Wiring fuax pas

A couple of wires got swapped around during a new gear install and the subsequent damage was north of $7000. You had to look closely at the wiring to see what went wrong. This is the terminal block inside a Garmin GSD26 CHIRP sounder module, and the wiring is coming from an Airmar 2kW/3kW r109LH CHIRP transducer. This costly error was made when it was installed and resulted in the failure of two sounder modules, and a very expensive transducer.

Turbulence City

There are a some things right with the picture below and things really wrong, at least from my perspective. I labeled the pic so there weren't any doubts about orientation. I'll speak slowly for the benefit of the more boating challenged. This is an aft bilge compartment. The arrow pointing down is the direction towards the pointy sharp end of the boat. The one pointing upward is towards the square back end of the boat. This is a boat that has a "Liner," meaning there is a layer of foam in between the hull and the top shiny fiberglass surfaces you see can see. The foam layer provides floatation and the laminated nature of the construction makes the boat structurally stiffer.

But our mystery deepens (bring in the Twilight Zone theme music here). What are the two liner cut outs about and why are they there in the first place? Are these the boating equivalent of crop circles? Is Turbulence city a real place? We're going to explore these weighty concepts and see if there are any real answers.

Ruh-roh! Transducer transplant time.

"Can you install these transducers without a fairing block?" I was asked. "I don't know, what transducers?" came my muffled squawk from the interior bowels of the boat. Let me climb out of this god forsaken  hole and take a look."

My response was, "Sure you can install them without the fairing block, if they are pointing straight down. But these aren't level, not even close to level. Who installed these things?" The factory was the answer. The fairing blocks were still in the box along with the apparently unread instructions. This was Thursday morning and the boat was delivering Friday afternoon. I still had a lot of other things on my do list like finishing the autopilot and the security tracking system. What is the art of the possible in this case? Not much methinks. A plan is needed.

Installing the Garmin GCV 10 SideVü and DownVü system

Installing the new Garmin GCV 10 (Garmin Clear View) SideVü and DownVü  system is a snap, and well suited for DIY installers. As with most Garmin gear everything you need is in the box down to the wire clips (lamentably never enough of them), fasteners and other minor bits and pieces. Without further adieu find your floppy hat, grab your tools, count your fingers, and head down to the boat. 

Splitting the transducer

The Parmain top secret laboratories have been bombarding a transducer with protons trying to get it to split. The DARPA program funding was pulled when the janitor said, "Just add a wire pigtail to the transducer, it's simple." Drat, time to write another grant request to DARPA. Maybe this time we could design a talking GPS for a boat. It should be simple enough for the average boater to use. To guide you to your destination it could say "Colder" or "Warmer." If you lurch to a stop it will say "Freezing."

Of all of the electrical things that exist on a boat, your transducer is the most reliable. It's always immersed in a salty chemical soup, gets dragged through the water often at very high speeds, and yet it keeps on working year after year. When I get a call dealing with a "no depth reading" problem, the first thing I suspect is the depth finder itself. Second could be the transducer face is covered with marine life having a rave party, and or has gotten knocked up. Third is damaged wiring. Fourth, and only very rarely the transducer has failed. There is an exception here. If it is a Garmin system, it may be suffering from thermistor-itis.

Ripped out, ripped off, and other meanderings

Yep it's gone. About the only thing you can say about this install is whoever did it apparently couldn't read, because the directions tell you not to use the sealants they did, and at least two types were used. The second layer was smeared on no doubt to stop the leaks found after the first layer was glopped on with a precision that could only have only been done by a drunk organ grinder's monkey, or maybe just a drunk organ grinder. And I don't even want to know what that disgusting black stuff was in the lower corner. Okay, I won't contest the fact that this is the only place on this boat for a in-hull transducer to be mounted, and that it is damnably difficult to access. So what makes this so irritating, is the previous owner ripped it out before he sold the boat, thus ripping off the new owner.

Stiffening up a small Garmin GPS

I have thrown, metaphorically speaking, a zillion of these small Garmin 4x and 5x chart plotters into boats. They are compact, full featured, and a good choice for smaller boats. In most cases they are good to go as installed, but on occasion it would be nice if the mount was a wee bit stiffer. Don't despair, there is an easy way to make the mount a little stiffer, for under a dollar or less, even if you're paying full retail. 

