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Old 01-04-2010, 01:04   #1
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See a Grown Man Cry - Corroded Prop !

Six months ago, this was a beautiful, factory overhauled Brunton Autoprop. Needless to say with a brand new zinc. When we had the boat lifted last week at Cowes for a quick scrub and changing one sea cock, this is what we found:

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The horror, the horror!

I had no idea the marina was so hot. I'm putting in a galvanic isolator, but that is a bit like closing the barn door after the cow's already long gone.

So what now? Can I just polish it out and hope for the best? Or will the metal be weakened and dangerous? Change blades? The whole prop? Your advice (and sympathy) will be much appreciated.
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Old 01-04-2010, 01:18   #2
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Some more dirty prop porn:

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Old 01-04-2010, 02:56   #3
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Horrible. Have you looked at your through hull fittings and shaft? As to repair, how deep are the pits, how much metal would you have to grind and polish away? Is it enough to risk the structural integrity? Check with the factory, there may be corrosion in the working parts.

P.
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Old 01-04-2010, 03:21   #4
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I have repaired a prop in similar condition - had to clean out the pits with a brass or bronze brush - then used Marinetex epoxy and filled cavities and then smoothed it of with 800 grit water proof paper. then anti fouled with Hemple's Oceanic, the pits were still OK after 6 months when prop was anti fouled again
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Old 01-04-2010, 04:23   #5
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Hard to tell for certain from a photo, but it looks like the ends of the blades are pink, a very bad sign. If you tap the prop with a small hammer or wrench does it go ting, ting or thunk, thunk. Start tapping close to the hub and work toward the tip of the blades and listen for a change in the sound. The damage usually starts at the tip of the blades and progresses towards the hub.

If the prop doesn't ring like a small bell then the prop has probably lost metal in the process and probably weakened. This of course is not a qualitative test and it might take a prop reconditioner to determine how bad it is.

You can try it like it is, but I wouldn't go far from home or rev the engine very high until I had run it a few times and built a bit of confidence. Other options, a prop shop can weld new tips on the blades if the base and hub are good. Or try to buy all new blades from Autoprop if that is possible.

Good luck
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Old 01-04-2010, 07:06   #6
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Oi, veh. Well I've put a hundred miles on since then, but mostly sailing. It motors normally, and I've had it up to near max revs, with no vibration or abnormal behavior. But I would not want to risk a blade disintegrating when I'm in the middle of a crash stop or difficult docking manuever.

I guess I'll need to show it to an expert (which will require another expensive haul-out). The metal is not deeply pitted; it's like there's this excrudesence of metal debris all over it. I was able to rub some of it off with my hands, and the metal underneath was fairly smooth.

The shaft and throughulls are fine. The hull anode (the boat is bonded) was heavily wasted, like 85%, but still had a decent mass of zinc left, so must have still been working; lot of good it did my prop.

All new blades from Brunton will cost a fortune, I am guessing. I suppose the prop itself must be near $10k, although I haven't been able to find any price lists.
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Old 01-04-2010, 07:25   #7
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DH, you might want to have a search on the MOA forums about bonding underwater fittings. Ours aren't, and although it's a personal decision I would cut them if they were on my boat.

Topics - Moody Owners Information Exchange

The GI would be good too. Is she moored at Swanick with shorepower permanently connected? we noticed a huge difference in anode loss when we moved from Moodys yard to "el cheapo Gosport mooring" with no shore power.

The best person I have found for prop repairs is Geoff in Aldershot, if its to far gone or you just want it polished. Old time served skilled engineer, been using him for a couple of decades. Doesn't have any staff as it's a one man band, but I couldn't tell which blade he replaced a 10p sized chunk of metal and it was my prop

Streamlined Propellers - for boat propellers, propeller repairs, rebushing, balancing, stainless propellers, racing propellers

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Old 01-04-2010, 07:41   #8
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DH, you might want to have a search on the MOA forums about bonding underwater fittings. Ours aren't, and although it's a personal decision I would cut them if they were on my boat.

Topics - Moody Owners Information Exchange

The GI would be good too. Is she moored at Swanick with shorepower permanently connected? we noticed a huge difference in anode loss when we moved from Moodys yard to "el cheapo Gosport mooring" with no shore power.

The best person I have found for prop repairs is Geoff in Aldershot, if its to far gone or you just want it polished. Old time served skilled engineer, been using him for a couple of decades. Doesn't have any staff as it's a one man band, but I couldn't tell which blade he replaced a 10p sized chunk of metal and it was my prop

Streamlined Propellers - for boat propellers, propeller repairs, rebushing, balancing, stainless propellers, racing propellers

Pete
Thank you for the useful leads!

