Maxprop anodes

[Ex-SolentBoy]

I have a new Maxprop with the circular anode that is held onto the hub by 3 screws. When I lifted out this season, most of the anode was still there, but the screws are very near the edge (see the picture) so I had to replace the anode as it would soon have fallen off.

These anodes are quite expensive so I would appreciate advice on:-

1. Has anyone modified theirs to work with a central screw. which would be a better approach.
2. Potential sources of reasonably priced anodes.
3. Is it feasible to melt down the old ones and remould them. Seems such a waste to throw away when 90% of the thing is still there.

Any other creative ideas?

Many thanks

 

[Roberto]

90%

not sure it's 90% left, this is brand new I just bought from the MP dealer, it is rather hollow inside, the overall thickness seems to be around 10-15mm

same dilemma every year... :sad:

 

[Tranona]

I have a new Maxprop with the circular anode that is held onto the hub by 3 screws. When I lifted out this season, most of the anode was still there, but the screws are very near the edge (see the picture) so I had to replace the anode as it would soon have fallen off.

These anodes are quite expensive so I would appreciate advice on:-

1. Has anyone modified theirs to work with a central screw. which would be a better approach.
2. Potential sources of reasonably priced anodes.
3. Is it feasible to melt down the old ones and remould them. Seems such a waste to throw away when 90% of the thing is still there.

Any other creative ideas?

Many thanks

Think you will find the multiple screw fixing is to ensure a good electrical contact across the whole of the anode and a single central screw would not be a better approach. Remember this anode is protecting a very expensive piece of kit and you should see one where the anode has not been replaced in time!

It is worth considering a hull anode close to the stern gear and bonded to the shaft. I have one on my boat with a feathering propeller and prop anodes last up to 3 years. If you are in a marina with lots of steel around and you plug into shorepower a galvanic isolator for the shorepower circuit may also be worth investigating.

 

[npf1]

Paint around the screw holes/head (but ensuring there is still conductivity). We use an Autoprop and do this as it does help.

 

[impact30]

Hi Solentboy
I used 2 of the biggest ones last year. I bought here just last month
http://www.zincsmart.com/

They supply good heavy ones so maybe there will be better life. After the anode is fitted to your satisfaction paint or apply sealant over the area where the mounting holes are so that this area will not corrode. Be careful to maintain good contact though and not have sealant contaminating the mating faces for future anodes. My prop has pinned screws which were not allowed for with the new anodes so I had to make a small hole. no big deal.

 

[Ex-SolentBoy]

Think you will find the multiple screw fixing is to ensure a good electrical contact across the whole of the anode and a single central screw would not be a better approach. Remember this anode is protecting a very expensive piece of kit and you should see one where the anode has not been replaced in time!

It is worth considering a hull anode close to the stern gear and bonded to the shaft. I have one on my boat with a feathering propeller and prop anodes last up to 3 years. If you are in a marina with lots of steel around and you plug into shorepower a galvanic isolator for the shorepower circuit may also be worth investigating.

Thanks. We already have the hull anode bonded to the shaft and a galvanic isolator. The boat was not in a marina for most of the time as well.

It's actually not the cost of the anode I object to - it's the £250 lift-out to change it! I am a qualified diver. Perhaps I should just buy a dry suit!!!!!

 

[Ex-SolentBoy]

Hi Solentboy
I used 2 of the biggest ones last year. I bought here just last month
http://www.zincsmart.com/

They supply good heavy ones so maybe there will be better life. After the anode is fitted to your satisfaction paint or apply sealant over the area where the mounting holes are so that this area will not corrode. Be careful to maintain good contact though and not have sealant contaminating the mating faces for future anodes. My prop has pinned screws which were not allowed for with the new anodes so I had to make a small hole. no big deal.

Thanks. Looked at the site. Which anode do you mean specifically. They say that they do not have the round Maxprop ones.

 

[Talulah]

The Maxprop anode thing is an expensive problem.
I know of one person who had a fitting machined in bronze that fitted between the anode and the hub.
This fitting bolted onto the Maxprop using the standard bolts around the edge but had a threaded central hole so he could attach anodes with a central bolt.
However, a much cheaper and easier solution is to buy plastic bolts off ebay. This solves the problem. Don't worry about the electrical connection. There is sufficient with the anode tightened up against the hub.
(There is one feathering prop manufacture who supplies plastic bolts for this purpose but I can't remember who.)

 

[rtchina]

changing anodes

Thanks. We already have the hull anode bonded to the shaft and a galvanic isolator. The boat was not in a marina for most of the time as well.

It's actually not the cost of the anode I object to - it's the £250 lift-out to change it! I am a qualified diver. Perhaps I should just buy a dry suit!!!!!

If your'e a diver, then do it. I have the same max prop as you and changed the anode by diving down with a Hooka system.
Would recommend passing a line under the hull so that you can hold yourself in position. takes about 10 mins in total. I also clean the copper coat hull in the same way, though I did have the boat lifted so I could grease the prop, though with a bit of care you could do that as well.

 

[Quandary]

Paint around the screw holes/head (but ensuring there is still conductivity). We use an Autoprop and do this as it does help.

I always apply a tiny squeeze of sealant around bolt heads before tightening, this does not affect electrical contact on my prop. but means that the bit of anode around the screw head is the last bit to go. If you don't when the zinc erodes at the screw seat it allows the anode to loosen, vibrate, wear around the holes and eventually fall off. It more than doubles safe life. I was first taught to do this on shaft anodes to keep them in place while they eroded.
Vital to make sure the anode is in good electrical contact with the bronze though.

 

[VicS]

Can someone please explain why the anode is so vital to Max-props.