Big trouble in Transducer town

"That ain't going to grow back, it's broke, it's done, no glue or goo will fix it, did you really look closely at it?, and that is my professional opinion." This is my pronouncement as I look at the transducer while the boat is on the forks of the lift. The damage is the result of an untimely meeting of the transducer, and the wood bunk of a storage rack. Ah the miracle, and power of misapplied hydraulics. The boat, a middle aged 30'esque Searay had a Raymarine system, and I instantly knew what transducer was needed. 

This unfortunate event occurred in a condo high and dry marina facility I often work in, and given the obvious mortification of the lift truck driver, I said I would do the replacement of the transducer at no charge, if the marina purchased, and paid for the materials. Karma is a wonderful, and cosmic thing.

So a few days go by, and the new transducer shows up. A local mechanic friend is there, and he comes over to give me a hand. I open the engine hatch, and stare down into a compartment which is dominated by two huge engines. I squeeze myself into a space that was never meant for human occupation, and doing a sort of awkward half hunched kneeling thing, I reach down, and feel around for the nut of the bolt that holds the front end of the fairing block in place. Much to my chagrin, I can't find it, it's just not there, and I also feel a in-hull transducer mounted right next to the broken transducer.

I wriggle back out, dragging my wrist across a sharp edge of a tie wrap (Inset your favorite expletive here), and cut myself in the process. I take Plavix, (a price I pay for earlier lifestyle indiscretions), and any small cut instantly looks like a gunshot wound, and sends onlookers fleeing in horror. Out to the truck I go, and with some liquid bandage, and waiting the sixty seconds for it to dry, I'm back in business. I climb under the boat to stare again at the transducer, and realize I missed something when I first looked at it. Among all of the carnage, I didn't notice there wasn't a bolt installed in the front of the fairing block. Look at the picture above at the triangular area, and you can see it's missing, and worse, it was never there at all.

Who ever installed the transducer mis-measured where to drill the two inch hole, and the bolt would now be forward of the engine room bulkhead, in an inaccessible area under the fuel tank. The good news is they didn't drill the hole at all in that location. The bad news is the bolt's job is to stop the fairing block from twisting at high speeds, and causing it to leak. The installer's solution to the problem was to apply copious quantities of 3M 5200 everywhere to keep it in place.

The transducer still has to be removed, but the access to the big nut in the engine compartment is so limited, I can't break it loose, so out comes the angle grinder with a cut off wheel, and twenty minutes later it's history. A few minutes later all of the goo has been has been removed with an assortment of sharp implements.

Now it's time to talk to the owner about the problem. I don't want to install the new identical transducer, for obvious reasons, and my solution is to replace it with a low profile tilted element transducer. No bolts, much harder for the fork lift operators to break, it will cost less, and all will be better for everyone.

A marina staffer dials the number, hands me the phone, and everyone retreats. Hi, I'm Bill, nice to meet you, this is the problem, and I think this is what we should do, no it won't have a paddle wheel, but you won't miss it, no SOG does not come from the paddle wheel in a Raymarine system, in the Raymaine system you only see paddle wheel "Speed" in a data box, and you don't currently have one set up, I'm sorry, but I didn't install it, this is really a better solution, no the transducer is made by the same company, and I can get one on Monday, you're doing a burial at sea on Sunday?, and you're  going on a trip Monday that has been planned for weeks?, can't cancel the reservations?, but you have depth from the other transducer, the problem is that you are running both transducers at the same time, and they interfere with each other, and on and on we go.

The owner is really a nice guy, on the phone at least, but I have not met him in person. In the end, I took an old Garmin transducer I use to test sounder modules, and installed it, to plug up the hole so the boat is usable. The owner will advise me when the boat is back from the long planned trip, and that boat had better be used on Sunday, and gone on Monday.

I write, I eat, I deal with marine electronics, and I'm hungry for more.

I install transducers in boats with "No Reservations".

The lines above are a small homage to Anthony Bourdain's "No Reservations" show on the Travel Channel. I love his writing style. The mix of both witty, and cynical ennui, with an almost childlike exuberance for all things pork, is most clever. His show is one of my favorites, and you can find his blog here. 

Transducer meditations

The installer sits down in a lotus position behind the hull, lights incense, clears his mind of extraneous thoughts, slows his breathing, and enters a trance. He sees the hull sitting in the water, and starts to move it forward at a very slow speed. The flow of the water passing under the hull is smooth, and laminar.

In his minds eye, he picks up the speed. The water flow becomes less laminar, and a turbulent boundary layer starts to develop next to the hull. This boundary layer is caused by friction of the hull as it passes through the water.

