Madrone’s propellor is an Autoprop. Designed and built by Brunton’s Propellors in the UK, the Autoprop dynamically adjusts its blade pitch in response to engine RPM and the current sea state. When the boat is sailing, the blades feather to reduce drag and increase speed.
Angie scraping 20 years of accumulated marine growth off a prop blade
The Autoprop is expensive and more complicated than a fixed prop, and we likely wouldn’t have purchased one on our own. But it was already installed on Madrone when we bought her, and we have really come to appreciate the increased motoring efficiency and good sailing performance.
Madrone’s engine hour meter is almost at 2000 hours, and Autoprop recommends a rebuild between 1000 and 2000 hours. Since the boat would be out of the water and the prop would need to be removed to replace the shaft seal, it was a perfect time to do the rebuild.
A few of the pieces of the prop
We ordered a rebuild kit from King Propulsion here in the US, and after a short delay because of a database mixup we had our parts.
Our Autoprop is an H6 Ball Bearing version – that means that each of the three blades includes two sets of bearings, and each set of bearings has a pair of bearing races. Newer versions of the Autoprop feature captive bearings, but a model of our vintage still has individual ball bearings free in the race.
One of six sets of ball bearing in place. We used dishsoap to help hold them in place while reassembling the prop
The rebuild was surprisingly straightforward. As is typical of a part that has spent 20+ years immersed in saltwater, the primary challenge was cleaning off the accumulated corrosion and marine growth. Once cleaned, we replaced the old bearings and the bearing races and then put the prop back together. The final step was to adjust the blade tension to allow for free rotational movement without any lateral play.
Adding a set of cutting blades just in front of the prop hub – hopefully this will help to minimize the impact of running over stray fishing line…
It was clear that the rebuild was necessary. Many of the ball bearings had flats worn in one or more sides, and some of the bearing races had clear signs of brinneling. Once reinstalled and back in the water, the action of the blades when moving from sailing mode to motoring mode is noticeably smoother.
