Thru hull transducer in C17.

Power Boats only. Please include the boat type in your question.
fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: Thru hull transducer in C17.

Post by fallguy1000 »

A glass tube could work, but you need some reinforcing around the hole and you only get the inside. I'd say 3 pieces of 1708 starting at plus 1/2" bigger than any inside flange. Inside the boat flat..

First, cut the plywood for the tube. Well, after the tube is made.

Then glass over the hole.. you may need to ship tape and put the cutout back in place so it won't stick (much).

Then glass.

Then hog out the plug of plywood, leaving the fiberglass intact. Use an oscillating tool or utility knife early about 12 hours after laying the glass.

Then glue the tube in from the outside. It won't be able to break up or out with the glass backer.

Then cut out the inside hole.

How to make the tube....epoxy shrinks when it cures. You can use pvc for the piece, but the id is 4", so it'll be way big...1/8" all around gap for 5200.

So, instead what you do is get 3" pvc which is 3.5" od and then you wrap it with some rope jist under 1/4", leaving the ends of the rope out and taped in place. Wrap the rope with shrink wrap or cling wrap. Then make the part with about 1.5" of rope turns and one inch of glass wide. Say like 3-4 noce tight turns. 1708 is about 0.050 per turn. This should get you close to a inside diameter under 4" and an od of 4", but the id is all that matters really. You can always find a way to cut the plywood out.

After it cures, pull out the rope, sand the part to fit the ducer and the hole, glue it in, bottoming on the glass. The ducer will never break in or out and a pinhole in the sealant won't do anything. The inside of the hole will have ridges from the rope that will help hold the sealants.

You'll need to find the right rope. Something on the order of baler twine seems close. You can always add cling wrap for final dimension.
My boat build is here -------->

viewtopic.php?f=12&t=62495

OneWayTraffic
* Bateau Builder *
* Bateau Builder *
Posts: 1662
Joined: Sat Jan 10, 2015 7:13 pm
Location: New Zealand

Re: Thru hull transducer in C17.

Post by OneWayTraffic »

Sounds overengineered. I like it. I'll wait for the transducer to arrive before I start cutting and drilling. One thing to consider is removal in 5-10 years should I need to. Hopefully any further transducers will fit the same hole. But I'll cross that bridge when I come to it.

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: Thru hull transducer in C17.

Post by fallguy1000 »

The main goal of all the bs is to make sure the plywood never cracks or a pinhole in the sealant can get to the plywood, so you are basically wrapping the plywood in glass. Am extra piece of 6 oz glass on the outside edge would also be some insurance.
My boat build is here -------->

viewtopic.php?f=12&t=62495

Dan_Smullen
* Bateau Builder *
* Bateau Builder *
Posts: 912
Joined: Tue Aug 13, 2019 3:02 pm
Location: VA

Re: Thru hull transducer in C17.

Post by Dan_Smullen »

Is there an angled block that keeps it pointed straight down, or does that not matter?

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: Thru hull transducer in C17.

Post by fallguy1000 »

Dan_Smullen wrote: Thu Apr 28, 2022 5:11 pm Is there an angled block that keeps it pointed straight down, or does that not matter?
Transducers are generally mounted level to the world, so he ought to consider a mount. The fancier ducers come with fairings for this reason.
My boat build is here -------->

viewtopic.php?f=12&t=62495

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: Thru hull transducer in C17.

Post by fallguy1000 »

If you read the specs, this is mounted even to the hull and angle expected.
My boat build is here -------->

viewtopic.php?f=12&t=62495

OneWayTraffic
* Bateau Builder *
* Bateau Builder *
Posts: 1662
Joined: Sat Jan 10, 2015 7:13 pm
Location: New Zealand

Re: Thru hull transducer in C17.

Post by OneWayTraffic »

I wouldn't install a thru hull with fairing block in a boat this size and type. These are low profile thru hulls. Install involves a bigger hole, but only 1/4" protuding below the hull, and shaped so as not to catch on anything in the event of a collision. They have a tilted element inside tilted at 0,12 or 20 degrees depending on what model you get. The deadrise at the transom is about 9-10 degrees, so the 12 degree is almost perfect. I could slightly adjust the angle of the install to get it spot on, but that would have other implications with respect to fitting the hull bottom.

Edit hull ->hole.

TomTom
* Bateau Builder *
* Bateau Builder *
Posts: 736
Joined: Thu Nov 22, 2012 10:29 am
Location: East Africa

Re: Thru hull transducer in C17.

Post by TomTom »

Why don’t you cut an oversized hole through the plywood in your hull bottom. A square one with an oscillating saw would probably be easiest. Cut only through the plywood and be careful not to cut all the way through. Use a chisel to carefully peel up the layers of ply as you go. You want to leave the outer layer of glass (your hull bottom) intact. So go slow.

Then fill this depression with glass cloth patches and epoxy mixed with chopped pieces of glass. You can overlap lap a few layers of glass on the inside over the edge of the joint. If you can taper the plywood edges towards the bottom of the hole - like a scarf joint- you will have a strong bond between your glass “plug” and plywood.

When it is cured and your transducer arrives you simply cut the right sized hole with a holesaw through this section of “solid glass” hull.

I did this when I forgot to do it before finishing the outside of the hill and I didn’t want to mess up the finish/ anti foul on the bottom. I’ve had no problems.

OneWayTraffic
* Bateau Builder *
* Bateau Builder *
Posts: 1662
Joined: Sat Jan 10, 2015 7:13 pm
Location: New Zealand

Re: Thru hull transducer in C17.

Post by OneWayTraffic »

To be honest I think I'd have trouble sleeping if there wasn't plywood reinforcing around the hole to make the panel locally stiffer. Whether needed or not, I'd have more confidence in it. It also gives me more surface area for sealant. A glass/epoxy lining is mandatory of course. To be honest I'd be happy just coating the hole as far as protecting the plywood is concerned. I do that in several steps: First wet with a finger or toothpick around the edge, then thickened/filled epoxy on that, and fairing wet on green. Then I sand once cured and recoat with epoxy. I can repeat this as much as required to build thickness. I'm more concerned with water getting past the sealant etc, and like the idea of a bit of glass tube to provide more surface area for the sealant to grab onto. I'll use the inside cut out of the holesaw to make a mandrel for the tube. Easy.

Your idea would work as well, but I don't see a benefit except for in Hull transducers. At least as much work and more epoxy.

All of this is probably overthinking it. I could probably just cut, epoxy, 4200 and install and it would be fine. But I won't. I'm no professional paid by the hour.

Fuzz
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 8920
Joined: Tue Aug 02, 2011 4:23 am
Location: Kasilof, Alaska

Re: Thru hull transducer in C17.

Post by Fuzz »

For what it is worth I have been in the bilge of a lot of work/rec boats and they always have a backing plate on every thru hull that is below the water line.

Post Reply

Who is online

Users browsing this forum: No registered users and 10 guests