DIY stern mount for radar?

[xslim]

How do you make a gimball for the pole?
I heard people make them from trim tab.

Anyone has some photos maybe?

[Stu Jackson]

Check out Garhauer gear. I don't recall their price for one, but it is not exorbitant.

[bobmcd625]

Originally Posted by Qayaq

I made mine from Bimini and balustrade fittings and lengths of 316 stainless tube(not pipe). Didnt have access to a welder at the time so it's all Bolted and riveted together. Pretty happy with it and managed to make it in the cockpit. 1" tube for supports and 2" for the pole. I also found bolt on pipe supports/hangers that are used in factories, could only get them in 304 but they haven't corroded yet so I used those to tie into the Pushpit for added support. Through bolted a balustrade fitting through the coaming for the bottom of the pole.It has a T piece above the radar for AIS and bullet aerials. Radars about 13/14 ft above the waterline and seems to work fine, it's on a leveler as there was one on the boat. Next time I would weld it, and probably will on some of this one when I bump into a welder. Good luck with yours

Good plan! Thanks. I just have to start scrounging. I have concluded that , for me at least, the gimbal mount for the dome is not a must. U-joint at base does make sense .

[W3GAC]

No, decided not to paint the mast, at least not at this time. Easy enough to do later given the ability to undo the braces and tilt mast away far enough to apply the necessary aluminum primer and one or two part epoxy paint options. I don't like any more electrical splices than absolutely necessary/ and I like things to look neat. So in my construction I drilled a hole up at the top area of the mast/ radar mount plate to allow the radar, GPS, vhf coax to enter/ run down inside of mast. At the bottom of the mast/ U mount I drilled a pass-through hole for all to get below deck w/o exposure to chafing & with liberal application of tape/ sealant for Sun and water into deck blockage. As fas as height of the mast/ radar... generally higher is better... for range. But too high just looks funny/ out of balance. So I painstakingly mounted the radar (loosely) and tied in place and looked from various angles/ distances. Cut off 6"... and repeated until it looked right. Started at 10' but don't recall where it ended up. Support each boat will have its own sweet zone for radar mast. By the way, no need to weld rail mounting tabs. Just use the 'clamp around rail' fitting from Sea Dog and their surface mount Bimini 'hinges'. You can easily dry fit, drill the screw/ fry-boot holes into mast for the 'hinge' and the rail clamp arounds do just that and offer final adjustment and no drilling into rail for final tight down. Been through a lot of rough water a few dock bangs and heavy winds... no issues.

[bobmcd625]

Originally Posted by W3GAC

No, decided not to paint the mast, at least not at this time. Easy enough to do later given the ability to undo the braces and tilt mast away far enough to apply the necessary aluminum primer and one or two part epoxy paint options. I don't like any more electrical splices than absolutely necessary/ and I like things to look neat. So in my construction I drilled a hole up at the top area of the mast/ radar mount plate to allow the radar, GPS, vhf coax to enter/ run down inside of mast. At the bottom of the mast/ U mount I drilled a pass-through hole for all to get below deck w/o exposure to chafing & with liberal application of tape/ sealant for Sun and water into deck blockage. As fas as height of the mast/ radar... generally higher is better... for range. But too high just looks funny/ out of balance. So I painstakingly mounted the radar (loosely) and tied in place and looked from various angles/ distances. Cut off 6"... and repeated until it looked right. Started at 10' but don't recall where it ended up. Support each boat will have its own sweet zone for radar mast. By the way, no need to weld rail mounting tabs. Just use the 'clamp around rail' fitting from Sea Dog and their surface mount Bimini 'hinges'. You can easily dry fit, drill the screw/ fry-boot holes into mast for the 'hinge' and the rail clamp arounds do just that and offer final adjustment and no drilling into rail for final tight down. Been through a lot of rough water a few dock bangs and heavy winds... no issues.

Thanks for those details. I was wondering about getting the cables inside the tube. I think I'd paint prior to mounting or have it powder coated (where?).
Getting exciting. Appreciate your help.

[UNCIVILIZED]

In lieu of a gimballed system, you can make the unit such that the mounting plate for the dome pivots on a pin through it's center. Thus allowing it to be canted to compensate for the heel of the boat.


