Installing Radar - Degree of dip?

W

Wanderer

New member
What angle do you think the water line makes with the water when a CD 22 is on a plane?

The Raymarine I've just bought scans in a horiz plane +/- 12.5 vertical degrees. I want to introduce a dip in the radar when at rest so that on a plane the sweep is horiz.

The 5 inch high mounting bracket has holes to attach to cabin top 5 inches square. So, I have to solve this equation:

x = inches to raise rear to achieve desired angle of dip over 5 inches

y = angle of dip in degrees

x = 5 tan(y)

So, another way to ask the question is what is y?

What have some others done?

Does the bow pulpit show up on the radar when tilted down, say 10 degrees?
 
George, a lot depends on how you've got your engines set and how you load the boat. Mine has a few degrees down tilt, see pixCptns_Choice_underway.sized.jpg

and is not adjustable. You get some shims with the dome (I think) that you can put under the aft mounting bolts to give you some tilt if the mount doesn't have a built in tilt. Mine does.

charlie
 
Thanks Charlie.

If I can get out tomorrow with a level and a ruler I can get the tangent of the angle when on a plane. However, I'd rather be working on the installation.

Did you ever get the pictures I sent you?
 
I too bought a radome strut mount. Mine has a built in 5 degree tilt and it seems to work out extremely well, regardless of how I load the boat.

Don
 
George,

I have the Raymarine radar on Naknek as well.

I'd don't recall exactly how high the mounting bracket is, but probably about five inches. As far as I can tell there is no shim to change the angle; just bracket on the cabin top, and the radar antenna.

I have had no complaints whatsoever with the radar performance as installed. In fact, my recollection is that when in-the-soup we usually in a displacement cruise mode, hence no appreciable plane angle.

I think the only issue might be exactly where (ie. how far aft) the unit is mounted, but again I'd say it's simply back far enough as to avoid the downward sweep of the forward edge of the cabin roof. Did that make sense??

Casey
C-Dory Naknek
 
Hi Geroge,

If you're calculating all this because it's part of the pleasure for you that's just great; it's part of what makes this boating thing so much fun for different folks.

However (to keep it simple), if you get a 5" Power Tower (now Seaview Power Mount; I typically use the 5" forward leaning Pathfinder (Raymarine) model) and mount it on the cabin top directly and then mount the radome on that you'll end up with a very nicely performing installation. At speed where you typically want a little more range for picking up distant objects the radar will be very close to level; when you drop down to slower speeds when "in the soup" or at night the radar then is slightly down getting the best returns on close in objects which is exactly what you want. Even at slow speed you're still near the middle of the 25-degree range and you'll still pick up objects quite well at distance (especially the big guys you'd like to stay away from!).

You can calculate all this very precisely but the reality is that on a small boat such as the CD22 just the load (fuel, water, passengers, etc), the use of engine trim (and/or trim tabs), and pitching from sea conditons can vary the angle far greater than the shimming angle you might incorporate. The radar scanner is meant to be pretty forgiving as they're used on small power boats and sailboats which (except under very ideal conditions) are never "level".
 
I got rid of all the formulas , I installed the radar on my arch, stood behind it and it looked good . Then I put the boat in the water ,did the radar set to factory specs , then proceeded checking what the screen was seeing . Worked 100%. Use it in good weather to practice , and it is working find.



Gary SEARAM
 
each 10% of tilt on a 5" base is 1/2" up or down.
or each degree is just a shade over 3/64 of an inch.

on edit
I meant each 1% of tilt is 3/64" not degree. percent and degree are different.
 
I guess I've forgotten my Calculus of Variations....

What is "10% tilt"? is 100% tilt a full 360 degrees?

