Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 25-08-2015, 10:48   #1
RDW
Registered User

Join Date: Dec 2009
Location: Lexington, Kentucky
Boat: Morris 1996 46' Lexington
Posts: 378
Radar Height and Range

I admit I am being lazy but I will appreciate your information.
Is the height of the radar mount a big factor? How much difference in the radar range would there be in a radar 35 feet off the water versus 15 feet?
Thanks
RDW
__________________

__________________
RDW is offline   Reply With Quote
Old 25-08-2015, 11:06   #2
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,062
Re: Radar Height and Range

There is a mathematical formula that will tell you that, based I believe on the Earth's curvature.
I was going to buy a 4G Radar and wondered about the exact same thing, I called Simrad asking that as I wanted to mount it on a Radar pole, but wouldn't if it reduced the range. Their answer is that there is no practical difference in performance based on numbers very close to what your giving, and if a pole mount was available, they preferred it largely based on any future maintenance that may be required.

Now of course for larger, much more powerful Radars, I feel that may not be the case
__________________

__________________
a64pilot is offline   Reply With Quote
Old 25-08-2015, 13:40   #3
Registered User
 
Hydra's Avatar

Join Date: May 2009
Location: Lorient, Brittany, France
Boat: Gib'Sea 302, 30' - Hydra
Posts: 1,229
Re: Radar Height and Range

The distance to the radar horizon is roughly proportional to the square root of the antenna height above sea level. Then, raising the antenna from 15 to 35 feet increases the range by 52%.

In metric units, distance to horizon in NM = 2.2*sqrt (height in m)

Alain
__________________
Hydra is offline   Reply With Quote
Old 25-08-2015, 13:42   #4
Registered User
 
Dsanduril's Avatar

Join Date: Aug 2011
Location: South Pacific
Boat: Outremer 50S
Posts: 1,451
Re: Radar Height and Range

Raymarine says essentially the same thing:

Quote:
The height of the scanner above the water is directly related to the range the scanner can see. The equation to calculate the distance to the radar horizon is 1.17 times the square root of the height of the scanner. Therefore, a scanner mounted 20 feet above the water line will be able to see about 5.2 miles before the beam is completely blocked by the curvature of the earth. This may seem to run contrary to the advertised maximum ranges of the radar systems, at 24, 48, or 72 miles. We must also factor in to this equation the height of the radar target, and the fact that its height makes it stick up over-the-horizon. The same equation can be used to determine that target's radar horizon as well. Knowing that, we add the distance to the target's radar horizon, to our maximum radar horizon, and derive the maximum detection range for that target. For example, our 20 foot high scanner, radiating on a target that is 20 feet tall, can detect that target at a maximum range of 10.4 miles or so. Atmospheric conditions and weather will also play into this somewhat, and can either increase or decrease the range.
__________________
Dsanduril is offline   Reply With Quote
Old 25-08-2015, 14:30   #5
Senior Cruiser
 
Jim Cate's Avatar

Cruisers Forum Supporter

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 11,467
Re: Radar Height and Range

Another factor is that with low mounts large seas can obscure the normal horizon a significant part of the time, and that high mounts can "see over" low lying land features better than low ones. Finally, I believe that with a low mount sea clutter is a bigger factor, but I'm not sure about this. Whether either of these matter to you depends a lot on where you propose to use the radar.

Jim
__________________
Jim and Ann s/v Insatiable II , lying Port Cygnet, Tasmania once again
Jim Cate is offline   Reply With Quote
Old 25-08-2015, 15:10   #6
Registered User

Join Date: Apr 2012
Posts: 570
Re: Radar Height and Range

Water vapor of the atmosphere varies with height and the radar beam is refracted downward by the normal density distribution of the atmosphere.

Radar horizon for this condition is about 4/3 x the geometric horizon. And that range, in NM, is 1.43 times the sq root of HOE (in feet).

Radar horizon at 15 feet HOE is about 5.5 NM, vs a horizon at 35 feet of about 8.5 NM.

