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Computers at Sea

The Cruising Computer

© David Kerr 2001-2004

Computers have a role to play in cruising. David Kerr describes how he uses a computer to reduce effort, assist safe planning and enhance cruising communications.

Two extremes:

An American billionaire Steve Clark (founder of Netscape) has built a huge yacht where the sails, engine, lights, toilets and even the galley table are completely controlled by sixteen computers and a team of six onboard programmers who enhance the software and fix the bugs. At the other end of the spectrum is the cruiser who eschews an engine, GPS, autopilot, self-steering, electric lights and other modern technologies. Both of them enjoy their boats and cruising. There is a huge range of boat sizes/types, people, cruising styles and cruising locations so it would be senseless to be dogmatic about computers and cruising yachts. My intention here is to give some practical ideas and food for thought on the use of computers to assist cruising by describing our own experiences. As with every major system on our boat, there is either a backup or we can do without the system if it fails. Most of us already have multiple computers on board within specialised electronics and other marine equipment. The last time I counted, we had at least 12 specialised computers on our boat, in various pieces of equipment, so adding one more to perform general purpose tasks was not a large step.

Our boat and cruising:

We own a 11M Swarbrick designed and built Spacesailor 36 named "Pastime of Sydney". Last year we sailed to Lord Howe Island. This year, we completed a 2,700NM cruise from Sydney to the Whitsundays, explored the islands and returned. Next year we will sail to the Louisiades and the Solomon Islands. For that trip, we will have two of our six children with us, one of whom will be in Year 9. The computer will be used for remote schooling and our son will maintain contact with his school via email as there will not be many Post Offices where we will be cruising!

Laptop or desktop?

We use a Toshiba laptop on the boat and for many boat related tasks at home. We chose a laptop for reasons of portability, power consumption and size. Computers are intricate electronic items that do not take kindly to salt air, moisture or excessive forces so ours is housed in a bright yellow Pelican case which is robust, waterproof and airtight. The computer sits in a snug-fitting, custom-made foam cutout within the Pelican case and there is also space for our digital video camera. We use a container of silica gel to keep the air dry. At home, the laptop can be connected in a matter of seconds to a desktop computer (via ethernet) to transfer files, backup data to a tape drive or access the Internet. Other cruisers build in computers or use thick, sealing plastic bags for protection from the elements.

Trip planning:

We do our navigational trip planning on both the computer and paper charts; we download way points to two Garmin GPS units (76 main unit and the backup 75). We deliberately chose compatible GPS units with a good, cheap computer interface and plenty of functionality, despite one GPS being eight years older than the other. We also print out the way points, chart-plots and other data at home before the trip and take them with us as hard copy backup. We monitor the weather via the Internet before our trip. We keep records of our food stocks on a computer database. Through practice, we have previously determined our usage rate for food and other supplies like toilet paper, soap, toothpaste and a plethora of other things. These usage rates are kept on the computer, with a paper backup. This makes shopping easier before and during a trip. We keep track of food usage en-route as well as the location of items. Space is always tight, so we store things in a number of lockers. It used to be a nightmare before we knew our quantities and locations. We believe the food database will further prove its worth with Customs and Quarantine services when we come back to Australia as we can track all food items from purchase through storage to consumption. While we are sailing, we use paper lists printed from the database (sorted and indexed in several different ways). We update these as we go along and do not go to the extreme of updating the computer every time we open a can or eat an orange!


We still use paper charts, in conjunction with GPS, for navigation. We have a sextant for backup of the two GPS units, along with a Merlin navigation computer and spare batteries in a waterproof bag. (Yes, there is also free software that effectively emulates the Merlin on the PC!) We are usually happy with the small GPS track plotters, but sometimes download tracks to the laptop for further analysis of tacking angles, currents, speed over ground etc. If we should lose GPS memory, we can reload all data very quickly from the laptop to either GPS.

In common with many cruisers, we have a large number of paper charts. These are all indexed in a spreadsheet with the scales, descriptions, chart numbers and latest NTM (Notices To Mariners) numbers. We get the NTMs from the Navy Hydrographic Office's web site via our home computer. Chart updating was becoming a nightmare until we started the spreadsheet. We use the spreadsheet sorting functions to sort which charts we need to update and take for different passages.


At sea, we use email from the laptop, via Sailmail, as a primary communication medium with friends and members of our family, some of whom are overseas. It is interesting to recall that when we travelled around Australia by land, 20 years ago, we used to send and receive telegrams via the Royal Flying Doctor's HF (High Frequency) network for the same purpose. We have found that mobile phone reception is poor along the East Coast, particularly when we are well offshore so we are glad we did not opt for Internet access via a cellular phone. Satellite communication is available and good, but still too expensive for us. Whereas we will sometimes make Radiotelephone calls, we find it is much more definitive to use email or have a friend ashore fax an email to a repairer or supplier. For instance, the small autopilot which we occasionally use to drive our Cape Horn windvane failed at the start of a passage from Sydney to Mooloolaba. While we were still at sea, I was able to compose a well-considered email about what was wrong with it and what I wanted from the repairers before they received the unit. I certainly would not have been able to provide accurate, well-reasoned information in a radiotelephone call. We were able to post off the autopilot from Mooloolaba and it was properly repaired by the time we arrived in Laguna Quays.

