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Old 17-01-2020, 11:50   #1
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Mast-mounting radar

I'm looking to upgrade my 20yo radar to one of those broadband, chartplotter-integrated deals, and at the same time I want to move it from the rear post it's on (not very secure as installed and interferes with solar panels) to about 10' up the mast.

I want to drill a hole in the mast, run the cable through the mast to the bottom in the bilge (it's keel-stepped), drill another hole down there, snake the cable through, and route it into my nav station underneath the cabin sole.

I can't find any decent advice on how to safely accomplish this, and/ or how to reinforce the holes I make so that they don't lose any strength. Has anyone done this before, and what should I be watching out for.
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Old 18-01-2020, 06:10   #2
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Re: Mast-mounting radar

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Originally Posted by jholovacs View Post
I'm looking to upgrade my 20yo radar to one of those broadband, chartplotter-integrated deals, and at the same time I want to move it from the rear post it's on (not very secure as installed and interferes with solar panels) to about 10' up the mast.

I want to drill a hole in the mast, run the cable through the mast to the bottom in the bilge (it's keel-stepped), drill another hole down there, snake the cable through, and route it into my nav station underneath the cabin sole.

I can't find any decent advice on how to safely accomplish this, and/ or how to reinforce the holes I make so that they don't lose any strength. Has anyone done this before, and what should I be watching out for.

Holes shouldn’t be a problem

One hassle with mast radar is that you must cut the radar cable plug off, then make a junction box inside the boat

I prefer radar that is on the side of the mast , just above the first spreader
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Old 18-01-2020, 06:27   #3
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Re: Mast-mounting radar

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Originally Posted by jholovacs View Post
..........
I want to drill a hole in the mast, run the cable through the mast to the bottom in the bilge (it's keel-stepped), drill another hole down there, snake the cable through..........
I'll address just one step of your task. After you've drilled the two mast holes for your radar cable you can drop a fishing line with a small lead weight crimped on it down from the top. Crimped within the lead fishing weight include a 6" to 12" strand of dental floss with a cotton ball tied to the end. A vacuum cleaner at the bottom hole will draw out the cotton ball and your lead line. Most radar cables have a terminal connecting to the radar unit that has a larger diameter than the cable end at the control panel, so you'll likely want to drop the cable from the top.
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Old 18-01-2020, 07:57   #4
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Re: Mast-mounting radar

I believe a mast is in compression and therefore holes aren’t as big a problem, however smoothing out the edges of the holes with sandpaper etc will go a long way towards preventing cracks.
Just like the serrations on a candy bar wrapper, a hole with nicks on it has stress risers and you can be sure where the crack will start.
A tremendous number of boats are out there without cleaned up holes, it’s just good practice is all.
Besides it will help prevent chaffing of the wires.
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Old 18-01-2020, 08:17   #5
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Re: Mast-mounting radar

I replaced my Furuno 1715, the only victim of Hurricane Michael, with the Fruno wireless for similar reasons. The cost was low - $120 for a refurbished iPad and under $1,000 for the antenna. The wireless has less manual adjustment available than the 1715, but better precision and color graduations of reflectance. The only wiring is large 12v DC, which comes with it.
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Old 18-01-2020, 08:23   #6
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Re: Mast-mounting radar

Instead of the trick with the cotton ball from Hudson Force you can also use a fine iron chain at the end of the line and pick it up with a small magnet.
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Old 18-01-2020, 08:23   #7
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Re: Mast-mounting radar

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... to about 10' up the mast.
If you are moving it to the mast why would you mount it so low? Radar is (mostly) line of sight. The higher you get it the further away you see.

10 feet is high enough to be out of reach and not reachable for repair, but not really high enough to get a real horizon boost.

If it was me, I'd have it up by the spreaders. The advantage here is that the spreaders also help (a little) keep sails from wrapping around the radome.
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Old 18-01-2020, 08:38   #8
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Re: Mast-mounting radar

"I believe a mast is in compression and therefore holes aren’t as big a problem"

That doesn't work. With wind/load from starboard, with the standing rigging tight, the port side of the mast is in tension and the starboard side in compression. With the wind/load from the stern, with the aft stay taking the load, the forward side of the mast is in tension and the aft side in compression. Both have zero load points between compression and tension, a nice place to put a hole (as in lightening a beam), but a mast is loaded both ways, and that's before we add in speaders and their rigging.

