Boatbuilding Blog

December 8, 2010

Using an iPad as the Primary Navigation Instrument

Filed under: Building - Electric & Plumbing, Hardware — tomlarkin @ 10:56 am

I’m planning on using an iPad as my primary navigation tool instead of buying a standard chart plotter. To start out, all I need is a $700-$800 GPS-enabled iPad and the $50 iNavX software. I don’t need to buy the cell plan because the GPS works without it.  For that price I could buy an entry-level plotter like the Garmin GPSMAP 546 or the Standard Horizon CP300i, both with substantially smaller screens than the iPad and without the advantages listed below. 

I don’t like Apple’s ‘closed garden’ business model, but there’s no other tablet on the market yet with anything close to the usability of this setup, and laptop computers are a very bad fit for this. I’ve been using OpenCPN on a netbook for navigating, but the screen is too small, the keyboard is in the way, and trying to use a trackpad in a moving boat, especially in the dark, is really difficult.

There are a number of navigation applications for the iPad, but iNavX seems to have more features than the others. Here’s a short video on setting waypoints and creating a route using iNavX. The US NOAA charts are free with the iNavX purchase, and charts from X-Traverse  for much of the rest of the world look reasonably priced.

I found about 20 ways to mount the iPad, but this one looks best so far. The rubber balls should soak up some of the vibration, and it’s easy to adjust, rotate, and remove the iPad. I’ll probably get two sets, one for the dash and another for watching videos below.




  • Wireless – pick it up and use it anywhere onboard
  • Take it home to set up routes and plan trips
  • Huge screen – for the price, the screen is 2 to 4 times the usable size of comparably-priced Chart Plotters
  • Multi-use – surf the web, play music, send emails, watch videos
  • Active development of navigation apps for iPad
  • Easy export of tracks to online maps
  • Switch from portrait to landscape instantly


  • Screen not as visible in direct sunlight as some displays, should be OK in the pilothouse
  • Not waterproof without adding a cover
  • No radar overlay for it (yet)

Hardware & Software:

  • iPad with GPS and 3G, 64 GB: no need to subscribe to the cell plan – the GPS works without it, and the charts are store locally ($830)
  • iNavX software: displays charts and shows current location. Shows data received via WiFi ($50)
  • iMux WiFi NMEA multiplexer: combined information from NMEA devices and transmits via WiFi ($179)
  • iAIS ANT200 Receiver: dual channel Automatic Identification System (AIS) receiver ($299)
  • NMEA-Enabled Depth Sounder with display: example
  • Through-hull transducer for speed and water temperature
  • GPS antenna: external antenna for the AIS receiver and VHF radio (for emergency broadcast)
  • iPad accessories: there are many add-ons for the iPod – chargers, keyboards, speakers, etc.

Everything in the drawing below is optional, except for the iPad itself. I can add parts as necessary.




Analog-style instruments:

AIS overlay on chart:

Track exported to Google Maps:

July 12, 2010

Grounding a Plastic Gas Tank

Filed under: Building - Electric & Plumbing — tomlarkin @ 1:50 pm

I have a permanently-mounted 25-gallon roto-molded plastic gas tank for my outboard motor. Gas sloshing in a tank (even a plastic one) can generate static electricity. Gas flowing from a fill hose into the tank can do the same. If the electricity sparks, it can ignite the gas fumes, causing an explosion. Grounding the parts should keep that from happening.

Here’s how I plan to ground the tank parts:

  1. Run a green, 10 or 12 gauge stranded wire from the deck fill to the fill fitting on the tank.
  2. Run the same type wire from the fill fitting on the tank to the outboard (somewhere) as an ‘earth-to-ground’ connection.
  3. Connect the fuel tank sender to the gas gauge as in the diagrams below.
  4. Unknown: connect the ‘earth-to-ground’ wire to the fuel tank sender negative wire?

My tank is made by Moeller Marine.  Here are sections from their literature. They left a lot of questions unanswered:


Moeller Wiring Diagram


My notes:

  • They don’t show the deck fill fitting being grounded at all. Everyone else says this is the most important thing to ground. See the Coast Guard regulations below.
  • They don’t connect this ‘earth-to-ground’ wire to the sender. The Coast Guard regulations say to bond ‘each metallic component’ together.
  • Others say to ground all the parts to the battery negative, not just the sender.
  • They don’t suggest a wire gauge, for grounding, or for the sender wires.


Here are the Coast Guard regulations.


183.572 – Grounding  (

Each metallic component of the fuel fill system and fuel tank which is in contact with fuel must be statically grounded so that the resistance between the ground and each metallic component of the fuel fill system and fuel tank is less than 100 ohms.

Fuel flowing from the dispensing nozzle into a fuel tank is a potential source of a static electric charge which could cause a spark between the dispensing nozzle and metal component of the fuel tank fill system. To prevent such a spark from occurring, metallic components of the fuel tank fill system and metallic fuel tanks must be grounded.

