Auto steering

http://hitecrcd.com/products/servos/waterproof-servos-2/hs-5646wp-high-voltage-high-torque-programmable-digital-waterproof-servo/product

http://www.ebay.com.au/itm/22RPM-to-50RPM-11KG-12V-24V-DC-Worm-Gear-Motor-Magnetic-High-Torque-Gear-Motor/331579625297?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20140106155344%26meid%3Dcb513d304872475b92b8cace590b253b%26pid%3D100005%26rk%3D4%26rkt%3D6%26sd%3D221708542442

https://www.radioyachtsuppliesaustralia.com/products/Hitec-water-proof--Digital-servo%2C-part-%23-HT%252d5646WP.html#

https://www.reddit.com/r/sailing/comments/25czvb/diy_tiller_auto_pilot/

https://www.pololu.com/product/2375/faqs

Commercial

https://www.whitworths.com.au/main_itemdetail.asp?cat=114&item=1628
http://www.simrad-yachting.com/en-US/Products/Tillerpilots/TP10-Tillerpilots-en-us.aspx