Technical on Merrimac

Splitting the NMEA 2000 bus: a simple switch trick

Sat, 04 Jul 2026 07:35:01 +0200

On Merrimac we carry a lot of NMEA 2000 equipment. The backbone runs the length of the boat and serves some two dozen physical devices — autopilot computer and controllers, two big chartplotters, instrument displays, the H5000 Hercules CPU, wind, depth, heading and GPS sensors, AIS, and the ship’s computer. Together they claim fifty addresses on the bus.

Up and downloading files to Navico NOS chart plotters

Sun, 19 Jun 2022 22:36:24 +0200

The Navico (B&G, Simrad and Lowrance) chart plotters running on NOS, so the Zeus, Vulcan, NSS, NSO, Carbon etc. devices have a little known feature that is an enormous help if you regularly need to transfer files onto or off the device from a different system. The Linux operating system on these devices has the FTP protocol enabled. This allows you to transfer files using the Ethernet connection of the device. It doesn’t matter whether this is wireless or not.

Washing

Sat, 07 Sep 2019 13:46:41 +0200

For some reason our washing machine has a mind of its own and doesn’t listen to us anymore, it only runs a centrifugation cycle of one minute and then stops. We tried to arrange an AEG mechanic, but we didn’t succeed. So yesterday we bought a new one and it will come this afternoon. To remove the old one we got some help of Miguel, son of our Madeiran friends Paz and Carlos, who lives and works in Lisboa.

Bearing given all clear

Mon, 29 Jul 2019 19:46:13 +0200

Ricardo of KM did an excellent job in getting the troublesome thrust bearing into shape. It’s not perfect but good enough for us to go.

Here is the bearing in action, if you watch carefully you can see there is a slight wobble remaining – look at the steel part towards the bottom of the film.

Medical supplies

Tue, 23 Jul 2019 11:27:28 +0200

Better not fall ill in Harlingen for a while, we’ve cleaned out the pharmacy!

Departure delayed by a bearing

Sun, 21 Jul 2019 13:57:28 +0200

Last Thursday a final check-up was done by one of the yard mechanics and he found an issue with the thrust bearing (Dutch: stuwdruklager) which is supposed to transfer the thrust produced by the propellor into the hull.

This bearing is used so that the engine itself doesn’t have to, and can be used with (very) soft engine mounts. This gives much less noise and vibration, which is always an issue in an aluminium ship – the aluminium doesn’t dampen this the way that GRP or wood do.

L&S Ecopilot reduces hydraulic autopilot current consumption

Thu, 02 Jun 2011 17:42:00 +0200

I just installed an Ecopilot device made by Lecomble et Schmitt from France. Let me tell you what this does and how much of a difference it makes to our power consumption.

Our autopilot uses a reversible pump that sends hydraulic fluid backwards and forwards through a rather stout cylinder. It has ample power to steer the boat, much more than I have certainly!

SRT proprietary AIS commands

Fri, 25 Feb 2011 11:19:00 +0100

My Navico NAIS-300, like most other commercial AIS class B products that have been available for a while, uses the SRT AIS class B OEM board. I know the same board is used in the Raymarine 500, True Heading AIS-CTRX, Transas, Digital Yacht AIT250/1000, and many more. The tell-tale seems to be that the AIS transponder comes with Pro AIS software. I have hooked up a serial data logger so that I could find out what NMEA-0183 commands the Pro AIS software sends to the transponder. Unfortunately neither SRT nor any of the vendors publish the protocol.

CANBoat Design part III - Choosing the server hardware

Tue, 21 Sep 2010 22:32:00 +0200

The server that CANBoat runs on was always designed to run 24 by 7. This means that it must be reliable and use little power. Power usage adds up over longer periods. Something that uses 3W will use 6 Ah @ 12 V per day. So every Watt counts!

CANBoat Design Part II - why a website, and why TCP and JSON

Tue, 21 Sep 2010 17:13:00 +0200

One of the first things that people ask me when I show them my app on the iPhone or iPad is where they can download it from in the App Store. My answer is simple: you can’t. Nor do you need to. It would be bad design if you had to!

CANBoat Design part I - A simple data viewer and boat remote control

Tue, 21 Sep 2010 16:51:00 +0200

Today I’d like to tell you a little more about the hardware/software stack that I have developed to control and navigate a small to medium pleasure boat. The basic idea is to re-use the mobile devices that most boaters will have, such as their smart phones, tablets, laptops or computers.

Navico yellow Ethernet cabling

Thu, 06 May 2010 11:07:00 +0200

The Navico ‘yellow’ ethernet connector used on new Lowrance devices such as the HDS series has the advantage of being watertight and easy to make a reliable twist-on connection:

In case you want to use a standard Ethernet switch, or have guys lay ethernet cabling through some narrow ducting you cannot use the normal Lowrance Ethernet cabling and have to crimp an RJ-45 jack onto the Lowrance cable.

Basics of Electrical units and quantities

Sat, 01 May 2010 17:26:00 +0200

I’m sick and tired of stories in the general boating press by confused writers that mix up electrical numbers and quantities.

This is probably because electrical units are a bit different than the units used for length, speed and distance.

Are Eco Ethernet switches Greener?

Sun, 06 Dec 2009 10:23:00 +0100

There was a recent discussion on Panbo where some people proposed that Ethernet, and more specifically using the IP protocol with a 100BASE-TX or 1000BASE-T physical layer. I am still sceptical of that for several reasons. One of them is that an IP stack rules out using small micro controllers, or requires extra hardware. This drives up the cost of the minimal hardware node. A zigbee or bluetooth based system is much more low-end friendly and has the added benefit of needing no wires.