Then lead a pair of lines from the mounting plate to a location which is easy to reach from deck level. With the lines running through cam cleats, so that you can manually adjust the angle of tilt of the dome. That way you can get the dome to be pretty much level, regardless of what angle of heel you sail at. And it's a KISS adjustment system.

[W3GAC]

Power coating is hard to find... while I didn't on this project, I found a manufacturing shop (does cable TV outside pedestals,... things like that and has been happy to thrown in my projects in a next regularly scheduled 'load' at very reasonable rates...

[bobmcd625]

Originally Posted by UNCIVILIZED

In lieu of a gimballed system, you can make the unit such that the mounting plate for the dome pivots on a pin through it's center. Thus allowing it to be canted to compensate for the heel of the boat.


Then lead a pair of lines from the mounting plate to a location which is easy to reach from deck level. With the lines running through cam cleats, so that you can manually adjust the angle of tilt of the dome. That way you can get the dome to be pretty much level, regardless of what angle of heel you sail at. And it's a KISS adjustment system.

Interesting approach. I guess you could also put the pivot at the base of the pole and adjust the whole rig for heal.

[UNCIVILIZED]

Originally Posted by bobmcd625

Interesting approach. I guess you could also put the pivot at the base of the pole and adjust the whole rig for heal.

That's an awful lot of extra work. Here's what I'm suggesting:

- Get a piece of aluminum plate, & machine it to size for the mounting footprint of the radome.
- Bolt radome to said plate.
- Mount 2 pieces of angle aluminum to the underside of this plate, front & back, with enough space between them for the radar pole.
- Drill a hole through the above plates & the pole.
- Insert a mounting bolt to connect them all together.
- Attach a line to the underside of the radar mounting plate on both it’s port & starboard sides.
- Run these lines down to cleats on the pole or pushpit, & use them to adjust the angle of cant of the radome itself (on the mounting plate).
- Run wires for unit from power source, & viewing screens, up inside of the pole to the radome.
Done.

It's as easy (or easier) than building a fixed mount, but for running the lines which control the angle of tilt.

[UNCIVILIZED]

EDIT: FWIW, Making the above mount self-gimbaling is quite simple. Just bolt a vertical “tail” onto one of the pieces of angle aluminum which the mounting bolt goes through.And attach a counterweight to it.

[bobmcd625]

Originally Posted by UNCIVILIZED

EDIT: FWIW, Making the above mount self-gimbaling is quite simple. Just bolt a vertical “tail” onto one of the pieces of angle aluminum which the mounting bolt goes through.And attach a counterweight to it.

Great ideas. That pivot bolt will have to be pretty robust. Would be good to have some sort of dampening device to keep it from flopping. Maybe a rubber tube over the bolt. Thanks for your help.

[bobmcd625]

Looking back at old posts regarding the benefit (or not) of having a self leveling radar mount. Opinions seem to be pretty well evenly split. Also discussions about the wisdom of using the back stay for support. Comments?

[Steadman Uhlich]

Originally Posted by xslim

How do you make a gimball for the pole?
I heard people make them from trim tab.

Anyone has some photos maybe?

How do you make a gimbal for the pole?
On the boat I recently sailed on, the owner had taken a gimbal mount that was designed for a backstay, and modified it to fit on the top of his homebuilt DIY pole at the stern of his boat.

How is a trim tab used?
As I understand it, the "trim tab" that is mentioned by some was use of a piece of what is used on motor boat trim tabs, the "hydraulic arm" or actuator that moves a trim tab to a new position. In other words, just the hydraulic piston/arm is used, and used to move the mount of the Radome to a new position, where it remains (semi-fixed).

This is not the same as a "gimbal" mount that moves on its own due to gravity and the motion of the boat as it rolls.

Some experienced sailors (John Harries of Morgans Cloud, for example) think the trim tab with a semi-fixed position pole mounted radome is best. He chose that for himself, but his boat does not have a SOLAR arch. Others think the gimbal mounted (freely swinging and matching the horizon at all times) radome is best because it matches the horizon, keeping the beam of the RADAR at an optimum level regardless of boat motion or heel.

