SIB mounted transducer question

[Mattster]

Another transducer mounting question, sorry!

So I am setting up my Elling for next season and I need to mount the (very large) 3 in 1 sidescan transducer for my HDS unit. I've realised that on this "cat like" hull, the transom really isn't low enough to use the same solution that I had on the Honwave. Not only would the transducer perhaps be too high above the water at speed, but worse is that the tubes and the central "sausage" keel would likely block much of the sidescan (being able to view and record high quality sidescan is very important to me). I also had some issues with the engine blocking sidescan to port on the Honwave, because of the distance that the transducer protrudes from the transom.

It seems like the guy in this video

https://www.youtube.com/watch?v=dhERqWsBoJo

had similar issues on his Elling, and came up with quite a neat solution (see 10 mins on in the vid, or pics below). Transducer is mounted centrally and reversed (front/back), so that it sits directly underneath the sausage. It has a totally unobstructed view, and hopefully gets clean water when under way. The sleeve arrangement glued to the underside probably makes this rather secure also:





I want to do the same, but I've got a couple of issues. 1/ the transom plate is much deeper on my version of the Elling, so I can't fit one of the borika mounts between bung and transom plate and 2/ I don't think I quite have the clearance engine/transom to allow it in any case (I need to check this).

My proposed solution is to mount HDPE blocks, one each side of the bung hole. Then make a sort of T section, probably out of 4-5mm alu bar, which attaches to the blocks and also the transducer. Transducer then slots into a simple sleeve of PVC that I glue to the sausage. This should be a very low profile mount.

My transom:


A very rough idea of the mount:


A simple, open fronted sleeve that is glued in such a way to be snug to the transducer but still allow removal:


My transducer:


Questions!

How best to attach the aluminium T bracket + transducer to the transom blocks. This has to be tooless and removable. One idea I have is to get some threaded brass inserts for the HDPE, and some stainless thumb bolts. Should work? I worry it won't be secure enough and may work loose through vibration, but is there a better way? It needs to be fairly low profile, also.

I am hoping I can arrange things so that the transducer is snug to the underside of the keel, and within the sleeve. If this works out, I think it should be fairly secure and not kick up a lot of extra spray etc. Any thoughts? If water can get in at the top, I imagine that may apply a fair bit of pressure when underway which might pop the transducer out. Perhaps it is worth trying to craft some sort of fairing at the front? Followup question, how will the sleeve behave with no transducer mounted?

Open to any bright ideas!

[Oldman2]

Have you considered ratchet strapping the bare transducer to the back of one tube and testing if that gives clearance from the outboard for sidescan? There are btw other shapes of transom engine mounting plates that would give you more room if you were using a mount between it and the drain bung but I dont see that you could easily gain the space needed if the outboard was in pin hole 1, too close to the leg I would think.

[Mattster]

Thanks for the response. Yes, I have considered it and it would probably work, but I think it would work better centrally in terms of image and sonar usability (I'd have a metre offset to one side if tube mounted). Also I'm not convinced it would be much/any easier to achieve? Certainly I couldn't use the existing bracket, so would I just go over the transducer or fashion something with a slot that sits above? The other thing that worried me was trailing the wire up. All in all I think central on the keel would win on a few fronts, if I could achieve it neatly (and no issues with wires, or transducer rooster tails etc because it would all be neatly placed behind the sausage).

[Limecc]

Originally Posted by Oldman2

Have you considered ratchet strapping the bare transducer to the back of one tube and testing if that gives clearance from the outboard for sidescan? There are btw other shapes of transom engine mounting plates that would give you more room if you were using a mount between it and the drain bung but I dont see that you could easily gain the space needed if the outboard was in pin hole 1, too close to the leg I would think.

Similar to the thought I had except split the bracket and strap or monster cable tie it to the underside of a tube, not to the rear of it. Wow it's a monster! You win on top trumps.

[Mattster]

Originally Posted by Limecc

Similar to the thought I had except split the bracket and strap or monster cable tie it to the underside of a tube, not to the rear of it. Wow it's a monster!

It's horrendous, but a lot of them are now! Humminbird do a much smaller sidescan transducer than the rest, but I did hear a rumour that they have a patent on whatever tech it is that allows them to do it, which is why they are the only ones. Their sidescan is probably the best in the business as well.

Could remove the ducer from the bracket which leaves a smooth plastic top, then ratchet over it. It might work OK but there would be a fairly fat trailing wire which would need a bit of management.

Central is still the ideal - lots of hard boat users now glueing their ss transducers to the keel in a similar manner. A bit less up and down movement with boat rock in that position, which helps the image - although probably not a huge issue at the sort of speeds you use sidescan.

