I need some help and advice on Radar mast placement and radar operation

[Barking Sands]

The original mast is long gone and I would not like the placement anyways. It was in the middle of the upper deck and of course resulted in leaks over the years. The previous owner had it removed and patched the area.

Now I am plotting out where the radar will go and I need a radar pole or mast. My boat is advertised as a 31 foot and is a loose copy of a Grand Banks 32 or an Island Gypsy 32. See pictures.

I do not want to through bolt it into the cabin. I have already decided and purchased 3 inch OD 6061 T6 aluminum pipe .125 wall. Should be plenty sturdy to Hold the Garmin GMR Phantom 18x inch 50 watt unit.

So I have basically 3 choices from what I can see.

1) Mount it to the aft upper deck overhang. Through bolted and then tied to the aft upper rails with 2 supports from the mast to the rails. Doing this I have access to run the wires under the headliner where the other wires are. It will be tricky to run the wires but should be doable. The wires will terminate behind the overhead panels at the lower helm. Wire running difficulty would probably be a 6 or 7. This would be the weakest configuration as far as lateral strength. The pipe needs to be very tall to have good line of sight over the bimini.

2) Same as above but run a continuous pipe through the over hang and down to the deck . There would be a flange welded to the pipe at the pipe pass through on upper deck as well as lower mount pad. This would be very strong. Strong enough that if enough force was applied at the top of the pipe, the pipe would likely give way before the structure. There would be exposed pipe between the door threshold and the window. But it should fit. Running the wires would be a much more difficult. The pipe needs to be very tall to have good line of sight over the bimini.

3) Run the pipe through the upper helm flat surface near the gauges and extend it through all the way to the floor. This again gives 2 mount point as the pipe will have flanges at the upper pass through as well as the bottom mount. Wiring will take about 15 minutes since there is a pass through and the network GMS10 router is just below the floor. It also gives the clearest line of sight forward and the mast only needs to be just higher than the bimini. See example of the bottom picture with the fwd mounted radar/mast.

I am leaning towards #3. But my wife HATES the idea because there will be a 3 inch pole in the way. But IMO the pole is so off to the side when seated on either side it will likely only impede a degree or so of view that is easily overcome. I would trade the loss of 1 degree of sightline in great day time weather in exchange for completely unobstructed forward radar view when needed most. I of course can get the same unobstructed radar view from the rear mounted radar but it will have to go quite a bit higher. That makes the boat look goofy since its a smaller boat IMO.



But..I may be way off base. For instance. How far out in front of the boat do you guys want to see in bad weather or fog on the radar screen? The GMR Phantom is a dual range radar advertised from 20 feet to 48 miles so I would like to have good close in performance when needed.

This is the first boat I have owned that will have radar so I need you more experienced cruisers advice on what is important.

Thanks in advance and here are a couple of pics of my boat and other examples of fwd mount and aft mount radars.

 

[Pete Meisinger]

I got rid of my mast because it was a pain. With it went the radar, so far I have not missed the radar or the mast. If I ever decide to replace the radar I will mount it below the windshield on the flybridge. Higher would be better but I don't want to have to look through the short mast as in the third picture (the green stripe boat).

pete

 

[heysteve]

If you can live without the rearward radar scan, you could mount it on the front of the flybridge. Seaview makes an adapter for their mast mount here but you could also have a bracket fabricated. There's no health risk as modern digital radars are very low power and can often be configured to turn off scanning to the rear.

 

[Jeff F]

I have that radar, and went through a similar exercise with my Mainship 34.

I'd say height is your friend in terms of overall performance. The rear mast opens possibilities for configuring a hoist. I'd go in that direction. Part of it is aesthetics too.

Have you thought about how to lower the mast? Maybe it's not important to you, but it might be some time. Lotta low bridges around.

Also it's worth thinking about mounting other antennae on the same pole. Maybe it makes sense. Also anchor light. I stuck one on top of the radar unit on my last boat.



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[Jeff F]

Just reread your post carefully. More comments.

1) I'm not sure why 2 has to be harder to wire than 1. Can't you cut an exit port in the pole to go to headliner?

2) don't discount aft line of sight for the radar. I often use mine as a rear view mirror of sorts. The Phantom has very useful target coloring and is good at picking up fast moving targets.

