Fishfinder question

[dizzyfish]

Hello, I have read alot of your forum topics about fishfinders, and your members obviously have alot of information regarding them. I am hoping you can help me. I am looking at purchasing a fishfinder, but unusually it will be used on multiple boats - my own foldable dinghy (pike fishing and light sea angling), reserviour boats (pike/trout fishing) and hopefully a sea kayak (hoping to purchase Ocean Kayak trident some time this year).

 

Before I get into techie questions about transducer location/attachment - I have some simple questions regarding fishfinders which may seem stupid/simple but no-one has answered :-

 

Q1. I thought looking at the images of fishfinders, that they gave a contoured view of the bottom to the left and right of the boat (with the boat being in the middle of the display). However, after looking further, it seems that the display scrolls, and is made up of the history of foward movement. ie. If the boat is stationary for a period of time, then a flat horizontal line will eventually be drawn across the bottom of the screen. Is this correct ?

 

Q2. If this is correct, then what is the point of having dual frequency/wide scanning units ? It seems to me, that if I am correct, then you cannot tell from the display, where the fish/bottom features are, in relation to the boat. ie. all you know is that they are within the SONAR beam cone somewhere (could be to the left or the right, or directly under the boat !!). In fact, it seems that in a way, you are worse off with a wide angle 90 degree 83 khz beam, because all you know is that there may be a fish within 30 yards of the boat, somewhere to the left or right ????!!!

 

Q3. Again, if I am right on Q1, then what IS being drawn to show the bottom at any given instant - is it the highest point within the scanned area (ie. the highest point on the bottom in the 60 degree slice beneath the boat) - or maybe the lowest point ?

 

I would really like someone to help me with this before I go on to ask about units/transducers/attachments. Sorry if the answer is obvious, but if I am right, then I think a fishfinder is probably a waste of time and money, and I would be better off with a cheap digital depth finder.

[Newt]

If the boat is stationary for a period of time, then a flat horizontal line will eventually be drawn across the bottom of the screen. Is this correct ?

 

Only if the bottom is completely flat and as a person who has used them since the days when a flasher was state of the art, I've never seen that happen. Even with a boat at anchor you will continue to see the actual bottom contour with the occasional shape swimming through.

 

The assumptions in Q2/3 are based on a faulty premise and are also incorrect.

 

As to the question of what system you want to move easily from boat to boat,

- you will not be able to get a real top-of-the-line unit for this as they don't port well.

- I'd suggest a self-contained unit that has a carrying case/display base that contains batteries (and use rechargible ones to save yourself a fortune over time). The suction cup mount they usually provide for the sounder head does fine unless it is in the water when a powerboat is running at speed and even if it pops loose, it is firmly attached to the base unit by the cable.

 

Something like this would be (was) my choice.

 

[dizzyfish]

Thanks - But if you are right, then why does the Humminbird PDF documentation (for 565) refer to the display window as showing "a historical view" and "the most recent reading is inserted on the right hand side" ?

 

Also, if the display always scrolls (right to left) regardless of the boat's speed; then what is the display showing if you are stationary ?

 

And (sorry to labour the point) if you are correct (and I hope you are) - where is the boat in relation to the display - is the boat in the centre of the display (so features on the left hand side of the screen really are to the left of the boat and vice versa) ?

[Mark Crame]

Q1. I thought looking at the images of fishfinders, that they gave a contoured view of the bottom to the left and right of the boat (with the boat being in the middle of the display). However, after looking further, it seems that the display scrolls, and is made up of the history of foward movement. ie. If the boat is stationary for a period of time, then a flat horizontal line will eventually be drawn across the bottom of the screen. Is this correct ?

 

The Humminbird Matrix 3D ones do. Bucketboy is the man to ask on that. If the boat remained perfectly still both vertically and above the same spot then theoretically yes. It does move a bnit though, and swell will lift you too. Fish etc moving under you will show though but in all honesty once you have found your location you may as well switch it off in most situations.

 

http://www.humminbird-gcomm.com/humminbird...atrix-47-3d.htm

 

http://www.humminbird-gcomm.com/humminbird...m-matrix-12.htm

 

Q2. If this is correct, then what is the point of having dual frequency/wide scanning units ? It seems to me, that if I am correct, then you cannot tell from the display, where the fish/bottom features are, in relation to the boat. ie. all you know is that they are within the SONAR beam cone somewhere (could be to the left or the right, or directly under the boat !!). In fact, it seems that in a way, you are worse off with a wide angle 90 degree 83 khz beam, because all you know is that there may be a fish within 30 yards of the boat, somewhere to the left or right ????!!!