Of course, targets have height as well, and will extend above the horizon (above the shadow zone mentioned above) into the radar's energy field, which extends the effective range above the horizon...to a range dependent on the radar's power, the reflective characteristics of the target, and the receive sensitivity of the system.
__________________
fryewe is offline   Reply With Quote
Old 25-08-2015, 15:44   #7
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jul 2005
Boat: Outbound 44
Posts: 4,584
Re: Radar Height and Range

The need for distance is overrated for Radars on a cruising boat. Resolution is far more important. A 24"dome will have much better angular resolution that a 19" - no matter what the power and distance spec'd by the seller is. We are most interested in good resolution and closer in operation for traffic avoidance and navigation. We use long distance ranges to look for storm cells. In this case it doesn't matter what your radar height is as the storm height is way up there. We also use long distance ranges to verify that our charts match up with reality, again dome height is not important in this case. The lower dome height might have some issues with big seas, getting blocked at the bottom. In this case the dome mounted at 45 feet off the water is going to be swinging wildly about as the mast gets bounced around, so the radar single is not going to be that good anyway.
You can play with dome height and target heights here to get max distances:
Radar Horizon Calculator
Example that might apply to a freighter in the distance
Radar height 15ft, target height 60 ft = range 14miles
Radar height 35ft, target height 60 ft = range 17miles
__________________
Paul L
http://svjeorgia.blogspot.com
Paul L is offline   Reply With Quote
Old 25-08-2015, 23:01   #8
Registered User

Join Date: May 2012
Location: Central California
Boat: Catalina 30
Posts: 873
Re: Radar Height and Range

And will it be mounted above your
lower shroud attachment or above it? If
you lose the top portion of your
mast, you might still have the
radar if mounted under.
__________________
Bill
...........................................
You can't buy happiness, but you can buy ribeye.
jongleur is offline   Reply With Quote
Old 26-08-2015, 00:13   #9
Moderator
 
Adelie's Avatar

Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 4,639
Re: Radar Height and Range

Don Dodds in his book "Modern Seamanship" has a chapter on radar. He make good arguments for mounting in the 16'-25' range, too low and you had radiation issues with crew on deck as well as sea clutter and too high you started eating into your short range returns, shorelines at about 1/8 nm.

You could put the radar at the top of your mast and only gain a couple/five miles max range while also severely cutting into your near field returns. To me I would rather see ships at 15nm instead of 18nm in exchange for being able to tell if that low rock is 100m vs 300m away.




Sent from my iPhone using Cruisers Sailing Forum
__________________
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
SailboatData
Adelie is offline   Reply With Quote
Old 26-08-2015, 08:46   #10
Registered User
 
wolfesmy's Avatar

Join Date: Mar 2013
Location: Winnipeg Manitoba Canada , Florida, Bahamas
Boat: Morgan 383, C&C 34, Kirby 25
Posts: 67
Re: Radar Height and Range

There have been a number of formulas bandied about the actual formula is 1.17 x (sqrt) height of eye.

Bottom line higher is better based on you radars range. if it is a 6 mile radar not much advantage of putting it at the top of the mast where it becomes unnecessary weight aloft. Your target has elevation as well.
Hope that helps
__________________
wolfesmy is offline   Reply With Quote
Old 26-08-2015, 10:03   #11
Moderator
 
Adelie's Avatar

Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 4,639
Re: Radar Height and Range

Quote:
Originally Posted by wolfesmy View Post
There have been a number of formulas bandied about the actual formula is 1.17 x (sqrt) height of eye.

Bottom line higher is better based on you radars range. if it is a 6 mile radar not much advantage of putting it at the top of the mast where it becomes unnecessary weight aloft. Your target has elevation as well.
Hope that helps

That's the formula for visual range, radar will refract around the curve of the earth slightly giving significantly more range hence the different formula.




