Where to put a radar? Politely!

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pbeard

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I am about to nail a radome to the mast just above the lower spreaders and have a query. Our masthead sloop has a 140% genoa, would it be advantageous to fit it to the side of the mast, rather than on the front, to avoid it being 'swept' by the genoa? Does anyone know of any other considerations to take into account for each position?
 
the disadvantage will be in the radar performance, with it at the side of the mast you will have a very large blind arc to port or stbd depending on what side you fit it. However if you fit it at the front you will have a much smaller one (due to shape of mast) and it will be towards the stern, where it dosn't matter so much. If you are worried about the sails put it on a pole towards the stern, saves all the problems and weight up high, and not that much difference in range.
 
Rather than have a radar on the main mast, would it be worth putting up a pole on the stern ? You could then add aerials, GPS, etc in a place which is out of contention with the flappy bits.
 
Unfurl the genoa in calm conditions and walk it around the mast. As it narrows towards the head, you'll see where there is sufficient gap to fit the radar. This is why some people fit it above the spreaders (including us!)

If you think it will be too high (think weight also - about 8kg for a Raymarine IIRC) then plan B is a stern pole

Ours is about 3 feet above the spreader with a 150% genoa on a masthead rig
 
Re: Side-mounted radomes...

I noticed in Scandinavia a few boats with radars mounted on cross trees or on a bracket at cross trees 45° to fore and aft axis.This would seem to eliminate most Genoa probs.
My favourite would be on pole aft,high enough that it didn't fry your brain(allegedly),but low enough that you could reach it for maintenance.Also solves mast down situations and simplifies wiring run.
Only prob with that is that it looks silly on small boats.
 
Re: Side-mounted radomes...

I mounted my radome at the start of this year on the side of the mast, above the spreaders for much the same reasons. Lots of people expressed concern ref the 'blind arc', but I can honestly say that we noticed no significant issue. in fact, I couldn't really find a blind spot at all. However, I will add that ours was a 24" 4Kw raydome, and so the outer ends of the sweep were quite a way clear of the mast, and the power was that bit higher than many budget radars offer... and that may have been a factor.

Since mounting on the side, I have noticed a substantial amount of boats that have done the same. We really had little choice. With a 150% genoa of fairly heavy construction, a large raydome, and a babystay that would have enforced either a very low or very high mount, a forward facing position was pretty impractical. A pole on the stern would have helped, but firstly I aready had a wind generator on the port side on a pole, and on the starboard side the gps aerial on another pole, so it would have been a big project, and secondly, the poles are cripplying expensive.

Edit.... just for completeness... I didn't mount the raydome at exactly 90deg from the centreline, but biased towards the bow slightly, by perhaps 15deg.....
 
Re: Side-mounted radomes...

Of course one limitation on radar range is how high up you put the radar. As a guide the standard formula is that the radar horizon is 1.3 times the square root of the antenna height above the waterline in feet. Eg if radar is 9 feet up then horizon is 4 miles away, if 16 feet up then horizon is 5.3 miles away etc. Of course almost any contact will stick up above the water and so can be seen further away than the nominal horizon. So putting a yacht radar, (say max range 16 miles, better at 8 miles ) on a post at the back, say 16 feet up, will mean that your detection against very low lying coasts or the smallest fishing boats will be reduced in range compared to having the antenna up the mast, but against merchant ships etc there will be no difference. Hope this helps.

PS: the 1.3 figure depends on what frequency the radar is but its a good starting point. Incidentally the visible horizon is about 1.1 times the square root of the height in feet.
 
Re: Side-mounted radomes...

You couldn't see a blind spot? Do you wan't to think about that a minute?
Sounds a bit like Nelson putting his telescope to his blind eye........ I see no ships...
 
Re: ZEBEDEE!

"The Blind Arc will be towards the stern where it doesn't matter so much".

Where are most passage making yachts run down from - from astern. Tired or inept watch keepers will usually see what is forward of the beam, but all too rarely look aft particularly if they are snuggled into an oilskin hood and, horror of horrors, listening to an MP3 player or similar.

Use your radar to look particularly at the zones that the crew tend to ignore.
 
Many thanks for all your replies, this was such a good illustration of the benefits and/or drawbacks of a forum. several different views and ideas, but no real concensus that you can go away and say yes, this is what I must do! But doesn't it stretch your mind to other possibilities - again, many thanks!
 
Just a word on blind spots...

This "blind spot" issue is maybe worth another comment. I have an 18" radome on a stern post on my 35' sloop. In a rain squall, the radar display clearly shows the narrow blind sector caused by the mast. I can't believe that a mast-mounted radome won't suffer much more from this effect.
 
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