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Fish finders

Skykomish E29 4:32pm, 10 April 2011
Can anybody tell me if the image of the seabed on a fishfinder can be relied upon, the reason I ask is that being on the East Coast here we often have to negotiate shallow creeks with winding narrow deep channels and whereas a depth sounder is fine for telling you the depth below your keel, it doesn't really give you much idea which way to turn to get back into deep water. Whereas with a Fishfinder I get the impression that with the image on the screen you should get a picture of the terrain beneath the boat and a clear picture of where the channel is... or am I asking the impossible? Before I invest my very hard earned cash in one of these I would like to know it is going to do the job. I did have one some time ago on a much smaller boat but never really used it much as the boat could float in 12 inches of water, having swing keels. Now with Skykomish things are different with a metre and a half pointing down at the mud, and a few times making close aquaintance with it
Snow Goose Tim 8 years ago
i have just fitted one, I should be going in next weekend i will let you know then!
rothwell_neil 8 years ago
You can see the profile of where you have been and the track of how it shelves etc, also it does give you a clue as to whether soft or hard, mushy signal for soft bottom and firm line for hard.
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NormanKlipspringer 8 years ago
Malcolm as I understand them fishfinders average out the depth over the transmiited cone and display this. So all you are getting is a trace of average depths in the general area of where the boat has been. This is fine for detecting shallowing water but does not tell you wether to turn to starboard or port. The nature of the trace i.e hard line or fuzzy, can give some indication of of whether the bottom is sandy or rocky. If you want to know what is happening in front of the boat you need forward scanning sonar. Sidescan sonar gives a complete picture of the underwater scene but the kit is very expensive (thousands of pounds). Fishermen use sidescan to accurately locate their marks. I have found the basic units to be reliable and better than a plain depth sounder. The one I bought from you (Garmin Fishfinder 90) has worked very well.
Mike A1 8 years ago
Can't help you with your question about fishfinders, but my usual technique for tricky creek-crawling situations is to deliberately head slightly towards one side or the other, so that when it starts to get shallow I know which way to turn. You can then either zig-zag along or stay close to one side. This has it's dangers - you can end up going along a side-channel - but it's worked for me most times.

Psychologically I find it nice that the transducer is at the forward end of the keel, although in practice this would only make a difference when travelling very slowly.
Skykomish E29 Posted 8 years ago. Edited by Skykomish E29 (member) 8 years ago
mmmmmm yes thanks all for the info Norman I agree with your comments about side scan etc and think that perhaps we shall just carry on with the depth sounder, our NASA apparently does give some indication as to which way to turn for deeper water but this is not reliable when "mud plugging".
Mike
This is the technique that we used in our Achilles particularly when inching our way up the Walton back waters, but I remember thinking then that there must be an easier way as Linda was calling out the depths as I meandered like a drunken walrus from side to side to find the channel
The channel that is the lead in to our marina is frighteningly narrow when viewed at low tide which causes all sorts of heart stopping moments when you have a large boat coming in the opposite direction, on the whole you are safe if you stay in the centre of the buoyed channel but as the banks shelve steeply either side it doesn't take much deviation to find yourself in quite literally alarmingly shallow water. www.flickr.com/photos/8644331@N08/2944942166/
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