They are made of nickel aluminium bronze which is described as having "outstanding " resistance to corrosion by salt water!

Tranona, whose contributions are usually on the mark, said, "you should see one where the anode has not been replaced in time!" Why do they corrode so badly if they are made of NAB?

 

[Ex-SolentBoy]

Thanks for the replies. Interestingly, I also asked the question on our owners forum and got the replies below. Seems everyone is on the same basic line.


"I had a similar problem with the anode on a Brunto autoprop. Painting the inside of each hole with Duralac seemed to work"

"What I do to avoid the problem, and it seems to
work fine, is to paint a little antifouling around the seating of the
set screw with a small stripe down to the edge of the anode (about
3/16" wide). I use a small artist brush.
The anode doesn't wear away under the paint and the seating remains
intact. Given this simple solution, I have not tried to modify the
fitting with another screw arrangement."

 

[Quandary]

Can someone please explain why the anode is so vital to Max-props.

They are made of nickel aluminium bronze which is described as having "outstanding " resistance to corrosion by salt water!

Tranona, whose contributions are usually on the mark, said, "you should see one where the anode has not been replaced in time!" Why do they corrode so badly if they are made of NAB?

When you are paying something like £4-5k for a prop you will not want to take risks with it. My Volvo three blade folder (somewhat cheaper) is on a stainless steel shaft with a stainless steel rope cutter emerging from a saildrive with nearly every metal alloy invented in it. The little anodes are a pain to replace, and pay for, but I am much comforted that they do erode away and that the bronze still glistens.

 

[VicS]

When you are paying something like £4-5k for a prop

If I was paying even half that for a prop I'd expect it to be made of a material that was fit for the purpose, not have to rely on a stupid bit of zinc thats going to corrode at an alarming rate purely because its bolted directly onto a great chunk of copper alloy and likely to fall off once 10% of it has gone from around the fixing bolts.

However it does not answer the question. WHy does a Max-prop need to be protected by a zinc anode anyway when it is made from an alloy that is said to have double the corrosion resistance of manganese bronze.

 

[john_morris_uk]

If I was paying even half that for a prop I'd expect it to be made of a material that was fit for the purpose, not have to rely on a stupid bit of zinc thats going to corrode at an alarming rate purely because its bolted directly onto a great chunk of copper alloy and likely to fall off once 10% of it has gone from around the fixing bolts.

However it does not answer the question. WHy does a Max-prop need to be protected by a zinc anode anyway when it is made from an alloy that is said to have double the corrosion resistance of manganese bronze.

VicS, Your question has got me thinking as well. I had to leave Serendipity in the water last winter and didn't dry her out to replace the anodes for over 12 months. The Max-Prop anode had gone altogether and there was only a bit of shaft anode left and I am now faced with polishing out the patches on the prop where electrolytic action has started. This is a bit annoying as the Maxprop cost me over £2000 a couple of years ago. Classic signs with patches of copper coloured disfiguration. Nothing structural yet, and they will polish out I hope. (I had a polishing kit as a Christmas present!) If the prop is made of such good material, why did this happen?

 

[Tranona]

Can someone please explain why the anode is so vital to Max-props.

They are made of nickel aluminium bronze which is described as having "outstanding " resistance to corrosion by salt water!

Tranona, whose contributions are usually on the mark, said, "you should see one where the anode has not been replaced in time!" Why do they corrode so badly if they are made of NAB?

I don't know why either, but just a couple of examples. A few years ago there was an article in YM about buying a big bluewater cruiser. One of the boats under consideration was a neglected HR (a 42 I think). The Max Prop was well dezincified because the anodes had gone. The teak deck needed replacing along with much of the interior due to water leaks - was not recommended despite a low price! I looked at another Max Prop last year in Corfu, mainly because it had picked up a rope and was a good example of why you need to fit a rope cutter. This had also lost its anode and the gear mechanism was very sloppy and rattly. Could just have been wear or lack of maintenance, but there were pink patches on the blades as well.

 

[Quandary]

Metal?

Surely the problem is the need to combine dissimilar metals. The pivot pins and shafts for instance are stainless steel and the effect of this is simply demonstrated by the way anodes tend to go fastest near the securing bolts. It would be wonderful if someone had invented one metal alloy suitable for all purposes that was also completely resistant to electrolitic corrosion. The best chance is perhaps the direction taken by Kiwiprop, but it would seem that so far carbon fibre does not lend itself easily (or perhaps economically) to the subtle shaping needed in the best folders.

 

[davidej]

We fitted a brunton autoprop last winter and seem to be having similar problems.

We put varnish around the screw holes of the first one we fitted. That had completely gone within three months leaving the three three plastic screws behind. The second one (which we didn't bother to varnish), was gone by the time we hauled uot in the autumn. This time only one screw was there.

Bonding the prop shaft to the main anode sounds sensible. Presumabvly we would have to arrange some sort of 'brushes' to contact it

Any suggestions?

 

[davidej]

P S

We are on a swinging mooring!

 

[VicS]

Surely the problem is the need to combine dissimilar metals. The pivot pins and shafts for instance are stainless steel

Yes I think that could be the reason. There is probably sufficient difference in the electrode potential of NAB and 316 stainless steel to cause the problems.

Such a pity because a plain manganese bronze prop will last for donkey's years without any need for anodes.

Aluminium bronzes have pretty good mechanical properties but presumably not good enough to make the props without resorting to stainless steel bits and pieces.

Bonding the prop shaft to the main anode sounds sensible. Presumabvly we would have to arrange some sort of 'brushes' to contact it

Any suggestions?

MG Duffs electro-eliminator.