Through hull fitting for transducer

[nzmal]

Hi everyone,
We're replacing our old depth transducer with a new Raymarine i50 unit at next haul out and I'm contemplating what I need to do to achieve this.
One aspect that I'm contemplating is whether the through hull fitting needs to be fitted in such a way that the depth transducer points vertically down or whether I'd be better off having it slope forward with the bow.
It's going into a 39 foot Cavalier under the v berth in the bow section of the boat.
The unit is on my boat 2 hours away with the instructions but presumably the fan of the sonar is spread wide enough that I should be able to install at a forward angle... which would then give me ability to pick up a hidden coral head or rock just before I hit it...

[nzmal]

Just realised, if i angle the transducer then I'll get false depth readings relative to how deep I am with the straight line to seabed becoming a slanted length instead of a straight line down. Doh!
...so in a curved hull do I need to create a built up flat surface that is parallel to seabed to get best results? ...that seems a bit of a hassle... and not the simple job I was contemplating... but typical of most jobs on board.

[JimsCAL]

It's a bit more complicated than that. The transducer sound doesn't travel is in narrow line, it's a cone. The angle of the cone depends on things like the frequency that the transducer operates at. If it wasn't a cone, the sound would not reflect back off the bottom and back to the transducer when the boat is heeled or pitching. So your concern that if the transducer was angled slightly forward would result in high readings is really not something to worry about.

[nzmal]

Originally Posted by JimsCAL

It's a bit more complicated than that. The transducer sound doesn't travel is in narrow line, it's a cone. The angle of the cone depends on things like the frequency that the transducer operates at. If it wasn't a cone, the sound would not reflect back off the bottom and back to the transducer when the boat is heeled or pitching. So your concern that if the transducer was angled slightly forward would result in high readings is really not something to worry about.

Thanks Jim. Yes that makes sense re pitch and roll.
The transducer is a p319 and has online specs of 600w 50/200kHz.
Specs say it has hull deadrise " up to 8 degrees"?... presumably that gives me ability to mount at 8 degrees from horizontal.... which wont be enough in its proposed position.
So now Im looking at using a fairing block to provide appropriate mount... am I on the right track of thinking?

[Orion Jim]

My transducer is mounted on the centerline forward. Access is under the v-berth. It is installed looking straight down without a fairing block, but it is faired with Marine-Tex putty.
Not a very good photo but you can see the result. It's been trouble free since 2002.

[nzmal]

Thanks Jim
So if I get this straight... I create a fairing block out of ...something...(epoxy coated teak or oak perhaps) ...then glass it into place, then drill the hole for the transducer mount vertically down, then install the transducer hull fitting... and Bob's my uncle...

[a64pilot]

Can you return the transducer and swap it for a P79?
Those shoot thru the hull and require no hole and come in different flavors if you will for different manufacturers, actually it’s only the plug that is different.
There just isn’t much of anything to be gained by mounting it real close to the bow, maybe 2 sec additional warning if that.

It’s my understanding that even forward scan Sonar is only good for poking around real slow when your expecting trouble, underway it has little use.

[nzmal]

I could return and swap it... but my wife has already fed the wiring all the way back to the switchboard and wired it in so it wouldn't be wise... besides I read that there are reliability benefits to the traditional fitting that pokes through the hull.
I'll look at the existing transducer set-up when I return to the boat and see if I can utilise it's fairing block. I haven't been into the space where all the installation will take place yet so options may be limited when i discover other stuff going on.
Thanks everyone.

[malbert73]

Try taking a 6 inch piece of PVC pipe and cutting it at an angle so it sits vertically on the inside of your hull near the bow. Glue it to the hull, fill it with water or propyleneglycol, and put the transducer in it. If your hull is uncored you may get a good depth sounder signal through your hull. Obviously then fit a cap to the top of pipe and screw tranducer through that.