Captains log 20160101


Welcome Summer in Australia. unfortunately that means Winter is coming to the USA.


Yesterday we fixed the steering. We tried to find a place to berth to get supplies and were headed to Hurricane Patty's in St Augustine, a very well known cruisers restaurant with a dock. No room there and with a tiler the areas we could access were not going to be easy. So we headed back as we saw a marina that was still being rebuilt after Hurricane Mathew. As we were coming in a worker came out to let us know we can't dock. I asked if we can stay long enough to fix the steering and he said that was ok so long as we didn't stay the night. I threw him the lines and we were docked on a new floating dock with no one else around.


A walk to the shopping center was only a short distance so we grabbed some lunch in the shopping center instead of Hurricane Patty's as that was too far away. The mil and I had lunch, wifey didn't like the style of food so she went to do shopping at the Windixie (supermarket). After we ate we went to the West Marine and I got the stainless steel cable to fix the steering and an interface cable to the chart plotter's NMEA2000 network port. The idea was that I'd fix the steering and later hook up the chart plotter to the engine so I could get RPM and engine data like fuel rate and mpg figures. For the record, the food tasted ok but the repercussions were not worth it.


I fixed the steering in about an hour. No real problem except I didn't want to pull out and mount the vice to the workshop table to hold the old cable so I could cut out the thimble. Instead I told the mil I was too lazy and held it by hand against a rest. Naturally the hacksaw slipped and the bade cut a 1/4 deep gash through my index finger. It's a quality blade. That sucker cut through the stainless cable like it was nothing. So my finger was no real challenge. Luckily the blade was very dirty after cutting through the grease and grime on the cable so that stopped the bleeding real fast.


We moved on and found the same anchorage we went to the first night here. The night was warm, it didn't drop below 70 overnight. We decided to just take a break, play uno and drink some wine. Lunch was pretty late so we didn't make dinner and instead I made nacho's as a light snack. The steering worked very well. I re tightened everything and removed most of the freeplay. It's very responsive now.


This morning I made a big breakfast. Fried bacon, eggs, potato's on a tortilla with lettuce and tomato. I got to work on the chart plotter to engine cable. If you have no real desire to read the technicalities about the NMEA2000 network, stop right here. The rest is nothing but how to hook up a NMEA2000 marine network on the cheap along with a few rants about the marine industry. I did get it working so you won't miss much unless you like that sort of thing.


According to Garmin and all marine sites you need special cables, T fittings, terminal connectors, a hub backbone and a drop cable. Some sites even claim it can't be done. I just bought a single drop cable so I could plug it into the chart plotter which means I bought the cable just for its plug end. I cut off the other end and ran an oil/water proof marine cable to the engine. I cut off the Yamaha proprietary connector and spliced the cable to the end of it. The other chart plotter end was more tricky.


Typically the NMEA2000 network does require a backbone, two 120ohm termination resistors and two T connectors just to connect two devices together as that makes the system future proof. I'm not interested in future proofing. If I ever want to add more devices to the boat later I'll go the normal way but all I want is two devices connected together.


I've read a lot of information about the NMEA2000 network. Most of it is total garbage written by people who were taught by people who don't understand the hardware to begin with. So then they just propagate the same misinformation and usually add their own twist to it. Bottom line is this: NMEA2000 is on the hardware (electronics) level exactly the same as the automotive CAN based system used in cars since the 90's here in the USA and standardised now pretty much world wide. The difference is the connector choice and the software. There are no special NMEA chips if someone wanted to design a NMEA2000 network system, because it is the same thing. Knowing that I pulled out a datasheet for a couple of CAN bus controllers and got to understanding the basics of the system.

It is a very simple differential two wire serial control system with a few things thrown in to make  multi drop networking arbitration simpler to achieve. NMEA based the entire system on the CAN bus then changed the protocol and charged a fortune to manufacturers to use the NMEA name. A complete wank really. They could have used the same protocols as the automotive industry and made life easy for everyone including diagnostics, but then they wouldn't be able to charge people a fortune for having a board meeting to make a new protocol. Welcome to Marine ripoff bullshit 101 folks. 

