Prop shaft material
- Thread starter Ken13559
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I think the standard SS prop material is Aquamet. It comes in several alloys. Marine Machining & Manufacturing - Home
A few years back I used this company. At the time the prices were good and the service was excellent. Boat Props, Inboard Prop Shaft Seals, Cutlass Bearings, Zinc anodes, Marine Hardware
A few years back I used this company. At the time the prices were good and the service was excellent. Boat Props, Inboard Prop Shaft Seals, Cutlass Bearings, Zinc anodes, Marine Hardware
According to MaineSail from my similar inquiry last year: "AQ-22 or AQ-19 shaft (Aquamet or Aqualoy shafting) ...
Western Branch Metals is the leader in prop shafting ..."
https://forums.sailboatowners.com/i...eel-vs-bronze-prop-shaft.181158/#post-1321481
Normally the labor is the worst part of this type of job and the few bucks difference between average and superior parts is really not worth the trouble.
Western Branch Metals is the leader in prop shafting ..."
https://forums.sailboatowners.com/i...eel-vs-bronze-prop-shaft.181158/#post-1321481
Normally the labor is the worst part of this type of job and the few bucks difference between average and superior parts is really not worth the trouble.
Aqualoy 22, Aquamet 22 or Nitronic 50 (all very similar compositions) are the shafting materials you'll want..... Neither 304 nor 316 should be used and far too often are by corner cutters and penny pinching builders..... AQ-22 or Nitronic 50 shafts should have approx 22% chromium, 13% nickel, and 2% molybdenum..
Be aware that there are MANY disreputable shops out there, especially on the net, selling "AQ-22" shafting that is nothing more than cheap 304 or 316..... Always buy from a REPUTABLE shafting shop...
We offer A19:
https://shop.hunterowners.com/hp/part.php?m=326&c=12&p=53809
If your shaft is compromised from electrolysis, you should check your strut and propeller as well:
https://shop.hunterowners.com/hp/part.php?m=326&c=12&p=52248
https://shop.hunterowners.com/hp/part.php?m=326&c=12&p=54827
https://shop.hunterowners.com/hp/part.php?m=326&c=12&p=54341
https://shop.hunterowners.com/hp/part.php?m=326&c=12&p=53809
If your shaft is compromised from electrolysis, you should check your strut and propeller as well:
https://shop.hunterowners.com/hp/part.php?m=326&c=12&p=52248
https://shop.hunterowners.com/hp/part.php?m=326&c=12&p=54827
https://shop.hunterowners.com/hp/part.php?m=326&c=12&p=54341
Here's the photos of my prop shaft and FoF prop. The shaft doesn't look good and the prop I see it started to pit.
Do I have a problem here? Will the prop breaks off should the FoF prop hit some logs? There's a crescent shape on the shaft. Didn't notice it till I see the photos. Could it be pitting?
I've my shore-power connected 24/7 charging batteries. Perhaps I should remove the cable when I'm not onboard.
Ken
Do I have a problem here? Will the prop breaks off should the FoF prop hit some logs? There's a crescent shape on the shaft. Didn't notice it till I see the photos. Could it be pitting?
I've my shore-power connected 24/7 charging batteries. Perhaps I should remove the cable when I'm not onboard.
Ken
Ken
Grossly - the pitting looks symptomatic of stray current but we do not know the shaft alloy you have. So measure your hull potential - plugged into shore power and also not plugged in. When you do this make sure your regular neighbors are is their slips so as to replicate conditions. Chances are this problem is originating from your own boat (in which case plugging in and unplugging will show no difference in hull potential) but it is impossible to say without hull potential measurements/assessment. I would imagine you must be going through shaft and prop zincs at a very high rate of decay too.
For replacement use the alloys MaineSail lists and no other. In any case you need to install galvanic isolation - never mind whether the shaft corrosion is caused by galvanic activity or by stray current. However, if stray current is the culprit you must identify the source and fix it - or your repair will be for naught - galvanic isolation will not protect you from stray current at potentials above about 1.3 vdc or thereabouts.
Hull potential = the difference between your shaft/propeller/its zincs compared with a reference probe silver/silver chloride (or in my case a very inexpensive all zinc reference anode.)
Charles
Grossly - the pitting looks symptomatic of stray current but we do not know the shaft alloy you have. So measure your hull potential - plugged into shore power and also not plugged in. When you do this make sure your regular neighbors are is their slips so as to replicate conditions. Chances are this problem is originating from your own boat (in which case plugging in and unplugging will show no difference in hull potential) but it is impossible to say without hull potential measurements/assessment. I would imagine you must be going through shaft and prop zincs at a very high rate of decay too.
For replacement use the alloys MaineSail lists and no other. In any case you need to install galvanic isolation - never mind whether the shaft corrosion is caused by galvanic activity or by stray current. However, if stray current is the culprit you must identify the source and fix it - or your repair will be for naught - galvanic isolation will not protect you from stray current at potentials above about 1.3 vdc or thereabouts.
Hull potential = the difference between your shaft/propeller/its zincs compared with a reference probe silver/silver chloride (or in my case a very inexpensive all zinc reference anode.)
Charles
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Good morning - here is a diagram. The notes refer to results using a zinc probe - not silver/silver chloride probe.
