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14-12-2019, 09:49
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#16
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Commercial Member

Join Date: Dec 2008
Location: St. Petersburg, FL
Boat: Gulfstar Long Range Trawler; 53'; BearBoat
Posts: 1,607
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Re: Prop shaft bonding brushes?
@boatpoker Post #8
Thank you for these two articles. They highlight a very dangerous condition that every corrosion and electrical marine tech should be aware of as well as the boating public.
__________________
Charlie Johnson
ABYC Master Technician
JTB Marine Corporation
"The Devil is in the details and so is salvation."
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14-12-2019, 10:34
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#17
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Registered User
Join Date: Feb 2018
Posts: 5
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Re: Prop shaft bonding brushes?
Every thing is bonded together except two throu hulls. I use a piece of welding cable hanging on the shaft. It is connected to battery, and out to anodes. Since I put solar panels on my zincs have lasted four years, and before lasted about one year. Also, there was very little growth on my boat. I was shocked and so was the shipyard. I still had 50% of zinc left. I think solar panels made a very big difference.
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14-12-2019, 10:35
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#18
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Marine Service Provider
Join Date: Nov 2008
Location: Port Credit, Ontario or Bahamas
Boat: Benford 38 Fantail Cruiser
Posts: 7,579
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Re: Prop shaft bonding brushes?
Quote:
Originally Posted by Rorzech
I couldn't find out anything about 316 SS fittings and valves ! What wound their life expectancy be compared to bronze ?
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Stainless is not a good material for this application due to potential for crevice corrosion. Bronze or Marelon will outlast you and your grand kids.
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If you're not laughing, you're not doin' it right.
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14-12-2019, 10:36
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#19
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Registered User
Join Date: Feb 2016
Location: Canada
Boat: T37
Posts: 2,338
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Re: Prop shaft bonding brushes?
Quote:
Originally Posted by Rorzech
I couldn't find out anything about 316 SS fittings and valves ! What wound their life expectancy be compared to bronze ?
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Being less noble than most bronze alloys they have a shorter service life.
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14-12-2019, 10:37
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#20
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Marine Service Provider
Join Date: Nov 2008
Location: Port Credit, Ontario or Bahamas
Boat: Benford 38 Fantail Cruiser
Posts: 7,579
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Re: Prop shaft bonding brushes?
[QUOTE=YANDINA;3035863]that aren't as anal as you for blocking electrolysis.
./QUOTE]
What does hair removal have to do with it ?
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If you're not laughing, you're not doin' it right.
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14-12-2019, 10:39
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#21
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Moderator Emeritus

Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,348
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Re: Prop shaft bonding brushes?
So no one will explain the need for shaft brushes?
My shaft is electrically connected to the engine, which in my boat is the central if you will ground connection.
I can see some boats may have a non metallic flex coupling and that my require a jumper wire to maintain continuity, but why would anyone want brushes on their shaft?
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14-12-2019, 10:41
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#22
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Marine Service Provider
Join Date: Nov 2008
Location: Port Credit, Ontario or Bahamas
Boat: Benford 38 Fantail Cruiser
Posts: 7,579
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Re: Prop shaft bonding brushes?
Quote:
Originally Posted by tugboattom
Every thing is bonded together except two throu hulls. I use a piece of welding cable hanging on the shaft. It is connected to battery, and out to anodes. Since I put solar panels on my zincs have lasted four years, and before lasted about one year. Also, there was very little growth on my boat. I was shocked and so was the shipyard. I still had 50% of zinc left. I think solar panels made a very big difference.
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No anode can last 4 years unless it is not working at all i.e. incorrect material or no continuity.
Please explain how solar panels could possibly have any effect on anodes.
__________________
If you're not laughing, you're not doin' it right.
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14-12-2019, 10:52
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#23
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Moderator Emeritus

Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,348
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Prop shaft bonding brushes?
Quote:
Originally Posted by boatpoker
No anode can last 4 years unless it is not working at all i.e. incorrect material or no continuity.
Please explain how solar panels could possibly have any effect on anodes.
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Well I feel sure he was saying not being connected to shorepower has increased his anode life.
But I agree with you, unless it’s a ridiculously large anode, it’s not going to last for years, if it’s electrically connected.
I had one anode on my Mercury Verado that didn’t waste at all, until I took it off and scraped some paint away for it to be bonded with the rest of the engine, then it wasted just like the rest did, the Verado had multiple anodes.
But this brings up a thought, the anodes on my little outboard are aluminum and do waste away, which surprises me as It’s only in the water when we are actively moving the dinghy or it’s tied to a dinghy dock, the rest of the time the motor is tilted out of the water.
The dingy however is also aluminum, should it have some kind of anode, and if so what kind, magnesium?
I do have a depth finder in the dinghy powered by a rechargeable Lipo battery, but it has no ground connection to the dinghy. No other electrics, lights are battery powered and installed when necessary and are isolated by a lot of plastic.
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14-12-2019, 11:02
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#24
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Marine Service Provider
Join Date: Nov 2008
Location: Port Credit, Ontario or Bahamas
Boat: Benford 38 Fantail Cruiser
Posts: 7,579
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Re: Prop shaft bonding brushes?
Quote:
Originally Posted by a64pilot
Well I feel sure he was saying not being connected to shorepower has increased his anode life.
But I agree with you, unless it’s a ridiculously large anode, it’s not going to last for years, if it’s electrically connected.
I had one anode on my Mercury Verado they didn’t waste at all, until I took it off and scraped some paint away for it to be bonded with the rest of the engine.
But this brings up a thought, the anodes on my little outboard are aluminum and do waste away, which surprises me as It’s only in the water when we are actively moving the dinghy or it’s tied to a dinghy dock, the rest of the time the motor is tilted out of the water.
The dingy however is also aluminum, should it have some kind of anode, and if so what kind, magnesium?
I do have a depth finder in the dinghy powered by a rechargeable Lipo battery, but it has no ground connection to the dinghy. No other electrics, lights are battery powered and installed when necessary and are isolated by a lot of plastic.
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I believe it would depend on the motor mount. If there is absolutely no electrical connection between the dinghy and motor, there can be no galvanic cell. The ideal protection for aluminum in fresh or salt water is aluminum (actually an aluminum indium alloy).
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If you're not laughing, you're not doin' it right.
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14-12-2019, 11:35
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#25
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Moderator Emeritus

Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,348
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Re: Prop shaft bonding brushes?
Well there is electrical contact from the motor to the dinghy as of course the motor mount is aluminum and welded to the hull. there are plastic pads but the engine sits down on the aluminum hull.
AB dinghy.
I’ve wondered why the aluminum dinghies don’t seem to ever have an anode.
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14-12-2019, 14:28
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#26
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Commercial Member

