Fishfinder goes crazy at speed

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F239141

F239141

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Lower Alabama (Fairhope)
My fish finder works great up to about 8 MPH, over that it shows fish everywhere and that Im in 500ft of water.

How far from the bottom of the boat should the transducer be and does anyone have a pic of their transducer on a flat bottom boat that works like it should over 8MPH

Thanks
 
More than likely your transducer is in the wrong spot. You are probably getting distortion from the cavitation from either your bow wake or motor. If you find the owners manual it should show you the location and depth that the transducer mount. If you still have problems you could always step it up to a thru-hull ducer away from the back of the boat. They cost more but if properly installed you can read the most depths at full speed. My buddies boat will read the bottom in 2500 fsw at 25kts, and I have another friend that has the bad *** simrad that will read any depth at 60 mph. That unit cost about 10k though.
 
Make sure you don't have it located too close to the motor, or behind anything that could cause turbulence like a rivet or chine....then lower it a little at a time until you get what you're looking for.
 
It sure sounds like transducer location...it might be picking up turbulence/bubbles from the bottom of the boat, or from the prop, or it could be located too high and comes out of the water on plane.

Check the mfg's instructions, be sure that it's not mounted directly behind any strakes or rivets on the bottom of the boat, and should be (generally) at least 15" or so from the prop. Also, if your prop turns clockwise, you'll get more turbulence on the port side, so locate the transducer to the starboard side (or visa versa on counter-clockwise).

Pics of the transducer location would help...
 
I'd try adjusting height before moving it. Most likely lowering it will help. Most will have about 1/2" height adjustment, but then can also angle the transducer down more, to see if that helps. Rooster tails might become the next issue, and depends on transducer on how to help reduce that.

After height then try moving, and if you haven't used a mounting board, time to install one.

PS: moving can be just an inch or two to port/starboard, not to a whole new location. If this is a large transducer, like many Humminbirds, they typically take more trial and error to get them to read while getting on plane and on plane.
 
FuzzyGrub said:
If this is a large transducer, like many Humminbirds, they typically take more trial and error to get them to read while getting on plane and on plane.
Click to expand...

Not to hijack the post, but that's what I'm into right now. My Humminbird Si transducer works great at fishing speed, but I don't get much on plane. I've tweaked the height / tilt several times, and it looks like the only solution to getting readings at speed is to add a second, 2d, transducer and a Y cable at the head unit. So, while I'm mounting a board for the new 2d transducer I might just add one for the Si. Adding the 2d transducer also has the benefit of (probably) being able to raise my Si transducer up a little, and avoid the possibility of it hitting anything in the water.

Rooster tails can be a problem (it is on mine), but I saw this solution on another site. Haven't done this myself, so can't say if it works or not. BTW, the transducer board in this pic looks a little low, probably should be mounted 1/4" higher to avoid becoming a trim tab.

splashguardc.jpg
 
RivRunR said:
FuzzyGrub said:
If this is a large transducer, like many Humminbirds, they typically take more trial and error to get them to read while getting on plane and on plane.
Click to expand...

Not to hijack the post, but that's what I'm into right now. My Humminbird Si transducer works great at fishing speed, but I don't get much on plane. I've tweaked the height / tilt several times, and it looks like the only solution to getting readings at speed is to add a second, 2d, transducer and a Y cable at the head unit. So, while I'm mounting a board for the new 2d transducer I might just add one for the Si. Adding the 2d transducer also has the benefit of (probably) being able to raise my Si transducer up a little, and avoid the possibility of it hitting anything in the water.

Rooster tails can be a problem (it is on mine), but I saw this solution on another site. Haven't done this myself, so can't say if it works or not. BTW, the transducer board in this pic looks a little low, probably should be mounted 1/4" higher to avoid becoming a trim tab.

Click to expand...

Adding good SI (both sides) to the mix on one transducer, makes it even more fun!

If you have the compact si transducer, make sure it has the rubber plug in it. If you have the HDSI wrap some black electrical tape around the gap between the transducer and the mount.

If you are going to split SI and 2D, I'd try some temp mounting of SI at more center of boat to get both sides imaging well, but the transducer has to be out of the water on plane. Many bass boats mout it on the their jack plate.

I have a single HDSI transducer for my 798ci. I have it mounted on the port side, to get clearer SI as I generally work shoreline in a clockwise fashion. The starboard side image is slightly darker, because it has to send/receive through the boat/motor gap. My 2D at wot plane (30mph) is noisy but tracks bottom. It is the best I have been able to tweak on only using one transducer. The tape prevented the rooster tail from getting water on the engine or in the boat.
 
My Si images are great right now, and I get depth readings at speed (20 - 35 mph), but I loose bottom tracking, which is why I'm adding a 2d transducer. I already have the 2d transducer from another unit, so it only costs me the Y cable.

Altho my image is slightly darker on the port side (starboard side mount), it's not that noticeable. Don't have a pic of my Si mount, but the "groove" between the 2 halves is even with the hull, and it's tilted down 1 or 2 clicks. Since I'm going to mount boards on both sides now, it'll be pretty easy to switch sides for the Si mount. I see what you're saying about moving it more to the center, but I'm wondering if a center location would give me a lot of prop turbulence?

I don't have the compact Si transducer (898c SI), so there's no rubber plug (thanks Humminbird!). I'm going to try raising the Si transducer up a couple of inches to eliminate the rooster tail, and to eliminate the possibility of it getting smacked. If the Si imaging isn't as good in the raised position, I'll re-mount it where it is now and try your tape trick, or add a shield like the one in the pic I posted.

Not sure I understand your comment about the Si transducer has to be out of the water on plane...could you explain?
 
RivRunR said:
My Si images are great right now, and I get depth readings at speed (20 - 35 mph), but I loose bottom tracking, which is why I'm adding a 2d transducer. I already have the 2d transducer from another unit, so it only costs me the Y cable.

Altho my image is slightly darker on the port side (starboard side mount), it's not that noticeable. Don't have a pic of my Si mount, but the "groove" between the 2 halves is even with the hull, and it's tilted down 1 or 2 clicks. Since I'm going to mount boards on both sides now, it'll be pretty easy to switch sides for the Si mount. I see what you're saying about moving it more to the center, but I'm wondering if a center location would give me a lot of prop turbulence?

I don't have the compact Si transducer (898c SI), so there's no rubber plug (thanks Humminbird!). I'm going to try raising the Si transducer up a couple of inches to eliminate the rooster tail, and to eliminate the possibility of it getting smacked. If the Si imaging isn't as good in the raised position, I'll re-mount it where it is now and try your tape trick, or add a shield like the one in the pic I posted.

Not sure I understand your comment about the Si transducer has to be out of the water on plane...could you explain?
Click to expand...


If you center mount it, you want it out of the water such that it doesn't cause turbulance that could cause cavitation or cooling problems for your outboard. BTW, prop wash is only an issue in reverse. ;) Now the water will be swirling around in this area, depending on your hull, loading, and speed. As I said, many Bass guys mount the SI transducer on the bottom of the jack plate, and use a thru hull 2D to track bottom at the speeds they see.
 
My depth reading would start flashing at speed, but not always. I ended up taking the transducer off and put a mounting plate on and then remounted the transducer, the FF was on the boat when I bought it. I took the boat out yesterday and it was working at speed. https://www.tinboats.net/forum/viewtopic.php?f=5&t=24141&start=15
 

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