Echosounder transducer mount/sea chest design

[pdwiley]

Hi.

At the moment I'm welding up the keel assembly for my toy 38' sailboat. The perfect time to put a hole in the keel shoe is now, while I can easily set it up under the radial arm drill.

When I worked on our research ships, we were always servicing the echosounders and I know how their sea chests work and are built better than I ever wanted to. Now, for a toy boat with a 4' draft, all I want is something simple and cheap to tell me how much water is underneath me down to 50m or so. I'm thinking of a fish finder/depth sounder setup.

Does anyone have a design for the transducer housing or references to where I can find one? Is there a huge variation in sizes & mountings so I really need to choose a brand first, then see what fits?

If it matters I have a full machine shop so can make anything I need to make, though I'd prefer to keep things simple.

The keel shoe is a 200mm x 40mm flat bar.

All advice & suggestions welcome.

Peter Wiley

[gonzo]

Do not mount it on the keel. The first grounding will destroy it. Depthsounders come with o rings that allow you to take them out in the water. There is a flapper valve and a cap to keep water from coming in.

[pdwiley]

This is not an accurate statement. I spent over 10 years sailing on, working on and servicing icebreakers. We always mounted our transducers in sea chests in the fwd part of the hull, slightly recessed behind HDPE or polycarbonate windows transparent to the echosounder frequencies. Over the years we lost only 2 transducers to impact damage. This is far more severe usage than a pleasure vessel.

I am going to mount the transducer through the keel. My question is for an appropriate sea chest design, if anyone has one, before I re-invent the wheel.

Thanks, Peter

[gonzo]

If you make a sea chest of the same plate as the keel it should be OK. I assume there is a space in the aft part of the keel where it is hollow with no ballast. Why do you want it in the bottom of the keel for?

[TollyWally]

Not to state the obvious but if the transducer is the lowest point of the hull it is likely to be the first thing to touch ground. The keel shoe is the last place I would mount a transducer.

http://airmartechnology.com/ will lead to a treasure trove of all things transducer.

Nice to be able to build your boat from a clean slate. Good luck with your project and keep us posted with pics as the project progresses.

[pdwiley]

The keel is 7.6m long for an 11.8m hull. It's a long keel shoal draft design. Draws 1.2m of water to the DWL, max draft right aft in front of the rudder.

The idea is to cut a hole through the keel shoe of the appropriate diameter and weld in a sea chest which could be as simple as a piece of stainless steel pipe with a cable gland on the top. I was planning on keeping the transducer itself slightly recessed into the pipe so it wouldn't be the first thing that hit. I've got all the specifications etc for Simrad transducers for big vessels and the cable gland drawings etc because that's what we used to use. I could scale it all down but I don't like reinventing the wheel.

This recessed design does work in practice, we used them for years in our icebreaker where the transducers cost over $10K USD each and swapping one over was a job for divers if you were lucky, or dry dock if you weren't. I'm not real worried about distorting the keel shoe or bending it and if the transducer is recessed slightly it is pretty safe against any impact other than a narrow point load coming almost vertically. If that happens, so be it. I'm totally ignorant about consumer level boat electronics and their requirements and I tend to over-build things, hence doing some research. As I have lathes & milling machines as well as my welding & cutting gear, fabricating something is not difficult if I have a design to go off.

Photos etc of the build - when I have more than a pile of frames and a partially fabricated keel shoe, I'll post something. I keep getting dragged off to do work interstate which slows progress. This is my retirement project but other people keep paying me and I keep buying more tools....

[pamarine]

Just to throw this out there:

Unless you are looking at a scanning sonar, pick a depthsounder that has the features you want.

90% of all retail Depthsounders use transducers manufacturered by AirMar (the other 10% are specialty transducers and the Radarsonic oddball frequencies).

So, once you find the sounder you like, then ya just order it with the transducer that suits your mounting location.

[TollyWally]

"This is my retirement project but other people keep paying me and I keep buying more tools...."

You have my deepest sympathies

[pdwiley]

Originally Posted by pamarine

Just to throw this out there:

Unless you are looking at a scanning sonar, pick a depthsounder that has the features you want.

90% of all retail Depthsounders use transducers manufacturered by AirMar (the other 10% are specialty transducers and the Radarsonic oddball frequencies).

So, once you find the sounder you like, then ya just order it with the transducer that suits your mounting location.

Excellent. Tollywally posted the Airmar URL and I've been browsing their site & downloading some of the pdf brochures WRT mounting. The transducers are a lot different to those I'm used to so this has been really helpful. Thanks to all of you.

Peter

[pdwiley]

To wrap this up, I decided to drill/bore a 52.5mm clearance hole through the 200 x 40 flat bar keel shoe, then counterbore an 80mm dia x 10mm deep recess for the transducer head. From the Airmar specs, this allows the face of the transducer to sit 5mm below the surface of the keel.

In theory it's still possible to damage this by a localised impact coming almost vertically, but - shrug. I'll take the chance. It's little or no more likely than the same thing happening to a transducer mounted through the hull plate offset from the centre line.

Thanks for the advice, I'll probably start another thread with some different questions.

[yachtwork]

Greetings and to throw my two cents in-

A simple way to build the sea chest inside the boat is to use a pipe nipple. In my book "Metal boat repair"

http://www.tongacharter.com/book-repair.htm

I cover this idea. Cut the pipe nipple to match the angle of hull and then cut a small hole in the side of the pipe nipple to pass the transducer wire and an orifice penetration gland, or just some 5200. Weld this nipple over the transducer and put a pipe cap over the top. When you need to get to the transducer you can pull the cap, but if you ground out or break the plastic transducer water can't enter the boat.

It's the ten dollar solution.

Hope that helps.

Scott

[pdwiley]

Yeah, I saw that. It'd work. Personally I'd prefer a short length of 100 x 100 x 6 RHS with a custom fitted insert and bolt-on lid. The problem with pipe nipples is that the cap doesn't always want to come off when you want it off if it's metal and you can't always get the leverage you need. I know you used a plastic cap, but I don't like that idea either. If I was going this route I'd probably use a stainless steel camlock type fitting. Horrible price tho.

As it is, it may break but I doubt it. It can't be scraped off from the outside and it's in the box keel so quite difficult to accidentally hit from the inside.

PDW