Line of Sight

[Jackman]

Just trying to remember the line of sight equation at a given height above the water without going back to my coastguard manuals. Anybody remember it?

 

[Passages]

D=1.33(SQRT(2Hr))+SQRT(2Ht)

D=Distance on miles
Hr- Height of Rec Ant (ft)
Ht- Height of Tx Ant (ft)

 

[Jackman]

Thanks. I was just trying to calculate how far a radar antenna on my boat mounted on the hardtop could actually detect land. I know the extra power is for seeing the smaller objects and boats from a distance, as well as the birds, but I just wanted to see what the line of sight from where I mount the antenna would be.

Now on the opposite end of the spectrum....In stone cold pea soup fog how close to my boat can I detect something? Our inlet at Indian River Inlet Delaware is pretty narrow. I was wondering if in complete darkness or fog whether I could detect the uprights of the bridge and the jetties on the way out? Remember, I never had a radar on this boat so most of my questions aer most likely stupid ones!

 

[Passages]

The only stupid questions are the ones not asked. Regarding how close you can see, the quantifiable answer is ...it depends!

The clutter you pick up immediately around your perimeter is largely a function of the quality of your RADAR, your gain/sensitivity settings and weather conditions.

I have an ancient Furuno open array. On a good day with RADAR set to 1/8 mile range I can distinguish objects about 100 feet out.

 

[DeeRow]

...whether I could detect the uprights of the bridge and the jetties on the way out? ...

I too have an ancient Furuno open array. I can pick up pilings and jetties, but a bridge only shows the horizontal bridge deck, not the supports.

Mark

 

[StratPlan61]

I too have an old Furuno, open array and I can pickup indiviual pilings 100ft in front of the boat. It is a 10kw, with a 6' open array.

Bear'
1984 61 MY Strategic Plan

 

[34Hatt]

I have a koden 4kw open array I can pickup pilings in front of a bridge but only tried this on a nice day. Don't forget the fog while degrade this. The more power the unit is the better it will work when its THICK out there.

 

[REBrueckner]

How close to your boat you can detect an object on radar depends on its height above water, the height and orientation of your antenna, and the radar cross section of your target. When I installed a second radar aboard, I tilted it down from horizontal just a bit to be sure that when underway with the bow up a bit, I'd have best close in opportunity. You can usually tilt your antenna down a bit for looking forward after installation by inserting a wedge or washers at the aft mounting bolts. The only way to tell for sure is to use it and see in clear, calm weather, when you can compare the display to a visual view.
If trying to see a low target 100 feet forward of the radar in large seas, you might be hard pressed to keep it clearly aligned; in calm water I've never been concerned.

 

[SKYCHENEY]

Bear,

I think I have the exact unit that you have. It is circa 1985, but it is a great radar. I often wonder if it died whether i would be better off to buy a new one or find used parts for this one since it works so well.