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vincentc
11-25-2011, 08:50 AM
I have started building a mast to mount the radar dome for our 43 Hatteras MY. A plywood mast may seem a little different, but it is the wood medium I can work with at my skill level and I believe it will work.

Parts cut (1088 Meranti plywood) for 8' mast 4"x8" at bottom, 4"x4" at top, to be mounted on 2.5' high base. 9mm plywood sides and 12 mm nail strips. Radar dome in background, will mount fwd of mast and above bimini. Nail strips will allow me to round the edges with a 3/4" rounding ove bit. It is all held together with Raka epoxy thickened with colloidal silica and wood flour.

http://i1123.photobucket.com/albums/l554/vjcast/Radar Mast Construction plywood epoxy/IMGP7324rc.jpg

Epoxy 2cm x 1.2cm strips to one fwd / aft piece.
http://i1123.photobucket.com/albums/l554/vjcast/Radar Mast Construction plywood epoxy/IMGP7325rc.jpg
Strips glued to both fwd and aft sections
http://i1123.photobucket.com/albums/l554/vjcast/Radar Mast Construction plywood epoxy/IMGP7326rc.jpg
Fwd aft pieces nailed and glued to side piece
http://i1123.photobucket.com/albums/l554/vjcast/Radar Mast Construction plywood epoxy/IMGP7329rc.jpg

wizbang 13
11-25-2011, 09:12 AM
My radar is also mounted on a home made wood mount. It is gimbaled with a lead diving counterweight. Works fine!http://members.tripod.com/mark_boden/sitebuildercontent/sitebuilderpictures/woodwind8.jpg

vincentc
11-25-2011, 10:48 AM
Good picture, Nice Boat.

Heeling better not be a problem with my boat. Does the gimbal weight scrape against the mast?

BBSebens
11-25-2011, 12:33 PM
Interesting.... does the heeling motion of the boat effect the radar? Does 10-20 degrees make a difference? I've never seen a gimballed radar mount, and had never given it any thought.

rbgarr
11-25-2011, 02:44 PM
Will you mount your radar mast on a tabernacle or hinge for getting at it for repairs, adjustments or storage? Highly recommended.

Mad Scientist
11-25-2011, 04:22 PM
Interesting.... does the heeling motion of the boat effect the radar? Does 10-20 degrees make a difference? I've never seen a gimballed radar mount, and had never given it any thought.

There are some gimballed mounts on the market. I would hope that the radar manufacturers include the effects of heeling in their documentation.

I know that radars radiate a certain amount above/below the level of the plane they're on. This is supposed to be accounted for in the mounting, so that people at the ends of the vessel don't get irradiated. That's usually a concern for powerboaters - sailboats have those nice, high masts to use.

Tom

Bill Huson
11-25-2011, 09:42 PM
There are some gimballed mounts on the market. I would hope that the radar manufacturers include the effects of heeling in their documentation.

I know that radars radiate a certain amount above/below the level of the plane they're on. This is supposed to be accounted for in the mounting, so that people at the ends of the vessel don't get irradiated. That's usually a concern for powerboaters - sailboats have those nice, high masts to use.

Tom

A concern for powerboaters? Good grief. I know Navy ships have various radar-like devices that can take a sailor from sneaking-out-for-a-smoke to crispy critter in less than 30 seconds because my friend spent a large portion of his working for dollars life designing antennas, antenna mounts, and ship superstructures to prevent such tragedies. But I wasn't aware that the average rec boat radar put out enough juice to cause a problem.

Is this like the ol' cell phone use will rot your brain scare fest? Or should I wear my tin foil hat when on a boat with radar?