What NMEA did was change the connector style (even though the original CAN had suitable connectors) then they changed the meaning of the codes. The underlying protocol and electronics stayed exactly the same as the original CAN system. So instead of a code that represents engine temperature, in NMEA rit might represent wind speed. We really don't know what it represents in NMEA (unlike the automotive industry) because they kept that proprietary and if you want to know, you pay the licensing fees. It's really tough stuff to do the code re-labeling. So hard that I'm sure they appointed the brightest minds in the Universe to this task and charged a licensing fee that just barely cover the cost of this huge ground breaking undertaking which makes the Apollo Moon program pale into insignificance on a complexity level.


Ok, now that I got that out of the way, lets go to the solution to my particular problem. The standard CAN network uses a two wire differential serial communication system with termination resistors that total to 60 ohms. There is much debate about the marine ripoff version of the CAN bus as to how these resistors are meant to be wired, and so far nothing I've read by any "expert" on marine electronics demonstrates that their knowledge is based on anything other than hearsay and speculation. They really need to read a datasheet, it's all in there.


The funniest one I read was that using a 60 ohm instead of two 120 ohm resistors (one at each end makes 60 ohms total) will only work on a test bench with the cable length less than about a few cm. rofl. Last I checked, the CAN bus didn't operate in the Giga Hertz region for this to be a problem. Garbage in garbage out. As I wrote, people just make stuff up or pass around garbage that they heard.


The real reason you want to have two 120 ohm resistors is to reduce reflections on a cable, iff (read as if and only if) the cable run is exceptionally long and the propagation time across the cable is significant enough to cause sizable reflections that might interfere with the negotiation of two devices placed at the opposite ends of that long cable. Otherwise, feel free to place a single 60 ohm resistor in and it will work fine. In the case of a single device connected to the chart plotter a 60 ohm resistor will meet any DC component requirement and load the line enough to increase the noise immunity so the system works with no degradation.


My run of about 6 meters (NMEA claim 20 feet max on a drop cable, another wank I might address in a future post if anyone is interested) was done with one resistor about 2m from the chart plotter end and it works perfectly. I didn't have any 60 ohm resistors but I did have a failed portion of some LED strip lighting. This had two 150 ohm and one 330 ohm smd 1/2 watt resistors on it. I un-soldered them and made a 61 ohm resistor out of them rated about 1 watt. This was put across the CAN signal wires. I tested the system and it didn't work. Turns out that Garmin doesn't use the 12 Volt power supply for the chart plotter to drive the CAN bus. The CAN controller is powered off the network power source. If this was done correctly (optically isolated) then in theory the Garmin chart plotter could run a 24 volt CAN bus while the plotter itself ran 12 volts. I wouldn't trust this assessment unless you were happy to possibly blow up a chart plotter. In any case. Once I put power onto the network wires the system fired up and the chart plotter and engine were happily communicating.


I configured the system and now we have mpg, gallons/hour, rpm, inlet manifold pressure and alternator voltage being displayed on the chart plotter. This means I can now run the engine at the most economical speed, do tests on propellers and it also allows me to input a fuel tank figure and it automatically keeps track of how much fuel I have left.


On the alarms page I can configure it to sound an alarm when we're running low on fuel. So no more running out of fuel unexpectedly. It also allows adding fuel to the total when we fuel up by inputting the amount of gallons we fueled up with. So I'm very happy about the setup. I'm even happier that it cost me $25 to do when the options from Garmin and Yamaha came out in the several hundreds.

The cheapest official solution I found was $100 if I already had a CAN bus on the boat that used NMEA connectors (iow an NMEA2000 network). The cheapest NMEA2000 network starter kit is about $100 so the best price this can be done is about $200 if one goes the official NMEA2000 route. It goes up fast from there if you want them to do it or you use "name" brands.


There you go. Through misinformation people are being told what you can and can't do and are being charged a fortune for a simple setup. Feel free to go the official route but if you have a small boat with an outboard that supports the NMEA2000 protocol (all new Yamaha 4 strokes do) then this is an under $30 solution to get data to your chart plotter.


For reference:

My chart plotter is a GPS740s and my engine is a 40hp fuel injected Yamaha 2013 model.

The Yamaha NMEA connector is a white 4 pin connector with two wires, blue and white connected to it located at the very back of the engine. To connect it to the chart plotter, cut the drop cable and the Yamaha connector. Strip it back and join blue to blue, white to white and put a 60 ohm resistor across them. To finish, connect black to 12 Gnd and red to the same power supply as your chart plotter so they bot come up at the same time.

The drop cable is about $25 and you can even get longer lengths than the 2m I got which was the only one they had in stock. You only need the thinnest cable so get the micro rated one.