Transducer placement
Printed From: The Fishing Website
Category: General Forums
Forum Name: The Boat Shed
Forum Description: Discuss all things boating.
URL: https://www.fishing.net.nz/forum/forum_posts.asp?TID=127339
Printed Date: 21 Jun 2026 at 10:05am
Topic: Transducer placement
Posted By: AdAstra
Subject: Transducer placement
Date Posted: 25 Feb 2018 at 4:47pm
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No clear view of bottom when planning including 'on again/off again depth reading. I have by trial and error obtained an excellent image by using a gadget that allows easy vertical movement of the transducer and set it below the level of hull bottom. But my planning view is, although a little better, still quite unacceptable Could this be the cause? The bung for the Stbd air chamber  Unit is Lowrance Elite7. Boat Fi-Glass Warrior. Cheers |
Replies:
Posted By: Kevin.S
Date Posted: 25 Feb 2018 at 4:52pm
| A view showing the underside of the hull and the transducer would be good. In a lot of cases it's something on the hull causing the issue, especially as I think you are saying it works well at rest but badly when moving. |
Posted By: AdAstra
Date Posted: 25 Feb 2018 at 5:12pm
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Best I can do with small camera in awkward position. Focus is not the best! Look pretty clear to me though.  Here's another from flatter angle of transom  |
Posted By: Tagit
Date Posted: 25 Feb 2018 at 8:23pm
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It isn't the bung causing it. Doesn't appear to be anything on the hull bottom either. Positioning out from hull centre looks to be OK. So a few things to check - 1) Have you set up or tried playing with the filters in your depth sounder to minimise surface nose? 2) Is the face of the transducer angled slightly forward? 3) Have you got the right transducer selected in the depth sounder options and the right frequency and right power setting? If all that is OK and the transducer is good then you are looking at a possible 'cavitation' issue as the water flows off the bottom face of the hull. What happens as you plane along is the water under the hull rises rapidly behind the hull and the transducer face needs to get into the clean flow not the aerated stuff. Normal answer is to go deeper. Transducers like this that mount back from the transom can be awkward to get set right. One thing that you could try is to make up a bit of timber that you can fit under the bracket that has the effect of extending the bottom of the hull back to the point of the transducer. The idea is to get the laminar flow all the way back to the transducer rather than rely on a clean flow off the bottom edge of the transom. Just mock something up and install it with some cheap and easy to remove silicon initially to see if it helps. You need to get the joint to the transom edge super smooth though. If that does work you can do a more permanent install.
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Posted By: ofthesea
Date Posted: 25 Feb 2018 at 9:54pm
| Its not a helpful photo, stand further back please behind the boat and take a photo. Reason being I wonder if the transducer is breaking clear of the water at planing speed? |
Posted By: smudge
Date Posted: 25 Feb 2018 at 10:13pm
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I think it is a smidgeon too high
------------- Best gurnard fisherman in my street |
Posted By: Tagit
Date Posted: 25 Feb 2018 at 10:28pm
| In the photo it also looks like it might not be angled forward at all but it is hard to see clearly. |
Posted By: clank
Date Posted: 25 Feb 2018 at 10:34pm
| I've had this problem on a past boat, it was just the face of the transducer facing slightly down so make sure the transducer is flat. Obviously any adjustment of the angle may subsequently need height adjustment |
Posted By: Steps
Date Posted: 26 Feb 2018 at 8:18am
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No clear view of bottom when planning including 'on again/off again depth reading. What speeds are you talking about? Have you set up exactly as per the instructions in the manual? Get the leading edge height wrong or the angle slightly off, just a mm or so too high , makes a huge difference. Also dropping too low low works, but sends up fine spray around the outboard that get sucked inside.. bad news for the engine.    |
Posted By: AdAstra
Date Posted: 26 Feb 2018 at 8:53am
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I must admit that I have not taken notice at what speed boat come up on plane, but that's when image deteriorates. Yes, fitted to instructions except that I have sunk it lower (for reasons said in original post. The upward angle is much less than that shown in your diagram. The degrees of up/down movement on this mechanism is I find rather coarse. If I lifted it to the next notch it would seem (to me at least) too angled as to create quite a disturbance in the water! Hmmm. Spray coming into the engine. I've heard of that. I have looked, can't say I have noticed any. Friend of mind made up a shield because it was happening to his boat. Regardless, any alteration I make will be done after my weeks fishing holiday at Mahia. The sounder works fine as long as I am off the plane. That's a good speed anyway for poking around looking for structure, fish etc. Will post results then Thanks Dave
