Steve and others interested in Arduino based full size boat autopilots. I have been working on a marine autopilot for a 40 foot sailboat for a couple of years. Last summer the autopilot steered my boat 500 miles up the inside NW passage from Seattle to the north end of Vancouver Island and back. I have just finished putting together a YouTube video showing the boat under sail and being steered by the autopilot. The video also does a brief walk through of the hardware and operating modes.Here is the link to the video. If anyone wants to adapt this project to their needs I'll be glad to help.http://www.youtube.com/watch?v=-nA6wo9PXlsJack Edwards
My feeling is that using the GPS to determine which way you are going, is bound to fail.If you take a GPS and walk around with, it will calculate it's position from time to time and calculate an apparent direction you are moving based on those points. If you plot them on a map ( Google earth is the easy way ), you will see a zig-zagging series of straight lines. This would be useless for steering a yacht.Secondly, I think it would be futile to try steering a boat without knowing which way the boat is facing. A GPS cannot tell you which way the boat is facing. A digital compass which costs about $4 will tell you which way the boat is facing. In simple terms, the boat needs to be pointing in the direction that you want to go. You can then adjust this for leeward sideways drift, currents or whatever else you like. In the short term, to control the tiller to keep the boat pointing in the direction you want to go, you need a digital compass chip, not the GPS. Then, in the medium term, you use the GPS position to compare where you are, to where you want to go, and adjust the course reference that the compass is using. I wouldn't use the GPS course heading information for anything, because it is basically useless IMHO.