Grounding or bonding may be accomplished by connecting the metallic components electrically by running a wire from one component to the next, and so forth to the boat’s ground. Grounding can usually be accomplished by a connection to the common bonding conductor or the engine negative terminal.

If the fuel tank deck fill fitting is nonmetallic, and nonconductive hose is used as a fill pipe, there is no need for grounding the fill fitting. Chrome-plated plastic fill fittings are treated the same as metallic fittings.


1. If a metal hose attachment fitting is used, it must be grounded.

2. Fill cap retaining chains need not be grounded.


And here are some of the most reasonable-sounding snippets on the topic I could find:

Here’s why it’s a good idea to connect it to the negative terminal on the battery. You would do this to create an inductor that will absorb the energy of a static discharge and thereby create a path of lower resistance. This is called a floating ground and is the most common type of grounding found in marine vessels.

You are putting a plastic tank in an aluminum boat. If a metal fill and metal vent are used, they need to be grounded, as well as any lengths of metal tube in the fill or vent hoses. The plastic does not need to be grounded. Grounding (according to the Coast Guard regs) should be done with marine grade 14 AWG green jacketed STRANDED wire. 

On boats without a grounding plate, the chassis of the outboard motor is considered the ground to the sea. Usually the outboard motor will have some bare metal anodes in contact with the sea. Even if the motor is tilted up, usually there are anodes on the mounting bracket that are still in contact with the sea.

All metallic components of the fuel system should be bonded together with a 10-AWG wire with green insulation. The fuel system ground should be connected to either the vessel ground plate on the hull or, if the vessel does not have a grounding plate on the hull, to the battery negative terminal. It is assumed the battery negative terminal is bonded to the chassis of the outboard motor.

If you have a fuel gauge for the tank the sending unit must be grounded or the gauge won’t work unless it is a gauge in the cap of a plastic tank that is mechanical. If this is a aluminum boat make sure to ground to the ground bus or negative terminal do not use the boat as the ground source. You probably should bond the SS filler neck to ground also use a hose clamp if you can’t bolt it somehow.

If you look at factory tank installations, this is what you will probably see:1. The tank is grounded itself to the battery either via a fuel gage or a separate wire.2. The deck fuel filler receptacle is grounded to the boat battery and/or the tank.

The most important ground is between the metal deck fill and the fuel/tank so that there won’t be a spark between the nozzle and deck plate when fueling. All tanks, but perhaps the plastic ones more than others, tend to build a static charge as the fuel sloshes.

Grounding (Bonding): All metallic components of the fuel system that are in contact with fuel must be electrically grounded to prevent a static discharge from causing a fire or explosion.

Edit: July 16 – updated image with new version – see comments by Ike below

This seems useful:

Installing a new fuel gauge

Installing a new fuel gauge may not seem like a cause for celebration, but if you install and wire it yourself, you’ve saved enough money to throw a couple of very good steaks on the grill. Wiring a fuel gauge is much the same as wiring any other gauge on your boat: one wire comes from the ignition to the instrument, one wire comes from the sensor to the instrument, one wire comes to the instrument light and one wire from the instrument goes to the boat’s common ground. The wires may follow a seemingly unusual path, but the system works.

Step 1   Disconnect your boat’s battery. Look at the back of the gauge. There are four male blade terminals, one for the lights (marked "L"), one for the power (marked "I"), one for the ground (marked "-") and one for the wire from the fuel tank sender (marked "S")

Step 2    Slip the female blade terminal of the stranded copper wire onto the "L" blade terminal of the fuel gauge. Remove the blade terminal for the instrument light of the instrument nearest the fuel gauge. Slip the stripped end of the stranded copper wire from the "L" terminal of the new fuel gauge into the female blade terminal for the instrument light for that existing instrument. Replace the female blade terminal on the blade terminal for the instrument light of the instrument next to the fuel gauge. This is called "daisy-chaining" the instruments.

Step 3    Daisy-chain the "I" wire of the fuel gauge to the power terminal of the instrument next to the fuel gauge. Daisy-chain the "-" wire to the ground wire–which may be also be marked "-" or "GND"–of the instrument next to the fuel gauge.

Step 4    Pull the wire from the fuel sender up through your boat’s dash. Slip the female blade connector on the wire from the fuel sender onto the "S" terminal of the fuel tank gauge. Install the newly wired fuel gauge in your boat’s dashboard.

February 21, 2010

Wiring Diagram

Filed under: Building - Electric & Plumbing — tomlarkin @ 1:52 pm

I’m working on the 12 volt DC wiring design. The ACR (Automatic Charging Relay) makes the battery charging automatic. Either charging source (the 110 volt charger or the outboard motor charger) will charge both batteries, but will disconnect them as they’re being discharged. This way, I can safely draw down the house battery without taking the chance of draining the starting battery and not being able to start the engine.  I’m still not sure what size wires to use, or if it’s best to have the starting battery under the pilothouse sole or in the stern next to the motor.

