Thru hull transducer in C17.

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OneWayTraffic
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Thru hull transducer in C17.

Post by OneWayTraffic »

I'm going to put an Airmar SS175m thru hull into my C17. Prefer these to transom mount in that size due to the potential for a better picture at speed, cleaner mounting location and better looks. But involves drilling a 95mm (3.75") hole in the hull bottom, which is a serious commitment.
https://www.airmar.com/uploads/InstallG ... 458-01.pdf

What kind of reinforcements would I need around this hole?

I'm thinking that I could locate the hole in the center of the rear panel in the sump between the motorwell frame and the transom, with a minimum of a 12mm backing plate of plywood, glued in and glassed over. I could double or even triple this reinforcement and the transducer will still fit.

Any feedback?

Edited typo.
Last edited by OneWayTraffic on Tue Apr 26, 2022 12:56 am, edited 1 time in total.



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Re: Thru hull transducer in C17.

Post by Fuzz »

I would feel pretty good about a 12mm backer that is glassed over. Pretty hard to ever have a lot of force applied to it.

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TomW1
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Re: Thru hull transducer in C17.

Post by TomW1 »

OneWayTraffic 95mm is 3 3/4" not 3/4" big difference. Also, you need to beware of turbulence from the skeg. It needs to end a minimum of 2' or more in front of your sounder so that there is no turbulence on it. Just a few thoughts for you.

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Re: Thru hull transducer in C17.

Post by Jaysen »

OWT, I’m assuming the hole is needed because you can’t shoot through composite panels. Does the transducer need to be contact with the water?

The way I’ve seen this done is by building a solid plug (replacing the core) 2x the diameter of the TD then mounting the TD to the plug. I’ve also seen support tubes created from PVC and/or glass. The big things have been keeping the TD securely attached, often with screws and straps.

Let us know how you move forward.
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Re: Thru hull transducer in C17.

Post by fallguy1000 »

I don't really like the ply backer. The edges of the airmar hole need to be solid glass and epoxy. This will prevent any leak from rotting the boat. It can work, though.

But you could use a ply backer if it were encapsulated with thickened resin.

So, how? Well, the 3.75" hole could be cut out as a 4" hole and you could backwards ship tape the edges of the hole using the nonstick side of the tape for a mould and then add the thickened epoxy back to say 3.25", let it cure and sand..file it back to 3.75 or a bit bigger for 5200.

Another way would be to glass about 6 layers of fiberglass about 5-8" circles each half inch smaller, but big enough for any internal flange, so could be 8-12" for all I know. Then, cut this for the airmar and use an oscillating tool to remove the plywood for about 1/4" around from the outside and then fill the edge of the plywood with thickened resin so no wood is exposed to the ducer.m and the 5200 seal is made against thickened epoxy.

Either way, make sure to avoid hard edges on the ply or fiberglass patches. You can fillet the 1/2" ply edges or scarf it down an inch all around.

Anyhow, I did decore all thru holes in my boat that are below waterlines and I recommend same. Decoring plywood is hard for a large hole, but wise.
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Re: Thru hull transducer in C17.

Post by OneWayTraffic »

TomW1 wrote: Mon Apr 25, 2022 9:38 pm OneWayTraffic 95mm is 3 3/4" not 3/4" big difference. Also, you need to beware of turbulence from the skeg. It needs to end a minimum of 2' or more in front of your sounder so that there is no turbulence on it. Just a few thoughts for you.

Tom
Thanks. Actually fat fingered the / instead of the . key.

My skeg goes all the way to the transom, and that is not changing at this stage. The sounder will not be directly in line though, it's a tilted element, and I'm currently planning to put it to one side of the skeg, about 30cm to the starboard, just in front of the transom. There are no planning strakes or other protrusions directly in front at all. Speeds won't be excessive, which should help, and if there's turbulence I would expect that to be an issue for a transom install as well.

I'm hoping that that will be sufficient. If not :help:

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Re: Thru hull transducer in C17.

Post by OneWayTraffic »

Jaysen wrote: Mon Apr 25, 2022 9:54 pm OWT, I’m assuming the hole is needed because you can’t shoot through composite panels. Does the transducer need to be contact with the water?

The way I’ve seen this done is by building a solid plug (replacing the core) 2x the diameter of the TD then mounting the TD to the plug. I’ve also seen support tubes created from PVC and/or glass. The big things have been keeping the TD securely attached, often with screws and straps.

Let us know how you move forward.
It's a thru hull, rather than an in hull. The terminology is a little confusing. It's a low profile, only 6mm (1/4") protruding below the hull. Got a link here to the install procedure, which has some diagrams. Supposed to be ok to run trailer rollers etc over it, and a lot harder to dislodge in a collision than a fairing transducer. Hopefully I'll never put that to the test. :D

https://www.airmar.com/uploads/InstallG ... 458-01.pdf

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Re: Thru hull transducer in C17.

Post by OneWayTraffic »

fallguy1000 wrote: Tue Apr 26, 2022 12:27 am I don't really like the ply backer. The edges of the airmar hole need to be solid glass and epoxy. This will prevent any leak from rotting the boat. It can work, though.

But you could use a ply backer if it were encapsulated with thickened resin.

So, how? Well, the 3.75" hole could be cut out as a 4" hole and you could backwards ship tape the edges of the hole using the nonstick side of the tape for a mould and then add the thickened epoxy back to say 3.25", let it cure and sand..file it back to 3.75 or a bit bigger for 5200.

Another way would be to glass about 6 layers of fiberglass about 5-8" circles each half inch smaller, but big enough for any internal flange, so could be 8-12" for all I know. Then, cut this for the airmar and use an oscillating tool to remove the plywood for about 1/4" around from the outside and then fill the edge of the plywood with thickened resin so no wood is exposed to the ducer.m and the 5200 seal is made against thickened epoxy.

Either way, make sure to avoid hard edges on the ply or fiberglass patches. You can fillet the 1/2" ply edges or scarf it down an inch all around.

Anyhow, I did decore all thru holes in my boat that are below waterlines and I recommend same. Decoring plywood is hard for a large hole, but wise.
I was thinking along similar lines to your first idea. Possibly glue in a fiberglass tube inside the wood.

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Re: Thru hull transducer in C17.

Post by BarraMan »

OneWayTraffic wrote: Mon Apr 25, 2022 4:58 pm I'm going to put an Airmar SS175m thru hull into my C17. Prefer these to transom mount in that size due to the potential for a better picture at speed, cleaner mounting location and better looks. But involves drilling a 95mm (3.75") hole in the hull bottom, which is a serious commitment.
https://www.airmar.com/uploads/InstallG ... 458-01.pdf
What kind of reinforcements would I need around this hole?
I'm thinking that I could locate the hole in the center of the rear panel in the sump between the motorwell frame and the transom, with a minimum of a 12mm backing plate of plywood, glued in and glassed over. I could double or even triple this reinforcement and the transducer will still fit.
Any feedback?
Edited typo.
I considered a thru hull transducer for my boat but in the end I just couldn't get my head around how to do it successfully.
I don't agree that you get a better picture than with a transom mount and looks are in the eye of the beholder!
I have two transom mounted transducers, both mega side-scan - one on each side, and get excellent images that hold well past 30 kts. Its all in the setup!

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Re: Thru hull transducer in C17.

Post by OneWayTraffic »

Set ups a big part of it true. I’ll have a side scanning sonar on the transom already, but that might be situated higher up so it’s out of the water on the plane. There was little difference in cost from the transom mount, and I have enough things on the transom as it is. Anyway I just prefer it to be tucked away.

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