Yes, the boat's at Swanick (we're very happy with the marina other than the high cost). Must be a very hot marina; we'll see if the galvanic isolater helps. I'm going to keep much closer tabs on my zincs going forward. I wish someone had warned me.

Obviously if you're not using shore power, you have a different situation entirely.

And it makes me think that there is something wrong about the idea of leaving a boat hooked up for weeks at a time when the only thing you're doing is trickle charging the batteries. Maybe I should put in some wind or solar and leave the shorepower disconnected. Or maybe the galvanic isolater will deal with it.

Actually, a neat gadget would be a timer you can set when you're off the boat, which will connect the shorepower for you just for an hour or two every other day to top off the batteries; leaving the boat disconnected at other times.
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Old 01-04-2010, 08:11   #9
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Thank you for the useful leads!

And it makes me think that there is something wrong about the idea of leaving a boat hooked up for weeks at a time when the only thing you're doing is trickle charging the batteries. Maybe I should put in some wind or solar and leave the shorepower disconnected. Or maybe the galvanic isolater will deal with it.

Actually, a neat gadget would be a timer you can set when you're off the boat, which will connect the shorepower for you just for an hour or two every other day to top off the batteries; leaving the boat disconnected at other times.
EXACTLY...for the reason you discovered and many others, I never stay plugged in just to charge batteries. Solar is easy..And you sure can't tell what mess the neighboring boats might be doing to the AC line. This past winter while connected, in-order to keep a heater powered, a neighboring boat's AC went haywire and caused all kinds of problems. It took out my battery charger. good luck
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Old 01-04-2010, 08:13   #10
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I think a nice solar panel would do the job and avoid the need to be permanently plugged in, particularly during the summer. I can understand the need during the winter for low powered heating etc.

We have just fitted a 45 watt panel but the weather is rubbish so can't really take any readings at the moment.

With shore power, our shaft anode didn't last the year, now without shore power it seems almost a shame to replace it because so much is left. The hull anode now just gets a polish with the angle grinder and a S/S wire brush attachment, which incidently also makes the bronze prop very shinney with a great smooth finish.

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Old 01-04-2010, 09:03   #11
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Dockhead: bite the bullet and install an isolation transformer, not a galvanic isolator. With a marina that hot, a galvanic isolator might not protect you at all. Good expensive ones will just sound an alarm telling you that they can't handle it (and those cost half the price of the transformer... or more)

I have posted many times about choosing the transformer option and have the idea many or most read it, smile and go on without. But everyone should understand that there are many posts concerning problems with boats that have either nothing or have a galvanic isolator (just last week one with galvanic isolator) but there never is a problem with a boat that has an isolation transformer. In an environment like yours, it will pay for itself quickly and that's not just because of the prop but just for zincs alone.

ciao!
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Old 01-04-2010, 09:04   #12
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Ah, and how about hiring a diver to remove the prop instead of hauling out?!

But I agree, remove it and present it to an expert.

cheers,
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Old 01-04-2010, 09:24   #13
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Dockhead: bite the bullet and install an isolation transformer, not a galvanic isolator. With a marina that hot, a galvanic isolator might not protect you at all. Good expensive ones will just sound an alarm telling you that they can't handle it (and those cost half the price of the transformer... or more)

I have posted many times about choosing the transformer option and have the idea many or most read it, smile and go on without. But everyone should understand that there are many posts concerning problems with boats that have either nothing or have a galvanic isolator (just last week one with galvanic isolator) but there never is a problem with a boat that has an isolation transformer. In an environment like yours, it will pay for itself quickly and that's not just because of the prop but just for zincs alone.

ciao!
Nick.
Hmm. Well, it wasn't just cost that bothered me about isolation transformers, but bulk and weight as well. Maybe easier just to unhook from shore power and let a solar panel keep up my engine start battery. I don't think my house banks will die because of a few weeks of no trickle charging.
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Old 01-04-2010, 10:20   #14
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I would start by unplugging now.

I just dont plug in anymore. I have never had any trouble from my gelcells. During the summer you could trickle charge with solar.

However this doesn't fix anything.

Jedi is right about the transformer thats the way to go.
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Old 01-04-2010, 10:26   #15
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A few weeks or, in case of gel or agm batteries even months without charge isn't a problem. My posts are always based on our situation which is living aboard and thus shore power when in a marina. I really should put that in my footer... I don't even have a footer yet... ;-)

Dockhead: on your boat, bulk & weight are no problem. The Victron 3.6kW isn't even that big or that heavy (uses modern toroidal transformer not the old tech)

But in any case, do not install a galvanic isolator instead.

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