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Old 15-11-2016, 11:49   #1
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Radar Dish location

Hi All -

I'm new to radar and the boat I purchased has the dome mounted to a port connected to the backstay. This raises it about 6 to 8 feet above the deck.

Boat is a tashiba-31 with cutter rig.

This is part of a pretty old Raytheon system and I'm not sure it works. I'm planning to upgrade soon.

What the general opinion of locating the dish here as opposed to mounting in up the mast?
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Old 15-11-2016, 12:56   #2
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Re: Radar Dish location

I have a Radar dome fitted quite high up the main mast to clear the inner forestay and it does get effected by rolling. (15 Metre cable)

Next time I would look at one of the back stay gimballed mounts and not try to get too much height
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Old 15-11-2016, 13:46   #3
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Re: Radar Dish location

Quote:
Originally Posted by dmksails View Post
Hi All -

I'm new to radar and the boat I purchased has the dome mounted to a port connected to the backstay. This raises it about 6 to 8 feet above the deck.

Boat is a tashiba-31 with cutter rig.

This is part of a pretty old Raytheon system and I'm not sure it works. I'm planning to upgrade soon.

What the general opinion of locating the dish here as opposed to mounting in up the mast?
What is the system? The older Raytheon 10x and 20x systems are pretty robust and reliable although they don't have all of the bells and whistles of some of the newer gear. Keep in mind that the horizontal beam angle of the transmitter will influence how near your radar will be effective. Having a dome high up on the mast with a 15º-20º vertical beam angel will blind you to targets close to the boat which are more important than a target 6-12 miles away.

FWIW...
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Old 23-11-2016, 10:29   #4
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Re: Radar Dish location

dmk,
In your present configuration, your radar line-of-sight (to horizon) will be approx. 4 to 5 miles (assuming radar scanner is about 10' - 12' off the water)...and this should allow you to easily see any targets at distances of 6 to 7 miles, and any reasonably-sized targets at 10 miles...and, 6' to 8' above deck is a reasonably safe distance from crew sitting in cockpit...
And, unless looking for tropical squalls, etc....for most sailors/cruisers using radar ranges beyond 8 miles is rare, so no worries there..

Quote:
Originally Posted by dmksails View Post
I'm new to radar and the boat I purchased has the dome mounted to a port connected to the backstay. This raises it about 6 to 8 feet above the deck.

Boat is a tashiba-31 with cutter rig.

This is part of a pretty old Raytheon system and I'm not sure it works. I'm planning to upgrade soon.

What the general opinion of locating the dish here as opposed to mounting in up the mast?
So, assuming it works, I wouldn't change a thing!!

And, since you're new to radar (assuming you're sailing in areas with poor visibility / fog), you're going to want to learn how-to best use the radar....
The good news is that when in fog, you're usually motoring thru the calm....so no worries with being heeled-over...

I'm not familiar with the handling of the tashiba-31, so it could be an exception...but, many smaller boats (even heavier displ ones) will become a bit tender if too much weight is placed aloft....so, while seeing mast-mounted radar scanners on bigger cruising boats is typical, it is less typical on smaller cruisers...


Further, HyLylte is quite correct....the older Raytheon systems are quite robust....and since radar unit lifespan is almost entirely about number of hours of actual transmit time, it might still be quite useful to you!
I know of an old Raytheon model 3100 (from the mid-1970's) that was still being used by some amateur "storm chasers", just 2 years ago....how many other marine electronics are still going strong 40 years on??
(just be sure to educate yourself in radar operations!)


Fair winds...

John
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Old 23-11-2016, 11:27   #5
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Re: Radar Dish location

Don Dodds in "Modern Seamanship" has has an appendix that discusses radar location and usage. He argues for at least 12 feet above cabin top to minimize radiation exposure to people standing there, especially near the front of the boat.

For a 16' transmitter height and 20' reflector height (another sailboat) your radar range will be about 10.5 nm.

For a reflector at 60' (ship) range would be about 14.5nm.

http://members.home.nl/7seas/radcalc.htm

Dodd also discusses in his book not setting the radar too high because that limits your close in returns. Targets within 100-200y are below your radar beam.
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