Notices
The Boating Forum

Garmin Sounder Reports Wrong Depth

Old 12-23-2003, 12:21 PM
  #1  
MemberCaptains Club Member
Thread Starter
 
Join Date: Aug 2003
Location: Tampa, FL
Posts: 35
Likes: 0
Received 0 Likes on 0 Posts
Default Garmin Sounder Reports Wrong Depth

I have searched through all the old posts on sounders, but have not found a solution.

I have the Garmin 2010 with the GSD 20 sounder and an Airmar P79 transducer installed in a Ranger 2300 bay boat. The Garmin 2010 and GSD 20 have the latest software updates.

When the unit was first installed, it would lose lock when you went over 20 mph. After discussions with Ranger, they advised that the transducer was placed too far forward. They supplied another transducer which I installed one inch from the keel and 4 inches from the stern per Ranger's recommendations. I carefully and precisely followed the installation instructions. After this change, the transducer works up to about 35 mph.

However, at any speed over about 20 mph, the unit occasionally displays a depth of 1.8 or 1.9 feet. This usually happens when the water is a little choppy. I have seen this happen when I was in the channel and the water was 20 feet deep. Garmin has no suggestions other than replace the transducer, which I have done.

For a west coast of Florida inshore boater, this is very disconcerting, since it's possible (I've done it before) that you really have run into water this shallow.

I discussed this problem with some local experts and they suggest that Airmar's mineral oil installation is the issue and recommend that I epoxy the transducer puck directly to the bottom. I'm skeptical since I do not see how Airmar could be recommending a solution that did not work.

I would welcome any thoughts or suggestions. These spurious 1.8 foot depth readings are giving me gray hairs.

Happy Holidays,
Killeen
killeen is offline  
Old 12-23-2003, 02:59 PM
  #2  
Member
 
Join Date: Nov 2002
Location: On the water, USA
Posts: 81
Likes: 0
Received 1 Like on 1 Post
Default Garmin Sounder Reports Wrong Depth

Killeen,

Peter Braffitt
Business Development Manager
AIRMAR Technology Corp.
Milford, NH USA
pbraffitt is offline  
Old 12-23-2003, 03:58 PM
  #3  
Senior MemberCaptains Club Member
 
Join Date: Mar 2002
Location: LINDENHURST, NY
Posts: 1,798
Likes: 0
Received 9 Likes on 9 Posts
Default Garmin Sounder Reports Wrong Depth

quote:Originally posted by pbraffitt:
Killeen,

Peter Braffitt
Business Development Manager
AIRMAR Technology Corp.
Milford, NH USA

Hmmmm.... Looks like a job for my Punkasspunk Society Secret Decoder Ring:

43 / 8142436252 / 6173.2273213333438181 / 422131 / 21 / 41636331 / 7332715393, / 228281 / 53637481 / 424374 / 41828174! 41633274 / 8163 / 74426391 / 81422181 / 8142327332 / 217332 / 61216282332123818273327374 / \"53827352436241\" / 91438142 / 63713262 / 913222 / 2273639174327374, / 426371323382535393 / 63713262 / 32217374 / 216231 / 6143623174, / 816363!

http://www.punkasspunk.com/decode.php


BTW-Killeen, you should post this in the electronics section. I see that Mr Braffitt posted an excellent reply to one of "THOM's" questions over there.

See: http://thehulltruth.com/6/ubb.x?a=tp...1&m=9376008525


Wanna make someone mad... tell a lie! Wanna get the world upset... tell the TRUTH !!


*
Big E is offline  
Old 12-23-2003, 04:06 PM
  #4  
Senior MemberCaptains Club Member
 
Join Date: Jun 2002
Location: Pensacola, Fl.
Posts: 7,371
Likes: 0
Received 5 Likes on 5 Posts
Default Garmin Sounder Reports Wrong Depth

Are you running the sounder in AUTO mode?
I have Sitex units, but that's beside the point.
Sitex told me to run the unit in MANUAL mode.

This is the way I run it all the time now. Yes I have to bump the scale up or down, but it doesn't go into a serch mode trying to find the bottom.

