Radar, VHF, a main mast and a mizzen

Scout · Post by **Scout** » Tue Apr 17, 2007 2:12 pm

What would you put where to get the best result?. (both the cables and the radome). Interference issues? Range issues?

Ceasar Choppy · Post by **Ceasar Choppy** » Tue Apr 17, 2007 2:53 pm

How high is the spreader on the mizzen? What kind of boat?

You want the VHF on the mast-- range = line of sight

Radar is best higher up but can affect tenderness putting it up too high on the mast. You also want to keep the plane of microwaves away from anyone. Something gimballed works even better for when the boat is healed.

I sailed to Bermuda on a boat with the radar mounted on the back stay, up about 10 feet. It was no gimballed. We couldn't see the aircraft carrier on the radar 10 miles in front of us because we were healing. It was night, we could see the lights, but I expected to see a football field show up on the radar and didn't.

Post by **Tim** » Tue Apr 17, 2007 3:33 pm

Mizzen masts are tailor made for radomes, in my opinion. That's where it belongs on any yawl.

If you pull your masts regularly in winter, you'll want to ensure an easy way to break or pull out the radar cable when you pull the stick. This is one of the pains in the neck of radars on the mast, but it can be worked around.

Height improves range, but most of your real radar work on a 5 knot boat will be at close range anyway, so after a point additional height is relatively irrelevant.

Of course, any mounting location is a compromise in one form or another.

Scout · Post by **Scout** » Wed Apr 18, 2007 3:59 pm

There is no spreader on the mizzen.

38' Pearson Invicta.

Tim, our concern is that the radome might be too much weight on the mizzen. Not sure what the height of it is. They sure do look good there though, I agree.

Ceasar Choppy · Post by **Ceasar Choppy** » Wed Apr 18, 2007 4:14 pm

I would guess that as long as it was no more than 2/3s up the mizzen (lower being better) and still allowed for clearance of the topping lift of the main etc., you'd probably be OK. Agree with your concern about the extra weight on the mizzen, but there I think it would be whether the spar could support it rather than any big balance issues.

Post by **Tim** » Wed Apr 18, 2007 5:29 pm

That little Furuno radome only weighs a few pounds. I think it's negligible.

I agree that roughly 2/3 the way up the mizzen should be about the right point, allowing and accounting for proper clearance with the mainmast backstay or topping lift.

Scout · Post by **Scout** » Wed Apr 18, 2007 9:35 pm

I have to agree the radar would be better located on the mizzen and VHF antenna on the top of the main.

I think we will check with our rigger to see what they think about the extra weight. The mizzen mast is stayed with two shrouds aft that go almost to the top and two forward that go about 3/4 of the way to the top. I would think that where the forward shrouds end (3/4 from the top) is where the radar should be mounted if we do decide to put it on the mizzen. The mast is keel stepped with a strong partner.

I have to wonder what the radar return from the mainmast would look like if we do mount it on the mizzen? Does anyone here have a radar mounted behind the mainmast?

catamount · Post by **catamount** » Thu Apr 19, 2007 6:09 am

Just for information, I've heard of some boats that have removable mounts for their radomes that attach to their spinnaker pole track on the forward side of the mainmast. When conditions warrant, they bring out the radome (stored below), attach it, raise it up to the top of the track, and turn it on. When it is not needed, it is lowered and stowed below.

Post by **Tim** » Thu Apr 19, 2007 7:10 am

SCOUT wrote:I have to wonder what the radar return from the mainmast would look like if we do mount it on the mizzen? Does anyone here have a radar mounted behind the mainmast?

Yes, I do--on a pole at the stern.

Any returns from your boat, and the very immediate environs, are found in the "clutter" at the center of the radar screen, which covers a circle of some indeterminate distance around the entire boat; the radar doesn't effectively work at such close range anyway, so there's no additional return or other problem from a mast or other similar obstruction in the radar's path.

Your mizzen would have to too weak to even support a sail for it to be a concern with a small radome. They just don't weigh much at all. This may have been different with old, huge, heavy radomes from 20-30 years ago...but the small 14" or 16" versions are a whole different story today.

That said, it doesn't hurt to check with someone you trust. The point at which your stays attach seems like a logical and effective mounting point for a radome in your particular case.