Thursday, July 31, 2014

Installing the Garmin Side and DownVü through hull transducers

The Garmin Down/SideVu through hull transducers come in two versions. One looks left, right, and down in a single transducer (deadrise of 5 degrees or less and does not require a fairing block). The ones I'm installing are a pair. The port side transducer just looks to port, and the right side transducer looks both down and to the right (deadrise angle from 5-25 degrees. The kit I used consisted of the transducer pair, two fairing blocks, 2 anti-rotation bolts, bushings, washers, nuts, pigtail to connect the transducers together, twelve pin transducer cable, and GCV 10 with a power and network cable. In sum all of the hardware you need is supplied. Let's get messy!

The boat is a 35' center console stepped hull fishing boat. Like many stepped hull vessels transducer placement can be challenging. The small area forward of the steps has a tilted element transducer installed there. No room is left now for new transducer pair.

There is room aft on the hull bottom but the combination of the trailer design, and location of the water pickups eliminates those locations.

This boat also has a stepped transom. I'm going to place the transducers on the hull portion behind the transom step where I placed the white box in the picture above. It really doesn't matter much. Here is my logic why. On a stepped hull boat any transducer placed anywhere aft of the hull steps will not work at planing speeds period.

Transducers placed aft of hull steps only work at much slower speeds. This speed is defined as the hull is moving slow enough the turbulence created by the steps won't affect the laminar water flow the transducer needs to see the bottom well. For this boat, in this location it is up to 7.5 knots. This is good as it will ever be.

To begin the process we need to template the hull angle. You can use a smart phone app to measure the angle, and it works. I prefer a much simpler tool, a piece of paper. Often low tech does the trick.

My photo is a dramatization of the actual event. What you're going to do is fold the top of paper at an angle that makes the bottom of the sheet of paper parallel to the ground. You will need to make a few refolds to get it right. The fold needs to end at the upper right hand corner. Your eyeballs will tell you when its right. If you're off a couple of degrees it won't make any significant difference in the transducers overall performance.

It's tool carnage time. I have laid out the important things on the table saw. The paper template I'm going to use to set the saw angle, the fairing block, my screw gun and a couple of screws? Huh, what's that for?
This without a doubt is the cleverest idea I have seen in a long time. This fairing block has screw holes in the corners. This allows you to attach it to a 2x4 or the ilk that rides on top of the table saw fence. You could also attach it to a piece of lumber that would ride against the fence side.  A piece of 4x4 would work well.

This lets you feed the fairing block into the high speed whirling blade of death giving you great control while keeping your hands and fingers well clear of the blade. A most excellent piece of real world insight, and I personally want to thank the designer for this finger saving stroke of genius.

That little piece of tape at an angle on the fairing block is there to remind me of the correct orientation. It's easy, at least for me, to get distracted. Cutting it ass backwards is not desirable and costly.

Here is our finished piece de resistance assembled. The bottom portion of the fairing block was flat sanded with a stationary belt sander to remove any saw blade grooves. The edges and holes have been deburred. You can see the bushings in the gap between the pieces. It's time to tell the boat to turn its head and cough while you punch some holes.

At this point you will need mineral spirits, acetone, full roll of paper towels, two tubes of fast cure 5200, 1/2" spade bit, either a 1 1/4" hole saw or spade bit and something to abrade around the hole edges.

There are good templates included with the transducers, but I didn't use them. This is something I have done for years because most transducers don't come with templates in the first place.

I locate and drill the stem hole. In the case of this transducer, I insert the transducer stem into the fairing block, twist the actual transducer about 20 degrees off center and shove it up into the hole wire and all.

This does two things at once. It verifies the stem hole angle is good because if it isn't the fairing block won't fit well against the hull. While holding it against the hull rotate the fairing block until it's positioned where you want it.

Mark the anti-rotation bolt hole through the fairing block hole. I stuck some blue tape in the approximate location of the hole so it's easy to mark with a pen or pencil. This is a 1/2" hole. Drill it, and dry fit the transducer assembly again to make sure it fits. If not make corrections.

A couple words about the holes are needed. The template shows the hole diameters with and without the bushings. I suggest you use the bushings and I will talk about this later. The anti-rotation bolt hole using bushings is 1/2". The stem hole for bushings is 1 1/4". Technically a 1 3/16" hole will work, but the slightly larger hole diameter provides some margin for drilling errors. When done, abrade the areas around the holes to help the sealant stick really well. I used a small wire wheel in my drill to speed things up. I wiped down the rest of the area with acetone.

