Radar Mount----help?

[hangman1176]

Once again i turn to great grady.

I have a furuno 1721 with an 18" dome. I have a factory hardtop on the 1997 22' Seafarer. I want to raise it 4" and reposition it from the direct center of the hardtop to roughly 1/4 the distance from the front of the top (as seen on most boats). I was looking at the "sea scan" basic mount for $129. plus shipping. I also noticed the "sea view" mounts which are quite a bit more. I'm aiming toward the sea scan mount but don't know if the 4 degree forward lean and 4 degree tilt is enough. Any comments?

 

[JeffN]

I have an arch on my Kingfish and am redoing all my antennas this season. I too needed to angle the radar downward I bought the Pro-Mount "Line of Sight" mount it looks like it it will raise the dome about 4" and will adjust to a 10 degree down angle. I have not mounted it yet so I can not comment on the effectiveness but it does seem to be well made and looks like it should work as I envisioned it. I too was concerned about not having enough down angle with the sea view etc even with the 4 degree spacer, anyway I purchased it here http://www.scubasteve.biz/store/manufac ... omount.htm
It came quickly and seemed to be about the best price. Check it out

 

[BobP]

Is the boat in the water? Put a small bock of wood in the location of
choice and place a short level on top, is it level? If not, shim the level to get it level, measure angle.

The radome can be level at rest, you don't want the front pointed up, a little down is ok. With too much down angle then you will lose rear vision close to the boat.
Wherever you locate the radome you don't want the leading edge of the hardtop to restrict forward vision, that's why they are located closer to the front.

The radomes typically have a 13 deg up and 13 deg down beam angle off the horizontal for a 26 deg window, which is a very tall so it will eventually see water, but you want it to see close to the boat as possible. This is way more prevalent an issue on much larger boats with the scanner on top of the flybridge - sky high where the birds fly!

Though not cheap, you may want to consider also the angled shaped starboard blocks for use as shims.

 

[OUTCAST]

I respectfully disagree with the previous post. A radome that is level at rest is not OK. You don't run into much at rest (yep, someone could always run into you.) When underway, bow is typically pointed up at an angle. That angle is usually more pronounced at the slow speeds when relying on radar-you're not going to be planing that hull at night or in a fog, relying on radar, are you? That radome needs to be pointed down at least 10 degrees to make it closer to level when running. Also, losing a little of coverage close behind the boat is not nearly as critical as the coverage in front of you. I raised my radar unit (I think five inches,) to make sure the scan went over the search lite mounted on top. I put a couple washers under rear mounts to tilt it further forward, then used sealer to fill the gap under mount. You seem to be new to radar, so I will offer this suggestion. Learn to use it when vision is clear, when you can relate blips to what you see-and practice this often. If you're not proficient before you need it, the radar will be close to useless when you do. Lastly, front edge of hardtop obstructing scan is not usually an issue, even without raising the radome. The scanner occupies only the top half of the radome, and, as you can see, it would take an extreme tilt of the radome for that 13 degree down beam to catch the hardtop. Good luck,
Capt. Bob

 

[rolltide]

Is it OK to mount the antenna directly to the factory top?

 

[OUTCAST]

Is it OK to mount the antenna directly to the factory top?

I'd be very reluctant to mount it directly. You're risking cracking a very expensive hardtop with the stresses that come from a mild pounding in the boat. I've seen it done on some "big ole boats" where hardtop was constructed with heavy layers with little regard to weight. That's not the case with most recreational boat hardtops. At a minimum, I'd recommend something like 1/8 to 1/4 inch aluminum plate top and bottom, to spread forces out across hardtop (rather than just concentrate them on the four bolts.) You might also consider rubber grommets top and bottom of plates-i.e. "shock mounted." The weather will rot these out after couple seasons and will need replacement-minor chore if compared to possibly cracked hardtop.
Lastly, but importantly, contact G/W via email or phone. I think most of their hardtops in the past have been provided by a third party contractor, but the question has undoubtably come up many times. Good luck, let us know what happens. Capt. Bob

 

[Capt Bill]

I've installed many radar units directly on hardtops as well as on scanner supports, over the past 30 years. The only problem is what was mentioned above; you need to angle the scanner down 7 degrees or so. You can buy or make a wedge to go under the rear mounting bolts, that will do the job, or buy a scanner-mount with the downward angle built-in.

In either case, just use washers under the bolt-heads, and it will be fine.

 

[BobP]

Let's discuss the 10 degree added down angle recommended.

Depending on when and how you use your radar, it can made a difference in ways that are good, and ways that are not so good.

In the spring out here you can arrive at the marina 7:00 am to heavy fog, leave the dock and spend all day fishing in it, and I mean heavy, and all day. See no boats or land, but hear boats all day.

Since I never run faster than I can stop or otherwise avoid an obstacle upon visual sighting, the main use is for drifting and trolling - mostlty to avoid getting nailed by others who run faster than they can stop, but also for lobster trap floats, etc. So the boat is at the same attitude it has in the marina, and is irrespective of what direction a target is approaching while drifting and trolling.

