rhys wrote:
On Mon, 14 Feb 2005 04:22:24 GMT, otnmbrd
wrote:


rhys wrote:

Sidebar question: Am I woefully ignorant on radar implementation or am
I correct in assuming that a target heading directly for one's bow
would be invisible to a mizzen mounted radar due to the three-to-four
degree "screen" of the main mast directly ahead?


R.

Quite possibly, IF you where an expert helmsman at all times.


Agreed, and I know what you are getting at. But if seas are flat, wind
is calm, and you are on a misty seaway at dusk/dawn motoring at five
knots under autopilot, I can see where a trawler or small frieghter
doing the same on a reciprocal course would be nearly invisible to you
simply due to the fact that your radar's proximity alarm or "range
guard" or whatever they call it would not go off until the ship on the
collision course was on top of you...solely due to the mizzen
placement.

Doing some geometry, the mast blocks about a 1 degree angle from the
mizzen. The horizontal beam width of the low power units is about 5
degrees, so most of the energy will get past the mast. The higher power
units have a tighter beam and thus would loose a bit more, though the
Ray 4kW dome is still at 4 degrees. The high power, open arrays tend to
get down below 2 degrees, so they may get blocked more. Frankly, I
doubt this is really a problem.

On the other hand, a jib that fouls the radar on every tack is a major pain!

....


I suppose the other side of the equation is that a mainmast mounted
radome on a ketch has poor coverage aft, meaning that a ship
overtaking you from dead astern would also be hard to notice in such
conditions, particularly over your own exhaust note.

My radar doesn't seem to have a problem seeing "around" the mast. I
suppose the close proximity of the mast might absorb some energy, but I
haven't noticed it.

But such conditions are exactly when one would use radar, no?

This is why I avoid going in a straight line :-)