3) that section is plenty strong. I used the same for my sailboat, supported at the hull and deck less then 2' apart.

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[STB]

I really wouldn't want the mast in front of me. It would annoy the heck out of me. Your mileage may vary!

 

[mvweebles]

If you can live without the rearward radar scan, you could mount it on the front of the flybridge. Seaview makes an adapter for their mast mount here but you could also have a bracket fabricated. There's no health risk as modern digital radars are very low power and can often be configured to turn off scanning to the rear.

Surprised at statement minimizing health risk. Do you have a citation for this? Certainly, power requirements for modern radar are much lower than predecessors, but a person seated at an upper helm would be just a few feet from the dome where the beam is very concentrated.

I didn't know the beam could be turned off in certain sectors. Though I want full 360, I'll have to check my Simrad 4G next time I'm at the boat.

Peter

 

[Barking Sands]

Thanks for the input. 2 will be harder to run the wire because the pole will be off center to the right about a foot. I have a wire run and access panel on the underside of the overhang i put in place when redoing the headliner and nav/anchor/speader light. So to get the wire over I would have to cut a hole in the pipe and have exposed wire running over. I dont really like that option so my thoughts was to win the wires to the bottom of the pipe through the deck and down the engine bay, back up the helm stantion pipe/wire run to the overhead area. That stantion pipe is pretty full already.

 

[mvweebles]

Barking Sands - an arch or frame would seem a reasonable option. It could serve as the trailing support of your Bimini. Have you considered a fairly simple radar arch of two pieces of 1" stainless tubing?

Peter
View attachment 140845

 

[Barking Sands]

I really wouldn't want the mast in front of me. It would annoy the heck out of me. Your mileage may vary!

I dont think it would annoy me at all. But my wife certainly agrees with you. And that might result in a worse situation ?

 

[Barking Sands]

Barking Sands - an arch or frame would seem a reasonable option. It could serve as the trailing support of your Bimini. Have you considered a fairly simple radar arch of two pieces of 1" stainless tubing?

Peter
View attachment 140845

Yes..an arch has been considered. Both on the front and the back. The rear arch was my first plan actually. Built out of 3 inch aluminum and 2 inch aluminum supports. This would be strong enough to not only support the radar/lights and other antennas but also put a block and tackle or atleast a pulley to help rotate the dinghy up with the Weaver davits. But the work required is quite a bit more. I realize you said a "simple" arch using 1 inch but I am not sure the connectors and wires will make it inside.

 

[Barking Sands]

I have that radar, and went through a similar exercise with my Mainship 34.

I'd say height is your friend in terms of overall performance. The rear mast opens possibilities for configuring a hoist. I'd go in that direction. Part of it is aesthetics too.

Have you thought about how to lower the mast? Maybe it's not important to you, but it might be some time. Lotta low bridges around.

Also it's worth thinking about mounting other antennae on the same pole. Maybe it makes sense. Also anchor light. I stuck one on top of the radar unit on my last boat.



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Yes..depending on how high it might have to be i have a few plans to be able to fold in on a hings or at the base.

 

[ranger58sb]

3) Run the pipe through the upper helm flat surface near the gauges and extend it through all the way to the floor. ... It also gives the clearest line of sight forward and the mast only needs to be just higher than the bimini. See example of the bottom picture with the fwd mounted radar/mast.

But..I may be way off base. For instance. How far out in front of the boat do you guys want to see in bad weather or fog on the radar screen? The GMR Phantom is a dual range radar advertised from 20 feet to 48 miles so I would like to have good close in performance when needed.

Can't speak to your mounting ideas, except to note that a pole in front would probably drive me crazy. OTOH, we had a mast on the bow of our older Mainship 34, and I don't remember being bothered by it except for when we needed the (blinding) masthead light. Go figure. OTOOH hand, we didn't have a radar mounted on that mast, aimed at our... er... uh...

Anyway, when it comes to scanning distance... for us, it varies depending on actual visibility, but in "can't see" weather we would often be dialed down to 1 NM or less for obstacles, maybe 2+ NM or so for other moving boats. And we'd usually be poking along at very slow speeds in those circumstances.

