Eliminating motor noise?

Gregotis98 · 05-12-2003, 07:10 PM

What's the best way to get rid of motor noise on a fishfinder? I hate the fact that my new $1,200 sounder only works at idle. I won't even mention our so called halibut trip out of Garibaldi this last weekend!

Mello-Yello · 05-12-2003, 07:43 PM

It sounds like your fish-finder is tied in with your ignition system (key switch). Your fish-finder should have it's own circuit, i.e. it's very own hot wire run directly to the battery.

My advice would be to run one hot wire from your battery's positive post, and connect it to a terminal strip located under your dash. This will allow you to run numerous accessories that don't like interference from your ignition. This will keep you from having to run a lot of 'hot' wires from your battery. I would also suggest you buy a can of liquid insulation. It's kinda like PVC cement, it comes in a can w/a brush. You brush the stuff on the bare metal on your terminal strips and it acts as a protective barrier and protect against water/corrosion.

M-Y

Gregotis98 · 05-12-2003, 08:02 PM

It's on a separate fuse panel I use for all my accessories already. I've seen noise filters for car audio systems that are put in line off the alternator and am wondering if this might help.

God, I feel ****y after getting my hopes up for halibut and only landing one keeper for the weekend, and am getting a bad feeling about the weather for this weekend. Please cheer me up.

05-12-2003, 08:08 PM

Try new high quality spark plug wires

Mello-Yello · 05-12-2003, 08:16 PM

Hmmmm, is this fuse panel hot all the time, or only hot when the key is on? What is your f-f grounded to?

There are filters you can get, but you shouldn't need one. One would think a $1,200 fish-finder would have one built in.

It sounds like you're getting 'dirty' power. As a last resort, put a 12v battery in your boat exclusively for your f-f to get you through this weekend. Speaking of which, the weather is going to make a turn by tomorrow. Thursday's forecast will be calling for 2' windwaves and long ocean swells. Each day will get progressively better, with completely flat seas by Saturday. Wide open baby!

Did that help?

Pilar · 05-12-2003, 08:35 PM

Gregotis98, I have been there and done that with the Plastic Jesus. Here's the extreme I had to go to in the search for a solution.

First a description of the problems.

1) Low voltage dropout on cranking the engine. Every time I started the engine, the GPS would reset and beeeeeeepppp!, my plotted track would evaporate and the setup course and destination would go away.

2) Snow or noise on the sonar screen. I noticed that I would get a reading of many fish under the boat everytime I fired up to run to a new spot. This happened every time so I began to realize the coincidence.

3) Loss of bottom tracking at high speed or in rough water.

So the end result was 2 different problems interacting to some degree. I have 2 batteries and problems 1 and 2 were solved by connecting the GPS to the instrument battery (a group 30 diehard deepcycle) with a 24 hour reserve for the loads on the boat and then running that battery isolated from the alternator. I charge by using ALL on long runs and an overnight on the charger when I get home. Instrument battery is #2 so the switch is on #1 most of the time. Starting battery is #1. Also if I use ALL on the switch the dropout problem is gone but the noise on the screen is still there. I used a pi filter on the power leads and it only improved the noise situation it did not eliminate it.

When I run the plastic jesus on battery #2 and it is isolated from the alternator the problem dissapears completely. From this I conclude that the problem is the alternator diode noise.

The last problem was much harder to solve. It was caused by turbulent flow across the transducer. The only way to find this is to let someone drive your boat and hang your head over the transom and put the eye on the transducer. The water should go by in a solid sheet with no foam or streaks in it. Moving the transducer up or down may fix it but sometimes a new location is necessary due to chines on the hull or obstructions disturbing the flow. You have to see it to figure it out though.

I moved my transducer up just 1/4" and now it reads perfect at any speed.

Just my $3.75, hope it helps, Greg.

As far as the weather goes .... come down to Newport and hang out with the dogs. Rogue has a pretty good selection of adult beverages and the company of your shipmates is hard to beat. Leave the Garibaldi fishery to the diehards from Tillamook.

If it blows we hang out at the beach and BS, if not then we run for glory and fish. Maybe we can get Wak to tell us more about Russia.

[ 05-12-2003, 09:36 PM: Message edited by: Pilar ]

Gregotis98 · 05-12-2003, 09:00 PM

Pilar, those are the same symptoms I'm having. I have two group 27 deep cycle's and a switch that I haven't hooked up yet, so thankfully this sounds like the fix.

Albacore Tuna Captain · 05-13-2003, 07:43 AM

Pilar, I have the same problem on my boat and deduced that it was being caused not by a bad alternator, but the inverter I use for my computer. The computer inverter is running off my isolated battery for my electronics because I don't shut anythig off when I restart the engines. But if I hook into the main power system, I will lose my computer set up each time I refire the engines. So can I put in a switch to switch the computer over to the isolated battery when I restart without causing a drop in the load????

Help me! I know some electronics stuff but just enough to make me really dangerous! [img]graemlins/dork.gif[/img]

Miss B Haven · 05-13-2003, 08:03 AM

The best way to do this is have a separate isolated battery just for the electonics. It's the cleanest power you can get. Put in a 3 way selector switch so you can use that battery as an emergency start and can switch and also charge it up when you are running for home!
Run the FF, GPS, and VHF off from it. A good deep cycle Group 27 will last all day and more (100 amp hours total, 50 amp hrs useable - 50% capacity rule).
There are other ways to do this (battery isolator, diodes etc) but this is the cheap, easy and low maint version. It does require you to remember what the 4 switch settings are for (1, Both, 2 and Off).

Pilar · 05-13-2003, 08:13 AM

Noise from an alternator is not because the alternator is bad. Diodes that are switching are just electrically noisy. Inverters use diodes and SCRs and they are very noisy. Some even emit an audible buzz or whine. This electrical noise can be transmitted back to the power source, transmitted like radio signals to other electrical equipment and of course be present at the 110v ac outlet.

Mike, it would be easy to use an inexpensive relay and let it switch over automatically when you restart the engines. You could go even cheaper and use a toggle switch. But then you have to remember to use it.

I suggest you trigger the relay off of the bilge blowers you are supposed to run before cranking the engines. The relay I am thinking of is available at radio shack with a 12 volt coil and make before break contacts. Normal position is relay off and the inverter on the main battery set. When you flip on the bilge blowers the relay fires and switches the inverter to the instrument battery to prevent the dropout problem. You start the boat and then when you shut down the bilge blowers the relay shuts off and you are back on main power for the inverter.

If you need more on this Mike, I would be happy to help. As long as we can do the work at sea and I can bring my fishin pole!!!!! :grin:

Seriously, E-mail me and I'll tell you more. I do this stuff everyday for a living.

[ 05-13-2003, 09:13 AM: Message edited by: Pilar ]

Pitch Pocket · 05-13-2003, 08:39 AM

I've got a similar group of problems.

The Furuno shuts down when starting the engine. It quickly reboots and doesn't take as long to fix a position as a cold boot, but is still annoying.

My stereo on AM is not useable when the motor is running and has an annoying click when at anchor. I determined that the sonar signal is the clicking at anchor.

I've got two batteries with a Perko switch. If I run a wire from the 2nd battery to the radio I run the risk of leaving it on and draining the battery. If I run the wire to a buss and run the Furuno and the stereo off of it, I won't lose the sonar click.

Any ideas?

Miss B Haven · 05-13-2003, 08:53 AM

Steve - Get a CD player, ditch the AM stations. Forget the dang ball games while you're out!