In hull transducer vs thru hull

[cdawgs65]

What are the going opinions on in hull transducers vs thru hull transducers? Raymarine has depth displays that work with both. thanks in advance

[Hirilondë]

I already had a hole, so I went with a thru-hull version. There is definitely something good to say about not drilling holes in boats below the water line.

[mitiempo]

I installed a Raymarine ST 40 with the standard transducer that is designed for mounting through the hull but epoxied it inside and it works fine. I agree there are enough holes already. Any transducer of good quality should be able to shoot through the hull as long as it is solid glass.

[Triton106]

The PO of Blossom installed a thru hull type of ducer. It works fine. The advantage of the thru hull type of ducer is that they can be installed plumb by using wedge shaped backing plates on both side of the hull. The disadvantage is that there is another hole in the hull and that there is extra drag from the ducer and the wedge. Although you can install ducer plumb in hull as well I went with a simpler installation of epoxying the ducer straight to the hull. As a result it is installed at an angle of 25 to 30 degrees to plumb. Although this type of installation introduces a bit of measuring error due to the angle it should not matter in most type of navigation (my opinion, of course). I esitmate the error is approximately 10% only on a hull that is approximately 25 to 30 degrees from horizontal (see my other thread for more detailed discussion - http://www.plasticclassicforum.com/view ... f=4&t=4678) which means if the depth guage shows 10 ft it could be only 9 ft, not a big deal.

[Hirilondë]

The advantage of the thru hull type of ducer is that they can be installed plumb by using wedge shaped backing plates on both side of the hull. The disadvantage is that there is another hole in the hull and that there is extra drag from the ducer and the wedge.

You can buy transducers that mount flush and have the angle built in. I had 3 options of angles for the one I bought and chose the one that aimed the closest to straight down.

[mitiempo]

I installed my ST40 transducer on my boat, a CS27, ahead of the keel on the centerline. After checking it in a baggie of water I built a dam around the area and poured in straight epoxy. Next day I epoxied the transducer on the new flat section after again checking with a baggie of water. It is also under the aft end of the V berth so is not in the way.

[Triton106]

You can buy transducers that mount flush and have the angle built in. I had 3 options of angles for the one I bought and chose the one that aimed the closest to straight down.

You are absolutely right Dave. In my case the PO installed an inhull unit that did not work and it does not have an angled design so I just reinstalled it with epoxy. If I were to buy a new unit I would have done it differently.

I installed my ST40 transducer on my boat, a CS27, ahead of the keel on the centerline. After checking it in a baggie of water I built a dam around the area and poured in straight epoxy. Next day I epoxied the transducer on the new flat section after again checking with a baggie of water. It is also under the aft end of the V berth so is not in the way.
I installed my ST40 transducer on my boat, a CS27, ahead of the keel on the centerline. After checking it in a baggie of water I built a dam around the area and poured in straight epoxy. Next day I epoxied the transducer on the new flat section after again checking with a baggie of water. It is also under the aft end of the V berth so is not in the way.

That's also a great solution. In my case, I reserve that space for a future water tank so it was ruled out.

[mitiempo]

Ray
My water tank if farther forward and I will have to drill a hole for the speed/log/temp transducer quite close to the depth transducer.