Happens we can split our radar screen, often do, and we did just that the other day because of weather. Had some "can't see" rain for a while, and I was running the radar at 1 NM on one screen, 6 NM on the other. With some additional ad hoc tuning for clutter. This was in open Bay water, though, so if we'd been in a more constricted area and/or in an area with more traffic, probably both of those distances (at least the longer one) would have been reduced.

-Chris

 

[RT Firefly]

Greetings,
Mr. BS. Why not go with option #3 BUT rather than mounting amidships, mount at the side of the flybridge similar to placement in post #5. The mast can be just long enough to clear the bimini and won't obstruct forward line of sight. Nothing says the location has to be amidships ie: symmetrical. Mount on whatever side allows easiest cable run.
If mounted on your starboard side it will allow you to fly courtesy flags when necessary.

 

[Barking Sands]

Anyway, when it comes to scanning distance... for us, it varies depending on actual visibility, but in "can't see" weather we would often be dialed down to 1 NM or less for obstacles, maybe 2+ NM or so for other moving boats. And we'd usually be poking along at very slow speeds in those circumstances.

Happens we can split our radar screen, often do, and we did just that the other day because of weather. Had some "can't see" rain for a while, and I was running the radar at 1 NM on one screen, 6 NM on the other. With some additional ad hoc tuning for clutter. This was in open Bay water, though, so if we'd been in a more constricted area and/or in an area with more traffic, probably both of those distances (at least the longer one) would have been reduced.

-Chris

Thanks Chris. That's the kind of operational information I am looking for and confirms that I don't want to hinder any performance in close. What do you think the closest range is that is actually useful. Again the unit I have states 20 feet to 48 miles.

Theoretically if I install the radar aft of the bimini at height X and then use an imaginary string from the radar to just touch the top of the bimini and carry that line forward to the water...what is the minimum distance you would want to be able to scan to? Having a good idea of the number/distance would help me configure the height if the radar if aft of the bimini. Again the unit states 20 feet to 48 miles. How high the radar has to be to clear the bimini to get 20 feet line of sight VS say 200 feet is drastic. So if 20 feet is useless but 50 feet or 100 feet is critical that would be nice to know.

Asked another way. when the weather or fog is at its absolutely worst, and you are in a river trying to make way (even if only to a safe spot to anchor) what would you have your range set to and about what distance are you eyeballing?

 

[Barking Sands]

Greetings,
Mr. BS. Why not go with option #3 BUT rather than mounting amidships, mount at the side of the flybridge similar to placement in post #5. The mast can be just long enough to clear the bimini and won't obstruct forward line of sight. Nothing says the location has to be amidships ie: symmetrical. Mount on whatever side allows easiest cable run.
If mounted on your starboard side it will allow you to fly courtesy flags when necessary.

Great idea. I could put starboard (in my view) and then the wife could not complain

 

[Datenight]

Great idea. I could put starboard (in my view) and then the wife could not complain

Life on the edge!

Rob

 

[Barking Sands]

Life on the edge!

Rob

Definitely! Because sometimes she has to drive

 

[heysteve]

Surprised at statement minimizing health risk. Do you have a citation for this? Certainly, power requirements for modern radar are much lower than predecessors, but a person seated at an upper helm would be just a few feet from the dome where the beam is very concentrated.

I didn't know the beam could be turned off in certain sectors. Though I want full 360, I'll have to check my Simrad 4G next time I'm at the boat.

Peter

I was mostly summarizing my observations on this topic after making some Raymarine radar purchases over the years. The first 24" magnetron unit many years ago put out... I believe in the range of 2k watts. My 24" Quantum 2 unit I bought a few years ago only puts out 20 watts at max power. Of course there's more to it than that as the type of signal transmitted is of interest but the very low energy output is amazing. West Marine has a good overview of the technology here.

I'm no expert, but I believe the safety issue basically comes down to the amount of energy absorbed into the body which is a factor of transmission power over time. Despite the packaging warnings, some say that even the old magnetron units weren't much of a problem as their pulse transmissions were so short. I'm unfamiliar with open array devices but they seem to transmit at much higher power.

