Depth Sounders -- Beam Width

[Pete7]

Originally Posted by Dockhead

When I disconnect the FLS, the depth transducer seems to work ok.

Now you know why I like the kiss principle and have nothing connected.

You must be off shortly, fair winds and safe trip.

Pete

[a64pilot]

Originally Posted by Dockhead

You may be right! I can only speculate as I don't have actual knowledge, but how would it work without a gimbal? You're heeled over 20 degrees, and your depth sensor has a 12 degree beam -- it wouldn't even see the bottom under the boat at all, if it doesn't gimbal to vertical!

Maybe someone knows for sure?

They do not gimbal, the beam width has to be taken with a grain of salt, but yes I assume you could heel over far enough so that it would not work.
I’ve never had a problem with either of mine, but don’t know beam width to be honest, and we don’t heel that far, we will reef first, an IP isn’t all that tender and seems to sail just as well if you don’t let her heel that far, so maybe that is why I have never had a problem.
My shoot thru the hull xducer has to be adjusted if you will so that it is level, so that the beam shoots straight down.
Your 200 Hz xducer is only one frequency? See I have never used an Xducer that has the sounder in the Xducer itself, all I have ever used the sounder can adjust freq so if you could set one to 50hz

[a64pilot]

Mine is the P79, and apparently the beam width is hugely different depending on frequency, 12degrees high frequency, and 45 low frequency
http://www.airmar.com/uploads/Brochu..._products1.pdf

[KeelMe]

While there are transducers that are gimbaled standard transducers are not. The tilted version (12 or 20 degrees) are fixed and are meant for boats within a certain range of deadrise.

* Fixed 20° tilted version for 16° to 24° hull deadrise 

* Fixed 12° tilted version for 8° to 15° hull deadrise 

* Fixed 0° tilted version for 0° to 7° hull deadrise

Beam width should NOT be taken with a grain of salt. It is one of the most important factors when specifying a transducer for a sailboat. For example the P79 comes in two flavors the 50/200 kHz and the 235 kHz. As you said, the 50 kHz has a 45 degree beam, 200 kHz 12 degree beam; these beam widths are good for sailboats. 45 being better than 12. But the 235 kHz has a beam width of 7 degrees. Not good at all for sailboats.

12 degree beam width should be the minimum used on a sailboat but wider is definitely better. Fortunately, most transducers are at least 12 degrees.

You also need to take beam width into account when choosing a mounting location for a transducer. If you have a 45 degree beam and it hits your keel you will never get an accurate bottom reading.

[a64pilot]

Mine is mounted close beside of my full keel boat and works just fine with either frequency.
Assumption is that targets too close are ignored, there is a min range so to speak, typical for Radar, assumption is maybe it is for Sonar too.

The P79 can adjust to be dead level for deadrise from 2 to 22 degrees, so deadrise doesn’t have to be taken into account if you shim an Xducer to be level.

[Pete7]

Originally Posted by KeelMe

Beam width should NOT be taken with a grain of salt. It is one of the most important factors when specifying a transducer for a sailboat.

I suspect most transducers come with fish finders and therefore the buyer may not get much choice. I think I had the choice of transom, in hull or shoot through. Like A64 I chose the P97 shoot through as the easy option to fit but they do give a good image for depths I need to worry about. Mounted on the inside of the hull the adjustable mounting bracket takes up the angle of the hull quite easily.

The limited choice by the manufacturers is probably a good thing for the majority of users.

Pete

[guyrj33]

Try Defender model # DT800PV-235-N2