How much is that in furlongs per fortnight? :shock: :roll:

charlie
 
Percent is the amount of rise or decrease in a given distance
You have a 100% rise when the amount of rise is the same as the distance
a 100' rise in 100" is 100%
a 50' rise in 100' is 50%
a 10' rise in 100' is 10%
a 1’ rise in 100’ is 1%

a 100’ rise in 100’ is 45 degrees
a 50’ rise in 100’ is ½ of 45 or 22.5 degrees
a 10’ rise in 100’ is 10% of 45 or 4.5 degrees
a 1’ rise in 100’ is 1% of 45 or .45 degrees

using your 5” square
a 5’ rise in 5” is 100% (that does not mean one end is 5” higher than the other is. You would have to extend an imaginary line on the base so that it is 5” from the starting point on a horizontal line & 5" up at that point.)
a 2.5” rise in 5” is 50%
a .5” rise in 5” is 10%
a .05” rise in 5” is 1% (.05’ is just over 3/64 of an inch)

a 5” rise in 5” is 45 degrees
a 2.5” rise in 5” is ½ of 45 or 22.5 degrees
a .5 rise in 5” is 10% of 45 or 4.5 degrees
a .05” or just over 3/64” rise in 5” is 1% of 45 or .45 degrees

I think you can see the pattern here. Don’t need to know that fancy math to figure it out.
 
I thank each of you for taking the time to respond.

Most answers seem to fall in two catagories: it depends…, and doesn’t matter. Both are probably (real-world) good answers. For the record, I did notice that no one answered the question. Les has the experience to know what works. Me, I have no experience so I have to rely on thinking about it.

My thinking produced these results: Most of the time when I need the radar, I will not be on a plane – no dip needed. Sometimes, I will be on a plane and using the radar for monitoring converging vessels. While the +/- 12.5 degrees may be all I need, I see no harm and maybe a small benefit in building in a little dip. I plan to dip 5 degrees.

With respect to the “fancy math”, I think raising the radome 0.4374 inches five inches from the pivot point will give me 5 degrees. :!: :?: Anyone?

Dave said,

a 100’ rise in 100’ is 45 degrees
a 50’ rise in 100’ is ½ of 45 or 22.5 degrees
a 10’ rise in 100’ is 10% of 45 or 4.5 degrees
a 1’ rise in 100’ is 1% of 45 or .45 degrees
Click to expand...

Dave, I admit to sometimes taking an, I think, to 9 decimal places. I don't know about percent of rise but with respect to angles, I think:

a 100’ rise in 100’ is 45 degrees
a 50’ rise in 100’ is 26.57 degrees
a 10’ rise in 100’ is 5.71 degrees
a 1’ rise in 100’ is 0.57 degrees
 
I'm thinking of installing the radome so that I can carry my dinghy inflated and upside down with the bow forward of the radar.

Three issues come to mind: Will it work, will the signal damage the dinghy and if I move the radome back to allow room aft of the light pole for the tube will I have positioned it too far aft?
 
Wanderer":1ewsw5np said:
I'm thinking of installing the radome so that I can carry my dinghy inflated and upside down with the bow forward of the radar.

Three issues come to mind: Will it work, will the signal damage the dinghy and if I move the radome back to allow room aft of the light pole for the tube will I have positioned it too far aft?
Click to expand...

Hi George,

I'll selectively answer your questions because I really don't know where my scientific calculator is (or remember how to use it!).

You won't see the bow rail on the radar.

It never hurts to optimize things; I just wanted to make sure you were doing it out of your desire to be persnickety about it and not because if you didn't you thought your radar might not work.

I believe that the most difficult thing is determining what you think level is (fore and aft). If you believe that the cabin top represents "level" then the easiest thing to do is to purchase a 5-degree radar mounting wedge (there are a couple available in the West Marine catalog). If the cabin top isn't level then I'd get one of those angle gauges from the home building center hold it at whatever angle you determine is appropriate and mark your wedge base material. Seems easier then the math! :)

To the best of my knowledge the radar won't hurt the dinghy (I've just never heard anyone mentioning the possibility including the radar reps and lots of dinghies are near radar transmissions), and the dinghy won't interfere with the radar unless the motor plate (if there is one) ends up at the same level as the scanner.

The Power Tower is mounted on the flat portion of the cabin top; not on the sloping section just aft of the anchor light (just making sure!). Moving the dome back far enough to allow tube space will not cause problems for the radar.