In the context of this discussion, I simply wanted to suggest that installing on the front of the flybridge would likely be the simplest and least expensive option and that the new low power units seem very unlikely to raise any health issues... particularly if transmitting to the rear is turned off. Granted it's not ideal but may be good enough for intended use.

 

[STB]

The attached page from Halo20/Halo20+ manual might be of interest.

 

[mvweebles]

I was mostly summarizing my observations on this topic after making some Raymarine radar purchases over the years. The first 24" magnetron unit many years ago put out... I believe in the range of 2k watts. My 24" Quantum 2 unit I bought a few years ago only puts out 20 watts at max power. Of course there's more to it than that as the type of signal transmitted is of interest but the very low energy output is amazing. West Marine has a good overview of the technology here.



I'm no expert, but I believe the safety issue basically comes down to the amount of energy absorbed into the body which is a factor of transmission power over time. Despite the packaging warnings, some say that even the old magnetron units weren't much of a problem as their pulse transmissions were so short. I'm unfamiliar with open array devices but they seem to transmit at much higher power.



In the context of this discussion, I simply wanted to suggest that installing on the front of the flybridge would likely be the simplest and least expensive option and that the new low power units seem very unlikely to raise any health issues... particularly if transmitting to the rear is turned off. Granted it's not ideal but may be good enough for intended use.

I was walking down a dock with a knowledgeable friend several years ago. He pointed to a radar dome mounted on the forward flybridge brow of a power boat. "Hey Pete! That's what I'd call a Nut Roaster!" I asked him to explain but quickly realized that the dome was the same height as the seat on the flybridge.

I remember going through the Panama Canal rafted next to a container ship. The deck hands on the ship standing on a cargo gate on the forward hull asked me to shut down the radar (which I should have done beforehand anyway).

I have no direct knowledge, but my sense is soft tissues and organs are sensitive to radar. I am sure modern digital radar is much less powerful than old-school magnetron sets. Is it enough? Don't know. Not sure it makes a difference at my age.

Peter

 

[mvweebles]

The attached page from Halo20/Halo20+ manual might be of interest.

Good to know. Thanks for digging this out. I'm surprised.

Peter

 

[Comodave]

On a previous boat the PO had the radar mounted on the brow of the flybridge. It had a significant gap to the stern in coverage. Also the roasting thing. I installed a mast and mounted the radar there. I found a damaged spinnaker pole and used it. The damaged area was at one end and I didn’t need that end anyway. We ran 36 hours in fog coming down the west coast and the blind spot to the stern was really worrisome but I had just bought the boat and didn’t have time to do the mast before we ran it home.

 

[Jeff F]

Theoretically if I install the radar aft of the bimini at height X and then use an imaginary string from the radar to just touch the top of the bimini and carry that line forward to the water...what is the minimum distance you would want to be able to scan to?

I understand what you're getting at here.

First off, the bimini interferes with the radar less than you might think. But more importantly, the beam width is narrow. Garmin suggests keeping a range of 25 degrees clear, 12.5 on either side of horizontal. The specified beam width for the 18 is something like 6 degrees.

So if your bimini ends ten feet in front of the radar, a unit centered two feet above the bimini meets the 12.5 degree test, assuming the radar is mounted horizontally.

If you take that 12.5 deg as the slope of the radar blind spot cone, that gives a radius of ~5x height of the unit. So a unit 15 feet off the water has a blind spot of 75' at water level, less for a tall buoy or wall.

That aligns with my experience. On my trawler with an antenna height of about 17 ft I see buoys down to 30-40 ft away. With a height of 8 ft on the sailboat I never lose them.




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[Barking Sands]

Thanks for that Jeff. That is exactly the information I was looking for. Ill have to read some Garmin info since it sounds like they covered this topic somewhere. But I appreciate your great explanation.

I can lower the bimini a bit. Its too tall anyways and makes the boat look a bit goofy. I know you said it doesnt interfere much. But I would prefer that it doesnt interfere at all. Especially since I will be making the mast set up anyways and have the oportunity to make it how I want.

I estimate the radar unit will be about 14 or 15 feet off the water.

Thanks a bunch.

 

[ranger58sb]

Thanks Chris. That's the kind of operational information I am looking for and confirms that I don't want to hinder any performance in close. What do you think the closest range is that is actually useful. Again the unit I have states 20 feet to 48 miles.

