radar height

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emnick

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I bought a new radar and plotter from boat show, I am awaiting delivery but have been mulling over the installation, Looking at other boats it seems that radome height is more convenience than optimum height, is there a recommended height for the radome on a sailing boat, also, will drilling into the mast cause a local weak spot? Thanks for any help
 
Depends on the power of your radar. Most yachtie radar sets will not be powerful enough to see more than about 12 miles if you are lucky regardless of having a 24 mile calibration. As it is line of sight, you can look up the height in your almanac to the horizon at 12 miles ( I can't be bothered) Its not very much though. You don't want it too low or you will microwave your brain but most people depending upon the boat, find a convenient height about half way up their masts avoiding steaming lights and rigging. Your manual will give a minimum height for safety. Usually about 3 metres I think.
Drilling mast no problem.
 
For the radar to 'see' as far as possible, the higher the better. That has to be balanced against the heeling effect of weight aloft and potential interference with the rig, so the optimum height will depend on the weight of the radome and the size and stiffness of your boat. If you mount it on a post or gantry at the stern make sure that it is well above head height for a tall person standing on the highest part of the deck. You wouldn't stick your head in a microwave would you?
 
There is a nice balance to be struck between height for maximum range. I detect large ships and land - not necessarily at the shoreline - out to 24 miles with a 2KW radome half way up the mast of my 31 footer. However, in addition to the impact of weight aloft, you must consider sea clutter. The lower the radar scanner the shallower the angle of its radiation to the sea surface and hence the smaller the effect of sea returns. Personally, I am happy to trade this off against knowing who is barelling down Channel towards me at 24+ Knots in the murk!
 
I've heard the same about sea-clutter. My radar is on a post at the stern partly because I had it fitted after buying the boat, and partly because I wanted to keep weight low. In spite of being low, I can still pick up ships at 18 miles, so a mast fitting seems unnecessary from this point of view. Servicing and fitting are easier, and I can polish the radome whenever I wish!
Someone once told me that some craft will not be given A1 classifiction if they have radar on the mast as well as furling jib or main and whether true or not the effect on stability is something to be considered on smaller boats.
 
Mike, I have a 'rolling pin' type radar reflector. I am uncertain as to its effectiveness. A test in perfect conditions with a friendly yottie mate showed I was visible at 0.5M but at 1.5M I was invisible.

Q. What is the max range you can see a 10m yacht on your set?
 
A convenient position for mounting on the mast is just above the spreaders where you can conveniently sit on the spreaders while fitting it and have the radome at a convenient height for access.

From my own point of view its worth noting that there has been no investigative work done on people with stents fitted to their coronary arteries who are impinged upon by Radar beams.

FWIW I can see no good reason for putting it on a low pole and thus placing what is essentially a piece of lightweight waveguide in the path of a beam which could be a harmonic of the length of the waveguide (stent) Simple logic will tell you that the inside of a stent could become the holder of a standing wave with resultant intensities thousands of times larger than those radiated upon it. Being a person who has a heart condition I can see no good reason a) for suffering such a risk myself and b) imposing such a risk on others.

Thus I say keep all radars high up the mast .
 
Most yachts seem to disappear at between two and a half and three miles with my 2 Kw radar and target enhancement. Reflectors don't seem to make much difference.
 
We have a 2kw raydome on a 1.8M Scanstrut on the deck next to the cockpit. The radar beam can be hazardous (to the eyes) at short distances but is above head height to anyone in the cockpit.

We went for the strut to keep the weight and windage down. The radar is only used in poor visibility when the Mk1 eyeball is less reliable and fog and strong winds rarely go together in my experience. Equally we hoist the radar reflector to just above the first spreader at night or in poor visiblility rather than having a permanent installation. This is above the beam height of the radar.
 
Just had a look at some microwave safety stuff - for my own peace of mind. At 10 metres, a static (non rotating) scanner on a 10kw marine system provides a radiation dose of 1% of the NRPB minimum hazard level. By my calculation, at 1 metre that would be 100 times higher - so a 2 or 4 kw raydome is pretty safe at less than 1 metre. Still wouldn't stare into it tho ...

The Scanstrut is a nice piece of kit - but pricey at £500
 
Do you people run around with the array while continually banging out full power?

Yacht radar is like worrying about the phosphorous on an old watch compared to the power of commercial units. The only people who may need to worry are those wearing a very old type of pace-maker.

Or do you have your laptop up at the spreaders for safety when using wifi? Dangerous radar has very very conspicuous warning labels attached declaring safe distance, do you not find it odd, even with our litigious society that yacht radar has nothing to warn of this. They don't even bother to rename the power button to the euthanasia button.

This is not to distract from the obvious advantage of height, but the advice being given in this thread is wrong and will very possibly worry people into not using their sets when they should be.

Try switching it on in the rain, if the dome starts steaming as the rain drops boil off I will retract my statement, but until then, stop giving false advice.
 
Regarding mounting the scanner on the mast and particularly of drilling holes in the mast..... The mast is most susceptible to damage in the area between the points where it is stayed. So for a typical mast stayed with cap shrouds and intermediate stays the critical areas are at 1/4 and 3/4 height. So mount the scanner as close as possible to the attachment of the intermediate stays and you should be OK. ie within .6 metre of the stays. olewill
 
I have a Raymarine C70 with the antenna at 25 ft (ish) above the WL and it is very unusual to see any small yachts at all until within 10 miles at very best. 5 is more usual and without a good reflector many don't show up until 2 miles away if at all.
 
There is always one argumentitive radical on this forum whatever the post is about. For your information the installation advice that came with my own radar gives tons of "health and safety" warnings and suggests the minimum safe height to be 3 metres. I generally agree with the other posts on here though and believe this is probably a very safe estimate which often on a motor cruiser is unachievable anyway. Please try to maintain a polite stance though will you please? No one minds you disagreeing but why rant?
 
Mr D Watch will demonstrate that radar is completely harmless by standing in front of a powered-up scanner for say 15 minutes?

PS Advice cannot be true or false, only well or badly informed. I hope it's always well intentioned /forums/images/graemlins/smile.gif
 
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Equally we hoist the radar reflector to just above the first spreader at night or in poor visiblility rather than having a permanent installation.

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I don't think that is in the spirit of SOLAS requirements that state a radar reflector is to be "fitted" if practicable....
 
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