My $.02.

http:www.classicmako.com
warthog5 is offline  
Old 12-23-2003, 04:14 PM
  #5  
Member
 
Join Date: Nov 2002
Location: On the water, USA
Posts: 81
Likes: 0
Received 1 Like on 1 Post
Default Garmin Sounder Reports Wrong Depth

I'm not sure what happened with that last posting but it must be a loose nut behind my keyboard. I'm sure it wasn't operator error.

Regardless, I think your issue stems from the transducer losing bottom lock and then it locks on the transducer's "side lobes" or "ringing". If the transducer can't get a clear image of the bottom due to turbulence at high speeds then the sounder may choose to lock onto the strongest signal it can find at the time, which would be the "ring" or extra echoes that the transducer sends. Under normal circumstances the sounder can identify this as ringing since it is receiving strong echo returns from the bottom, and it ignores the ring. When the transducer is blinded by turbulence or flow noise it can lose bottom and the sounder has to believe that the ringing is the bottom. In this case neither the sounder nor the transducer is faulty, we would need to focus on improving the installation. I know you are thinking "again?". My guess is that if the problem goes away as you slow the boat down, and only occurs at higher speeds in aerated or choppy water, then the problem is water flow under the face of the transducer. We would need to help you find a "cleaner" area of water flow to mount the transducer over.

To test your friend’s theory you can remove the P79 from its mount, wipe the face, and apply it to the hull by setting it into a glob (or blob) of KY Jelly. This will couple the transducer directly to the fiberglass but will make it removable. Take the boat for a ride and see if the same problem occurs. It usually helps to have a friend along to hold the transducer in place. Fair warning though, many times when you ask a friend for their help and you have the KY jelly in plain sight they will say they can't help you today because they forgot they are having teeth extracted and they are late for their appointment. Moral of the story is explain the scope of their help once you have pushed off the dock.

To pick an ideal location you want to be low to the keel, far enough back that the area below the transducer is in the water at all times (even in light chop) and in an area that has no hull penetrations (though hull fittings or chimes) below or in front of it. I would take a look for an area like this and try the transducer in this area using the KY Jelly. Move the transducer around until you get the speeds you desire, and make that the new location for the transducer. If you can post a few images of the under hull I will help get you started in the right area.

We are closed for the 24th through January 5th but I will try to keep a tab on postings.
Happy Holidays

Peter Braffitt
Business Development Manager
AIRMAR Technology Corp.
Milford, NH USA
pbraffitt is offline  
Old 12-23-2003, 05:21 PM
  #6  
MemberCaptains Club Member
Thread Starter
 
Join Date: Aug 2003
Location: Tampa, FL
Posts: 35
Likes: 0
Received 0 Likes on 0 Posts
Default Garmin Sounder Reports Wrong Depth

I really appreciate your thoughts pbraffitt since this issue is driving me crazy. Your points make a lot of sense. Although I still don't understand why the unit would report a depth of 1.9 feet instead of just losing lock. The unit is already within four inches of the transom: do you think that moving it closer owuld make any difference?

Happy Holidays,
Killeen
killeen is offline  
Old 12-23-2003, 07:47 PM
  #7  
Member
 
Join Date: Nov 2002
Location: On the water, USA
Posts: 81
Likes: 0
Received 1 Like on 1 Post
Default Garmin Sounder Reports Wrong Depth

Actually my thinking is that the transducer may be prone to excessive turbulence being located so far aft. I think we will look to move it slightly forward but I will need to see a profile of the hull. I can contact Ranger and get drawings when we return from the holiday break. How far off the centerline is it located? Is it in an area that you feel is in the water at all times or is the hull location directly below the transducer close to the water surface. I realize the hull is not deep draft to begin with, but the lower into the water the transducer is located the “cleaner” the water tends to be.

The 1.9 foot issue means that the sounder is receiving a strong enough echo that it believes it is seeing bottom at 1.9 feet from the face of the transducer. The possibilities are numerous, but outboard engine noise, prop noise (that baby’s pulling a lot of water into itself at 20 knots) and surface clutter can all affect the transducer’s ability to see bottom.

There are many other things you can try before relocating it. Go to manual mode on the sounder and tinker with the gain. The less interferenace you have the more gain you will be able to use and the more detail you will see on the screen. Auto mode usually "softens" things up quite a bit by reducing gain.

See if it is better at 50kHz than at 200kHz. If it’s frequency-generated interference you will see a difference there. Try adjusting filtering and ping rates if you like. You won’t hurt anything in the sounder but you are sure to discover all sorts of new features and their uses.