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Posted By: Steps
Date Posted: 26 Feb 2018 at 10:56am
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The above instructions is for Lowrance I must admit that I have not taken notice at what speed boat come up on plane, but that's when image deteriorates. Most get over the bow wave around mid 20s mph, then can slow down to around 19/20 mph and remain on the plane.. very generalised. I can travel around 39/ 40 mph clearly see the bottom, but bit fast to see anything except a reef or channel go past. 30/ 32 bait balls etc are clear. I did find if was a fraction lower than recommended, or angle in relationship to straight line off the bottom of the hull, it tends to deteriorate.. think maybe would pick up air bubbles and direct under the transducer... The smallest sign of bubble passing underneath (cavitation/ venation as mentioned in posts above screws it up. NO AIR BUBBLES If I lifted it to the next notch it would seem (to me at least) too angled as to create quite a disturbance in the water! What is the difference in height between notches? As I said, a couple degrees here and/ or a mm or so is the difference between working reliable and not. Did you dummy fit the angle AND the height, attached to the bracket THEN fix the bracket? Friend of mind made up a shield because it was happening to his boat. I had an long issue getting min to work.. then discovered the main issue was ther hull was designed / builts yrs before Sounders/ gps where an item not affordable for rec/ non commercial , joe public users... Hence I have mine a smidgen lower than the above. I also got a mist spray that sucks up over the engine (salt deposits on the cowl a sure sign) and would suck back into the deck area.. damp back occasionally. Played around with shields.. this is mark1....works so well .. simple, cheap (free, square 5L plastic container ) easy to fix to stern (mounts behind the transducer bracket using the bracket screws.) , its become permanent. And as mentioned in posts above, the settings.... There are some real good tips etc in these forums the site search button above, excellent resource. and links to web sites for setting these right.  |
Posted By: letsgetem
Date Posted: 26 Feb 2018 at 11:51am
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You say at higher speed the image deteriorates. Does it show black spotting all over, that appears to be interference of some kind. My Elite-5 does that. Faster the speed the worse the black spotting. Ive noticed the spotting gets worse as the motor is trimmed further forward (ie bow down); so I assume the interference is caused by turbulence from the propeller being nearer the transducer (when the motor is further forward). The only way I can think of reducing that is to move the transducer further away sideways, but on a small narrow boat (1.85m beam) that's not feasible. So I have to put up with it.
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Posted By: AdAstra
Date Posted: 26 Feb 2018 at 2:06pm
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Mine is a Lowrance - Elite7 Chirp. Height between notches? From the trailing edge of t/cucer to ground below at present setting = 410mm Lift trailing edge by one increment = 432mm Photos attached. Straight edge fixed to underside of hull represents the continuation of hull.   |
Posted By: AdAstra
Date Posted: 26 Feb 2018 at 6:08pm
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No I don't get what you are seeing on your unit. Mine is more like 'noise' or 'clutter'. I can see the surface and bottom. Just not clear enough to be of any real use! With my limited knowledge of such matters and at great risk of being 'shot-to-shyte' by them that have plenty. I understand that if your transducer is mounted on stbd side of transom within the limits of the fitting instructions and you have a normal 'clockwise' rotating prop with no damage to the blades, then there should be no turbulence between the propeller blades and your tranny. It all goes out back providing thrust. |
Posted By: viscount
Date Posted: 26 Feb 2018 at 7:58pm
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As per your new top photo, drop the back of the transducer down so it will be just under your straight edge, start there and see how it goes. ------------- Calling fishing a hobby is like calling brain surgery a job - Paul Schullery |
Posted By: AdAstra
Date Posted: 26 Feb 2018 at 9:20pm
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OK but tranny is as low as it will go on track. Will have to refix it. Thanks
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Posted By: ofthesea
Date Posted: 26 Feb 2018 at 10:49pm
Yes I agree, the rear should be slightly lower than the front of the transducer
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viscount wrote:Posted By: letsgetem
Date Posted: 27 Feb 2018 at 9:24am
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Adastra - the stuff I see looks like "noise or clutter" to me too. And - visually, I can see what looks like prop turbulence out where the transducer is. And - what else could it be, given that it changes as the motor trim is changed.
