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Old 09-10-2004, 16:13   #16
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As for why bottom paint affects transducer performance ... it's the cuprous oxide! Sending a signal through plastic is much easier than through copper! There are several specialty "transducer anti-fouling" paints available .. you will notice none of them contain copper.

L/SV Eva Luna
Bob
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Old 09-10-2004, 16:56   #17
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I have had to replace my depth sounder. I just used some silicon to bond it to the inside of the hull until I can swap the thru hull at the next haul. The new transducer is shooting through about one inch of FRP, a heavy coat of coperbot paint, and two coats of Trinidad SR botom paint. It works fine.

If I didn't already have a hole with a dead transducer in it (it is not a "pull out" kind) I might just leave it there.
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Old 10-10-2004, 13:11   #18
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Hi Wahoo, What I was meaning is why will a internall bonded tranducer work when anti-foul is STILL applied to the hull directly on the otherside of it. And yet they often don't like anti-foul applied directly to the face of the transducer. That was my question. You would think the coating would upset a transducer no matter what. But then, maybe it does, but I just haven't come across one yet. I have a copper anti-foul on my transudcer face right now and have had no issues, so it doesn't always seem to cause a problem. It maybe adherence to the surface. You only need a small airlayer between the paint film and transducer surface to stop it working.
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Old 11-10-2004, 05:57   #19
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Spent 5 years as the electronics department manager at the local Boat U.S. ... and have run into many problems regarding transducers. If you check with Airmar (the company that produces about 90% of all transducers) they will tell you that gluing them to the inside of the hull with silicone simply doesn't work (absorbs too much of the energy) ... they also say that applying bottom paint to the transducer face is an absolute no-no. Yet .... I have had dozens of customers tell me that they have done both with absolute success. Go figure. I've even had one customer tell me that he just stuck the transducer to the hull with duct tape ... and it worked just fine.
One thing does occur to me ... how many of us are looking to see if the transducer is working at 200' ? Personally, if my depth sounder (a Raymarine ST60, by the way) only read to 10' ... I'd be happy! South West Florida is the land of skinny water ... and nobody I know uses their depth sounder to follow contour lines, all we do is try to limit going aground. Lower powered transducers clearly work better in skinny water (Lowrance used to sell a model with only 50 watts output and it worked great here!) and I suppose it's possible that silicone ... and even bottom paint, actually helps the shallow water situation by limiting the actual output of the transducer.

L S/V Eva Luna
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Old 11-10-2004, 06:43   #20
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A transducer's cone angle determines its coverage area. The wider the cone angle, the greater the area that's covered. There are a variety of 192 kHz transducers with either a wide (20̊) or narrow (8̊) cone angle, and also a variety of 200 kHz transducers with either a wide (20̊) or narrow (12̊) cone angle. The 50 kHz transducers come with a 35̊ cone angle. And the dual frequency transducers come with both a narrow (12̊) 200 kHz and a 50 kHz cone angles.

Generally, use a wide cone angle for fishing shallow to medium depths. The narrow cone penetrates to deeper depths, but shows less fish and structure due to its narrow beam.

The depth capability of your sonar units depends on its transmitter power, receiver, sensitivity, frequency, transducer and transducer installation. Other things that effect depth capability are: water conditions and type, (all sonars will show deeper depth readings in fresh water than salt) and bottom conditions.

Contrary to conventional wisdom, you SHOULD paint your transducer; but use water based anti-fouling paint only. Never use ketone-based paint, since ketones can attack many plastics possibly damaging the transducer. Airmar recommends brands such as MDR, Woolsey and Petit. These water based anti-fouling paints can be found at your local marine supply store or contact Gem Electronics (US distributor).
Telephone: 800-543-6326, or 843-394-3565, Fax: 843-394-3736

Some Transducer Tips (From Airmar): www.airmar.com

1. The primary maintenance requirement is keeping the active face of the transducer free of any buildup that may impede its performance, according to Peter Braffit, business development manager at Airmar Technology Corp., a major manufacturer of transducers and sensors located in Milford, N.H.
Caked-on dirt, marine plant life and barnacles can detract from the effectiveness of the instrument by causing turbulence or trapping air at the face. These conditions can interfere with the transmission of sound and attenuate or muffle the reception of the return signal.

