View Full Version : fishfinder and boat speed

10-24-2005, 09:58 AM
I have seen people discussing fishfinder and high speed operation before, but what speed is considered "high speed"? I have a Matrix 17, it doesn't work when speed reaches 12 mph or so, and gives lots of fause signals below that speed until the boat really slows down. I adjusted that angle down a little after the first try but not seemed to help. Wondering if this is normal or there is anything wrong with my installation. One thing I can think of is the mounting bracket was welded a bit high by the factory so my transducer was slightly higher than the manual suggests.

10-24-2005, 10:11 AM
Location of the transducer and the shape of the hull determines whether or not you can track bottom at speed. The irony is that the "flat" spots on the transom that seem to be the best places to mount a transducer are actually not ideal on many hulls. The problem is entrainment of air under the planning surfaces. This is what causes the hull to lift up and ride nice. But the air has to escape somewhere at the transom and it usually exits right under the flat parts of the hull. On my present boat, it is impossible to mount a transducer that will let me track bottom at planning speeds. That's just the price of a great riding hull. All lift = all bubbles.

On deep V hulls, it often helps to mount the transducer perpendicular to the bottom on the V part of the hull. This causes some disruption of the wake and can even produce a silly rooster tail on occasion. But it often lets you track the bottom when going fast. The best solution, but a real PITA, is a through hull transducer along the V with a faring block to guide the flow of the water around the transducer.

10-24-2005, 11:00 AM
I have the same problem with my matrix 10. As soon as I put a little speed on the boat (6-8 mph) the false returns and erratic readings appear. I mounted my transducer on the transom of my 14' gregor and have made many adjustments to no avail. I think besides the problems with hull characteristics the Doc mentioned, the fish finder may be part of the problem. I haven't been terribly impressed with the matrix. I have heard of others who like thiers but it seems to be a mixed bag. I don't think I would buy one again. You get what you pay for it seems.

10-24-2005, 11:21 AM
ON fiberglass(not aluminum) hulls a transducer can be epoxied in the bilge area. It loses a little signal strength through the hull, but works quite well. It's easy to install and doen't require drilling a whole in the boat bottom. Used this setup on two different bass boats and could read bottom depths at over 60mph. I quit using the paddle wheel transducers for speed. They don't seem to be accurate enough over a wide speed range for my liking.. Larry

10-24-2005, 11:24 AM
Isn't there a speed at which the transducer is gone before the signal has returned?

10-24-2005, 11:29 AM
this morning after launching i raised the engine cover and i was taking on water. went back to the dock and the bilge pump took it down to the point i could see it coming into the bilge from the forward hull drains. i cannot see any holes-cracks or anything wrong other that some gel- coat knocked bt whoever had it before me. the keel at the bow has the gel- coat rubbed of by beaching on sand it looks like. i just finished putting resin on after sanding and cleaning with acetone. Question--i didnt think it would leak becase gell coat was damaged or wore of. waiting for answers or opinions

10-24-2005, 11:43 AM
Thanks for the interpretation, Doc. At least I should feel good about having a nice planing hull ;) Indeed it lifts up easily.

Does it mean when people go salmon fishing they usually cannot find bait balls underneath on the way unless they travel slowly or there are other signs like birds or boiling surface?

I had a Humminbird Piranha portable on my small boat for a few years and had no problem with it (that boat never could go above 6 mph though), that's why I bought Humminbird again.

10-24-2005, 11:48 AM
I still hope that it is operator error that makes my matrix act up. I put the gps speed feature on it and it only works 1/2 the time. I replaced the earlier humminbird system because some person decided they needed the screen more than me. I am a bit more careful now.

10-24-2005, 03:49 PM
I've got the Matrix 17 and get a good bottom read well into the 35+mph range. My boat's big (25.5 feet) with a deep V - she planes in the low 20's with hydraulic trim tabs.


10-24-2005, 04:51 PM
Isn't there a speed at which the transducer is gone before the signal has returned?

Yes. It's called the speed of sound. I doubt that even your boat is that fast Hinrid. ;D

10-24-2005, 05:42 PM
I had the vision 3d finder which was an earlier version of the Matrix I believe. Same thing happened. Couldn't track bottom above about 10mph.

If I remember right sometimes you have to specifically purchase the highspeed transducer. I would check your transducer model number and see if it is considered to be a righ speed transducer.

My Lowrance that I replaced the unit with tracks bottom at 20+ miles an hour just fine. Its almost in the same screw holes as the other unit was.

10-24-2005, 06:09 PM
my old alum. crestliner had a lot of trouble with "high" speed (<30mph) loss of signal until I found a spot on the transom where it got good readings. The key was not too close to the prop, and not on a flat part of the hull; on that boat, there was a step in the rear V of the transom, and it worked best there.

That was with an Eagle FishMark 320, with the standard skimmer Xducer. I think it is the same as the Lowrance version.

My last boat was a deep V fiberglass, and I had no problem with the readings at speed, but they got real flaky when going slow trying to locate structure. That took some tweaking of the angle of the Xducer, and it finally worked out. That was for a a Matrix 47 3D model, with a very wide 6 element Xducer.

I think location of the mount is more of an issue than the maker or style of electronics. All these companies have been in business for some time, and they all have good stuff; the thing is that most of the time the product is made for a wide range of applications. As such there is always a trade off. I was very happy with the Eagle (poor mans Lowrance IMHO), and the Humminbird. Would not hesitate to use either one any time soon. In fact, I gotta get another one for the newest boat, and it will likely be one of those makers.

10-24-2005, 08:03 PM
From your replies looks like the deep V hull may have a better chance of reading at higher speed, maybe because you can get the transducer a bit away from the hull because of the angle? Too bad mine is a modified V, the bottom at transom is almost flat. I guess I may have a better reading if I could lower the transducer a few milimeters. Maybe I should try that, since it is mounted higher than recommended because of the pre-mounted bracket.

10-24-2005, 08:51 PM
Yes. With a relatively flat transom that is the first thing to try.

10-25-2005, 08:13 AM
Most of the problems with erratic bottom redings at speed are do to incorrect transducer placement, as other have indicated. When adjusting the transducer, keep in mind that the rear of the boat at slow speeds is deep enough in the water to keep the transducer submerged well whereas as the transom rises the transducer not only rises in the water to where it may be just near the surface but is also exposed to the turbulence that doc mentioned. To be able to get a good return at speed, you may have to drop the transducer low enough that you get a rooster tail as previously mentioned. Each boat is different and to get the best results requires some experimentation with tranducer position and angle.

10-25-2005, 10:35 AM
Boy Howdy to that Lone,
I had the rooster as was mentioned earlier, so I went ahead and F%$#ed with the transducer, which only led me to have to make three trips back to the lake to get it right where the boat dealer had placed it in the first place.

My maiden voyage after my anti-rooster experiment was a total disaster, I couldn't read anything.

I also have the Matrix 17 and I like it (now that the transducer is back where it should be). I also found the paddlewheel speedometer to be usless.

Add the GPS that works great for low speed calc.

10-25-2005, 12:52 PM
In my case, I think Gregor welded the transducer mounting bracket wrong. Never allows me to mount the transducer low enough. Now I have to find a piece of aluminum or heavy plastics and lower the transducer.

I like the boat Gregor made for me, but they have been making some stupid mistakes. In another thread I mentioned the gear was backwards (forward goes back and backward goes forward). Turned out it was Gregor's mistake not dealer's (I was watching the dealer correcting the problem). Boy that almost cost me a collision with another boat at the dock!