Minimum height of radar above WL ?

[sarabande]

The Grand 2018 Plan includes a gantry to hold 1 or 2 solar panels, cockpit lighting, spare VHF aerial, stern light, etc, and I am beginning to wonder about a radar; one of the new small ones.

The Foruno 24 inch comes in at under 6Kg, which is less than the weight of the radome of the last radar I had ! And I reckon I can work out a self-levelling mount for it as well.

My area of uncertainty is the height above sea level. I don't expect (or need) long distance returns, but will a height above sea level of about 9ft be enough ? (And yes, I know the distance to horizon figures.... ) Or put the radar on a extending pole when needed ?

 

[macd]

I don't expect (or need) long distance returns, but will a height above sea level of about 9ft be enough ?

The radar on my last boat was 10ft above sea level, give or take a couple of inches. The range was all it needed to be. The bonus of lower mounting, apart from the obviously smaller effect on negative stability is a marked reduction in local sea clutter. That said, the latest 'broadband' radars suffer very little of this wherever you put them.

 

[pvb]

Yes, no problem with mounting it low, although make sure that the boom isn't in the way of the radar beam! As macd says, lower radomes suffer less from sea clutter.

 

[macd]

Yes, no problem with mounting it low, although make sure that the boom isn't in the way of the radar beam.

Daresay you're aware of this, sarabande: as well as the boom, make sure the radar beam won't be directed at crew's heads, which tend to be harder to replace. Low-power non-magnetron radar is harmless, or so they tell us.

 

[superheat6k]

Radar's on power boats are normally only 3 or 4 m and these work just fine.

Do not mount it at crew head level though as the radiation can be a hazard, especially to the cornea, I understand.

 

[Topcat47]

Radar's on power boats are normally only 3 or 4 m and these work just fine.

Do not mount it at crew head level though as the radiation can be a hazard, especially to the cornea, I understand.

Cataracts are a hazard associated with microwaves. Not only do you need to ensure the beam is above head height but my experience with small boat radar antennas, admittedly rather old now as I've been retired for 12 years or so, is that they "leak" radiation. This is omni-directional, and relatively low power due to scattering effects but you are still close enough to cop an unwelcome dose, if it's too low. This is why I don't like those mounted in the cockpit area. At least those mounted on the main mast are relatively safe as the foredeck crew don't spend too much time up there.

 

[fisherman]

Just a cautionary word: check your intended purchase guarantee covers water ingress. A friend found his didn't after it failed at sixteen months.

 

[macd]

Cataracts are a hazard associated with microwaves...

Latest gen radars ("broadband", "FM", "pulse compression", etc) radiate at well below microwave frequencies and with rather less power than a mobile phone. No doubt the OP, who's a bright lad, will be well aware if his Furuno is of this type.

 

[Caer Urfa]

If it's a sloop rig yacht you have without doubt the place to put it for best results is about a meter above the cross trees where it should be clear of the Genoa/head sail when out,
if you have a ketch rig then on top of the Mizzen is fine.

 

[RobbieW]

Having done something similar to the OPs suggestion, slung the radome under the solar gantry so its about 3m above the water I'm minded to move it. Why ? because sailing this year in 3-4 metre swell the fishing boats I knew were about would disappear when I or they were in the troughs. I now plan to move the radome back to a position somewhere up the mast. Though its a broadband scanner the other comments that have been made about radiation are a subsidiary reason for the change