Spurs cutter

[MCW]

Iam experiencing very rapid anode consumption on my cutter and would be interested in the views of the forum. The cutter is a 25mm dia mould 'A' type fitted to a conventional shaft/prop setup. The built-in anode only lasts for a couple of months, on a visual inspection it looks ok but on touching it it just crumbles away. Such is its ineffectiveness that this last season there has been corrosion of the stainless steel cutter itself. The fixed blade that carries the anode is not bonded to any other metal so the anode is not trying to protect anything but the small cutter. the shaft,prop,rotating cutter are all bonded to the main Duff pear anode and are all fine. The yacht is on a swinging mooring, so stray currents via shore supply can be ruled out, infact I did not use a shore supply at all this year.

 

[dickh]

This year I had a similar experience, but only one half of the shaft anode corroded away, the other half was OK. There does not appear to any corrosion on the Cutter - mine is the Stripper though. This is the first year this has happened, previous years the anode has corroded evenly.

dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[Sinbad1]

If you have a conventional set-up with your stern gear I assume that you are talking about the fixed blade of the 'spurs' which will be bolted to your aft bearing housing. If you follow the 'electrical' connection thru logically you will see where the problem is arising.

At present it sounds like you have your main hull anode connected to your shaft which will protect your shaft and prop. However the external/aft bearing housing will be bolted thru the deadwood to a matching flange which is on the stern tube. If this stern tube is metal you need to run a wire from the internal bolt of the hull anode to the stern tube. This will effectively protect both the bearing housing and anything attached to that housing, such as cutters. However if you have a glass fibre stern tube you need to ensure that the hull anode has a wire from its internal bolts to one of the bolts on the aft bearing housing. (inside the boat, obviously)

In simple terms it sounds to me as if the aft bearing housing is not galvanically protected. I would suspect that if you scraped all the antifouling off the bearing housing you would see a slight color change in the metal which would indicate mild electrolysis.

Its not a big problem to resolve. You will need 12 foot long arms made of rubber....but then thats the fun of boating!

 

[MCW]

Hi Sindad1,
The sternbearing is connected to the hull anode but the fixed cutter is electrically isolated from rest of sterngear etc. It runs on plastic bearings and is held in place by two nylon 'buffers' against the bracket on the sternbearing so ensuring it is isolated. The anode giving problems is only supposed to protect the fixed cutter blade. Originally there was a wire plus a stainless steel spring from the fixed blade to the sternbearing . When I raised the problem of anode consumption with the manufacturers the other year they recomended removing both, saying the problem was that the cutter anode was trying to protect the sternbearing as well, as the problem is still evident that cannot have been the problem. I suspect that the anode material is incorrect - what say you?