One of the sensors for the IOM SKA Autonomous model sailboat is the windvane. It is a crucial sensor because the sail adjustments will be done based on the input of this sensor. In the future even all the navigational logic will be based on this sensor (to tack or not to tack?). Therefore the actual wind direction will be calculated to predict the possible courses for example. But again, this is something for the future. First things first.
My starting point was to build a wind vane that was very easy to implement, has a optimal location related to the center of gravity and is not related to the rig (the IOM has three rigs for example and I don’t want to change the sensor every time).
The maiden voyage showed that the wind vane that was located at the deck was not very effective. Due to the heel of the boat (lee) or water on the bearings the vane was not pointing to the wind in every course. A sealing for the bearings will introduce more friction in the rotation and the heel was more that acceptable. A bigger wind vane is not possible due to the boom that will interfere with it.
In this photo the malfunctioning of the windvane is clearly visible.
There are better places to think of, but before I define this I’d like to share some more thoughts in this post of how to create the wind vane.
The first basic principles are used for the design of the
- Pointing to wind in very light winds – negligible friction in radial direction
I’d like to do other things with high winds…
- High accuracy ±1 degree
This accuracy will be effective when sailing close hauled (working to windward)
- High sample rate
Wind direction changes very quickly and or the boat will be very manoeuvrable. Noticing this will result in a good anticipation to the changes
- Absolute value
I just need to mount it on the model and start sailing
There are several possibilities for this so I will write a post for every option with all the pro’s, cons and results.
- Magnetometer (digital compass)
- Digital angle sensor (hall effect)
Results will follow in the near future.
The sensor need to be placed inside a housing that I will design first. Both sensors will work with a magnet and the components are so smalle they need to be soldered onto a PCB before mounting them in a housing. It is not likely this will change.
Due to space saving considerations the back of the hull or behind the hull is a good area to place the windvane, just like they did in the early days with vane sailing. In this case I’ve got no trouble rigging and the apparent wind will be sensed quite good, especially when I enlarge the vane.
The PCB will be enclosed in a watertight container. The bearings will be upgraded with grease to make them watertight and the closure of the housing will be done with an O-ring.
The vane is modular and bolted onto the hull. The bolts are also the electrical connection between the vane and the hull. In this case connectors can be avoided.