WX
11-25-2011, 10:42 PM
If you put some of that foil backed bubble wrap insulation inside the mast you will create a fine radar reflector.

http://1.bp.blogspot.com/_p-WTsj6n62A/SWCbhmSYIPI/AAAAAAAAAPs/JHD5o25qTU4/s400/reflective_insulation.jpg

JimConlin
11-26-2011, 12:38 AM
Radar manufacturers are pretty explicit about the vertical spread of the beam. It's worth considering.

wizbang 13
11-26-2011, 02:10 AM
A store bought one costs almost as much as the radar!
http://www.jamestowndistributors.com/userportal/show_product.do?pid=53893
Cruising sailboats usually have gimballed mounts, and my Venus heels much more than 20degrees
I have a light nylon line running down also and a stand off block and a bolt to dampen it.

vincentc
11-26-2011, 05:42 AM
Thanks for the suggestions regarding a hinge and aluminum foil insulation for a radar reflector.

I already planned on the hinge and have a very HD SS hinge that I found on ebay which was designed for a sport fisherman's transom door.

Regarding the radar reflector, I never thought or would have thought of that, but will do it. Appears to be a like a worthwhile safety feature at no cost, financial or asthetic. A very nice divident for starting the thread.

Regards,
Vincent

wizbang 13
11-26-2011, 11:15 AM
I take my reflector OFF when cruising by dangerous places.
Haiti , Columbia, Miami,( just kidding about Miami).

vincentc
11-26-2011, 12:22 PM
The corners are rounded, and sealed in epoxy. I am starting on the base support for the mast. The base will provide a little extra storage as well as some stiffening.
http://i1123.photobucket.com/albums/l554/vjcast/Radar Mast Construction plywood epoxy/IMGP7390mastvertical.jpg
http://i1123.photobucket.com/albums/l554/vjcast/Radar Mast Construction plywood epoxy/IMGP7386rcbasedryfit.jpg
8 foot long mast weighs 25 lbs and will support my weight in a load across a 6 foot span.

Cogeniac
11-26-2011, 01:52 PM
I designed radars in my early career. Any antenna will have a 3 dimensional gain pattern. Gain is the ratio of the radiated power relative to what is called an "isotropic" antenna. An isotropic antenna would radiate equally in all directions above a ground plane (the water), so it is a uniform hemispherical radiation pattern. If you change the shape of the antenna, then you lose power in some directions and gain it in others. Depending on how the radar is made the gain may be rather high. For example you might use a horn antenna that radiates in a relatively narrow and rather flat fan shaped beam. You then mechanically spin the horn inside the radome (the saucer shaped plastic cover). This rotation is what gives you the classic radar "sweep". You can't sweep it too fast since in takes a while for the radar signal to propagate out to a distant object and then reflect and propagate all the way back. Light propagates at 1 foot per nanosecond (billionth of a second), so if you have, say, a 10 mile range (which is a 20 mile round trip), then you have 52,800x2=105,600 nanoseconds, or about 0.1 millisecond. If the beam is, say 1 degree wide, then you cannot spin the horn faster than 360 degrees in 0.1 msec, or 1000 rpm (16 2/3 cycles per second). If it is 10 degrees wide it will have lower gain and will need to spin at 100 rpm (1.667 cycles per second).

Since you are seeking the highest gain possible (to get the longest range for a given radiated power), it is desirable to make the vertical spread of the beam as small as possible, however, since all boats roll and pitch, you need to be sure that the antenna bean vertical angle is at least as wide as the nominal roll and pitch of the boat. If this is not the case, then you will lose performance (and gain a lot of clutter or noise from the beam reflecting off the water when the boat rolls and pitches). To allow for this, you can gimbal the antenna, so the horizontal plane of the antenna is generally level. I am pretty sure the antennas are designed to support some amount of horizontal variation, and this would be in the documentation for the radar.

Regarding the mylar stuff inside the antenna mast, I am not sure of that will have much effect. It depends on the polarization of the antenna and the size of the mast. In general, the mast will not be large enough to create much of a radar cross-section, but it might be interesting to run some tests on this to see. A much better approach is to use an aluminum coated mylar corner reflector (those round thingys with a corner built in. It may be unsightly, but it is much better than a thin little mast.

