Topic: Helix Mega SI 10 Transducer Mounting Advice

[matt@reefmaster]

Hi all,
A long time since I visited this forum!

I have recently purchased a Helix Mega 10 SI, which I intend to run on a small inflatable boat ("SIB"). The boat is also quite new to me, and has a sort of catamaran hull design which makes transducer placement a little awkward. A standard mounting at the bottom of the transom doesn't work well, because the transom is short and also because the motor will block sidescan.

One potential solution is to mount the transducer underneath the centre of the boat, on the central inflatable keel (NB - all pics here are of a Lowrance totalscan transducer, but you get the idea):



In this case, the transducer is attached to the transom and mounted backwards, ultimately with a pair of straps that also secure the transducer to the cylindrical inflatable keel.

Close up of transducer on keel (you can ignore the arrows):



I want to do the same now with the mega transducer and I have a couple of questions:

1. I know I can flip SI Port/starboard if I run the transducer backwards, but this transducer is not symmetrical front/back. In particular the back is squared off. Any issues with turbulence here?

2. If I don't reverse the transducer, I will have to make a tight bend in the transducer cable. How tight is too tight?

3. If I was to build a protective cover for the transducer out of e.g. ABS or PVC pipe, for example, would this have any impact on SI quality? Obviously the pipe would be open to allow water through..

My main concern here is achieving high quality sidescan imagery at low speeds. I don't care about anything above a few knots, which makes me think (hope) that turbulence is probably not a major issue regardless of the hydrodynamics of the transducer?

thanks!

p.s. quick question on the screws that attach the transducer mounting plate to the transducer. Does anyone know the specification for the threads on these? I will need to create a new plate to go on top, and use longer screws. They measure exactly 4.00mm on my calipers, and I know that standard metric M4 don't fit (just tried), my M4 screws measuring a little under 4.00mm on the calipers (about 3.85). I assume this is something in US measurements..

[Rüdiger]

Hi Matt

If I understand correctly, the transducer from HB has the cable outlet on the top side, so flush mounting might be difficult.
There are two alternatives:
1. a simple towfish
2. You mount the Transducher on a pole or tube so that it comes into the water behind the engine

mvh
Rüdiger

[matt@reefmaster]

Thanks Rudiger - you are correct about the top wire, which is not ideal, but I think if I make a plate out of, e.g., 12mm HDPE and route a channel for the wire then I should be able to create a flat top. This plate would replace the stainless bracket top and have enough depth to hide the wire outlet. My main concern is about the effect of running with the non-hydrodynamic end forwards (it is square at the back/new front), and whether this is likely to be an issue with water flow?

A towfish would be nice but is simply not practical for my use. Apart from gathering test data, I intend to do a fair bit of fishing as well!

I've made my best guess on screws to mount the plate to the transducer at #8 UNC and ordered some - we will see how they fit when they arrive.

[matt@reefmaster]

OK, so here is what I ended up with - something similar to the idea in my first post.
I made a mounting plate out of 12mm HDPE plastic sheet, with a channel routed for the transducer cable. I screwed this directly to the transducer (FYI these screws are 8/32 UNC, not so easy to get locally in the UK but available online).
I then added foam on top to try and conform to the underside of the inflatable keel, and create the right pitch for the transducer. It is a bit ugly, but this is v1 proof of concept and I will make a new version now I think that can be a bit neater.

This is how the plate attached to the transducer, with the original transducer mount screwed to the plate (I think I will lose the original mount for v2 as it is too thick for my application):



This is how it looks mounted underneath the SIB, with a couple of small pieces of HDPE mounted to the transom with 6mm brass threaded inserts. The transducer assembly attaches with stainless/ABS thumb screws and it seems very secure:



First trip out was today, and was a qualified success since this was also my first time using the Helix and the first time I have used a Humminbird since my 997 bit the dust some years ago..

This is just an area in my local harbour with really nothing going on on the bottom - just mud, and lots of mooring blocks. Also very shallow today at low tide, with nothing really over 5m:



I think I will make another post with questions about ping rate, recording quality etc, but for now I will make the observation that when running on MEGA SI CHIRP I don't get any effective range beyond about 30m (90ft). Is this expected? Here is another image showing the full recorded range of 50m:



It is worth noting here that I had SI range set for 25m, which is what I was viewing on the screen. I was a little surprised to see 50m recorded in all instances except for the period I manually set the range to 60m, at which point 60m was recorded. I was hoping lower range would give increased ping rate, but I have a ping rate of 10/s across all channels in all of my recorded files. I'll write another post about this with questions.

All in all, I think the installation is successful and the quality OK - I need to try some more interesting terrain and perhaps some deeper water to make a fuller appraisal.