This makes almost no sense:
Larry wrote:
"Nicholas Walsh" wrote in
:
As to mounting it, there's a trade. You are a sailboat so nothing
happens very fast. 15 mile range is overkill at 8 knots as you won't be
there for 2 hours, yet.
Of course the RO-RO coming at you at 25 knots gives a closing speed of
33 knots or 3.3 miles every 6 minutes. He'll be on top of you in 15
minutes. Navigating, 15 miles off shore with radar fixes is nice when
your GPS fails.
If you mount it high up, you get excellent
range. Sounds good, eh? Unfortunately, high up also has a tradeoff in
how CLOSE to the boat you can see that big, heavy, CG bouy in the
whiteout fog bank.
Not!
High up, the radar's beam goes OVER the top of low-
down items, like bouys, and the closer they are, the worse they display.
So, I consider putting the radar antenna DOWN much more important to
safety, where the range is only 4-5 miles, but you can see the bouy 12'
in front of the bow just fine in the fog. About 10' off the water, no
more than 15' up is ideal.
So why do ships have theirs up on top of the bridge? Because the radar
is built with fairly wide vertical beams. You won't be able to get it
high enough that you can't see seagulls directly in front of you. In
addition, the pitch of the boat will have a greater negative effect than
putting the radar at the best height you can manage.
Your cheap Raymarine uses a phased array scanner antenna made out of a
cheap piece of printed circuit board just etched with the antenna
phasing elements and stripline matching sections, all on the board.
Not phased array. Check their website
http://www.raymarine.com/raymarine/D...age=4&Parent=2
Phased array scanners are not cheap or common. They are exceptional.
Check it:
http://en.wikipedia.org/wiki/Phased_array
It
has a quite narrow horizontal beamwidth, but a quite wide vertical
beamwidth, which is great for sailboats because this antenna works well
heeled over to 20 degrees without being leveled by some gimbal
mechanism.
If it was phased array, none of this would matter but it's not. Look it
up. The horizontal beam is about 5 degrees (for target separation) and
the vertical about 25 degrees (to account for pitching and mounting
height). Nothing to do with rolling.
We had one on a post mounted on the port corner of the stern
on an Endeavour 35 sloop and I could never see any range difference by
tilting the mount to level the antenna, much. The waves offshore are
what screw up the targets on the other side of them....
Hence the need to mount it higher than lower.
AIS is gonna fix all this....soon, I hope. Everyone needs a
transponder!....
And a receiver. But that won't help you spot logs, containers or other
flotsam and jetsam.
http://www.aislive.com/
take a look.
This is generally the worst advice ever. You should do some research
and talk to the guys in the shop.
I would put the dome at a strong point as high on the mast as stability
and common sense would allow. I am not an expert on radar mounting but
I use them daily in my job as a ship's master. I wish I had one on my
own sloop.
Gaz