2. Cleaning the face of the unit should be done as soon as possible after the boat is hauled to prevent the contaminants from drying and becoming more difficult to remove. Braffit suggests that marine growth or dirt be scraped off by carefully dragging a flat tool, such as a putty knife, across the transducer face. Finish cleaning by wet-sanding with a very fine-grit sandpaper. Wet-sanding paper is available at most marine, hardware and automotive supply stores.

3. The face of the transducer can become scratched or nicked, causing turbulence or trapping air on the surface and eventually affecting the unit’s performance. The outer “skin” of a typical transducer face is a fairly thick layer of polymer or epoxy, which means you can remove scratches or minor damage by wet-sanding the face.

4. The face of the transducer should be protected with antifouling paint, according to Braffit, but Airmar recommends that only water-based paint be used. Ketoses and other solvents that may be present in other paints may be harmful to polymers and sealant used in the manufacture of transducer units. If non-ablative antifouling paint is used, it should not be allowed to build up more than two or three layers.

5. The sealing provisions for through-hull transducers should be closely inspected every time the boat comes out of the water. Look for dried-out or missing sealant, or cracks that may indicate that some movement has taken place. If any of these conditions are evident, the transducer should be taken out; the old sealant removed and the unit then re-bedded into the hull. This can be a challenging task, one that may be best left to a professional who has the proper materials and expertise to handle it.

7. The wiring of your system should be part of your regular inspection, too. Electrical connections must be secure and free of corrosion. The condition of the transducer cable also is important. Braffit warns that nicks or breaks in its metallic sheathing can allow unwanted electrical noise or interference from other electronic devices to impact the performance of the depthsounder or fishfinder. For the same reason, cables for VHF radios, inverters and other potential sources of electrical interference should not be closely bundled with transducer cables. If the proximity is unavoidable, extra cable shielding may be required.
Contact: Airmar Technology Corp., (603) 673-9570. www.airmar.com.

Airmar to host transducer workshop at IBEX 2004 (Miami Oct 25 - 27):
Airmar Technology is to host a transducer workshop at IBEX 2004 that will help boatbuilders understand the relationship between the correct positioning of transducers and overall boat and fish-finding performance. Entitled "Transducer Placement That Assures Great Fish Finder Performance", the one-hour workshop will be held at 1:30pm on Tuesday, October 26, at the Miami Convention Centre in Florida and will be hosted by two of Airmar's leading professionals - Peter Braffitt, business development manager, and engineering lab manager Steven Mills.

Airmar Transducer FAQs:
http://airmar.custhelp.com/cgi-bin/a...er/std_alp.php

“Airmar” Transducer Catalogue c/w “Application Notes - which include electrical characteristics such as resistance”
http://www.airmar.com/Product_Catalo...cat_index.html

Sensor Design Fundamentals:
http://www.airmar.com/pdfs/technical/sensor.pdf

Sonar tutorial from “Lowrance”:
http://www.lowrance.com/Tutorials/So...ar_tutorial_01
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Old 11-10-2004, 16:45   #21
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Hey Gordie,
most of us have actual depth sounders ... not fish finders, so frequency & cone angle aren't considered all that important (all of them that I'm familiar with are 200 KHZ) ... ahhh ... but wattage becomes an issue! In very shallow water, high powered transducers tend to send a signal down, it reflects back up, bounces off the hull of the boat, returns down again .. and is read a second time on it's return upward ... resulting in a display that either shows 300' of water (when you're in 10') or a series of dashs. Some units such as Humminbird, require that you power down the unit to clear the misinformation ... all of this as you're just about to go aground! There are some cool new units on the market (such as Raymarine's digital sonar) with automatically adjustable power output ... from 10 watts to a whopping 1 KW ... but this seems a bit of overkill .... if ya just want to know how deep the water is! Guess what I'm tryin' to say is ... if you're gonna be in skinny water, look for a transducer with lower power outputs.

L S/V Eva Luna
Bob
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Old 13-10-2004, 21:31   #22
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So, I gathered all my courage and finally 'pulled the plug' and sure enough, I managed to replace the spare plug without letting too much water in. After running some tests it turns out that the transducer is faulty and needs to be replaced. At least now I know how to do the switch.

Everyone, thank you for your valuable contributions. Up to my next project (sail repair)

Jan
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