I don't claim to be an expert on RADAR or boats. So, you may take my opinion or comments below with a splash of saltwater.

But, based on my own reading on this subject, and recently watching a gimbal mount radome match the horizon at all times while I was on night watch, even as the boat rocked in swells on the beam and quarter as I was sailing in fog off Newfoundland, and after looking at the illustrations of RADAR beams (as they are tilted due to heel), I would choose a gimbal mount on a stern pole, or RADAR/SOLAR arch or mast for my own boat. Opinions on this vary, as do most things on choices related to boats.

There are reasons why a gimbal OR fixed mount is not wanted on a backstay, or on a mast, or on a pole. For example: If mounted on a backstay, it can be damaged or cumbersome when the mast is lowered for any reason. For another, it can cause some fitment issues with hydraulic backstays. When mounted on a mast, any radome may interfere or cause wear on sails as they move across it.

There are reasons "for and against" each location and type of mount. And, anecdotes from sailors will tend to favor each one they bought for themselves or how they rig their own boat.

For example, John Harries (Morgans Cloud) is a well respected sailor and writer. But, even as he described his own choice for his own boat (a semi-fixed pole mount radome at the stern of his boat) he admitted his boat did not have a SOLAR arch or installation (which is becoming more common on cruising boats).

You may also see some sailors say they have sailed with both types and did not see a difference in their operation of their RADAR. Or that they changed their mount and did not see a difference in how the RADAR view looked on their screen. In my opinion, there are too many variables in the situations described (briefly) in those anecdotes. For example, were the conditions "flat calm" or "high swells and waves?" Were the targets just large container ships or commercial ships (easy to spot large targets) or small boats or other hard target (buoys) hazards? In short, the anecdotes don't usually describe much, and those descriptions may only fit the memory and POV of the writer.

I tend to look at the physics and third party (e.g. Yachting magazine did tests) rigorous testing, because I don't have a sunk investment in a choice or on my own boat. Those tests I have seen, and the illustrations of the 25 degree typical beam height/width (12.5 degrees above and below the horizontal point of beam) convinced me that having the radome on a gimbal makes sense, because it keeps the beam oriented to the horizon at all times.

Why is that tilt or gimbal of the RADAR radome important?
Because the RADAR beam is designed to show what is on the horizon or around the boat, and has 12.5 degrees above and below the horizon/level when the boat is level. When the boat is heeled, as little as 12 degrees, it can affect the view the RADAR beam has, by tilting it up into the air (over close or low targets) or down to the water (below targets) thus causing more "blind spots" in your RADAR scan. I have read of sailors who saw these "blindspots" because they missed large targets that were approaching their boat from the sides (not from forward or from astern).

I found a webpage with an illustration of this tilt, but it does not show how a gimbaled mount would keep the radome level to the horizon. Instead, it shows how the heeled boat affects the beam (pointing it up more towards the sky). I will post that illustration here to illustrate that point, along with a link to the original source. I do not have any linkage to the author or artist or source. I am simply sharing to help inform others.

NOTE: This illustration points out that the tilted beam may not show things below it's height/scan. I think the author/illustrator was trying to make the point that having a radome on a pole (lower height) was better in some ways, as lower targets would be seen, whereas if the radome was on a higher mount (mast) it means that the RADAR beam may miss lower targets below the tilted beam.

Also, as pointed out on this page (the illustration location), the beam of a RADAR may pick up some targets or show some return outside of the beam, due to variable conditions and targets.

Illustration Source: Sailboat Radar Mounting (post or mast)


I hope that helps.

[UNCIVILIZED]

A hydraulic trim tab is more than a little overkill for this purpose. A set of lines led through cam cleats work just as well, with less cost, complexity, & maintenance.

[bobmcd625]

Thanks, Steady Hand. Good comments.
Having a self leveling mount has to be "better" than a fixed mount. How much better depends on the conditions. Automatic (i.e. gravity) self leveling vs manual leveling depends on affordability and ease of use. I would think that manual adjustment would add some stability to the system which might be a benefit. Decision, decisions!!!