Join Date: Dec 2008
Location: St. Petersburg, FL
Boat: Gulfstar Long Range Trawler; 53'; BearBoat
Posts: 1,607
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Re: Prop shaft bonding brushes?
@boatpoker #18: +1
@rbk #19: You have them reversed; bronze is more active (anodic) to passivated stainless steel (cathodic).
@boatpoker #20: +1
@a64 pilot #21: The only real necessity for a shaft brush is if there is no room on the propulsion shaft for an anode. The shaft brush will transfer cathodic protection current from the boat's CP system to the shaft.
The motor brush/phosphor bronze arm "shaft brush" is pretty inefficient for accomplishing this goal because the brush chatters on the shaft while underway and normal the normal passivation film that forms on most shaft materials acts as an insulator to the cathodic protection current with a potential of about 1.0VDC. If a shaft brush assembly is warranted, than the machined and silver plated apparatus with multiple spring loaded brushes does work well. Made by ElectroGuard. They are relatively expensive.
__________________
Charlie Johnson
ABYC Master Technician
JTB Marine Corporation
"The Devil is in the details and so is salvation."
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14-12-2019, 14:35
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#27
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Registered User
Join Date: Feb 2011
Location: Meandering about the Gulf of Alaska coast [NNE Pacific]— where the internet doesn't always shine... [Even Elon's...] Homeport: Wrangell Island
Boat: Nauticat 43 [S&S Staysail Ketch]
Posts: 1,796
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Re: Prop shaft bonding brushes?
Quote:
Originally Posted by a64pilot
So no one will explain the need for shaft brushes?
My shaft is electrically connected to the engine, which in my boat is the central if you will ground connection.
I can see some boats may have a non metallic flex coupling and that my require a jumper wire to maintain continuity, but why would anyone want brushes on their shaft?
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A64,
The reason I'm familiar with for installing a shaft brush is to reduce/eliminate any RF noise generated by the drive train.
I only had one boat [FRP Tayana 47 in salt water] come with a shaft brush installed [and I tested for continuity...] It didn't seem to make any difference whether connected or not to either RFI or (zinc) anode life.
Other boats may have different results.
Cheers! Bill
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SV Denali Rose
Learning every day- and sharing if I can.
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14-12-2019, 14:40
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#28
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Registered User
Join Date: Mar 2008
Location: On Barnegat Bay in NJ
Boat: Hunter 40.5 and C+C36
Posts: 241
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Re: Prop shaft bonding brushes?
I believe bonding of through hulls and the propeller shaft is just creating batteries eating away the metals. The only reason to have bonding is to have a controlled exit from the boat in the case of a lightning strike (I have had 2). Bonding to a lead or iron keel is much more effective. Another reason for bonding is creating a ground connection for a SSB radio. For this situation I use capacitors to each through hull to pass the RF and block DC currents. Lightning would blast through any capacitor. I especially don't want currents eating up the propeller. I install "shaft savers" which protects the transmission if you hit something; but, it also provides electrical isolation of the shaft and propeller from the engine and the remainder of the boat. I have never had any prop damage due to electrolysis. [I have found a better way to provide a SSB ground than the above. Contact me if interested.]
Jim
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14-12-2019, 14:47
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#29
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Marine Service Provider
Join Date: Nov 2008
Location: Port Credit, Ontario or Bahamas
Boat: Benford 38 Fantail Cruiser
Posts: 7,579
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Re: Prop shaft bonding brushes?
Quote:
Originally Posted by j.g.evans
I believe bonding of through hulls and the propeller shaft is just creating batteries eating away the metals. The only reason to have bonding is to have a controlled exit from the boat in the case of a lightning strike (I have had 2). Bonding to a lead or iron keel is much more effective. Another reason for bonding is creating a ground connection for a SSB radio. For this situation I use capacitors to each through hull to pass the RF and block DC currents. Lightning would blast through any capacitor. I especially don't want currents eating up the propeller. I install "shaft savers" which protects the transmission if you hit something; but, it also provides electrical isolation of the shaft and propeller from the engine and the remainder of the boat. I have never had any prop damage due to electrolysis. [I have found a better way to provide a SSB ground than the above. Contact me if interested.]
Jim
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1. Do you really believe an 8AWG wire can protect you from a lightning strike of up to 200,000amps travelling at 1/3 the speed of light. Bonding and lightning are unrelated.
2. Capacitor ? sure you don't mean diode ?
3. Electrolysis ? Never sure what someone means when they use this term as it is not applicable. Do you mean galvanic current or stray current ? No one trained in marine corrosion analysis will use the term "electrolysis".
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If you're not laughing, you're not doin' it right.
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14-12-2019, 16:15
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#30
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Senior Cruiser

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 51,756
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Re: Prop shaft bonding brushes?
A vessel bonding system electrically connects each of the submerged metal parts, allowing their individual electrochemical potential to be grounded via the circuit. The Shaft Grounding Strap is installed to provide an efficient, low-resistance, electrical connection between shafts and the bonding circuit (perhaps the engine block).
Propeller shafts really don't make a very good electrical connection to the rest of a boat's bonding system, since the propeller shaft is connected through the transmission (reverse gear) to the engine. Electrical continuity through the transmission is always poor, because they are interconnected via an oil-filled medium, and because oil is an insulator, such an interconnection cannot be considered electrically sound.
Hence, the shaft brush, cabled to the ground bus (or engine block).
FWIW: The bonding circuit should have a resistance of 1 Ohm, or less.
Most multimeters aren’t accurate below 1 ohm, and many can’t even measure accurately below 10 ohm.
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Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
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