Tuesday, February 21, 2012

Installing the Garmin GSD 26

It's large, heavy, and packed with high resolution analog to digital converters, and a dual core digital signal processor (DSP) system. Although installation is fairly straight forward, there are some nuances you need to deal with when wiring the broadband transducer into the box, as I have learned.

The sounder module is heavy enough, that you need to pay attention to how you mount it. In this case the module is attached to the inside wall of a center console boat. At best I can get slightly more than 1/2" of screw depth into the wall, without popping through to the other side. It could have been through bolted with finish washers used on the console exterior, but in this case, there was a well attached piece of Starboard being used to to hold the battery switches. I set the bottom of the module edge on this to reduce the vertical screw loading that will come from pounding in rough seas.

Here's the catch. When the transducer arrived, the sheath had been neatly trimmed back leaving the exposed wiring for hook up. The wiring is all color coded, but there are four shield wires you have to connect.

Inside the big wire, there are actually three separate bundles of wiring, each wrapped in blue foil. For example the low chirp bundle has a blue/white wire, black/white wire, and a bare shield wire. You have to connect the shield wire for each wire bundle in the right location. In order to identify each bundle, I had to cut off an extra inch of the cable sheath to see each bundle still wrapped in the foil. Once you do this, the rest of the hook up is a piece of cake. There is also an outer shield wire that you connect to a grounding screw below the blocks.

One of the bundles contains an orange wire (XID), brown wire (GND), and a shield. These connect to either one of the two identical blocks on the right, or left side. Since this is an inhull transducer unit we are not using the temperature, or speed connections.

Now for the transducer. This is an inhull R599LH 25 element, 3000W beast, and at about 6" x 15" it's large. The tank has to be cut to fit the dead rise angle of the hull so the transducer is pointing straight down, and then epoxied to the base of the hull. As a small side note, this unit is for solid hulls, if you have a cored hull, all of the core must be removed so the sounder is just chirping through solid fiberglass only. Also tap on the gelcoat in the transducer area to identify any de-laminated gelcoat, and grind these areas out if you find them. 

Because of the size of the tank, and the rounded corners, this has to be carefully done. In a perfect world, you could use a table saw to do the side cuts, but this requires some jigging of the saw because of the tank's top flange, and most likely, your saw won't get to the half way point, and a jig saw, or the ilk will be needed to finish the cuts. I did this one insitu with a jig saw. You have to do this carefully especially at the corners. A belt sander cleaned up the small deficiencies of my cut. This is an expensive box, so do this right the first time.

The tank epoxies to the hull using a 14 ounce Marine Tex putty kit you can buy at West Marine. It gives you an honest 30 minutes working time in moderate temperatures. Do the normal prep work on the hull surfaces, and have some extra popsicle sticks, you just get one with the kit. Don't leave big epoxy blobs on the hull bottom that the transducer is going to look through. If the deadrise angle is steep, and this one was, have something figured out in advance like tape, or a wedge to keep the tank from sliding down hill. Give the epoxy a full 24 hours to fully cure.

The tank actually has a foam layer inside of it, and a cork layer has to be cut to fit inside the tank to provide additional sound insulation. Do this before you install the tank, it will make your life much easier.
It's transducer time. Fill the tank, but not completely, with non-toxic antifreeze. In this case it took a little more than a gallon. You know you have enough liquid when some antifreeze pours out of the housing when you drop the transducer into the tank. It is important that the tank be completely filled. The transducer generates heat, and the liquid helps to transfer the heat. Attach the bolts and fill hole fittings, clean up and check for leaks. If all is good you can crawl out of the hole, stretch, and take a short break.

All in all the transducer install isn't that difficult, but the scale is substantial, and I think the transducer alone with its mounting plate weighs about 20+ pounds. A few other items to keep in mind. The GSD 26 comes with a software upgrade chip, but it may be necessary, and in this case it was, to do a fresh latest version software download and system update. I would just do this anyway out of principle. The software attached to the GSD 26 is sophisticated, and offers a lot of control and flexibility. We had just started up the system dockside, and the first thing we saw was a crab crawling under the boat on the bottom. The target resolution is staggering.

I'm almost finished with a guide to buying the right broadband transducer for your boat, whether you fish deep off shore, or in shallower coastal waters. I will cover both inhull, and through hull units, and will give you the tools you need to decide what's the optimum for your boat. These are large and expensive units, and you need to get it right the first time. There will also be lots of screen shots from both the eight element B265LH (1000W) and the 25 element R599LH (3000W) units.


  1. Your command of written English is a pleasure to read---some of the best expository writing I've ever read on the net. Excellent description of an install. Thanks!!

  2. What brand of catamaran is that in the pic at the top of the page? thx

  3. It's a Manta 44 power cat based in Sarasota Florida. I think it's hull 15. Most of the early production bugs were worked out by then. Yanmar powered, extensive electronics, 9KW genset, and very comfortable. It has done the great loop, and lots of trips to the Bahamas.

  4. A little note to the install instructions. It is imperative that you don't wire the high frequency transducer wires to the sounder's low frequency port, and the low frequency transducer wires to the sounder's high frequency port. Doing so will likely destroy the sounder module, and the transducer. Double check the transducer wiring before applying power.


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