The full length of the cabin top (from tip of visor to the rear overhang) is about 8 feet. The anchor light is 12" behind the forward edge of the visor and leans back at 15-degrees; this leaves roughly 6.5 feet of dingy storage space with the anchor light in place.

This is exactly the situation that lead to the development of the radar arches we designed. Once radar became all but standard I fought the conflicting space requirement (anchor light, radar and dinghy) continuously. I don't "push" any particular solution; it's for each person to decide what works for them but here are my thoughts on the arch...

1) The extra money you'll have to spend is the difference between the arch and the Power Tower.

2) With the arch in place the full 8 feet of cabin top is available for the dinghy since the forward anchor light base is no longer used; and you don't have to wrestle the dinghy over/past GPS, VHF antennas and such (they can move to the arch).

3) The arch makes a fantastic hand hold coming out of the cockpit onto the side decks. The cabin top handrails end up under the dinghy and that initial transition from bulkhead handgrip to the cabin top handrail under the dinghy can be a bit awkward. The arch is postioned so that you grab it before exiting the cockpit and you never let go on your way to the side deck.

4) The arch provides lots of places to attach rod holders, a radar reflector (it's sort of one on its own), a satellite radio antenna and so on.

I'm not against Power Tower mounts; I've done many and they work and look well...but they do create a bit of an issue for dinghy storage though not insurmountable.
 
George, I don't know about the angle issue - all I can tell you is that I mounted mine on the 5" Power Tower as Les has suggested and it seems to work just fine without shims. Great performance at speed and at rest. Don't kow if it could be improved by fidgeting with the angle a bit, but I've left well enough alone.

Are you all going to be at the Eastern Shore gathering this year? Hope to see you!
 
George & Penny - You are right about degrees. I was wrong. Guess I had better go back and relearn that fancy math. The smaller the angle the smaller the change per degree. While the larger the angle the greater the change per degree. Percent stays constant.
 
Good call Dave.

0.464375 Furlongs in a Fortnight....

George, stick it up there, angle it down a little and see how it works. I'm sure it'll be fine. Mine did. Too much calculation is like pole vaulting over mountains of mouse dung.... :shock:

There, I went ahead and said it. My profs at the PG school in Monterey would roll over in their graves. Most of them are there now... :cry :disgust

Les is right on (as usual). If you're in the soup, you're down off the plane and want to see the close stuff. Hence the down angle. If you're on plane, you play with it, put tracks in the automatic tracker and plot CPA's on up to 10 targets with the MARPA..... You can even set an alarm, which, unfortunately my ears can't hear if someone comes within your "danger area". These radars can do a lot of stuff that we never had to do before. (and probably don't need to do now).

But, it's a gadget, which I love and why I have HF, VHF, UHF, GPS and a couple of cell phones in my truck. Don't understand why my bride gets upset while they're all on, I'm talking on two radios at once, and then the cell phone rings....... :smileo

Oh, well....enjoy the radar... :thup
 
If you are going to apply all they angles of the dangles to your radar so you can see what is in front of you going 30 mph, you better install some outriggers to your C-Dory, because I have yet to see one of those boat running flat and level in the water at any speed, forget the weather ? Still think my theory work is best, use your radar in the day time and observe what your radar sees? If it sees what I see then it is good for me.


Gary SEARAM
 
With respect to the “fancy math”, I think raising the radome 0.4374 inches five inches from the pivot point will give me 5 degrees. Anyone?
Click to expand...

AutoCad says it's 0.43577871", but who's counting?
 
We decided on the radar arch and C-80 on Notayot, and have been more than satisfied with the performance. Les is right on all counts. We had Les ordering the arch before we even decided on radar! I use the arch to climb all over the boat as well as on and off at the dock. Whatever angle the arch sets the scanner at seems to work perfectly in all conditions. I will admit to doing a few drawings and calcs myself, but in the end Les' comments are correct! On plane I can see from Port Angeles to Victoria easily, and still see birds taking off the water at low speeds! Even the small PVC buoys used for water analysis show up at 15-20 mph.
 
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