 

Dual Frequency scans underneath (200khx) and wider (83khz - the freqs on mine anyway). The 200khz will tell you that there are fishy returns beneath you in a circle of x diameter at y depth (I'm algebraic on Sundays only, sorry) while the 83khz will tell you that there is something outside that but in the wider zone but of course you are correct that it doesn't pinpoint where. I have dual beam turned on generally as it gives an idea of what's happening. However, you mustn't get hung up on them finding you the fish! You have to use them to find where the fish might be.

 

Q3. Again, if I am right on Q1, then what IS being drawn to show the bottom at any given instant - is it the highest point within the scanned area (ie. the highest point on the bottom in the 60 degree slice beneath the boat) - or maybe the lowest point ?

 

 

depends on what view you ahve switched on. Most will give returns as far as they can penetrate and can thus show you the kind of structure etc beneath you, even the kind of bottom. I can't go into much detail there as in all honesty it's double dutch black magic to me and Humminbird are blasphemous sorcerers but if you have a look on the manuals for some of the top of the range stuff you'll get a good idea. http://www.humminbird.com/images/PDF/757_787.pdf

 

 

As to the portability, well...

 

I have a Humminbird portable unit and it's fine but it is a vvery basic unit (one like newt shows). However, the supplied transom mount for the transducer is no good for a yak - so I removed it and sikaflexed the transducer to the hull as per most of the kayak anglers. What I'd say is try the transom mount for the boats that'll take it and get a thru-hull transducer for the yak. IF you decide to go for one of the non-portable units (which are portable, display-wise, as they pull off) then there is the possibility of purchasing extra mounting parts and cables for them I think. For in-depth replies you want to 'phone Johnson Outdoors or G-Comm, both in Great Yarmouth. As I said i'm pretty much in the dark with them but have found them to be immensely useful - so much so i won't go out without one.

[dizzyfish]

Thanks very much Mark - you are a mine of information and it sounds like you have been there and bought the T-shirt - as I suspected - fishfinders are really useful for determining type of bottom and depth and some fish (if you are lucky), but not much cop for identifying where they are in relation to the boat. This was also confirmed by an engineering friend (I think they are the only ones who's algebra works on a Sunday !).

 

I am still wondering what the fishfinder shows for a given instant in time - given that some of the Humminbird models have a 90 degree cone (575 uses 3 frequencies) - but only display a single return for this. My engineering friend suspects they show the highest point on the scanned bottom (for obvious reasons when boating !) - but this could be really confusing. Imagine that in 30 feet of water the 60 (or 90) degree SONAR cone beneath the boat would cover quite a large area of sea/river bed which might have reefs (high) and hollows (low) - the single SOANR return on the display would probably only show the high reef point - thus you would not know that there was a large conger/pike/sea monster holding hollow just below the boat within the SONAR cone but not displayed on the fishfinder.

 

I think that all of the manufacturers are very cagey about this - when you see the screen shots they use, the natural assumption (one which I think even seasoned and experienced fishfinder users still believe) is that the display is showing you a sidescan picture of the bottom beneath the boat on either side - this is simply not the case (apart from maybe the 3D models you mention).

 

Thanks for the info. on the fishfinders - the Humminbird 565 and 575 both sound good - I noticed that they had a "quick disconnect mount" which presumably houses the conectors for power/transducer cables. You eluded to the fact that it may be possible to buy a separate transducer/mount - Do you know any more ? This would mean I could have a permanent transducer on a kayak, but then remove the unit to my dinghy and attach it to another quick release mount with (say) a portable transducer to attach to the inside of the hull ?

[Mark Crame]

A mine of information perhaps, but I'm not the best person to ask on this subject in all honesty, and I have only used Humminbird units so can't speak for others out there.

 

First paragraph sums it up nicely IMO.

 

Second paragraph - I see what you mean now. Projecting the cone down, does the finder show the highest/lowest/average point from within that cone? Hmm, good question that, very, very valuable answer! At depth that cone could be quite large. I would imagine (this is supposition only) that it would be weighted towards the centre of the circle.

