Transducers: Difference between sounder & Fishfinder

Petrolia

Petrolia

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Silly question maybe but what is the difference between the transducers on a sounder & a fishfinder ?

They obviously both bounce sound waves off the bottom but is the sound wave different ?

Is the fishfinder sound wave more sophisticated or is it the interpretation of the return wave that's different. Or is it just the representation that's different, ie graphical v digital.

I suppose what I'm asking is what would happen if I connected my sounder to my fishfinder ? (Assuming this could be done)
 
My guess, from my days as a hydrographic surveyor, is that it is in the graphical interpretation of the sound wave. Your 'normal' echo sounder would just display a mean return wherase the graphical interpretation allows it to send a mean return and also shows other 'reflections'.
Many survey sounders will have 2 or more selectable frequencies so that one may, for example, penetrate sea bed silt down to rock or hard sand.
I would have thought that the technical info for the instrument would state the transmitting frequency.
Regards
 
I have both and the fishfinder transducer was initially mounted near the depth transducer. Big mistake!!! They use the same frequency and when running both showed ridiculous depths. The fishfinder does run at two frequncies but the lower (and stronger) one 50hz clicks like crazy and is quite irritating. Running at autoselect the nromal frequency I tihnk is 200Hz and imperceptable.

I then moved the fishfinder to the rear of the hull. Luckily it was a surface mount and did not have a hull penetration. Much better now. However it shows that the basic technology is the same. The data is just handled differently. Incidently I rarely use the fishfinder. Too may years of looking at the depth guage I guess.
 
None - the transducers are identical.

The only difference is in the presentation of the results - a depth sounder will just give a single figure whereas a fishfinder gives a graphical representation and a history - they often interpret the results as well by plonking a big fish symbol /forums/images/graemlins/smile.gif
 
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I suppose what I'm asking is what would happen if I connected my sounder to my fishfinder ? (Assuming this could be done)

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It will depend on what frequency and the beam width of your present transducer is. Ususally its about 200 kHz for small units although there are some with unusual frequencies not far off 200. 200 kHz is fine for depths down to about 200 feet, actual depth capability will depend on the units power output and the beam width.

Deep water sounders will usually be 50 kHz or lower with narrower beams. If your present transducer is around 200 kHz and your fish finder is similar they should work together fine. The actual performance will vary depending on beam width and power available, angle the transducer faces forward etc. And of course what you intend to use it for.
 
I agree with most of what has been said. Most depth sounders tend to use around 200Khz as do most basic fishfinders. Some of the more advanced fishfinders use dual frequency (50Khz & 200Khz).

If you have a conventional depth sounder with a through hull (hole in hull) transponder and wish to replace the instrument head with a fish finder then it should work with most fishfinders.

If you wish to keep your existing depth sounder instrument then don't be tempted to connect both instruments together to the same transponder, This will not work and you may damage one or both instruments. If you want both instruments to work at the same time they need separate transponders, additionally you should try to place the transponders as far apart as possible to avoid cross-interference (more pronounced in shallow water).

I have 2 units on my boat, my depth sounder is a Raymarine ST60 and my fishfinder is a Navman fish400. Both run at 200Khz, both can use either transponder. Initially I mounted them next to each other but the fishfinder didn't work properly until the Raymarine was turned off. Now they are about 20ft apart and I don't get any problems unless the water is very shallow.

If you have a glass fibre hull you don't have to drill a hole in the hull, even with a through hull transponder you can mount it inside the hull, stuck down with silicone sealant to the inside of the hull; but it must be directly on the surface of the outer hull and not an inner lining. This allows you to experiment with positioning without drilling holes. You do get some loss of signal but my fishfinder is mounted in this way and works down to it's 200ft limit.
 
Thanks everybody for comments.

Reason for question is that the fishfinder transducer has been fitted with a thru hull transponder but despite my instructions to the contrary it has been fitted crooked at the hull angle. I see this as a problem in deep water.

I had asked them to fit inside hull transponder but they said they couldn't find anywhere where there was a single skin to put it.

The depth sounder transducer is also thru hull but it's fitted straight, not at hull angle. This is what led me to think I may be able to connect my fishfinder to the sounder transducer and get a more accurate response.

I kind of intuitively knew that connecting both FF & sounder to the same transducer wouldn't be a good idea.

On thinking further about frequencies it isn't the transducer that's deciding the frequency is it ? Surely it's only sending the signal its told to send then sending the return signal back to whatever unit it's connected to.

I think I'll try wiring the FF to the sounder transducer & see what happens.
 
Re garding frequencies the transponder is often designed to b resonant so work best at one frequency. But as you say the actuall frequency is generated at the transmitter reciver unit.
DickB there are in fact 2 frequencies in a sounder the first being the actual signal ie 200 kilohertz but which is transmitted in bursts at a rate of around 50 hertz (this is a repitition rate for pulses) this can be varied because you have to be slow enough for the pulse of high frequency energy to go to the bottom and return so high frequency as i9n rapid repition is only ok for shallow depths but needs longer pause period to listen for a return from very deep.
To confuse things the actual signal ie 50 kilohertz or 200kilohertz has different reflection and transmission characteristics for different bottoms and water depth so as pcatterall says sophisticated survey machines may use different frequencies as well as different repitition rates.
So if you are using just one frequency of signal then transducer is probably the same considering that you don't get and don't want a small angle opf radiation from the transducer else it would be no good on a healed yacht.
Just waffling I went on a spoorts yacht on Sat with a 2.3 metre draft where the sounder was set to show under keel depth. There were lots of shallows such that with the boat heeled over we could sail apparently ok with sounder showing 00 metres. (a bit nerve wracking) It didn't go to negative depth. The sounder appeared to work happily at 45degrees of heel. But when standing up it was amazingly accurate as you could feel the bumps at 00 on the gauge. olewill
yes it had a huge bulb smooth and flat bottomed that seemed to bounce on the sand. (and loads of sail area to heel the boat on demand.
 