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Posted By: AdAstra
Date Posted: 27 Feb 2018 at 9:32am
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I'd like to give you an answer, but I cannot. If you can imagine that all the knowledge available on sonar and stuff would fill a 200lt drum. My total knowledge will fill the bottom of an egg cup!
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Posted By: Steps
Date Posted: 27 Feb 2018 at 9:35am
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Is that your speedometer pick up is right next to the transducer? How close is it? If so that will most likely cause an issue. most outboards have provision to connect to speed o meter And agree As per your new top photo, drop the back of the transducer down so it will be just under your straight edge, start there and see how it goes. Go back up to the lowrance instructions above.. thats what they say Think of it this way. off the plane, or stopped the transducer is simply buried in the water , maybe 2 to 3" down.. nil air bubbles boat on the plain, there is no water against the back of the stern.. initially comes out on the line from under the hull surface, then slowly rises in an elliptical curve till eventually reaches normal sea level around the rear end of the motor cavitation plate (if engine has been mounted correct height) you need the bottom surface of the transcducer.. generally 1/2 the thickness approx of the transducer to be in this flow of water ... bottom fully covered and not have any bubbles from 1/ air that maybe trapped from up the bow end and flow under the boat (could be a crack or defect or even a rib designed to flow trapped air under, or running back down the keel ) 2/ Air bubbles forced back from the prop.. in reality even if mounted either side and far closer than recommended , when on the plane boat goes to fast to interfere.. but at idle speed yes. This from your description can be eliminated. 3/ transducer mounted so maybe high and/ or flick up while on the plain, and rear section bottom surface is not fully under water.. has air. 4/ the leading edge is a mm or so too high, and can drag air under. I mentioned above I had issues because of older keel type hull. I have the old mounts holes from what remained of some large trim tabs. Therefore did a LOT of real life playing with a lot of expert and non expert suggestions, with locations both sides of the motor without having to make new holes. If you have too much angle.. it usually works, must understand the sounder cone is not as square and directs further under the boat. I THINK not being very square with the sea surface MAY also distort fish sign readings. This MAY result in while not moving or slow drift a lot of sign is not seen.. but seen as you move. (???) |
Posted By: AdAstra
Date Posted: 27 Feb 2018 at 9:53am
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Thanks Steps. The positioning saga is bordering on "Dark Art" 
As said in a previous, I am off to Mahia for a week starting Friday and do not want to make any drastic alterations involving drilling new holes and/or filling in old ones. But I can undertake changes to angles and very small adjustments to depth. Will let all contributers know of results Cheers
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Posted By: Fissure
Date Posted: 27 Feb 2018 at 11:06am
| as others have said, the stern of the tranny needs to be lower than the bow to force water/air off the face. make sure your'e not too close to the centre line of the boat, otherwise you may get interference from motor/prop. carefully observe whilst on the plane. tranny should only just be just slightly under water, not way deep or barely submerged/breaking surface. try and find what other people have done with same boat. make sure that sliding bracket is solid, not moving around. my 2 cents. |
Posted By: AdAstra
Date Posted: 27 Feb 2018 at 11:33am
| Thank you Fissure. Your 2 cents to me are worth several $$$ |
Posted By: AdAstra
Date Posted: 27 Feb 2018 at 12:11pm
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Speedo intake is 200mm from t/ducer. I have though removed it. It is not necessary. I just didn't like an instrument not doing anything! Have altered angle. We'll see what happens  |
Posted By: Steps
Date Posted: 27 Feb 2018 at 12:52pm