As water travels down the hull, it finds its first obstacle, a through hull fitting sticking out from the hull. As the water flows over, and around the fitting, an adverse pressure gradient is formed behind it. As the speed further increases, the water behind the object becomes increasingly turbulent, and is swept aft down the hull. The picture below is a computer model of a fluid passing over a sphere. Note that the flow is laminar at the front of the sphere, but becomes very turbulent at the back side. This is how water behaves as it passes over a hull water inlet, and your transducer doesn't like this.

As the installer studies the water flow traveling down the hull he looks for a spot with the smoothest water flow to mount the transducer. It has to be clear of the turbulent flows coming from things sticking out of the hull, and the transducer bottom must be mounted lower than the boundary layer turbulence that is against the hull.

Looking at the port side he spots a large plastic water pick up. That's okay, it would be better if the transducer was on the starboard side anyway.

Doh! There is another pick up on the starboard side. The meditative trance abruptly comes to an end. Why couldn't the builder have put both pickups on the port side? There was plenty of room for both, and the water flow would have then been reasonably clean on the starboard side. There is this weird thing about the desire for symmetry, even at the expense of performance, especially in an area you don't normally see. This is a typical example of boat builders not thinking about what kind of equipment will be installed on the boat.

There is actually some art, along with the science involved in placing a transducer on a boat, and you really do have to try to visualize how the water will flow under the hull. The transducer bottom needs to be below the turbulent boundary layer next to the hull, and must be clear of upstream turbulence from inlets and the ilk.

Avoid placing the transducer behind protruding strakes, because they can carry air entrained turbulent water aft to the transom. You also need to make sure that turbulence coming from water flowing around the transducer doesn't cause propeller cavitation, or interfere with the cooling water flow to an outboard motor.

So the basic rule of thumb is to get the bottom of the transducer into the smoothest possible water flow, which translates to getting it as far below the hull as possible. In many cases, it is a Zen thing. The transducer will work okay on this boat, but I would have had an easier time placing it if the starboard side water pick up was on the port side.

Keeping the hull clean is important to transducer operation. The dirtier the hull, ie barnacles, and other icky growths, the more turbulent, and thicker, boundary layer becomes, and it will affect transducer performance at speed.

And a last gentle reminder, at 20 knots, when your depth finder tells you it is too shallow, it is to late.

The photo of the computer model is from an article written by Claes Johnson, and Johan Hoffman, and is no longer available online.

No worries mate, we are precisely in 176.2 feet of water

The owner of this boat called me and said his depth finder wasn't working correctly on a short "Shake Down" cruise from Sarasota, to Egmont Key and back. This was about a 70 mile trip up and back, and he said the Furuno depth finder acted weird on the whole trip. Since we were in about 10 feet of water, the Furuno RD30's depth of about 176 feet, did seem to be a wee bit on the high side. The Nobeltec sounder right next door does have the correct depth.  Look at the picture closely, and above the depth number on the Nobeltec system, you can see the the wording "200 khz "Cruising."

So playing the game of "What's different between these two pictures?", we can now see the Furuno RD30 is  reporting the correct depth, and the Nobeltec sounder is also. The difference is the Nobeltec sounder is now using the "50 khz Cruising" setting. So by now, a lot of boaters have figured what has happened, but for those who need some enlightenment, this is what is going on, in Americanized English. 

The piezoceramic devices in the two transducers are pinging out sound waves, and listening to the returning sound waves as they echo back from the bottom. They are designed to send out a certain frequency sound wave, and hear that frequency when the sound wave bounces back from the bottom. In this case, since both transducers are using the same frequency, they are hearing each other, and the Furuno unit is getting confused. I suspect, but I'm not dead sure, that the Nobeltec sounder module, has a more powerful transducer (I did not climb into the engine room to verify this, it is what it is), and the lower power Furuno transducer just gets overwhelmed. In other words, the Nobeltec transducer is not adversely affected by the Furuno's transducer, but the Nobeltec's transducer bugs the heck out of the Furuno's transducer, if they are operating at the same frequency. Both transducers are made by Airmar, and I hope I got this dialog generally correct Ms. Robb.

The owner now knows, that if both sounder systems are operating at the same time, they must be set to different frequencies, if you don't want to be in 176.2 feet of water all of the time. There are transducer technologies, that can overcome this issue available, and the link below to Airmar will provide wealth of transducer information.

Airmar's FAQ page will answer about 99.1% of your transducer questions.