Radar Arch?

[Pelican]

Long as I'm gettin' all this here free information, any y'all ever built a radar arch?

Seems to me you could build a form of thin plywood and layer it with glass cloth but wouldn't it need some metal somewhere? I assume the purpose of the arch is to reflect radar.

To tell the truth I am venturing into an area where I could write all of my knowledge on the subject on the back of a postage stamp with a magic marker. HELP?????? :confused:

[M_Man]

The Radar Arch is a structure that holds the Radome (AKA antenna) above the cabin etc, so the radar has a 360 degree view.

A radar Reflector is more diminutive, some are less than 12" in diameter.

[Pelican]

So then it's only purpose is to hold the ant. Why not just put it on a mast? (Told ya I were eggnorant bout this) :confused:

[Art Read]

That's just what people have been doing for years... 'Till some "yacht" designer decided boats would look cool with "roll" bars! Actually, a lot of dragers used to just mount 'em on top of the wheel house.

[ahp]

What are you trying to do? Mount an active radar system, or build a passive reflector so that you show up well on other peoples radar? Big difference.

[Pelican]

Here be what I doin'. I am converting an old Pearson 28" cabin cruiser into a pure fishing boat. Today I got the cockpit roof off and and used recip saw to cut the windshield assy loose.

I thought the arch was to make you more visible. Like has been said it appears the arch is more of a "style" thing.

Hey, I learned sumpin'! :eek:

[ahp]

Pelican,

If you want a passive radar reflector so that you are visible in other folks radar you can build one yourself out of sheet metal, or buy one from a marine supplier. Usually they are hung up in the rigging when the visibility is poor.

[Pelican]

ahp: You are very versed in this subject so might I ask a couple more questions and then I find something else I no nothing about (that should be reeeal easy :D ).
The passive reflector, how big and what shape?
On radar ant, comparing an open to a closed dome is there an advantage or disadvantage to one or the other. Only thing I can see is the open might snag something, say if a young lady threw her bikini top in the air (hey, I can dream can't I ;) )

[mmd]

Forgive me if I am mis-stating the case, but I think that Pelican is presuming that a radar arch will have the same effect as a radar reflector. The arch is just a structural component with usually no other purpose than to hold things up above the deck; it is just a more streamlined mast. To reflect a radar signal back to it's origin, a metallic surface must be present. These are usually permanent or riggable, sometimes collapsable, balls or cubes of metal panels. Sometimes radar arches are constructed with radar-reflective materials built-in, but most are pretty transparent to radar.

Although I could easily be convinced that the first "roll bar" radar arch was designed for some whiz-bang go-fast frozen-snot behemoth, they have the unparalleled advantage to a designer and builder of providing a solid base to mount antennae, horns, lights, and radars up away from passenger or work areas without taking up valuable deck space. This is enhanced by the ease of access to the equipment mounting nuts underneath the platform, and a clean route for wires and cables. It also forms a good base for fixing foul-weather dodgers in some applications. Designing attractive and strong ones can be a challenge, and they are easiest to manufacture in fibreglass, but they are too useful a device to dismiss out-of-hand. Not for all applications, mind you, (can you imagine a Ditchburn with one retro-fitted? No, maybe you shouldn't... :mad: ) but suitable in a number of applications. I haven't yet seen one on a monohull sailboat that I liked, though. A lot of the Northumberland Strait boats (lobsterboats) have a low arch - about 14-16" high - at the back of the wheelhouse roof to mount radar, deck lights, antennae (usually four to six), satnav, horns, and navigation light. If you're counting, that's at least 28 bolt holes (potential leaks) that are no longer in the wheelhouse roof, and it looks good to boot.

[Pelican]

mmd: You made a point that I had not considered but very much like - the mounting holes. That I like. Less holes in the roof less chance of leakage. smile.gif Thanks for the input. Pel

[ahp]

Pelican,

If you make one yourself you will need to do some sheet metal work. You will need to buy some sheet aluminum, about 1/16 thick is ok and some aluminum right angle stock, say 1/2 by 1/2 by 1/16 thick. You need to have a pop rivet tool and the correct drill sizes for it.

