Boat Speed And Chart Speed: Effects To Si, Di And 2D Sonar

[Doug Vahrenberg]

Here are some examples of the effects of not adjusting the Chart Speed to match the boat speed and how it can distort the data.

Chart Speed matching Boat Speed...see the details?

Now the Chart Speed increased and loss of resolution and stretching of data...

Same thing happens with Down Imaging...

Too Fast...

Still a little fast...

Just Right...

Now Switchfire 2D Sonar...

Matched to boat Speed...

Too Fast... (elongates returns)

Adjusting your Chart Speed will help you get your images just like the images are naturally positioned under the water. To fast will stretch the images and too slow will shrink the data. Using the Chart Speed function is probably the Most Important element in creating picture perfect images. I try to match or drop a 1 number below chart speed for higher resolution images if you want to stretch them a little to see more separation of details adjust 1 or 2 numbers above boat speed but don't crank it up it will make the images lose alot of the resolution to the images

[getfished]

Thank you Doug. Understanding the function of chart speed will help me optimize my graph performance. It sounds like you have a sort of general rule of chart speed closely correlating to boat speed. I've been told to turn it up to fast and I've been told to turn it down to slow. This general rule will make it easier.

Thanks

[Smalliebigs]

Doug, once again great info and post. I love it when you post and I always learn something new thank you!!! I love my 788 ci di's

[Dutch]

Since I don't understand HB numbers, how do you know what your chart speed is anyway?

[Stoneroller]

you have three images one says 'too fast' the next is 'still too fast' the final is just right. first picture boat speed is 3.4 mph, 2nd is 3.1mph 3rd is 3.4 mph.... are you talking about chart speed in those instances? frankly it doesn't really matter what your chart speed is set to, as long as it's not in the lower half of the setting range. unless you run over the same area, again and again, while messing with the chart speed/boat speed the entire time, you won't really know what the proper speed is for the depth of water you are fishing. water density and depth can have a major effect on sonar returns.

best technique i've found for catching fish is to keep your lure in the water. people get too tied up trying to use their sonar to 'find fish'.

[Flippin]

Doug,

So to make sure I understand this, if the boat speed is 3 mph the chart speed should be 3?

[NuB2TR]

Okay, In my small mind and compact way of thinking..... it would seem to me that the variables would be boat speed, chart speed, and depth. (This, of course, would be discounting things like fresh water vs salt water, clear water vs cloudy, etc.) I would think that if you change any one of the three variables, it would affect the output (image seen on the screen). Perhaps Doug is just saying that if the image is not clear and crisp for the depth and typical speed your boat travels while using SI and DI, change the chart speed. Doug?

Perhaps HB's next break-though would be a system that would automatically acount for these and provide a sharp image all the time. But then dummys like me would expect to see a picture quality image with the boat sitting still.....