Transducer cone angles and their coverage area

[Bobr]

Is there a chart or web site or other accessable information that will tell you what the bottom coverage area is for different cone angles at different depths? I'm not a geometry whizz so I was hoping to find something where the calculations are already complete. With all of the various fish finders out there and the different cone angles available I would like to find something that would fit the majority of the waters that I fish which are 50 feet or less in depth. Thanks for the help!

[RJF]

vexilar.com gives you the numbers for their unit's 9, 12, and 19 degree transducers. I have not seen others.

[Eric_WI]

If you know the cone angle and the depth, you can calculate it using the following equation:

Sonar Cone Diameter = 2*depth*Tan(cone angle/2)

Note: "Tan" is short for Tangent. Most scientific calculators have a "Tan" key.

For example, if you have a 19 degree cone and you're in 10 feet of water,

Sonar Cone Diameter = 2*10*Tan(19/2) = 2*10*.1673 = 3.3 feet

I'm not sure if that is how the sonar companies calculate cone diameter but that is how you would do it Geometrically.

Hope this helps.

Eric
(Engineer with too much spare time)

[Bobr]

You da Man Eric. That formula will should get me close anyhow I would think. And I noticed that I can use the calculator with Windows 2000, choose the scientific view and WHALA. There is that Tangent button!

[Eric_WI]

Great!

One thing I neglected to mention is that you need to have your calculator set to Degrees when performing the Tangent function on this equation. If it is set to Radians, you will not get the correct answer.

My Lowrance has a 20 degree cone angle. I set up a worksheet in MS-Excel that lists the cone diameter in 2' increments of depth from 2-40'. I'm going to laminate it and stick it on my console somewhere near my sonar unit.

Note: MS-Excel works in Radians so you need to multiply the angle term by (PI()/180) in order to make it work. The Excel equation looks like this:

=2*d*TAN((PI()/180)*(20/2))

where d is the depth term and 20 is my cone angle.

Glad I could help. Good fishing!

Eric

[Toolman]

Eric,
I wish that I sat by you back in Calculus 201. I bet I would have done way better!! Ha!
Tim

[Bobr]

I just went back and checked that Windows 2000 scientific calculator and wouldn't ya know it lets you chose between degrees, radians and grads. Thanks again you have been a big help!

[Eric_WI]

Tim,

Wish I would've done better myself! Actually, we both would've probably done worse because we would've spent all of our time talking about Walleye fishing and equipment!

Eric

[Hooked22]

you dont need no stinking trig LOL depth x 12 x degree x .0175 and divide by 12 and walla . try it . hooked22

[Don in Denver]

I've always understood that with a 20 degree transducer the bottom coverage diameter is roughly 40% of your depth. So if you're in 50' of water you're viewing a circle on the bottom that is approximately 20' in diameter. I think I got that from an olde, old Eagle or Lowrance manual. One of you math whizzes, is that about right?

[WillieB]

On the Garmin site and in most of their manuals it states that the rough equivalent for a 20 deg cone is approx. 1/3 your depth....about a 7' diameter circle of the bottom in 21' of water. An 8 deg transducer would see a 35 inch diameter circle of the bottom at the same depth.

No foolin'

[Hooked22]

if you dont have one of them fancy calculators try this : 12 x depth x degree x .0175 divided by 12. try it hooked22

[Ristorapper]

There is one graph that has it built in to show right on the screen: Pinpoint!

BW(ND)

[marcbodi]

HI Hooked 2,
Yuu have a good fomula there but why muliply every thing by 12 then divide it by 12.It comes out the same if you dont use 12 and on a 20 degree cone it is awful close to 1/3 of the depth.

[WillieB]

Excellent point, marcbodi, I'm not sure what's gained by multiplying by 12 then dividing by 12.

For a 20deg. cone, the 1/3 bit gives me an error of 1.72%
Yup, I can live with that.

[Omega]

Ok, now to ruin your day. You have to realize that there is no set method or industry standard for measuring cone angles. One units 10 degree rating maybe anothers 20 degree! Darrel has a great explanation on his site at http://www.lowrance.com/Tutorials/Sonar/sonar_tutorial_06.asp
Hope everyone has a great 4th!
Rich

[bobco]

Most sonars rate there cone angle at the point of 1/2 power or -3db. In other word a 20 degree xducer has a -3db power transmitted at the outer edge of the 20 degree cone. Also the "cone" really doesn't look like a cone. If you are familar with radio transmission you will understand that the power is radiated in lobes, major and minor, with most power being in the major lobe ( centered from transducer). Another more important misconception is that you only see within your 20 degree cone, the new Lowrance sonars are claiming I think 60 degrees if I remember right. What this is all about is that if you know how to use your sonar and get max sensitvity you can see things well outside the 20 degree "cone". These signals outside the 20 degree cone reflect energy back to the sonar and can be seen if your sensitivity is set high enough to display it on the screen.

[x 12 divide by 12?]

the formula i used .0175 rise over 1" for every degree so i you wanted to do by feet it would be feet x .21 x degree. i just did it in inches thats all hooked