Mad Scientist
11-26-2011, 04:57 PM
A concern for powerboaters? Good grief. I know Navy ships have various radar-like devices that can take a sailor from sneaking-out-for-a-smoke to crispy critter in less than 30 seconds because my friend spent a large portion of his working for dollars life designing antennas, antenna mounts, and ship superstructures to prevent such tragedies. But I wasn't aware that the average rec boat radar put out enough juice to cause a problem.

Is this like the ol' cell phone use will rot your brain scare fest? Or should I wear my tin foil hat when on a boat with radar?

I have a Navy background, too. That's probably I was thinking of potential danger.

As for powerboats, I was thinking about a flying-bridge boat with the radar on a crossbeam structure about 7' above the flybridge deck and a few feet abaft the helm - I am sure that the manufacturers provide documentation about proximity, so I'm probably worrying about nothing.

Tom, RCN,ret'd

Breakaway
11-27-2011, 03:25 PM
I'd also add that for a powerboat, you take the nominal inclination (aka, "bow rise) of the hull underway into consideration. On boats I;ve owned, tilting the radome/antenna about 3-degrees down on its forward side keeps targets on the water in view while running.

Kevin

vincentc
11-28-2011, 09:35 PM
The base for the mast is almost complete. It will be held by the large stainless steel hinge in the front and the rear of the mast base will be attached by 3/8" stainless rods passing through the ss washers imbedded in the base and through the bottom of the mast. The hinge will allow the mast to pivot forward, if ever vertical clearance is an issue.

http://i1123.photobucket.com/albums/l554/vjcast/Radar Mast Construction plywood epoxy/IMGP7406rc.jpg
http://i1123.photobucket.com/albums/l554/vjcast/Radar Mast Construction plywood epoxy/IMGP7408rc.jpg
Regards,

vincentc
11-30-2011, 02:09 PM
I attempted a test of the mylar do it yourself radar reflector. A friends radar did not pick up a 6" diameter x 6' rolled up tube of the mylar insulation held vertically on the shore. Perhaps it would be different on the water, but not encouraging.

The mast and base is taking shape.
http://i1123.photobucket.com/albums/l554/vjcast/Radar%20Mast%20Construction%20plywood%20epoxy/IMGP7443rc.jpg
Quick and dirty drill bit alignment for hole through mast for locking pin.
http://i1123.photobucket.com/albums/l554/vjcast/Radar%20Mast%20Construction%20plywood%20epoxy/IMGP7441rc.jpg
profile.
Does this rake for the mast look right?
I can change the rake up until I secure and glue the mount for the radar.
I am now working on base for radar dome and will then finish and paint the wood with Brightside Hatteras Off-White.
http://i1123.photobucket.com/albums/l554/vjcast/Radar%20Mast%20Construction%20plywood%20epoxy/IMGP7438rc.jpg
Regards

Vincent

Mad Scientist
11-30-2011, 07:05 PM
It looks plenty shipshape to me; it'll look even better when it's painted. Also, it's high enough so that the frames on the awning won't interfere with the radar beam.

Tom

BBSebens
12-01-2011, 12:26 PM
Looks good! I think the rake fits in just fine.

vincentc
12-02-2011, 06:14 AM
I am having some custom boat T-shirts made (http://www.deeprivertraders.com/customtees/) and want the boat image to include the radar arch and would like them before Christmas, so I attached the radar dome and mounted it for some photos to send to T-shirt people.

I think it looks better than a radar arch on this more traditional boat.


http://i1123.photobucket.com/albums/l554/vjcast/Radar Mast Construction plywood epoxy/IMGP7462rc.jpg



http://i1123.photobucket.com/albums/l554/vjcast/Radar Mast Construction plywood epoxy/IMGP7454rc.jpg
The base was a little wobbly and I put a 6mm ship under the fwd corner so it shows a little more rake.