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Hull Thickness For In Hull Transducer

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Hi all,

Would you have any views on in - hull transducers ? I fancy a depth finders but not enough to drill holes in my boat to facilitate fitting one. I know that there are in-hull ones that you can stick on inside and also that you can buy ( or make ) kits with silicone - filled boxes that you can put any transducer in but I read that these will only work up to 19mm thick GRP.

Is this figure pretty accurate? Would it work on a thicker hull but only in shallower waters - which the broads surely are? Does anyone have any idea how thick the hull of my Aquafibre 37 1985 might be? 

Thank you very much for any advice and information you might be able to give me.

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NMEA suggests that transducers are not to be installed to cored fibreglass hulls due to their thickness.


you could take a look at transome mount transducers which are recommended.

Happy to discuss with you ☺️


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I doubt aquafibre hulls are cored so you should have no issues with in hull, the usual trick is to epoxy a plastic tube to the inside offset from the keel enough to not try to look through it and insert the transducer and half fill with oil or antifreeze to keep any air out of the gap, they "see" straight through solid grp very acurately, you can silicon them to the hull but you must get any air bubbles out of the gap.

make sure you mount the tube upright, angle the tube bottom to match the hull.

8 hours ago, Rbartram said:

NMEA suggests that transducers are not to be installed to cored fibreglass hulls due to their thickness.

The reason they don't work with cored hulls is the different materials and air if foam is used in the core, they don't work with any air under them as the ping won't travel through it.

In hull is by far the easiest and cleanest way to go.

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If it looks like water on the Broads you will probably float as the next foot or so, or more, will be liquid mud!

Different of course if you are going to sea but I must admit to never having felt the need for one on the Broads, nor can I remember ever getting stuck - different if you are a sailie as you have a big pointie thing underneath - usually!!

Having said that, as long as its not right next to the keel, my guess is not not likely to be more than 20mm or so, although in those days they did tend to lay them up more heavily.

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9 minutes ago, NeilB said:

I've been told the non drill transducers are generally OK for depth sounders but if you upgrade to a fish finder they may not work and will require a trough hull fitting.

I would be worried if you needed a fish finder on the inside of your hull, in the bilges. And if you did have fish in there, it may not be long before you don't need a depth finder, as you may have found the depth and be sitting on the bottom of the river by then anyway ...

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