Theoretically if I install the radar aft of the bimini at height X and then use an imaginary string from the radar to just touch the top of the bimini and carry that line forward to the water...what is the minimum distance you would want to be able to scan to? Having a good idea of the number/distance would help me configure the height if the radar if aft of the bimini. Again the unit states 20 feet to 48 miles. How high the radar has to be to clear the bimini to get 20 feet line of sight VS say 200 feet is drastic. So if 20 feet is useless but 50 feet or 100 feet is critical that would be nice to know.

Asked another way. when the weather or fog is at its absolutely worst, and you are in a river trying to make way (even if only to a safe spot to anchor) what would you have your range set to and about what distance are you eyeballing?

I'm afraid there's a whole lot of "it depends" involved. In full dark (no moon or starlight, etc.), full fog or smoke, "close in" for me would likely be as near as I could get it.... mostly for crab traps around here, tiny targets, hard to "see"...

OTOH, the boat can be moving, so I'd want warning far enough out to be able to react in time, and that could be 100-200 yards... For example, s setting of 500' or whatever shows us everything within that circle, whereas a setting of 100' wouldn't be giving us sufficient situational awareness to be comfortable.

And then the settings are about optimizing, and don't actually block out what would seem to to be out of (too far inside) the setting range. For instance, when trolling, we could see our planer boards, about 60' (?) off our quarters... even though our radar was often set to the 1 NM mark.

I can't think of any circumstance where I'd maybe prefer a setting of 20.'

-Chris

 

[twistedtree]

Re safe distance from a radar, all manufacturers publish the safe distance based on 10w/m2, a number established for cell phones radiating your brain while talking. Any modern dome is safe unless you give it a big bear hug. I'd still try to stay out of the beam, but it's not that huge a deal.


Perhaps more importantly, there is very little difference between a broadband radar and a pulse radar. The marketing and sales guys talk about the power output, but that's not what matters. Yes, a broadband radar outputs less power, but it's on 100% of the time. A pulse radar is higher power, but as the name implies it's only on for small fractions of time. The result is that the total emitted energy is nearly the same for the two, as shown in their safe operating distance. Comparing the Halo above and a 4kw Furuno pulse dome, the Halo safe distance is about 1 foot and the Furuno Pulse dome is about 4'. In most circumstances you would be hard pressed to be that close to a any dome.


Now when you look at higher power, open arrays, the numbers change a lot, both because the power goes up, but also because the beam is more concentrated. A 25kw pulse radar with a big antenna requires a keep out zone of 15+ feet. Same power but with a smaller antenna it drops down to 12' or so.


And Jeff's point about close-in detection is very important. Much of the marketing literature for broadband radar touts detection as close as 20'. That's true, but only in a tiny boat with the radar a few feet off the water. And then with the radar that low, you have no useful distance visibility over the horizon. If you put it up high enough to get reasonable distance detection, you correspondingly lose close-in detection. You can't have both at the same time.

 

[twistedtree]

Getting back to the original question, I would go for height, limited by your boat particulars and air draft desires. I too like the idea of an arch, and have fished radar and lots of other cables through 1" tubing. Stepping up to 1-1/4" would get you even more space.

 

[Barking Sands]

All fantastic information and feedback. I think I have a good grasp on things now. I need to get back on the boat and stare at it a bit to see whats possible in various configurations. I am actually leaning towards an arch right up front over the helm just higher than the bimini by a few inches and then raise the actual mount maybe 8 inches to a foot above that.

So figure 18 inches above the bimini so rearward scanning is probably only hindered close in where you would need it least.

It also allows for the easy wire run just below the upper helm floor.

It also allows for the wife to not have her view blocked. Then everyone is happy.

Thanks for helping me think this through fellas.

 

[Barking Sands]

Getting back to the original question, I would go for height, limited by your boat particulars and air draft desires. I too like the idea of an arch, and have fished radar and lots of other cables through 1" tubing. Stepping up to 1-1/4" would get you even more space.

I already have a ton of 1 1/4 as well as some 3 inch. So that works. Ill have to incorporate a way to fold it too. I have 4 fancy marine hinges that are premade to insert into the 1 1/4 and pre beveled for welding.