Sent from my iPhone using Cruisers Sailing Forum
__________________
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
SailboatData
Adelie is offline   Reply With Quote
Old 26-08-2015, 10:16   #12
Registered User
 
Cadence's Avatar

Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 6,063
Re: Radar Height and Range

Do what is most practical for you. The distance at those heights is academic. Good arguments have been made for both. As long as you're high enough not to nuke someone's brain.
__________________
Cadence is offline   Reply With Quote
Old 26-08-2015, 10:55   #13
Registered User
 
Capt Phil's Avatar

Join Date: Jun 2010
Location: Stateline NV
Boat: Prior boats: Transpac 49; DeFever 54
Posts: 2,749
Re: Radar Height and Range

Certainly a good idea to mount the radar at the highest practical point on your boat. However, these so called Mariners that have been sold a 48 or 72 mile open array radar by some slick sales person deserve to be parted with their hard earned or inherited $!
Must important when buying a new radar in my opinion is the signal strength first and ease of operating second. For coastal cruising where you want at least a 16 mile with a strong return or if you spend time out a few miles a 24 mile with a strong return would be fine. The only reason to go to a 36 mile would be if you occasionally close the coast and want a warning of how much lee shore you might have.
It might be fun to pick up Catalina as you leave San Diego but a 72 mile radar is overkill IMO. Many of these new radars have dropped in price significantly and are married up with chart plotters, autopilots and sounders/fish finders. Simrad which is the power boater version of the old standby, Brooks and Gatehouse, that sailors have used for years is one of these. Garmin have marinized their line of land based equipment with many cool options. Coastwise, prices have dropped to a small fraction of what you would pay even 3-5 years ago and competition has kept prices very attractive.
That's my two cent opinion.... cheers, Phil
__________________
Capt Phil is offline   Reply With Quote
Old 26-08-2015, 11:14   #14
Registered User
 
Cadence's Avatar

Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 6,063
Re: Radar Height and Range

Quote:
Originally Posted by Capt Phil View Post
Certainly a good idea to mount the radar at the highest practical point on your boat. However, these so called Mariners that have been sold a 48 or 72 mile open array radar by some slick sales person deserve to be parted with their hard earned or inherited $!
Must important when buying a new radar in my opinion is the signal strength first and ease of operating second. For coastal cruising where you want at least a 16 mile with a strong return or if you spend time out a few miles a 24 mile with a strong return would be fine. The only reason to go to a 36 mile would be if you occasionally close the coast and want a warning of how much lee shore you might have.
It might be fun to pick up Catalina as you leave San Diego but a 72 mile radar is overkill IMO. Many of these new radars have dropped in price significantly and are married up with chart plotters, autopilots and sounders/fish finders. Simrad which is the power boater version of the old standby, Brooks and Gatehouse, that sailors have used for years is one of these. Garmin have marinized their line of land based equipment with many cool options. Coastwise, prices have dropped to a small fraction of what you would pay even 3-5 years ago and competition has kept prices very attractive.
That's my two cent opinion.... cheers, Phil
I love the truth about a slick salesman but it's good bragging rights. "I have a 48mi. radar." but the horizon plus a little is 15mi. at your mounting height.
__________________
Cadence is offline   Reply With Quote
Old 26-08-2015, 11:34   #15
Registered User

Join Date: Jan 2011
Location: BC Canada
Boat: Marples 37
Posts: 66
Re: Radar Height and Range

I think the answer to radar height has changed with the introduction of the new broadband radar. Now with no radiation issues to deal with and a much improved close in resolution I feel that having the radome lower has significant benefits. The broadband radars don't have quite the long distance advantages as the pulse radars anyway and as previously mentioned apart from stormcells or headlands what do you need to see more than 6 miles out.
It's the close in stuff that's important.
__________________

__________________
CGirvan is offline   Reply With Quote
Reply

Tags
radar

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
What is considered the best GPS Radar Combo for cruising sailboats in 35-40' range? vtcapo Marine Electronics 12 19-10-2012 15:21
Radar Mast Pole Height Jimbo2010 Marine Electronics 17 16-10-2010 15:22
Furuno 841 Radar range problem barneyanddiane Marine Electronics 2 21-07-2009 10:47
Radar Reflector Height unbusted67 Marine Electronics 7 19-06-2009 10:38



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 09:12.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.