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Speedo intake is 200mm from t/ducer. I have though removed it. More holes.  As I said above check out your engine.. if a jonny, evinrude merc.. these I know have speedo ports built into the leg for the capillary tube. I have no idea why these are not used.. both the after market leg and outboard legs read damn near the same as the gps.. just not in 0.1x increments. When re route down thru the leg/ tilt bit in pieces, choose the route well, otherwise the tilt will chop the capillary tube Give you one guess how I know a lot of these things  Your have speed on the gps/ sounder, like you not having a gauge operational just doesnt 'look right' That last pic has gotta work. If it doesnt then I would hazard a guess that you are too close to the keel, or the hull design, like our older design hull, pre sounder 'pre economic for joe public' is designed to pull air in and down under the hull which decreases friction, increases economy fuel efficiency power/ weight ratios. What hull/ boat is it? Took months for me to figure out about the air friction thing, and only came across that talking to an old very retired marine engineer, designer. It was then I simply dropped the transducer 'too low' knew about salt spray engine issues etc, looked around the shed, including the rubbish bins and found the 5L plastic container, mounted and started trimming. Use the search button above , find a couple threads on this subject about 18 month 2 yrs ago.. lot good info and read the links re your settings. We are just 2m to 55m max, so the settings are just set .. cant rem what they are except.. blue background Very Important: DO NOT operate the transducer out of water |
Posted By: AdAstra
Date Posted: 27 Feb 2018 at 1:36pm
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T/ducer is 440mm from keel and 240mm from outside of diameter of prop. I was thinking the same re hull design. Mine would have been built when only research vessels looking for the Titanic or anti-submarine warships carried such gear. Now looking around for a suitable device to prevent any spray. To date I have not seen any neither is there any sign of salt deposits under the cowling. But......... Will look for that pick-up for speedo shortly. My motor is a 2000 Johnson115 Ocean Pro. Can only be on the lower casing facing front! Was not aware of using sonar out of water. Heard/read a few forums. Some saying yes others saying no. I guess if I'm switching on to say input way points, I should use the stop sonar function!
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Posted By: Steps
Date Posted: 27 Feb 2018 at 2:43pm
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T/ducer is 440mm from keel and 240mm from outside of diameter of prop. 240mm that full lock closest? Im 350mm from the prop if the engine is turned full lock.. about 510mm in straight ahead position. ( 2001 150hp 20" V6 johnny) And about 500mm from center of stern.. keel finishes well up under the boat, not at the stern. Now looking around for a suitable device to prevent any spray. Plastic 5L container mounted behind the transducer mounting screws  To date I have not seen any neither is there any sign of salt deposits under the cowling. you will see very little salt deposits, but will notice corrosion around plugs and stuff start.. the issue is sucking air with salt laden water into the intakes/ engine.. salt also acts as a grinding paste.. wear. The deposits tended to build up over a day far more on the top and sides of the engine cover.. outside. Couple times a yr I wash down and dry off then mist spray lanolin aerosol the power head, inside cover to protect... Dont use crc type products , they can attack certain electrical cable insulations/ HT leads. My motor is a 2000 Johnson115 Ocean Pro. Can only be on the lower casing facing front! Thats it... pic below I guess if I'm switching on to say input way points, I should use the stop sonar function! yes..or bucket of water.. or dont plug the sonar connection into the back of the sounder unit. The transducers, my understanding is what pulls most of the current of the overall unit... lot current= heat Same thing applies to submersible stern lights One thing not covered here is electrical interference.. running the transducer cable next to the main looms.. and issue I also looked into. I ended up separating the cable and loom from lay on the floor(about 500mm) no difference.. I think the modern transducer cabling is shielded far more superior than traditional sheilded cables.Even so mine are hanging 50/ 70mm off the main cable with cable ties up under the gunnels. Could be a very different story on big high end offshore type sounders and transducers thu johnson 2001/ 2004 leg speedo connection. PS irrigation capillary tube from mitre 10 fits, and the irrigation connectors also work well in joins knew had a pic uploaded a while back.. think its the old 2004 115 johnny  |
