Transducer inside hull

General boating discussion
OceanTrvlr
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Joined: Thu Nov 13, 2014 2:36 pm
Location: Boston's South Shore

Transducer inside hull

#1

Post by OceanTrvlr »

The transom-mount transducer on my 2018 North River RAIV loses bottom at any speed except slow ahead. I've lowered the transducer as far as it will go to try to reach clean water flow, without success.

I've had a cheap transom-mount depth transducer siliconed INSIDE the hull of one of my fiber glass boats for 15+ years. It's used only for depth, not fishfinding, and works well at all depths and all speeds.

I'm thinking of copying what I did on the old fiber glass boat by just gluing a transducer inside the hull. I'm wondering if plate aluminum hull bottom will have significantly different acoustical characteristics than on the fiber glass boat.

Ethan

MacCTD
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Location: MA

Re: Transducer inside hull

#2

Post by MacCTD »

I think I have read it will work with thin aluminum boats, like Lunds but not on thicker hulls like your boat or similar.
'05 Pacific 1925
Mercury 150

kmorin
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Re: Transducer inside hull

#3

Post by kmorin »

I've seen a couple of transducers mounted inside 1/4" 5086 H-32 hull plate. There was a compensation block or tapered plate welded to to the hull, to allow the transducer to be mounted at Vertical/Horizontal as the hull was at rest. Final thickness this transducer was working through was more than 3/8" of solid aluminum.... and the readings were 'bottom' only- not fish finder. But the unit was reliable (don't know brand or model) and was tested with several other boats' external systems and showed repeated accurate readings within the limits of the sounder. ( I think it was a fathom [or two?] plus or minus?)

The transducers were mounted with a very thin film of silicone adhesive, inside the hull on the welded Deadrise & Waterline compensation plate.

I'd ask the sounder's mfg Tech support for some guidance? Some may work this way and others may not?

Cheers,
Kevin Morin
Kenai, AK
kmorin

OceanTrvlr
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Joined: Thu Nov 13, 2014 2:36 pm
Location: Boston's South Shore

Re: Transducer inside hull

#4

Post by OceanTrvlr »

Thanks for the info.

I don't plan on worrying about the angle of the hull as I understand most transducers transmit a fairly wide beam. I guess that would effect the side-scanning features though, making the image lopsided. But, I don't really care. As you said, this is "bottom-only" usage.

I can easily reach the hull plating directly below the helm area inside the cabin so, I'm thinking I may borrow a transducer, stick it down there, and see what it reads.

Ethan

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Almar22
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Re: Transducer inside hull

#5

Post by Almar22 »

I think if you mount it that far forward you will get way too much turbulance to get a good reading. Transducers need to read through "clear" water to work right (if I recall correctly).

kmorin
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Re: Transducer inside hull

#6

Post by kmorin »

I'm going to make some comments about this topic that won't be evident to everyone unless they've spent some time considering the "RUNNING" waterplane outline. In other words, the outline view- from Plan View, (ABOVE) of the shape of a hull intersecting with the water - while on step/planing.

There are a couple different issues at play, but they do influence this shape. First, as a planing boat is pushed faster and faster the water becomes hard and harder (Reynold's Number increase) and the water's increasing "hardness" sort of Lifts the boat upward.

But, few if any, planing hulls lift uniformly vertically. Most lift by pitching up the bow, and the finally somewhat the stern lifts. The attitude of the balance is referred to as the Running Pitch where trim tabs, engine anti-cav plate and other contributing factors result in some 'angle by the bow'.

If the boat were totally glass bottomed and viewed in drone footage; we'd see the leading edge of the water plane as a V (or in the case of hydro-planes a U) of some or another shape.; the faster the boat traveled the more water's Reynolds would increase so the "lift" would increase and the leading edge of the "running waterplane" would move further and further aft and finally (as is the case with racing hydro planes the leading would become a narrow band at the transom and look like an airplane wing from the top)

Just in front of the changing 'leading edge' or a water plane's forward boundary area is a great deal of splash where the water is very disturbed and turbulent. This area forms a sound barrier. Where a transducer may send sound waves through a hull, and through the water; if there is a "noisy" interface layer due to violently disturbed water at or near the leading edge of a planing hull's waterplane forward edge: transducers are notoriously unreliable.

So, depending on your hull's V (deadrise) and the speed of that hull? That water plane's leading edge (disturbed and a sound barrier) can limit transducer performance to the extent the depth sounder loosing signal entirely.

Location of depth sounding transducers should be where the hull runs on clear water. So, many outboard skiff transducers are mounted at the transom so they're 'always' in clear water.

I haven't worked out the hull shape, running shape, or the forward boundary line of the running waterline for this hull- I have for others and its a "non-trivial exercise". My remarks are intended to contribute to the readers of this discussion who may not be as familiar why different locations of transducers may impact their performance in aluminum planing hulls.

Cheers,
Kevin Morin
Kenai, AK
kmorin

OceanTrvlr
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Joined: Thu Nov 13, 2014 2:36 pm
Location: Boston's South Shore

Re: Transducer inside hull

#7

Post by OceanTrvlr »

Great info. That midships transducer location did not work out so well.

I have to go back and try to get the transom transducer into better water flow.

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