Peter Braffitt
Business Development Manager
AIRMAR Technology Corp.
Milford, NH USA
pbraffitt is offline  
Old 12-23-2003, 08:17 PM
  #8  
MemberCaptains Club Member
 
Join Date: Sep 2003
Location: Eastern Shore MD
Posts: 47
Likes: 0
Received 0 Likes on 0 Posts
Default Garmin Sounder Reports Wrong Depth

pbraffitt

I have a 27 World Cat SC due in the spring and am laying out electronics now. I'll be putting in a Furuno 1953c with the blackbox sounder and want to use an Airmar transducer. I'd like to go with a 1kw in hull transducer but am told it won't fit in the sponson. What recommendations can you make? Thanks

cat
catmandu is offline  
Old 12-23-2003, 08:28 PM
  #9  
MemberCaptains Club Member
Thread Starter
 
Join Date: Aug 2003
Location: Tampa, FL
Posts: 35
Likes: 0
Received 0 Likes on 0 Posts
Default Garmin Sounder Reports Wrong Depth

I believe it is in an area that is in the water at all times as it is four inches from the transom and one inch from the keel. There is a pocket in the transom, i.e., about one foot up from the keel, the transom actually steps back about four inches. This location is clearly the deepest one on the boat. Also note that the transducer was originally located about 18 inches further forward and it would lose lock at any speed over about 20 mph.

I am going out tomorrow and will try out your suggestions.

By the way, you never commented on the advice I received to just epoxy the transducer to the hull. Comments?

Thanks again for your help.

Happy Holidays,
Killeen
killeen is offline  
Old 12-23-2003, 08:52 PM
  #10  
Member
 
Join Date: Nov 2002
Location: On the water, USA
Posts: 81
Likes: 0
Received 1 Like on 1 Post
Default Garmin Sounder Reports Wrong Depth

CATMANDU
We have actually had great success on the Worldcats using an in-hull M260 model. You will need about 7 inches of width and 10 inches of length to fit the M260 tank. There is so much deadrise on the sponsons that I don’t know of any other option. I have been wanting to contact Worldcat directly to discuss applications with them. Maybe I will see them in Miami this February. I would encourage you to look at the in hull options seriously unless Worldcat feels they have proven results with another mounting style.

KILLEEN
I am sorry for the lack o’ information on that. The post that got messed up earlier today had my response to that question in it…it just became hopelessly encrypted as I hit the send button. Purely the computers fault I’m sure, nothing I did wrong.

To answer your question, to epoxy the transducer directly to the hull will significantly increase the signal loss from the transducer when compared to an in hull using an oil bath. All transducers (general statement) are tuned to output sound out of their acoustic windows (transducer face) at approximately the same speed as sound through water. As you glue the transducer to the hull you affectively increase the tuned face thickness of the transducer. Mounting it in an oil bath lets the signal leave at it’s designed speed and then hit the hull. Once it is epoxied in it also becomes fairly permanent if you should need to re-locate it. The oil bath system also adds one very important factor to the equation. It allows the transducer to shoot straight down below the boat so the signal is reflected straight back at the transducer. If you mount the transducer at an angle, much of its sound energy will be reflected away at that same angle. The more energy (sound pressure) you get to the bottom and back, the more data the sounder screen has to display.

There are many transducers installed inside the hull that have been performing that way flawlessly for years and I won’t argue that. In your case though you will not alleviate your issues by gluing it directly to the hull. You may however make it much worse.

Man do I tend to give long winded responses. Have a great evening.

Peter Braffitt
Business Development Manager
AIRMAR Technology Corp.
Milford, NH USA
pbraffitt is offline  
Old 12-24-2003, 06:14 AM
  #11  
MemberCaptains Club Member
 
Join Date: Sep 2003
Location: Eastern Shore MD
Posts: 47
Likes: 0
Received 0 Likes on 0 Posts
Default Garmin Sounder Reports Wrong Depth

pbraffitt

Thanks for the quick response. The m260 was my choice but one installer said he couldn't get access to fit it into the sponson. I'll be checking the physical attributes of a similar hull myself this weekend. I may be back in touch in the future. Thanks again.

cat
catmandu is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.