[Mattster]

OK, reviving this one with a few more pics now I have got the boat out and taken a look. I had forgotten/never realised that the "sausage" on the Elling is actually "free floating" towards the transom, which opens up the possibility of strapping the transducer on, in a similar way to strapping to the main tubes. Main tubes are confirmed as not a great option for my boat, given strakes immediately fore, and also probably issues with getting it perfectly level etc.

Current plan is to go with the original idea:

Enlarge the openings in the side of the bracket on both sides, so that they can take (velcro?) straps. Stick a length of 10mm closed cell foam inside the bracket also, to fill the void between transducer/keel and protect the underside of the boat.



Go with the original idea of fitting a pair of hdpe blocks to the transom either side of the bung with brass threaded inserts (M6) in each. Attach a cross member of hdpe using M6 star knobs, far enough off centre to be out of the way of the engine (they'll poke out a bit):



And that's it. should be quite easy, and I'm hopeful it will work well. The question now is which sort of straps? There are some velcro elasticated ones around on the usual sites which look promising.

[Oldman2]

Not wishing to pe* on your parade but the sausage on my Elling is awful close to the outboard even on pin hole 2 on the saddle. Are you sure you will have the clearance to your outboard after mounting the transducer there?

yam on elling sausage clearance.jpg

[Mattster]

I remember your post on that one Oldman. Mine isn't - it is at least two inches further back than yours - so I *think* I'll get away with it, although I haven't put the motor on the boat along with my mockup to actually test it yet (have done a bit of measuring though). I'll probably end up using a 3mm stainless plate from cross member to transducer, which should keep the profile down a bit, so fingers crossed it will be OK. You're right tho, I don't think this would work with your sausage..

Edit: 2 inches may be an exaggeration, but you can see from the top pic in my last post that the sausage almost reached the edge of the black lip at bottom of transom.

[Blankton]

To put the studs in your hdpe blocks, I would try a couple of 316 stainless bolts, drill the pilot holes, heat the bolt heads with a blow torch and then push them into the hdpe. See if you can melt in a hexagonal recess on the back face, so they can't spin.

[Mattster]

Thanks for the tip - I did think of going with studs that remained attached to the transom mounting plates, but I didn't like the idea of the studs damaging the boat when rolled up. I've gone the opposite way, with threaded insert (M6 x 8mm) to go into the HDPE block that is screwed to the transom, and male M6 star knob. Both items pretty cheap on fleabay, the knob is allegedly stainless but the cheapest I could find were 25mm thread so that will need cutting down a bit. Here they are (arrived today), just need to get on with it now!



Still trying to decide on velcro vs standard buckle straps. Need 2, about 18 inches long each, perhaps 1 1/2 - 2 inches wide. Which will be stronger? Buckle could hide between sausage and underside of boat so not too worried about drag, although perhaps a bit of a near wear point.

[Mattster]

Well it's kind of ugly, but it works.. I'm treating this one as a v1 POC and I think I'll make a slightly neater/lower profile version without the original mounting bracket now that I know the concept is viable:

Here it is on the boat. I will say that I am impressed by the brass insert/thumb screw combination, which seems extremely solide and leaves me with a very low profile mounting left on the transom. I ended up with 5 screws and 10 inserts so I'll have to put my mind towards what else I can mount..

Eagle eyed might spot that this is a different transducer to the OP - this is a Humminbird Mega SI, abit smaller but not much:



And a quick run out today to take advantage of the weather. Only a short run up from Itchenor in shallow (3-5m) water, so not much to look at apart from mooring blocks:



Decent enough tho, and looking forward to scanning some more interesting stuff. Markedly better than the transom mount I had on the Honwave, which was badly impeded on one side by the engine (and mounting on the transom on the Elling simply won't work).

Still a little concerned at what happens at higher speed, or if I hit something - transducer is now the lowest part of the boat, which is great for sidescanning but perhaps not so great in other situations.. some sort of 3d printed protective cover like the kayakers used might be a good idea.

[Fenlander]

>>>Still a little concerned at what happens at higher speed

Looks a neat job and a good display result. Have you had it on the plane with this arrangement yet? I wondered if it would cause splash or even prop ventilation?

[Mattster]

Originally Posted by Fenlander

>>>Still a little concerned at what happens at higher speed

Looks a neat job and a good display result. Have you had it on the plane with this arrangement yet? I wondered if it would cause splash or even prop ventilation?

Not yet, although I am not sure how much the Elling really "comes up" on the plane compared to a more standard hull, so we'll see. I'll probably fettle it a bit to make it lower profile (drop the original mounting and use angle brackets is the rough plan). Hoping it will work because this is the only place I can really mount it. If you watch the vid in the OP of the Russian guy he certainly has no problem going fast with it! Admittedly his does seem a little lower profile than mine, and he has fashioned a cover out of PVC which might help with drag. Some spray from these big transducers is normal tho and probably can't be completely avoided.