Unit seems to work ok at trolling speed however if boat is going over 10 mph water depth jumps all over the place and tons of surface clutter

Hey Joe,
Wow.. where to start.. there are so many things that will cause the issue you are describing.What type of electronics do you have? Does this happen at all speeds? Where is the transducer mounted? I need more info about when it stops reading.
1.Wrong setting on the unit
2 Bad transducer
3 Bad transducer mounting (either inside the hull or outside the hull.)
4. (In hull) Turbulence going under the boat (mine quits reading at about 55 mph @ half trim...the boat is lifting so much it causes air pockets so the transducer loses contact with the water)
5. (Outside hull) Turbulence around the bottom of the boat where the transducer meets the water.
Good luck,, when you get the info.. reply to me..

Trolling speed TOO slow for units transducer to sense.

When my depth finder acted like this I found out it was the sender that had not done well over the winter and was giving me false readings especially when the boat was at speed. The sender and cable only cost around 30 or $40. The hard part was since I have a pontoon boat getting under the Pontoon and replacing the wire in the spring when the water was cold.

I had the same problem. I talked to 3 different technicians on the Humminbird support line about it. All 3 of them confirmed that this is how their technology works. They ping the GPS satellites continuously, and at low speeds the GPS accuracy causes the speed measurement to fluctuate wildly. It smooths right out when you go faster than 3 MPH, since your boat moves far enough at that speed that the GPS accuracy is no longer a problem.

Seems like they could easily overcome this issue by averaging GPS readings over a longer time period at low speed (i.e. give the boat enough time to move far enough to eliminate the accuracy issues), but they don't do that.

It was a big issue for me since I do a lot of trolling at low speed and need an accurate speed indicator, so I returned the product and bought a Lowrance instead. Lowrance doesn't have this issue.

Hello. Your observation is spot on and it is actually a characteristic that is always true when using sonar. Yes, your Lowrance uses the same sonar as a nuclear powered submarine does. The two factors you focus on, water depth and boat speed are perhaps, the two biggest factors when it comes to the quality of the fishfinder. The boat's engine should be in gear at an idle or just above. Experiment with your boat to find the best throttle location for good arches. Usually, a slow trolling speed works best. The depth of the fish can determine if the fish will arch on the screen. If the fish is in shallow water, the fish is not in the cone angle very long, making it difficult to show an arch. Typically, the deeper the fish, the easier it is to show an arch.
If you would like a complete tutorial on Lowrance sonar, go to this link. Enjoy. http://www.lowrance.com/Support/Tips-and-Tutorials/Sonar-Tutorial/

Your transducer needs to be adjusted so the return signal can be picked up. Some of these have to be super tuned to receive the signal. Also the transducer may be moving ever so slightly when the boat is traveling at speed. You may have some water turbulence interference all contibute to signal return.

The speedometer cable needs lubricating. It can be removed from the bottom where it connects to transmission, coated with graphite and reinstalled.

Had the same issue with another brand. Turned out the transducer cable was picking up noise from other cables (power, trolling mtr. etc). Try moving the transducer cable away from any other cables. I put the cable in a 1/4 " plastic housing up to the point where it was above deck and it stopped all the strange stuff. Not sure about the temp issue??

A test bucket wont work, A 200 khz transducer will generally not work in anything less than 2' of water, due to surface clutter. If the transducer is working, you should hear it make a ticking sound.

When you got the 17000 foot reading was your range set to auto?

How is the transducer situated on the boat? Sometimes turbulence and bubbles from the hull can cause erroneous readings, including unrealistic depths, or no depth at all. Stop the boat and turn off the engin e and anything electrical to see if problem repeats itself. If it only crops up when the boat is moving then it is most likely the transducer location.

The problem is not so much the flat bottom, although they are prone to this problem. The way the sonic waves have to travel through the water is affected by turbulence, especially by air bubbles and cavitation, and by the transducer actually leaving the water, which happens frequently on flat bottomed boats. The best solution to this is to have the unit mounted through the hull so it is completely flush with the hull surface - often they are mounted with a surface flange on the outside of the hull which although thin still causes cavitation around the transducer at higher speeds. about 14 knots will usually interfere with the accuracy of the readings on most hull shapes - forward looking sonars perform usually better. Another thing to check is that the transducer is actually seating right in the housing, if it is not flush with the flange then you have problems - even half a millimetre is too much. check no muppet has painted the transducer with antifouling paint - that never helps, also check if there is a build up of marine growth on or near the transducer - a smooth hull will always keep your depth working until a higher boat speed. if the transducer is growing stuff itself then gently scrape it off - be really careful not to scratch the surface. There are now available non-sonic depth sounders, especially ulf radio signal devices, but I have heard no good reports about them, last i saw they were very expensive and maybe they experience other problems at high speed. there also have been towed devices available that may suit your needs better, although probably a lot of trouble in shallow waters. If you can borrow a waterproof video camera, you could mount it behind (not too close) the transducer, this would be a pain to do, but it may give you an insight into what part of the hull if any is causing the problem (tie the camera to the top of the boat securely in case the mount fails) Hope this helps, sorry but your dealer is not totally wrong :)