Installing Radar - Degree of dip?

Wanderer · Posted: Mon Mar 13, 2006 3:13 pm Post subject: Installing Radar - Degree of dip?

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?

Captains Cat · Posted: Mon Mar 13, 2006 3:23 pm Post subject:

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 pix

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

Wanderer · Posted: Mon Mar 13, 2006 3:35 pm Post subject:

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?

Sneaks · Posted: Mon Mar 13, 2006 3:50 pm Post subject:

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

Casey · Posted: Mon Mar 13, 2006 5:06 pm Post subject:

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

Les Lampman · Posted: Mon Mar 13, 2006 8:06 pm Post subject:

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".

DodgeRam · Posted: Mon Mar 13, 2006 8:32 pm Post subject:

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

oldgrowth · Posted: Tue Mar 14, 2006 12:38 am Post subject:

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.

Captains Cat · Posted: Tue Mar 14, 2006 8:13 am Post subject:

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? Shocked

charlie

oldgrowth · Posted: Tue Mar 14, 2006 1:58 pm Post subject:

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.

Wanderer · Posted: Tue Mar 14, 2006 2:59 pm Post subject:

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. Exclamation

Anyone?

Dave said,

Wanderer · Posted: Tue Mar 14, 2006 3:12 pm Post subject:

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?

Les Lampman · Posted: Tue Mar 14, 2006 4:17 pm Post subject:

Bluecrab · Posted: Tue Mar 14, 2006 5:07 pm Post subject:

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!

oldgrowth · Posted: Tue Mar 14, 2006 5:49 pm Post subject:

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.