Think of three square (or circular) plates intersecting at right angles and having a common center.

Cut three squares of aluminum sheet about 18 inches on a side. The first one you leave square but mark its diagonal, corner to corner. On the second square you should mark one diagonal and cut in half along its other diagonal, and the third you cut in four pieces by cutting along both diagonals.

Then you join all the pieces together using the angle stock and pop rivets. Start by joining one of the half pieces to the whole piece. The cut diagonal of the half piece should touch the whole piece along the length of the diagonal line that you marked on the whole piece. Then secure the other half piece to the other side in the same way.

The quarter pieces are then used as fillets or gussets to finish it off. What you should end with is a three dimentional construction having eight right angle, inside corners.

The idea is that a radar wave entering any one of those corners is reflected back in the direction that it came from. The USCG also builds these into the tops of nuns and cans. The same idea is used in optical reflectors molded into plastic, and of course much smaller.

I suggest you try it out first just using some stiff paper. File folder stock would be fine. If you still have problems following my very brief directions I can fax a sketch to you.

[Pelican]

ahp: I'm trying to visualize this in my mind (quite an effort). I'll try like you said with stiff paper and see how it comes out. Thanks a ton, Pel smile.gif

[imported_Ola Sylwan]

You can make your own radar reflector from aluminum foil and plywood, easier and lighter than plate.

This is a test of the common types of radar reflectors:
http://www.ussailing.org/safety/Studies/radar_reflector_test.htm

[mmd]

Not to discourage your ambitions to build everything remotely related to your boat, but I have grave concerns over a) the effectiveness of home-made units vs. "store-bought", and b) the fiscal sensibility of the effort - after all, a radar reflector is under $20! smile.gif

[Figment]

the last time I seriously investigated radar units was when I bought the Furuno 10 years ago. perhaps manufacturing techology has changed since, but the laws of physics haven't so.....

enclosed (radome) radar antennae have a slightly (5% or so?) diminished capacity because of the housing, BUT, that housing prevents lines, sails, bikinistraps, etc... from fouling the rotation of the transceiver.

most of the big battlewagon sportfishermen you see on the water have the open-spinning type, and I've always suspected that the reason is a combination of (very slightly reduced) cost and because-it-looks-cool. ALL sailors go with the enclosed type.

type of radome isn't important. location is. get it as high as you can, and clear of absolutely everything. (I've often wondered why the manufacturer's haven't marketed a combination radome/anchor light unit).

MOST important.... LEARN HOW TO USE/READ THE UNIT. take a class if locally available. I think radar is probably the most misunderstood an underutilized piece of electronic equipment on boats today.

[Pelican]

mmd: uh, how can owning an old wood boat and fiscal sensibility work together :D :D :D

Sailortech: Thanks for the advice. I have a good friend that is a tugboat capt that said he will give me a crash course in radar. (get it 'crash course'- :eek: )

[ahp]

Pelican,

Read Ola's post, if you haven't already. It has an illustration of the type of reflector that I described, and a lot of other very useful information.

Some years ago I saw advertised in "National Fisherman" and active radar transponder for small boats. It senses a radar pulse and retransmits the pulse, amplified. It is supposed to make a real blip on the other guys screen. I don't know if these are still made for small boats or not. I haven't kept up, but I know they are required for aircraft.

[Pelican]

The pictures are a big help in understanding the design but a lot of it is technical to the point of being way over my head. I understand woodwork pretty good, mechanics very good, but electronics- NADA. Thanks for all y'alls help smile.gif

[mmd]

Pelican: Wooden boat fiscal responsibility is that practiced speech that you give to your wife in which you explain the (ahem) realistic budget that is required to afford the subject boat. The speech is based on the one given by your government's chief financial officer in which he explains that wildly extravagant government spending with no accounability is good for the country and that "deficit financing" isn't the same as "the piggy bank is empty, we're living on borrowed time and luck". As you drone on using as much financial mumbo-jumbo as you can remember, watch her eyes; if they glaze over you have the boat, if the pupils dialate and the lips go thin and white stop right away and say, "But that's just my foolish thoughts, what do YOU think, Honey?"