Servicing an Autoprop Sailboat Propeller
In this post we will run through how you service your Autoprop Propeller during your yearly haul out. It is possible to perform some of this work underwater, however re-greasing the propeller is best done when the sailboat is on the hard. A video of the servicing is given at the end of the post
The primary purpose of the yearly service is to protect the Autoprop propeller from galvanic corrosion by replacing the zinc anode and also to ensure the blades are free to pitch by re-greasing them.
Changing the Anode
The anode on any propeller should typically be changed once it reaches 50% of its original size. Beyond this its effectiveness diminishes and risk to the propeller increases significantly. The anode has been sized to allow a years ‘typical’ operation between haul-outs and the wear rate depends on many factors including where the boat is moored (steel piers) and so on.
To replace the anode the remains of the old one must first be removed. All Autoprop anodes are held in place with three nylon bolts. The choice of nylon bolts is intended to slow the wear of the anode around the bolt holes preventing the anode from failing and falling off. The only forces on the anode are those due to the inertia of the shaft and the frictional drag of the water as it rotates, both forces combined are well below the shear force needed for the bolt to fail.
Once the old anode is removed the contact part of the hub and anode should be lightly sanded to remove oxidation. A good contact between the two dissimilar metals is necessary to make the anode work. Once in place the bolts are to be tightened being careful not to shear the bolts and the anode replacement is complete. Autoprop offer three types of anode, a zinc anode for salt water, aluminum for brackish and magnesium for fresh water, all are available from our store.
Servicing the blades
The last part of the service is the greasing of the bearings for each blade. It is critical that the bearings be greased on a regular basis to ensure that the bearings do not corrode and remain free. If one blade begins to bind this will throw out the balance of the propeller and cause noise, vibration and potentially cavitation.
The Autoprop blades are greased through two grease ports on the blade cap of each blade. The ports are blanked off using metric M5 pan head bolts, two per blade, and these must be removed. Once the bolts are removed the grease can be applied through the nozzle on the side of the blade and vented through the port on the top of the blade cap.
An Autoprop grease nozzle is needed. The nozzle has a male M5 bolt on one side to fit into the grease port and a female NPT pipe thread on the other that fits a standard grease gun hose.
Once the port is connected to the grease gun, several pumps of grease will be required, maybe more, until the grease appears in the venting port. Once the gun has been disconnected the two M5 cap head bolts should be replaced taking care not to damage the O-rings on them. The bolts should be nipped up with sufficient force to pressurize the O-ring and keep all that good grease in.
In normal operation there should be no water inside the bearing housing, however it is not uncommon to find a teaspoon of seawater inside the housing when the blades are being rebuilt. If the grease is pumped underwater (not an ideal situation), this remains a risk and owners should be aware of the potential damage it may cause.
Wrapping it up
Once the blades are greased they each should fall under their own weight at a gentle rotational rate. If they are too floppy or too stiff then the torque on the bearing locking nut may need to be adjusted. This is covered in a later blog post when we look at rebuilding an Autoprop propeller and torquing the blades to factory standards.