Posted By: AdAstra
Date Posted: 11 Mar 2018 at 5:38pm
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ust returned from a weeks fishing at Mahia. I launched from Mahia Beach and within a short space of time saw that the image on screen was unacceptably cluttered at both low speed and on the plane. I returned and adjusted it back to previous setting. Clear image at low speed. Not so clear at high. That evening when boat back on trailer, I made some fine adjustments to this. Trailing edge very slightly higher than front  Bearing in mind picture quality on my screen dumps is much lower than that displayed on actual screen! These are the results.   |
Posted By: letsgetem
Date Posted: 11 Mar 2018 at 7:23pm
| Looks like what mine shows - that Im sure is prop wash. Does it change if you trim the motor forward or back. |
Posted By: JB
Date Posted: 11 Mar 2018 at 9:21pm
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If you want it sorted asap and in Auckland, give josh wester at railed fishing a call he does onsite transducer and fish finder sorting out. He's fixed heaps. It will be transducer position or settings. It's worth a couple hundred for his time to sort. Give him a bell on. You could be adjusting it for the next 10 trips before getting it right and he will give you a quick lesson in settings for you as well. https://m.facebook.com/981362045224956/photos/a.985555811472246.1073741827.981362045224956/1878324498862035/?type=3&source=44" rel="nofollow - https://m.facebook.com/981362045224956/photos/a.985555811472246.1073741827.981362045224956/1878324498862035/?type=3&source=44 |
Posted By: AdAstra
Date Posted: 11 Mar 2018 at 9:49pm
| The disturbed band on the far left is the point where knowing I was near or at the wreck site, I cut the motor and came off the plane. The clear is where I was at the low speed as displayed. |
Posted By: AdAstra
Date Posted: 11 Mar 2018 at 9:53pm
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I live down in Hawkes Bay. I'm quite happy with what I see. At planing speed, I am not looking for fish or any great detail. I can now see bottom structure clear enough for me to note and investigate if so desired.
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Posted By: Steps
Date Posted: 12 Mar 2018 at 11:41am
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Josh Wester This guy is the guru on sounders transducers... When we where having issues setting our transducer up.. every trip out a change position or angle, jump over board change angles heights. We came home late one evening at the ramp. At the wash down,( I knew who he was as had been to several of his seminars) We where in front of him and without even close examination, pointed out how the transducer was not mounted well.I asked..he suggested, told him even that didnt work well....little more discussion listening to him. Problem solved next trip out. We could not set up the transducer 'correctly' because the older hull design floated air under the hull from the bow. As to best screen settings, for what we use the boat sounder for, that was sorted at one of his seminars.. took a couple notes went home made the changes all good ever since. And hes a really nice guy to For those out of towners.. even locals.. if having issues , looking at updating .. booking a day out with him is very worth while...a learning curve way beyond you immediate needs, but very interesting....and a excellent day out on the water , good company. Sort of like a charter day out catch fish and learn about gps sounders in detail, in terms very easy to understand for the lay person. I can now see bottom structure clear enough for me to note and investigate if so desired. Accurate repeatable gps positioning and being able to see what is on the bottom, related back to previous historical records of time of yr , tides, water temps, time of day etc gets us far more fish than actually seeing the fish... except for bait balls getting live bait and schools around the balls in open water, |
Posted By: JB
Date Posted: 12 Mar 2018 at 6:48pm
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I think josh also does trips to the regions and looks at multiple boats etc at a time. If your interested give him a bell and see if he is down your way sometimes. It's like have a proper mechanic sort your car out |