Yes I've a galvanic isolator that comes with boat from factory. Since i moved back to this marine i saw a fast depletion of shaft anode and increased shaft pitting.
Several years ago when i was first at this location my stock 2blades prop has pin holes!! Shaft wasn't too bad. Anode changes every 6-9 months.
Now everything seems to be eaten fast.
Off topic a bit, are you connected to shore power? If so you may be providing zinc for the rest of the dock. The ground wire in the shore power connects you to every other boat on shore power. Test (carefully) between the shore power ground at the dock and the ground lug on the shore power cable. The shore power cable has to be connected to the boat of course and the boat should be in it normal electrical configuration when you leave it for home. There should be 0.000 volts (there never is BTW). If you see anything over a 1 volt the consider getting a galvanic isolator for your AC circuits.
Also I don't think the shaft is in any jeopardy of breaking with just the surface pitting show.
Also I don't think the shaft is in any jeopardy of breaking with just the surface pitting show.
The metal composition is almost the same as Alloy 20 . which is used to prevent Chloride Stress Corrosions. It is the high Nickel-Chromium content. Aquamet 22 appears to save $$ by lower Ni-Cr content since the Chloride content of sea water and temperature is low. All keel bolts should be made with this type metal too, since they could be Oxygen starved.
The picture is NOT Stress Corrosion.
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you lost your Zinc protection Rapidly.Jim..
I believe the isolator (if it's working, which can be tested) should prevent your boat from having it's ground linked to the rest of the dock.
SPEAKING of other boats in the marina...What's happening with them? Replacing zincs every 6-9 months in a marina isn't a huge depletion in my experience. If you're in question, I'd get a zinc "grouper", connect it to a solid ground on your boat, and hang it over the side. In some installations, the continuity of ground through to the shaft with some vibration isolators isn't clear.
SPEAKING of other boats in the marina...What's happening with them? Replacing zincs every 6-9 months in a marina isn't a huge depletion in my experience. If you're in question, I'd get a zinc "grouper", connect it to a solid ground on your boat, and hang it over the side. In some installations, the continuity of ground through to the shaft with some vibration isolators isn't clear.
Assuming the corrosion is not galvanic - it is nearly certain this is a DC problem. AC might effect aluminum but current density would have to be pretty big and this is not aluminum anyway.
The origin of DC induced decay is most frequently ones own boat. There are many candidates for self inflicted DC leaks - any wiring in the bilge water, any 24 hour circuit like bilge pump switch, starter or alternator connections corroded high resistance bridge leaks to the motor block, any bonding cable that ends anywhere other that a zinc or ships ground buss, battery charger internal failures, etc. Start measurements with your batteries 100% connected, then disconnect each one at a time. And measure with your shore power plugged in/unplugged too.
Your neighbor (probably the nearest ones) can be the culprit too. If he is putting out DC that is returning via your shore power cable and anything more then 1.3 vdc reaches your boat your galvanic protection will do no good at all. So measure with the neighbor boat plugged in/unplugged.
You are looking for changes as you sample - but anything over 1 vdc (zinc is about 1.2 or so) is not galvanic.
Charles
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Assuming the corrosion is not galvanic - it is nearly certain this is a DC problem. AC might effect aluminum but current density would have to be pretty big and this is not aluminum anyway.
I'm confused, Charles. How is the mechanism for damage not galvanic in this case?
I'm confused, Charles. How is the mechanism for damage not galvanic in this case?
We do not know whether the pitting we see is galvanic because we do not know the voltages involved. This why we measure. Consider a common shaft assembly - manganese bronze propeller bolted to a stainless shaft but no zinc on the shaft or the propeller. In that case the potential difference between the propeller and the shaft will be present and the less noble (the propeller) will become the anode and so it will corrode whereas the shaft will be the cathode and be protected from corrosion. Bolt a zinc on the assembly and the zinc anode corrodes while the rest of the assembly does not. This is the galvanic process.
Now instead imagine a battery connected to an alternator that has fault such that DC current passes via this fault to the motor then to the shaft then returns to the battery via sea water through your AC equipment grounding lead (safety green). Now assume the fault is high resistance - so maybe 5 volts pass through the motor. This situation consumes the zinc anode rapidly and when it is gone the propeller shaft assembly components are next. The ingredients in process are just like galvanic corrosion but the electrical potential involved is above 1.2 volts - and so we call it stray current corrosion.
Better than my explanation - and if this interests you - here is some bedside reading
https://www.navegandoconmarconi.info/cap/corrosion.galvanica/attachments/MDY 08.pdf
Charles
Now instead imagine a battery connected to an alternator that has fault such that DC current passes via this fault to the motor then to the shaft then returns to the battery via sea water through your AC equipment grounding lead (safety green). Now assume the fault is high resistance - so maybe 5 volts pass through the motor. This situation consumes the zinc anode rapidly and when it is gone the propeller shaft assembly components are next. The ingredients in process are just like galvanic corrosion but the electrical potential involved is above 1.2 volts - and so we call it stray current corrosion.
Better than my explanation - and if this interests you - here is some bedside reading
https://www.navegandoconmarconi.info/cap/corrosion.galvanica/attachments/MDY 08.pdf
Charles
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