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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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  #1  
Old 11-05-2002
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Radome Placement

Thoughts, please, on where to place a Radome. Mast or back of cockpit, along with pluses and minuses for each location.
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Old 11-05-2002
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Radome Placement

My wife vetoed an aft tower from an appearance standpoint, so I mast mounted a Furuno radome just above the spreaders. Works great with no problems but, of course, the wiring is more difficult.
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Old 11-05-2002
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Radome Placement

I would recommend that you not place the radome on the mast. The generally stated reason for doing so is that it provides for more range because the radome is higher. However, the range is proportional to the square root of the height of the radome plus the square root of the height of the target. The formula is:

d = 1.17 x (sqrt(h1) + sqrt(h2))

Where d is the range in nautical miles, h1 is the height of the targe in feet, and h2 is the height of the radome in feet.

Increasing the height from 10 feet to 25 feet increases the range by only 2 nautical miles. Large ships and shorelines will be seen many miles away in any case; the problem is smaller targets like other boats that get lost in the sea clutter or don''t provide sufficient return to be seen at any distance over a mile or so. A higher antenna won''t help that.

Putting the radome on the mast detracts significantly from the righting moment and creates an opportunity to foul the jib. The only advantage is that it might be slightly less expensive than a stern pole.

I placed mine on a pole on the stern and it has worked fine with more than adequate range. The pole has a manual adjustment to counteract heel. I don''t notice that adjusting the tilt changes much. For a lot more money you can get a tilting backstay mount. The advantage is a somewhat cleaner and easier installation. With a pole it was recommended that I mount it through deck, it was a lot of work to glass in a mounting base at the hull. A backstay mount (or deck mounted stern pole) would have avoided that extra work.

Nearly all racing boats mount their radars on stern poles.
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Old 11-05-2002
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Radome Placement

As described above, radar units have a maximum range which is dependent on the height of the antenna mounting and the height of the target. At extreme range, it is the curvature of the earth that gets in the way - radar is line-of-sight. However, this also means that there is an area immediately around your boat where the there NO coverage.

The radar beam is usually focused within 10 degrees of horizontal. This means that there is a "cone" around your boat which is not covered by the radar because no signal reaches into that space. You can calculate the minimum distance at which the radar is effective by multiplying 4.5 by the mounting height (assuming a 10 degree below horizontal transmission limit, sea level-height object).

Our 25 ft high installation means that any object at sea level closer than 140 feet will not show up. This means that "instrument landings" in narrow harbor entrances will more likely find a happy ending with properly functioning DGPS than Radar on our vessel. Any future vessels would have a lower mounted randome on them.

Even though the radar randome is not transmitting 100% of the time even when on, it''s a good idea to keep the transmitter well above the usual "head-levels" on board. Remember, microwave exposure can be harmful!
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Old 11-06-2002
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Radome Placement

You also have an option of mounting on the backstay...but a good Questus mount is expensive. Another negative with the radar directly overhead that you feel like it''s going to drop on your head even though you know it will not - although it is not a real threat, the fear can be quite discomforting.

Stern pole can be used for so many other things.

P.S. I put a tri-lens radar reflector on my mast. A sailboat in bad weather is not a good target for a radar. If someone has a radar, I want to me darn sure they see me.
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Old 11-09-2002
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Radome Placement

Mine is on a mast at the cockpit. Makes it easy to service. Make sure you install the weep hole. Mine is in the shop now due to an accumulation of condesation.
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