It's time to play "Squeeze Out That Goo." I'm going to use Fast Cure 5200. "Why?" you ask. "It's not as strong as regular 5200." You can't really tell from 3M's spec sheets but regular 5200 is less viscous the the fast cure version.

The day I'm doing this it's stinking hot. It's in the mid nineties, and the humidity is staggering. Both versions of 5200 become less viscous as the temperatures increase. If I used the regular 5200 it would run everywhere. Everywhere is mostly where I don't want it to go. The fast cure version is almost as bad in hot temperatures. My fix for this is to cool the goo so it generally stays where I put it. A couple of hours in frig does the trick.

Start by putting a good bead around the anti-rotation bolt. You want to have enough goop there so when you slide the bushing on, and seat down it in place you have a really good seal around the bushing.

Do the same thing with the stem. Now apply a second ring of goop around the base of both bushings. Don't chintz on the goo. Now generously fill the unused anti-rotation bolt hole. Remember there will be a fairing block hole above it.

Get a couple of paper towels. Slide the transducer into the fairing block, and set the now getting messy unit on the paper towels. Apply another generous bead of sealant around the base of the anti-rotation bolt and stem, and thoroughly fill the unused bolt hole. I filled the bushing tops but in retrospect I probably didn't need to.

Put a really heavy bead of goop all the way around the fairing block edge. Check things carefully and add more goo if you're not sure you have applied enough. Spare the goo, spoil the transducer I say.

You're going to need another pair of hands to help you. Someone needs to be topside with wrenches, washers, and the other half of the fairing block. The bottom person slides the transducer assembly in place and holds it in place. This is what the paper towels are for. The person in the boat slides the other half of the fairing block into place, puts on the washers, and then the nuts.

If you have put on the goo correctly you should have extruded 5200 360 degrees around the fairing block/hull interface. You will likely have some goo oozing out in locations around the transducer.

Give the guy on the bottom a break and just quickly hand tighten things and let him go free. Tighten the nuts so they are snug. Don't do a roid raged scene with the nuts. This is a plastic fairing block, and you could damage the transducer by applying a 1000 foot pounds of force just because you can.

You're almost done. Take some papers towels and scrape the majority of the excess goo off. Use mineral spirits wetted paper towels to clean the rest of the surfaces.

You may find some goo continues to extrude out. Take a break, drink some Gatorade, and check on the transducer about fifteen minutes later. If need be do some more clean up.

After the transducers are cleaned up, everything else is mechanical. Connect the two transducers to the pigtail. These cables are clearly labeled.  Attach the transducer cable to the pigtail and pull it to the GCV 10 module. Connect the GCV 10 to your chartplotter. Download the latest Garmin software for your unit, and do an update. Now go play and see things you have never seen before.

This boat went for a week long diving and fishing adventure in the Florida Keys for. I should get tons of sonar recordings and screenshots to check out. I will show them to you next week.


You don't have to use the bushings, and you can drill smaller holes in the hull but the fairing block holes will stay the same size. By using the bushings you reduce the area that has to be sealed increasing your chances of doing it right in the first place. The bushings are also used to isolate the transducer's metals from aluminum and steel hulls.

Like all transducers, the important thing to remember is location, location, location. Consider this carefully prior to installation. I have seen this transducer work well at 40 Kts if you put it in the right place.

The location of these transducers were very difficult to access, and I couldn't actually see the transducer itself. In my words it was a "Brailer." In a more accessible location I would add an additional step as follows: After sealants have been applied and the transducer is being held in place from below, from the top apply a generous bead of sealant around the anti-rotation bolt and stem where they pass through the hull. Then install the top fairing block part, washers, nuts, et al. I was extra careful with sealant application to compensate.

If using the left, right and down through hull transducer no fairing block is required, and the bushings are only used if the hull is aluminum or steel. An isolation plate is supplied to separate the transducer from a metallic hull.

19 SEP 14 A small postscript to this piece. There have been some subtle changes to the faring block design that eliminates the need to use the enclosed bushings when installed in a fiberglass hull. They are still required if they are to be attached to an aluminum or steel hull.

1 comment:

  1. Hi: Can you tell me how this performed in that location?