As far as the angle is concerned that may or may not be an issue.

Note that sounders and fish-finders actually measure the distance to the nearest bottom within a certain cone (usually about 20 degrees) rather than the distance directly below the transducer. Mounting the transducer at an angle may reduce its range when you are well heelled on one tack - but should not ever give incorrect readings.

As far as the frequency is concerned, the frequency is set by the instrument but it is important that the transducer is designed to work at that frequency so matching them is important - however it should be fairly easy to check the frequency of old and new units to compare them.
 
the frequency is a function of the transducer (crystals) not the head unit. You will need the correct frequency for the head unit as a bare minimum for compatability.

petrolia is unlikely to be heeling..........or concerned about fishfinding if it is!

agree the cone issue ie you will still get a realistic depth reading under most circumstances

quite frankly I would be getting whoever installed the thru hull to sort it out properly - which fishfinder unit is it?

Also if the two are the same frequency not only should they be a significant distance apart but the angled installation of one will be a further potential problem for interference. Clearly any competent installer would ensure that they are different frequencies just to make sure in the first place - and therefore you won't be able to mix and match.
 
It is always dangerous to generalise. Look at Raymarine transducers (not transponders as some have posted) and you will see several differences in frequencies and power. If I remember correctly, one fishfinder transducer uses 1kW. Try driving that with your ST60!

My earlier posts refer to extended discussions with Raymarine and one requirement is that if you use two transducers they should not be powered at the same time to avoid interference.
 
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It is always dangerous to generalise. Look at Raymarine transducers (not transponders as some have posted) and you will see several differences in frequencies and power. If I remember correctly, one fishfinder transducer uses 1kW. Try driving that with your ST60!

My earlier posts refer to extended discussions with Raymarine and one requirement is that if you use two transducers they should not be powered at the same time to avoid interference.

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Do raymarine make their own tranducers then (yes I do know the difference between a transducer and a transponder /forums/images/graemlins/smile.gif ) - I thought virtually every one uses Airmar tranducers these days - those I have installed are rated at 600W as are those for the domestic raymarine units - however I don't see why you shouldn't drive a 1kW rated one with an ST60

Incidentally I regularly sail with both depth sounder and fishfinder running and have not had any issue with interference - what do you think would cause problems?
 
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I don't see why you shouldn't drive a 1kW rated one with an ST60

[/ QUOTE ] manufacturers certainly use the same transducers with different power capable head units so there is scope there. Electronically there may be some issues - for example I know one manufacturer who has had problems with a particular head unit where it is the smallest designed to power one of their highest powered 'ducer's and it seems that failures may be associated with overheating.......but of course the unit is set up to generate the power, and is paired to a 'ducer using the power. Any head unit should be able to operate a compatabile 'ducer up to either the 'ducers capability or it's (the head unit's) rating.
 
The fishfinder is Simrad. The main unit is CX34 plotter/radar/fishfinder. As you know the boat is new to me & I haven't actually been out fishing in it yet due to weather & being away at work. (As I am now /forums/images/graemlins/shocked.gif)

I'm upset about the transducer being crooked because the guy did the same thing in old Petrolia. With that unit I was dissapointed in the fishfinder (Raymarine), it was not as good as the old Lowrance I had in the Hardy that only had the transducer glued inside the hull. Rightly or wrongly I put this down to the transducer angle. Now he has done it again on the new boat.

The thing is I didn't get to see the new transducer until I had the boat home as it was under the lazerette which was full of cruising gear. All the electronics were fitted in my absence. Now I've seen it I'm not happy.

Maybe I should just wait until I've tried it in anger. It's just that I'm sitting at work, not very busy, and got to wondering if I could connect the fishfinder to the straight sounder transducer if again I wasn't happy with the fishfinder. Maybe I just didn't set the old Petrolia finder up properly. With the Lowrance I just turned it on a could see fish. I think the more upmarket models have too many settings to fiddle with.
 
So is it the case that I'm worrying un-necessarily about the transducer being crooked ?

Will it work as well as if it was straight ? And is it looking directly under the boat or looking at the bottom away from the boat due to the angle ?

It makes a difference if I'm drifting over a wreck. If it's not seeing the bottom directly under the boat, depending on which way round the boat is I could be over the wreck before I see it on the sounder.

Is it the case that so long as the transducer angle is less than the cone angle it will be alright ?

I'll look at the whole deal more carefully when I'm next home. Maye I can switch the transducers around. Fishfinder on straight one & sounder on crooked one ?

Whatever happens though, next time I'm home the boat is getting bloodied !
 
yes - If it is giving a reading at all then it will be giving the correct depth - most transducers should be fine up to about 15-20deg. The one for my fishfinder is mounted at an angle of about 20deg and works okay - you may find that the range suffers at an angle - that doesn't bother me because I only really care about depths under 20m
 
Yes, both the "Raymarine" transducers I have are Airmar. I assume (also dangerous!) that an ST60+ would not have the power to drive a 1kW transducer (at 1kW that is).

I imagine that interference is caused by one transducer picking up the reflection off the bottom feature from a pulse generated by the other transducer.
 
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