 20.... sq rt of 20 = 4.5 stat miles (approx.
4 nm)

Ex #2: 12' high x 2 = 24.... sq rt of 24 = 4.9 stat miles (approx. 4.3nm)

Ex #3: 25' high x 2 = 50.... sq rt of 50 = 7.1 stat miles (approx.
6.25 nm)

Ex #4: 50' high x 2 = 100.... sq rt of 100 = 10 stat miles (approx. 8.8 nm)

Ex #5: 75' high x 2 = 150.... sq rt of 150 = 12.2 stat miles (approx.
10.7nm)

Ex #6: 100' high x 2 = 200.... sq rt of 200 = 14.1 stat miles (approx.
12.4 nm)

Ex #7: 125' high x 2 = 250.... sq rt of 250 = 15.8 stat miles (approx.
13.9nm)

Ex #8: 150' high x 2 = 300.... sq rt of 300 = 17.3 stat miles (approx.
15.2nm)

Ex #9: 175' high x 2 = 350.... sq ft of 350 = 18.7 stat miles (approx.
16.5nm)

Ex #10: 200' high x 2 = 400.... sq rt of 400 = 20 stat miles (approx.
17.6nm)


You simply add your vessel's radar horizon (based on how high your radar is mounted) to the "radar horizon" of the target, based on its "radar cross section" (typically its hull, shipping containers, biggest flat spots, etc.) height above the water (or the height of the "radar reflector"), to determine how far away you'll be able to "see" / acquire / track this target....



In order to dispel the myths of "maximum radar range"....
Typically in order to actually "see" to the maximum range spec'd on your radar, you'd need to be looking at either tall hills / cliffs / mountains, or rain clouds / precipitation....
A "36nm range radar" minus the 4nm to 6nm radar horizon of the typical cruising boat radar scanner, equals 30 - 32nm of distance to cover....which means the target height needs to be at least 600' to 665' high...and for a "48nm range radar", the targets would need to be 1150' to 1250' high....

Even the Queen Mary 2 (which is 200' high, to the tip of the funnel) isn't likely to be acquired / tracked until within 20 - 22 miles, at best....
Reports from sailors/cruisers who state that they regularly/typically track ships on radar from further than 24nm away, should be taken with grains of salt.....(AIS targets, yes....radar targets, no...)


BTW, if you want the exact "maximum radar range" using metric numbers (rather than my non-metric rule-of-thumb), here it is...
From the Furuno Radar manual:
Quote:
The radar horizon is longer than the optical one by approximately 6% because of the diffraction property of the radar signal. The Rmax is shown in the following formula.

Rmax = 2.2 x (sq rt h1 + sq rt h2)

where R max: radar horizon (nautical miles)
h1: antenna height (m)
h2: target height (m)


If the height of the antenna is 9 m and the height of the target is 16 m, the maximum radar range is;

R
max = 2.2 x (sq rt 9 + sq rt 16) = 2.2 x (3 + 4) = 15.4 nm


Note:
The detection range is reduced by precipitation (which absorbs the radar signal).
Comparing my "rule-of-thumb" to Furuno's metric calculations shows pretty close figures....

At 9m, approx. 30'....
Ex #11: 30' high x 2 = 60.... sq rt of 60 = 7.75 stat miles (approx. 6.8nm)

At 16m, approx. 51'....
Ex #12: 51' high x 2 = 104.... sq rt of 102 = 10.1 stat miles (approx. 8.8nm)

6.8 + 8.8 = 15.6nm (vs. 15.4nm from Furuno)


Danny, I do hope this helps.....but doesn't complicate things for you!!!

Fair winds...

John
s/v Annie Laurie
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Old 28-08-2013, 17:29   #13
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Re: Radar dome location??

Quote:
Originally Posted by ka4wja View Post
Danny,
First off, learning how-to use the radar, and specifically how-to use it properly / optimally is going to be MUCH more important to almost all sailors/cruisers, than where the radar scanner is mounted....
But, since yo didn't ask about that, here are the answers to your actual questions...


In general a "mast mounted" radar scanner/radome is usually better....
There are reasons for this that are not opinion, but are factual and based on both physics/math, as well as real-world experience...

a) "mast mounted" radar scanners are more likely than "arch-mounted" / "stern-pole-mounted", to detect targets when in heavy seas....i.e. less likely to have their antenna beam blocked by wave tops than the "arch mounted" or 'stern-pole-mounted" scanners....
Simply because of their respective heights....

The "mast mounted" scanners are typically 20' - 30' above the waterline (mine is about 25' off the water), and "arch-mounted" / "stern-pole-mounted" scanners are typically only about 10' - 12' off the water, at most...
I personally sail in sea heights that would blanket the radar beam, if my radar was mounted much lower (say at the typical "arch" or "stern-pole" mounted heights of 10' - 12').....



Danny, I do hope this helps.....but doesn't complicate things for you!!!



Fair winds...




John


s/v Annie Laurie

My radar is stern pole mounted and about 10' above the water. The reaons you mention is why I'm looking at remounting to halfway up the mast and that should give me about 20' above the water. Maybe then I could use the stern pole to mount something else.
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Old 24-09-2013, 19:18   #14
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Re: Radar dome location??

Excellent, really thank you very much , very clear..Nice Pics too..
D.
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Old 24-09-2013, 19:39   #15
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I built an "H" beam on my stern. Wind genny pole supported on one riser, radar mounted on the other riser and adjustable brackets for solar on the cross beam.

Supports the hard dink on occasion and everything is easy to get to.

It took me awhile before deciding to go that route. Works very well and sturdy as a rock.
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