The Blue Sea ACR came with a wiring diagram, but I found it unclear.  Adding the color-coding and additional detail helps me understand the design. The picture was drawn in Visio. The ‘Starting Isolation’ wire to the ACR will disconnect the house battery when the engine is being cranked to protect the house electronics from power surges caused by the motor starting.

I’ve got both batteries already, and am making the holders for them. The house battery is a Dyno 4D-size, with 180 amp-hours. It weighs about 114 pounds. It goes under the Port pilothouse sole.  I had initially intended on using an 8D-size battery, but our power needs should be pretty low, just LED lighting and electronics.  The starting battery is a generic deep-cycle starting battery. Outboards don’t take a lot of power to start.

The other task in progress is the dashboard. The frame is complete, and I added the steering wheel mount this afternoon. It’s heavily built because there’s a lot of stress on that area when you’re hanging onto the wheel in bad weather.

(Click the image for full-size)

Wiring - Blue Sea ACR

Edit 2-21 – Here’s a new drawing, with the parts in a more real-life configuration. All the stuff below the switch is below the pilothouse sole. I think this layout clarifies the relationship between the batteries and the ACR.

Original Wiring - Blue Sea

January 25, 2010

110-Volt Wiring and Sliding Doors

Filed under: Building - Cabin, Building - Electric & Plumbing — tomlarkin @ 12:29 pm

After a few weeks off I’m now working on the sliding doors and the 110 volt wiring. This wiring is pretty basic – three GFI’d duplex outlets and the battery charger. I’m running all the high voltage wiring in plastic conduit, most of which is installed now.

The sliding doors are coming along, but slowly. There’s a lot of work to make them. They’re 3/4 ply with 1/4-inch ply laminated on either side.  Here’s a mockup of a door, complete with window and handrail. It’s hanging from a plastic slug in a stainless sail track. There is too much resistance with this system, so I’m going to try a ball-bearing slider instead.
Sliding door mockup installed

I installed the bronze bow cleat today. I decided not to use the stainless bit I bought. It just seemed like overkill. The cleat uses 2 1/2 inch bronze bolts, through 1 1/2 inches of marine plywood, and a doubled 1/8 inch bronze backing plate. It should be strong enough 😉
IMG_0303  IMG_0304
Cleat backing plates

Conduit for 110 volt wiring is mostly installed.
Conduit and junction box below 110 volt panel
Conduit to battery charger and outlets

July 17, 2009

110 V Panel and Primer

Filed under: Building - Electric & Plumbing, Building - Painting — tomlarkin @ 1:38 pm

Starting the 110 volt wiring. Here’s the breaker panel and a GFI outlet. The 3 circuits are to the battery charger, 110 volt outlets, and the third one will lead to an inverter sometime in the future, when I have the cash to buy a nice one.  The black material is plastic board called Starboard.  It’s inset a bit to keep it from being bumped too easily. You can probably figure out it’s in the head area 🙂

110 Volt Panel

I thought this was an interesting shot. Facing forward. The interior is mostly primed, and now needs to be sanded and painted.

Interior primed

I’ve made about a dozen removable parts – sole supports, binocular holder, base for the toilet, etc. Here are three pieces with finish paint, drying in the sun. They’re sitting on some primed pieces.


And of course, my drowsy overseer, supervising from the pumpkin patch.

The Rain Cat

April 21, 2008

Stern Infrastructure Progress

Filed under: Building - After Flipping, Building - Electric & Plumbing, Hardware — tomlarkin @ 5:39 am

I’m installing all the stuff in the Lazarettes now because I know it will be impossible to do well after the tops go on. The Starboard side has all the hoses, gas lines and fuel filter, and the Propane tank.  I need everything to be accessible yet out of the weather. The Propane assembly has a pressure gauge, a regulator, and an electric shutoff solenoid. This whole thing was assembled for me by a cool guy at Fisheries Supply for a minimal cost.  The fuel-water separator has a clear container with a petcock to drain the water without having to remove the filter.  I think I’ll mount a little light next to it.
Starboard Lazarette 

The Port side has the starter battery and the 6-gallon spare gas tank.  A plastic battery box drops in the frame to protect the battery from the elements.
Port Lazarette

I’ve cut the stem piece and have started fairing the chain locker top. Once I have the lazarettes done I can add their tops, and then glass and fair the gunnels. At that point I can start finishing the inside of the hull in preparation for assembling the cabin. I’m planning on priming everything except where the cabin parts attach to the boat before building the cabin. It’ll be a lot easier to spray primer while I can still walk around inside.
Stem and Chain Locker