 

I've never assumed that it's a sidescan image. Basically right is your seat and left is behind you, best place to mount might be on the port gunwhale in that respect. The area you are above at any time is the extreme right.

 

Bucketboy has the 3d model and quite honestly it is exceptional. It looked far too confusing to me when i looked at a demo one and figured it was a gimmicky idea. Until yesterday that is. I was fishing a 20ft wide small that would have been perfect for it, absolutely made for the job.

 

I have the 757C and that has a quick disconnect mount too. Basically i remove the display unit. The mount is attached to the kayak with all wires (ie to battery, transducer and GPS) coming from that. it plugs right in to the top when I put it back. Buying those parts in duplicate/triplicate I could hot-swap one display between 2 or 3 boats. I see no reason why you couldn't buy the seperate parts, having dealt with G-Comm and Johnson Outdoors I'd say that if at all possible both would help you to find the best and most suitable method of dealing with your requirements. In fact , come to think of it, you can disconnect any of the units that aren't mounted into the hull itself anyway.

Edited December 30, 2007 by Mark Crame

[dizzyfish]

Just looked at that 3D model (thanks for the URL's) - the Humminbird Matrix 47 3D - really does look the business ! Will have to contact the suppliers you mentioned and ask if possible/how much would be for a spare mount and transducer for that model. Suspect that a spare transducer for the 3D model might be expensive.

 

What sort of thickness of hull will the transducer work through (my dinghy is made of marine ply which is quite thin). I have noticed that some of the reseviour boys mount their transducers at the bottom of a tube (guttering downpipe ?) and then attach the tube vertically to the side of the boat with a clamp so that the bottom of the tube where the transducer sits, is underwater (obviously no good for a kayak but might work for my dinghy/reseviour boat).

[Mark Crame]

Just looked at that 3D model (thanks for the URL's) - the Humminbird Matrix 47 3D - really does look the business ! Will have to contact the suppliers you mentioned and ask if possible/how much would be for a spare mount and transducer for that model. Suspect that a spare transducer for the 3D model might be expensive.

 

What sort of thickness of hull will the transducer work through (my dinghy is made of marine ply which is quite thin). I have noticed that some of the reseviour boys mount their transducers at the bottom of a tube (guttering downpipe ?) and then attach the tube vertically to the side of the boat with a clamp so that the bottom of the tube where the transducer sits, is underwater (obviously no good for a kayak but might work for my dinghy/reseviour boat).

 

can't answer the hull thickness question. it'll shoot through a kayak with no trouble. It doesn't like air bubbles or gaps though - might be an issue with the other boats? The tube system will work fine and if under power the extra drag will be of no consequence.

 

Been swotting up on my 757c. Right, you have a 60 degree 83khz signal and a 20 degree 200khz signal. Depth is from the 20 degree, fish, structure etc from the 60 degree. 60 degree gives you coverage of an area equal to your depth - ie 10ft depth is a ten foot circle of coverage, the 20 degrees (dunno if that equates to a third in this kind of formula) shows less. So, directly under you at 20 degrees is the bottom and the 'blue' fish, around you at 60 degrees is the rest and the 'red' fish. There is also wideside and quadrabeam SONAR available.

 

Now, with a colour finder you can read information about the bottom, its make-up and hardness etc. You can see structuure and all kind sof stuff. Have a look at the manual here, the first few pafges cover it in detail:

 

http://www.humminbird.com/images/PDF/757_787.pdf

 

It also has GPS, Chartplotter, Temperature, Time, Speed, Distance etc etc. I have one and it's great. Very pretty. I'm going to understand it soon too - call me the Sorcerer's Apprentice!

Edited January 1, 2008 by Mark Crame

[dizzyfish]

Was reading about the new humminbird sidescanning sonar - I really wish I had a spare £1,500 !

 

180 degree coverage - 150 feet either side of the boat - looks like a video. Can tell where everything is in relation to the boat. Can also mark points with the cursor on the screen and revisit with GPS. Very impressive.

 

Video below shows some highlights :-

 

http://www.youtube.com/watch?v=gOy5ml2GhiQ

 

Those Americans do get quite excited don't they !!!!

[Newt]

Indeed. We love our toys.