How high does a radome need to be?

Otter

Otter

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We've just changed back to a sloop from a ketch arrangement made by a previous owner. The radome was on the mizzen so where do we put it now? I could put it on the main mast but it's a big job and drilling and riveting at 20 feet up doesn't appeal to me. The original design for our Colvic Watson has it on the wheelhouse roof which is at least 10 feet above sea level and not interfered by any ropes etc. Its view forward will be slightly obstructed by the mast obviously, but no more so than when it was on the mizzen. Can anyone see a downside? What's the horizon distance at ten feet up? We never use RADAR beyond 5 miles range and have AIS.
 
Lazy Kipper said:
We've just changed back to a sloop from a ketch arrangement made by a previous owner. The radome was on the mizzen so where do we put it now? I could put it on the main mast but it's a big job and drilling and riveting at 20 feet up doesn't appeal to me. The original design for our Colvic Watson has it on the wheelhouse roof which is at least 10 feet above sea level and not interfered by any ropes etc. Its view forward will be slightly obstructed by the mast obviously, but no more so than when it was on the mizzen. Can anyone see a downside? What's the horizon distance at ten feet up? We never use RADAR beyond 5 miles range and have AIS.
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the height of the target will also extend range.
my raydome is on a pole approx 10` above sea level, i have in calm conditions tracked a box boat @ 10 mls, it wasnt visible to the eye
 
Not sure on horizon distance. Our raymarine manual states that a scanner at 3m above sea level will detect a target 3m above sea level at 7.8miles and a target of 10m above sea level at 10.9miles.

I would think that should be fine.

With regard to the blind spot, that should be much smaller than it would be if it was attached to the mast so I would suggest putting it where it was designed on the wheelhouse roof.

If going to the trouble of having to move it, could also consider a gimballed arrangement to make it useful when heeled.
 
Putting it on the wheelhouse roof will give you ample range. Plus, you'll get the added benefit of reduced sea clutter on the image, versus a mast-mounted radome.
 
Lazy Kipper said:
We've just changed back to a sloop from a ketch arrangement made by a previous owner. The radome was on the mizzen so where do we put it now? I could put it on the main mast but it's a big job and drilling and riveting at 20 feet up doesn't appeal to me. The original design for our Colvic Watson has it on the wheelhouse roof which is at least 10 feet above sea level and not interfered by any ropes etc. Its view forward will be slightly obstructed by the mast obviously, but no more so than when it was on the mizzen. Can anyone see a downside? What's the horizon distance at ten feet up? We never use RADAR beyond 5 miles range and have AIS.
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As others have written wheelhouse is good.
Offset it to starboard side, this will put the blind spot on port bow instead of in your heading.
 
Thanks everyone, pleasantly surprised by the replies, I thought it might be poo poo'd. I hadn't thought of reduced sea clutter - why so? No gimbal arrangement needed, CW's don't really heel.
 
I have a Raymarine RD42HD mounted on a pole about 4m above the waterline. We can see big ships at 7 or 8 miles, but yachts and small fishing vessels at only a mile or less. I guess this because they are relatively small RADAR targets.

This is worse than our previous analogue Raymarine RADAR, which was at least 10m up the mast.

If both vessels are on reciprocal courses and doing 6knots, it only gives 5mins to the closet approach if you first RADAR contact is at 1mile, so it means you have to keep a very close watch on the RADAR is poor visibility.
 
Ian_Edwards said:
I have a Raymarine RD42HD mounted on a pole about 4m above the waterline. We can see big ships at 7 or 8 miles, but yachts and small fishing vessels at only a mile or less. I guess this because they are relatively small RADAR targets.

This is worse than our previous analogue Raymarine RADAR, which was at least 10m up the mast.

If both vessels are on reciprocal courses and doing 6knots, it only gives 5mins to the closet approach if you first RADAR contact is at 1mile, so it means you have to keep a very close watch on the RADAR is poor visibility.
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A good argument for seriously reviewing reflector arrangements / active transponders and for users to get to know their sets and use guard zones with alarms.
 
A far-from-simple question.

More height = extra range, but far more movement and hence inaccuracy.

Fixed radomes are really for non-sailing boats - they're pretty useless when you're beating.

Most fitting recommendations seem to be @3-5m above sea-level.

I've personally found the shorter ranges <0.25nm to be the most useful.
 
Range in NM = 1.23 x square root of height in feet, so doubling height doesn't double range, and the higher you go the less benefit extra height will give you. Obviously higher is still better but if your max possible height is 20 feet and it's considerably less hassle to use 15 feet then you've not lost a significant range. I got the equation from the first website I found so apologies if it's not quite correct. I certainly recall the square root and disproportionate gains from the radar course so it's not far off.

5 feet high 2.75 NM
10 feet high 3.89 NM
15 feet high 4.76 NM
20 feet high 5.50 NM
25 feet high 6.15 NM
30 feet high 6.74 NM
35 feet high 7.28 NM
40 feet high 7.78 NM
45 feet high 8.25 NM
50 feet high 8.70 NM
 
Also worth asking, would you prefer an extra 1NM range on the radar for that one day a year, or less weight up the mast for the other 364 days?
 
Cheers lustyd and Charles that's v helpful. I hadn't thought about the reduced movement. 4nm is certainly good enough for us, at a closing speed of 25 knots which is my 5 plus their 20 I get 10 minutes on RADAR but I'll have had them on AIS for twice that long. Our main use of RADAR is the equivalent of eyesight in poor visibility, in other words using it in conjunction with the plotter and AIS to confirm a navigation mark, shoreline, obstruction or ship. I was convinced the wheelhouse would be far too low down, really glad I asked the question.
 
I'm not a particularly experienced radar user, but I reckon extreme range is more use for navigation than collision-avoidance, and navigation by radar is much less common since GPS came along.

Pete
 
prv said:
I'm not a particularly experienced radar user, but I reckon extreme range is more use for navigation than collision-avoidance, and navigation by radar is much less common since GPS came along.

Pete
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So much so that it was covered in detail on my course and I immediately filed it in the "never going to need that" category and forgot about it until you just mentioned it. It's surprising how many things I've forgotten about boating already, nice to have the forum keep reminding us of these details :)
 
0400 standards call for a minimum of 8 feet and a maximum of 20 feet, in practice 8 feet is a little low for collision avoidance at higher combined speeds but should be adequate for yacht speeds. A good compromise between range, sea clutter and excess array movement in relation to a target is around 12 feet so three metres is not far off the mark.
 
jac said:
A good argument for seriously reviewing reflector arrangements / active transponders and for users to get to know their sets and use guard zones with alarms.
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Quite agree. Another aid for weak / intermittent targets is the use of 'Short Trail'.
When I put my radar up the mizzen I wasn't sure what height to put it, so went for ease and put it at the height that I could comfortably reach with my extending ladder. 3 yrs on, I wished I had mounted it lower, as it's main use is in fog. I don't care too much what is more than five or six miles away, but what I did use it for was buoy hopping and picking up the sticks in the Wareham channel in fog. Now 13 yrs on the chart plotter guides me through narrow channels, the radar helps me avoid small boats in fog and warns me of approaching rain squalls.
I still wish that I had mounted it slightly lower, but it's height isn't as important to me as it used to be!
 
sailorman said:
Cambridge University Yacht Club have on one of their boats a radome on a gimballed bracket MOUNTED AT THE MAST HD :rolleyes:
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Noticed that, does look rather strange with the radar *above* the forestay on a Sigma 38! Fox's seem to like putting them high also, seen quite a few with the radar just above the upper spreader on a twin spreader mast.
 
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