Masts are rather weak beams, too weak to take the forces unless we are talking about a free-standing mast. We transfer as much as we can to the standing rigging, but that just reduces the load on the mast to the point that it (hopefully) doesn't demast.
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Old 19-01-2020, 19:42   #9
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Re: Mast-mounting radar

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If you are moving it to the mast why would you mount it so low? Radar is (mostly) line of sight. The higher you get it the further away you see.

10 feet is high enough to be out of reach and not reachable for repair, but not really high enough to get a real horizon boost.

If it was me, I'd have it up by the spreaders. The advantage here is that the spreaders also help (a little) keep sails from wrapping around the radome.
My understanding is that the "ideal" height of a radar was 12' above the waterline, to give you close range and decent distant range. Do you have different information?
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Old 19-01-2020, 19:44   #10
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Re: Mast-mounting radar

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Holes shouldn’t be a problem

One hassle with mast radar is that you must cut the radar cable plug off, then make a junction box inside the boat

I prefer radar that is on the side of the mast , just above the first spreader
My thought was to make a hole big enough for the plug to go through and then plate it over with some kind of cover that would reinforce the mast. Is that not a good way of doing it?
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Old 19-01-2020, 20:00   #11
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Re: Mast-mounting radar

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Originally Posted by jholovacs View Post
My thought was to make a hole big enough for the plug to go through and then plate it over with some kind of cover that would reinforce the mast. Is that not a good way of doing it?
You'd be trading one job for another.

I cut and re-spliced mine. Not without some trepidation, like you might have. But it turned out to be no big deal.
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Old 19-01-2020, 20:08   #12
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Re: Mast-mounting radar

I did stager the individual wire splices within the cable so as not to have one fat splice point. That can make things not just less fat, but easier to work with.
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Old 19-01-2020, 21:21   #13
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Re: Mast-mounting radar

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My understanding is that the "ideal" height of a radar was 12' above the waterline, to give you close range and decent distant range. Do you have different information?
A BIG plus one on this question specifically re the broadband radars please
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Old 19-01-2020, 21:36   #14
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Re: Mast-mounting radar

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Originally Posted by slug View Post
Holes shouldn’t be a problem

One hassle with mast radar is that you must cut the radar cable plug off, then make a junction box inside the boat
r
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Originally Posted by Hudson Force View Post
Most radar cables have a terminal connecting to the radar unit that has a larger diameter than the cable end at the control panel, so you'll likely want to drop the cable from the top.
I believe most new radars use an Ethernet cable for the interface plus a two conductor power cable. Holes for these can be very small. I freely admit that my radar is 20 years old and I could be wrong. Every radar I have had the large connector was on the display side and the radome side had very small connectors that were smaller than the cable. The thing to do was to drop a tracer line and pull the cable up from the bottom taking care not to put any strain on the fine wires or the flimsy connectors. With an Ethernet cable the bottom connector could be cut off,the wire pulled through and a new RJ45 connector attached at the base, preserving the factory made connector aloft. The hole sizes you would need would probably be about 3/8 inch - no threat to mast integrity. You could easily go to a 3/4 inch hole without compromising mast strength.

I also agree with other posters that even with the bottom spreader would be best. That is also where your shrouds attach so it is very strong. Smooth and round out the hole edges not to reduce the risk of cracking but to reduce the risk of chafing through the cable,
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Old 19-01-2020, 22:26   #15
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Re: Mast-mounting radar

How close in front of your MAST do you need to actually see something on the radar screen? The number you quoted was calculated by somebody who decided that they needed the radar to "see" things RIGHT at the bow. That's silly. It's NOT "ideal."

At -3dB the beam extends down 12.5 degrees, so touches the surface of the water only 50 feet in front of the MAST. It's actually way better than because the beam runs actually twice that wide, and in close there is no lack of return strength, and things don't POP up 20 feet away from the boat. It is also BAD for close in resolution to have the beam reflect off the deck or other parts of the boat that fall within the beam range.

The idea that you need to see as close to the boat as possible is not picking an optimum, it is deciding that you don't care about long range targets and only about things close in as physically possible for the radar to work.

Are you REALLY going to be navigating by radar alone right up to the moment you put the boathook on the mooring ball? Really?

At ten feet your radar horizon is less than 4 miles. While you might see a tanker at longer ranges, a low shore line will disappear from your scope at that range. I think you are limiting the utility of your new tool a LOT.

My 3g radome is 25 feet high, and I can drive my way through a crowded anchorage with it no problem, and I get almost twice the range on that low shoreline...

But whatever you think best...
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