Mounting Fishfinder Transducer

[jon_bailey]

I know this subject has been done to death but I have not found a solution to my particular problem.

Trying to mount the tranducer for a Garmin 240 Blue as a shoot-thru hull device on my Maxum. The problem is that the only places to mount transducer on inside of hull is sloping (by at least 20 degrees). To resolve this I cut a tube off at correct angle, sealed to hull and then filled with water before mounting tranducer level in the tube.

On last trip out depth shown was in accordance with factory fitted depth gauge but there was a lot of noise in the top third of the trace and certainly much more than on other fishfinders I have seen. I have the following questions:

1) Is this noise likely to be caused by the fact that the transducer is not bonded to the hull and not aided by the fact that the face of the transducer is at varying distances from the hull due to the slope?

2) If the transducer has to be mounted horizontally then how can this be done on a sloping hull?

As always, all advice gratefully received.

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[BarryH]

When I put an old seafarer unit in a past boat. I was advised by someone, cant remember who, to use castor oil to fill the tube. Whats the shape of the transducer. Is it the skimmer type or the round 'puck' type.



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[jon_bailey]

Barry,

I also heard about using silicone oil but didn't want to start messing around with this until I was sure I did not have to bond anything else to the hull.

It is the 'standard' transom mounted transducer that according to the manual can also be used as a shoot-thru device. I assume this is the skimmer type device you refer to.

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[BarryH]

Mmm, maybe the tranducer is moving about in the tube changing its orientation as the boat goes up and down. Would it be worth trying to mount it in the tube solidly near the bottom. Then fill it with the oil.

Failing that I would say contact the dealers. I mounted my tranducer on the stern. Gives a good picture, even at the higher speed ranges. Sorry can't be of more help.

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[jon_bailey]

Barry

My unit also came with a speed transducer which has to be mounted from the transom. Therefore may well bite the bullet and drill a hole in my hull - even if against my principles.

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[DepSol]

Use epoxy resin, wait till the resin has settled and there is no air bubbles then slowly insert the transducer at the correct angle and hold till it sets hard nuf. leave overnight and check next day.

Make a mould firs to pour the epoxy into.

<hr width=100% size=1>Dom

Now where is that Brendan hiding?

 

[Deleted User YDKXO]

If you mount the transducer 'horizontally' (I guess you mean at 90deg to the hull) then you will get incorrect depth readings as the transducer will be measuring the distance between itself and the sea bed at an angle
What you have done is basically correct but you must ensure that the tube is completely sealed at its base. Then use castor oil (buy it from a pharmacy) rather than water as any air bubbles will distort the readings. Ensure that the transducer is completely immersed in the oil not just sitting on top of the oil
The other problem you may have is that the transducer is receiving interference. It needs to be positioned at a point where there is a clean flow of water under the hull, not too far forward where the hull is starting to lift out of the water at planing speed and not to far aft where the water flow is distorted by the props. You need to experiment in order to find the best position. You need at least 2 people for this. Get a small plastic bag, fill it with water and immerse the transducer inside. You drive the boat at planing speed whilst the other person sits in the bilge (ear defenders are a good idea) moving the water filled bag around the hull until you find the optimum transducer position. The bag must be in solid contact with the hull for a good reading to be obtained. When you've found the best position, locate the tube there

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[oldsaltoz]

G'day Jon,

I strongly suspect the water has to be replaced with oil, but also ensure the location you have chosen in not one that is likely to have any bubbles under it at any time, any air or bubbles inside or outside the hull will cause bad readings / results.

The fact that the hull is at an angle should cause any problems.

Hope this helps...



<hr width=100% size=1>Andavagoodweekend, Old Salt Oz /forums/images/icons/cool.gif

 

[jon_bailey]

Thanks for all of the advice and I've decided on a strategy.

I'll start by using the plastic bag to find the best location, even though the choice is limited. Will then use an epoxy potting compund in a mould to 'flatten out' the chosen section of the hull, followed by a bonding of the transducer to the flat top of the potting compund. Provided I can avoid any air bubbles this all sounds good.

All I now need is someone prepared to lean into the engine compartment with a plastic bag and a transducer next to an engine rotating at 3000 rpm whilst on the plane in the solent and hoping for no large wakes. Any volunteers?


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[BrendanS]

Sounds like just the stupid sort of thing I'd do! /forums/images/icons/laugh.gif

I'll bring along my forward looking sonar and we can play around with that at the same time.

<hr width=100% size=1>Err, let me know if Depsol enters the forum, I'll go and hide

 

[jon_bailey]

If the cap fits!

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