Fishfinder transducer question

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Superaquarama

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Can someone tell me what these transom mounted transducers look like & how they work ? All the adverts just show the unit itself and say 'transducer included' but no pix and no idea how compatible it might be with our boat. Not keen on drilling holes in the grp.

The idea is to hopefully have a GPS / speedometer / depth sounder / fishfinder all in one little reasonably priced gadget.

Thanks.
 
A fishfinder or depth transduce considts of a piece of piezo electric quartz type material. It deflects when hit with a voltage and produces a voltage when deflected. Thus it works like a loud speaker and microphone both at once and only for quite high freqencies in the range 10 to 50 kilohertz. The quartz must nbe able to flex but is also coupled acoustically (mechinically to the water). A similar disc for sound creation is often found in a wrist watch for an alarm or for electronic toys. A thin disc often plated in places for wire connections.
it is possible to fit the tranducer inside the hull provided it is coupled acoustically through the GRP to the water. So often the transducer is mounted level with a reservoir of oil between it and the hull. Most depth sounders if fitted this way may have limited range but this does not matter compared to a fish finder application.
A fish finder usually has a pictorial trace of the bottom compared to essentially the same machine for depth which just gives a digital depth. Fish finders can be far more sophisticated.
A speed transducer usually consists of a paddle wheel in the water flow. magnets on the wheel convert rotation to pulses of current which operate the instrument. the transducer not usually in ne device even the readout can be. The paddle wheel can be transom mounted.
Again GPS is completely different and best IMHO for speed. data can be presented on one indicator.
 
I have a fishfinder ( Garmin £90 job ) with a transducer intended for transom mounting; I'd already checked with chums and this forum that I wouldn't have to do that.

I simply stuck the transducer ( which looks like a 3 pin plug without the pins ) to the inside of the hull with standard silicone sealant, in my boats' case aft of the keel where the bottom is flatter, just to one side to avoid turbulence from the keel.

It works very well.
 
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Seajet said:
I have a fishfinder ( Garmin £90 job ) with a transducer intended for transom mounting; I'd already checked with chums and this forum that I wouldn't have to do that.

I simply stuck the transducer ( which looks like a 3 pin plug without the pins ) to the inside of the hull with standard silicone sealant, in my boats' case aft of the keel where the bottom is flatter, just to one side to avoid turbulence from the keel.

It works very well.
Click to expand...

+1 , except I used araldite , and its in the bottom of the cabin, as close to the c/l as I could get.
 
Funny you should say that, I also have a NASA Clipper depth, in a tube but forward of the keel - used to have two depth transducers one each side of the CL but found there was interference.

The fishfinder aft & depthsounder forward give the same reading as you say which is encouraging.
 
Didn't know that a fishfinder would work if the transducer was fitted inside the hull. Think I'll get a fishfinder to replace my NASA depth unit which is a bit erratic sometimes.
 
Here is a picture:

http://www.fishfindersource.com/fish-finder-installation-checklist/

Mine used to show contour of seabed, depth, water temp, battery voltage, but that was it. Only cost £89 and a good make.

Superaquarama said:
Can someone tell me what these transom mounted transducers look like & how they work ? All the adverts just show the unit itself and say 'transducer included' but no pix and no idea how compatible it might be with our boat. Not keen on drilling holes in the grp.

The idea is to hopefully have a GPS / speedometer / depth sounder / fishfinder all in one little reasonably priced gadget.

Thanks.
Click to expand...
 
Many thanks for the helpful replies, everyone.

Actually I'm not particularly interested in the fishfinder aspect and really just want a depth sounder and that only to warn me of shallow water, so I'm sure I can work around the transducer problem somehow. Our boat's a Boston Whaler with a foam sandwich twixt floor and hull, i.e. there's no direct access to the inner hull, so unfortunately inside hull mounting's probably not an option.....is it ?

Yes, there are quite inexpensive fishfinders now which have GPS, such as Garmin & Hummingbird, so useful also to have speed as well and (presumably) a connection to a DSC radio if required.
 
bikerbill said:
Didn't know that a fishfinder would work if the transducer was fitted inside the hull. Think I'll get a fishfinder to replace my NASA depth unit which is a bit erratic sometimes.
Click to expand...

They not only work, but several people have posted that they work better than echosounders. Mine reads up to (and sometimes over) 300 feet where my echosounder gives up at less than 80. Admitedly the echosounder is a bit ancient. You also get a display showing the bottom profile which adds a bit of interest.
 
Seajet said:
Sounds like the transom mounting for you then ! After all it's intended for boats like the Boston Whaler.
Click to expand...

Yes, I'm sure you're right, as William H says there needs to be an acoustic coupling between transducer and water, on the Whaler it's broken by the foam space. So will have to devise some ingenious method of attachment without drilling holes !
 
Superaquarama said:
Yes, I'm sure you're right, as William H says there needs to be an acoustic coupling between transducer and water, on the Whaler it's broken by the foam space. So will have to devise some ingenious method of attachment without drilling holes !
Click to expand...

The bracket that came with the Garmin required two holes I think, both above the waterline. The bracket is then bolted on over a substantial rubber gasket and adjusted so that the transponder base is just below the normal waterline. So why no holes?
 
Holes in hulls = leaks and possible misery in various forms from internal osmosis, soaked foam buoyancy to sinking, my cruiser has no skin fittings and gets along fine, won't bore you with the details.

If one can glue the bracket on that's a helluva lot better than holes in hull !
 
Seajet said:
Holes in hulls = leaks and possible misery in various forms from internal osmosis, soaked foam buoyancy to sinking, my cruiser has no skin fittings and gets along fine, won't bore you with the details.

If one can glue the bracket on that's a helluva lot better than holes in hull !
Click to expand...

Yes, quite right, partic with the foam sandwich where you can't tell whether it's leaking.

But a question - if these are mounted just above or below the WL and thus above the bottom, how does the transducer see forward ? A depth alarm's not a lot of help when you've just gone over the shoal !
 
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Superaquarama said:
Yes, quite right, partic with the foam sandwich where you can't tell whether it's leaking.

But a question - if these are mounted just above or below the WL and thus above the bottom, how does the transducer see forward ? A depth alarm's not a lot of help when you've just gone over the shoal !
Click to expand...

they don't see fwd, they show the current depth, but the rolling graph showing the history illustrates the gradient much more readily than a depth sounder would, so If you're approaching a shallow and its getting toward your draft and still rising fast you can react. Most have two alarms, so you can have a "heads up!", and a "seriously!" alarm. mine are at 2.2 and 1.9 for a 1.1 draft. after that its eyeball on the FF.

btw I calibrate to depth from surface, but thats another argument.

I use the gradient to get over a bank between my mooring and a channel, and to guage tacks in channels.
if the gradient starts levelling off I can continue with enough water, If its still steeply rising I will tack.

I have no interest in the fish, they come frome supermarkets with breadcrumbs on..
 
Thanks for that useful info, Chewi.

Yes, I suppose that, especially with a short boat, it's not going to make much difference where the transducer is. After all, the likes of the old Seafarer only point straight down as well, so you're going top be caught by that rock or wreck just the same.

As to mounting without drilling holes, on the B/Whaler there are 2 drain outlets near the bottom of the transom and I think I could fit it into one of these by making up a couple of slightly conical discs and drilling several holes in them which will still allow partial drainage. Think I've got some old brass SU carb butterflies which may be a starting point.....
 
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