I did some calculations, a liitle rusty, but I think I got it right, others can check my numbers. I'm sure I did this also when I first mounted it 8 yrs ago.

If the radome is 8 ft off the water and level, the beam window will see water after 34 ft ahead of the radome measured straight in front, same for rearward and 360 deg around the boat. My radome sits about 12 ft back from the bow. So the blind spot if the first 22 ft. off the bow. About the same to the rear. More off the beam.

If on the hand, a 10 deg down wedge is added, the radar beam doesn't see water to the stern until 150 ft, on my boat the blind spot would be 138 ft.

That's too much to give up not knowing what's going on when loosing a target in a band of 138 ft off my stern. Boats fish way closer out here. If I can hear it I want to see it visually, or on radar in the heavy fog we get. A lot different to manage than 22 ft.

From one Capt. Bob to another Capt. Bob, if rearward vision is no concern or less a concern as you mentioned, fine, otherwise it needs to be considered.

Every skipper is responsible for the safety of his crew and ship.

 

[BobP]

I forgot to mention, the 138 ft blind spot is not just to the stern, it sweeps around to the beam both sides then drops off moving forward until adjacent to the scanner postion - there it's the equal to the 22 ft. of my level mounted radome. As it sweeps forward it improves to lbetter than 22 ft.

 

[JeffN]

That is the beauty of the mount I mentioned above - it is adjustable from 0 to 10 degrees down.

 

[Capt Bill]

Bob, I don't recommend 10 degrees; everything that I have done in the past has pretty much been from 4 to 7 degrees, but it would depend on the boat and the captains needs.

There is another factor that you may not be considering in your calculations. The time delay between when the radar transmits a "ping", and when the receiver switches on and is listening for the return. On most marine radar equipment, that translates into a minimum target distance of about 80', if I remember correctly. That spec (min target distance) is listed in the specs of each radar unit.

But the bottom line is that a target coming up aft, would be seen in plenty of time to react, even on a radar with your calculated 138' distance. I don't want any boats getting any closer than that in zero visibility in any case.

 

[BobP]

Capt Bill, good point.

I don't understand the 80 ft spec.
As a note, the 26 deg aperture window is the spec on my Raymarine 18 inch, 13 up and 13 down, other brands may differ. I based the calcs on 13 deg. and 8 ft off the water line.

When I turn on the radar in my driveway on winter drydock blocks, I can see a tree on the curb line within 25 ft. When I head out through the inlet I can see the jetties on both sides, I'd say I'm as close as 25 ft or less away. During the heavy fog in tight quarters around the harbor, if I slow too much I lose a heading on the GPS, have to count on the radar eyes !

For calibration, I position my boat 90' deg to the jetty line, then see if the screen shows the line in the same relative position otherwise have to add a correction factor. I'm within 25 ft. when i do this.

The boats out here fish close, can talk to each other at times. Share fish stories and the usual lies.

On another note. I find it ironic the devices used to raise the scanner higher and higher, when ideally, it should be lower to be most effective in taget recognition closer to the boat.

 

[Capt Bill]

Well Bob, of you are seeing a target at 25' on your radar, that is incredible. The delay of the electronic circuits rapidly switching between transmitting and receiving a radar pulse, in addition to a number of other factors, (pulse length, propagation, etc.) determine the minumum distance a radar can see a target. I honestly have never seen one, even of expensive commercial quality, with a spec of 25'.

For example, here's a link to specs of several Furuno marine units: http://www.barryelectronics.ie/catalogs/ledradar/fr8062.pdf. Here's a link to a Raymarine unit: http://www.marineelectronicshoppe.com/Raytheon/SL72Plus.asp Note the specs under "minimum range" are listed as 25 meters. Thats typical. Earlier in my career, (I was a certified radar technician back in the 70's), radar units had specs that had much greater minimum target distances than we have today, due to the improvement the circuitry (miniature solid state circuits, faster response times).

Those are guaranteed minimum distances. I suppose it is possible that someone could see targets closer than specified, but if you do, I would have to say that it isn't typical, nor anything that one should come to expect, and that the prudent navigator should take other measures to insure safety at sea in zero viz.

 

[BobP]

Yes I found it in the manual, minimum range spec as well as range descrimination is minimum 25 meters.

I reported what I've seen on the screen closer. A possible explanation is the inability to show accurately say grouped targets that are close to eachother or offset in distance, but screws up and shows it as one target, and may be off in actual range, or miss it altogether on a given scan.

I usually keep the range on 1/8 or 1/4 mile while drifting, or trolling, further when pushing more water. The longer ranges are usefull to me only as a backup to normal navigation equipment has been disabled. Then I can identify a shoreline and get a bearing on it.

In the marina on radar, no descimination on the individual boats, screen is filled but no sense to it.

Perhaps if it's a stand alone lobster trap float or bouy it has a decent chance to display it, irrespective of its range reported precisely.

I'd be happy to just see it on the screen and if it's on a collision course or not.

I have the pathfinder plus HSB2 integrated system.

Thanks for the technical info.