We maximise our HF radio communications by using an HF propagation programme that allows us to enter our location and that of the other station on a map of the world. There are a couple of solar variables which we obtain either from email or the WWV time signals and the programme tells us the best frequency to use for the time of day.

Weather Fax:

We do not use weather fax all the time, but it is fantastic to have it there when we need it. For example, before setting out from Lord Howe to Sydney or from Mooloolaba to Coffs Harbour. We have also used "Fleet Codes"; these are synoptic charts encoded as text emails and reconstructed on the laptop screen. Fleet Codes are only available for part of the South Pacific Ocean.


We use the Wxtide software for tide charts, backed up by tide charts (when available), personal observation and information from Coast and Limited Coast Stations. This was invaluable recently when our deep-keeled boat was in the Great Sandy Straight. We were able to plan earliest departure times down to the nearest five minutes in a number of shoalling areas. We also use this programme when we are anchoring, particular in areas of large tidal variation.


Our Log is still kept on paper and contains the essential information. We have designed our own log sheets which we keep in plastic sleeves during a passage. Previously, our log book was becoming just too tatty and salt stained from spray and rain. Individual sheets are much easier to handle and we have made them to fit our writing size and style of log keeping. The descriptive part of our logs is kept on the computer. We also email these descriptive logs to friends for safe keeping and as a communication mechanism; they make excellent reading and provide a great record of our trips and notes when we return.


As well as CDs, tapes and many books, we will take a number of Digital Video Disks (DVDs) with us next year. We rarely go to movies and almost never watch TV, so it will be enjoyable upon an occasional evening to pull out a video and watch it on the good quality computer screen. No-one has time for computer games at home so it is not likely that we will take any. We would rather be sailing, swimming, studying, snorkelling, diving, walking, looking or learning another culture.


We use our computer to enhance our cruising and it certainly does not rule our lives. This is one of the advantages of a laptop that is tucked away in a case; although it can be activated in less than a minute, it does not sit there tempting us to waste time. If the computer were to fail (which it has not done, even in very unpleasant conditions), we do not lose anything vital, although the long term loss of email would be a major inconvenience and we would certainly miss it.


Steve Clark biography "The New New Thing." Michael Lewis, published by Hodder & Stoughton.

Our laptop is a Toshiba 4360 with 192Mb RAM, 12Gb hard drive, modem, DVD/CD and floppy. We have a 12V adaptor to run or charge the laptop using ship power and we can also run it from our 240V inverter. We will be obtaining a small printer to use on board. This laptop is more powerful than necessary for everything we do at the moment, but we wanted something we could keep for many years and which would be useful for remote schooling.

We imported our model 1500 Pelican case from West Marine in the US and it arrived in less than a week, but they are available locally. See These cases are expensive but are wonderfully strong and waterproof/airtight. Many professional medical, photographic and scientific people use them to transport a huge variety of equipment. They are cheap compared with a laptop or camera.


"If the computer were to fail....we would not lose anything vital....however we would certainly miss it."

"It would be senseless to be dogmatic about computers and cruising yachts."

"We use our computer to enhance our cruising and it certainly does not rule our lives."

Further sidebars:

This article only identifies a small sample of the software available. Our criteria have been cost, reliability, functionality and ease of use.


Sailmail is a nonprofit organisation set up on a worldwide basis by several dedicated cruisers in the US. The HF radio station and interface to the Internet is run by Penta Comstat here in Australia and there are other stations all over the world. Sailmail uses the free Airmail software which is an excellent Windows based programme. It is intuitive to use and can also be linked into your favourite Internet email programme if you prefer something with which you are familiar. If you are not comfortable with HF, radio modems and computers, Marc Anderson of Philip Collins & Associates (PCA) can assist. The setup of modulation levels to the radio is of critical importance. PCA donated the transceivers and modems for the Australian service. On Pastime, we use an SCS PTC IIe modem with an ICOM HF radio, however the PTC will interface with many radios. I performed our own installations and we have had no problems. See for a lot of useful information, software and registration. See for PCA and their products and services.

Tide planning:

We use WXTIDE32 which is free shareware. This is an excellent program with thousands of tide locations all around the world. The package has graphical and text interfaces. There are literally hundreds of tide locations just for Australia. See

Route Planning:

We use Gartrip, an excellent, downloadable shareware program designed for Garmin and Magellan GPS equipment. Cost of the full version is US$30 (about A$60). See


There are many good spreadsheet packages available. We already owned Corel Quattro Pro, Lotus 1-2-3 and Microsoft Excel and tend to mainly use Corel.

HF Propagation:

We use HFProp. It is about A$80 for a fully functioned, down loadable version. See

Weather fax:

We use JVCOMM32. Another excellent package from Germany. Cost is approximately US$68 (A$136) and it is downloadable from the Internet. It can use the SCS HF modem or even a computer sound card if you do not own an HF modem. I have successfully received faxes with a small shortwave (SSB) receiver and the laptop. See

Food database:

We use Filemaker Pro, although we only use a fraction of the features. Other PC-based packages such as Microsoft Access will also work well.

Last changed: 9th May 2004

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