Drivesaver - sharing bad advice?

Justin_NSA

Justin_NSA

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Jul 7, 2004
8,481
Hunter 30T Cheney, KS
Is this correct? Did I read it wrong? A PO of Bella had installed a Drivesaver and added a ground strap that rides on the shaft aft of the 'saver. and connects to the engine to deliberately maintain the ground path. These guys say they intentionally break the path.
https://www.gcsmarine.com/content/drivesavers/drivesavers

Prevents Electrolysis
DRIVESAVER® provides an impervious barrier that blocks electrical currents from the water to protect your engine and transmission from damaging electrolytic corrosion.

 
Gunni

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
...or you could just install and maintain a magnesium shaft collar anode to protect your drivetrain. That is how Beneteau does it.
 
Justin_NSA

Justin_NSA

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Jul 7, 2004
8,481
Hunter 30T Cheney, KS
Do the Beneteaus use a Drivesaver?
There is an anode on the shaft but I'm not sure of the material. All this work is just because I decided to install a dripless shaft seal. The shaft and new split coupling are in the shop getting fitted and faced. I may have to remove the Drivesaver temporarily so I can slide the shaft seal on and then still have room to tap the new coupling on. argh!
 
jssailem

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
22,877
CAL 35 Cruiser #21 moored EVERETT WA
Sounds interesting @Justin_NSA
As I have been want to believe, "electrolytic corrosion" is based on the exchange of electrons through metal in a water environ. The DriveSaver appears to isolate the metal shaft from the transmission/engine. The bonding strap reconnects that bond. Function is unclear. I would suspect that anodes on the shaft would still be advised as the issue of electrolytic corrosion could still be at play in the water (between submerged metal parts on your boat and surrounding metal parts from either other boats or mooring buoys/docks). Just not the electrical connection from the engine/transmission of your boat (assuming no bonding strap).
 
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D

dlochner

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Jan 11, 2014
12,782
Sabre 362 113 Fair Haven, NY
Justin_NSA said:
Do the Beneteaus use a Drivesaver?
There is an anode on the shaft but I'm not sure of the material. All this work is just because I decided to install a dripless shaft seal. The shaft and new split coupling are in the shop getting fitted and faced. I may have to remove the Drivesaver temporarily so I can slide the shaft seal on and then still have room to tap the new coupling on. argh!
Click to expand
If the anode is nice and new looking and its been on your boat in freshwater for a while, it is probably zinc.

Order a new magnesium or aluminum anode compare the weight of the new magnesium anode to the old one. The one that is much heavier is zinc. In the photo below, 3 anodes, zinc, aluminum, and magnesium all from the same freshwater boat. I don't know how old the zinc one is, the aluminum was on for 1 season, the magnesium for 2 seasons. The zinc was clearly not living up to its name, sacrificial anode.

IMG_0536 (1).jpg
 
Justin_NSA

Justin_NSA

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Jul 7, 2004
8,481
Hunter 30T Cheney, KS
Mine must be zinc. I'm unclear why the need to re-ground the engine to the isolated shaft. The electrical system is grounded to shore power.
 
jssailem

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
22,877
CAL 35 Cruiser #21 moored EVERETT WA
@Justin_NSA while your boat is properly grounded not all boats are necessarily so managed.
 
Charles Erwin

Charles Erwin

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Jan 30, 2012
1,140
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
In this case - the shaft brush is there for one reason and that is to comply with ABYC secondary grounding path requirements for AC grounding. If the normal Equipment Grounding Conductor (safety green in the shore power cord and the rest of the on board AC wiring too) fails there is a second path backup path that returns errant AC leaks back to the source - the marina transformer.

You can accomplish the same thing as a shaft brush. Connect a jumper wire (16 AWG is plenty) from the transmission flange,over the drivesaver, then to the shaft coupler flange. This is a better method because resistance at the brush-to- shaft contact is lousy and unreliable. Anyway - while breaking the connection between the motor and the shaft means no secondary AC safety grounding path it also means there is no return for DC stray current (DC negative and safety green are connected to each other on the boat.) So breaking the connection between shaft and motor - as some drivesaver manufacturers say to do - will help prevent stray current corrosion.

In any case if you have a drivesaver and no matter with or without a jumper or shaft brush - you need anode(s) (zinc or aluminum/magnesium in fresh water like Justin's case) on the shaft to protect the shaft and propeller from galvanic corrosion. A shaft brush or jumper will not have any effect on normal galvanic corrosion in the unbonded boat case.

Charles

p.s. Especially in a fresh water case - never defeat the electrical connection between shaft and motor. Also - skip the shaft brush and use a jumper instead.
 
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Justin_NSA

Justin_NSA

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Jul 7, 2004
8,481
Hunter 30T Cheney, KS
Cool! Thanks Charles. I did read their instructions some more. In a footnote they mention the jumper that you describe.

"If a bond is desired, use a piece of strip copper, punched for bolt size between offsetting inserts."
 
Gunni

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
Justin_NSA said:
Do the Beneteaus use a Drivesaver?
There is an anode on the shaft but I'm not sure of the material. All this work is just because I decided to install a dripless shaft seal.
Click to expand
No, Beneteau does not use the Drivesaver. Metal to metal contact at the shaft coupling. Make sure your shaft anode is magnesium and fully bonded to the shaft. You may also have an anode on your prop, that should also be magnesium. Not sure why you need a drivesaver, especially if it is giving you fits, 86 it and drive on.
 
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Maine Sail

Maine Sail

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Feb 6, 1998
11,701
Canadian Sailcraft 36T Casco Bay, ME
The standards are pretty clear on this..

"ABYC P-06
6.5.5.2 If a non-conductive flexible coupling is used, an alternative means of grounding the shaft must be provided."

It is always interesting when manufacturers can't even take a few minutes to read the standards let alone the fact that your engine already has seawater inside it, before they begin their "marketing spin"...
 
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chuckwayne

chuckwayne

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Mar 20, 2004
1,743
Hunter 356 and 216 Portland, ME
I've had a drivesaver on Escape for 15 years, with the grounding strap per ABYC regs, and shaft anodes (zinc). I've never seen any adverse symptoms.
 
NYSail

NYSail

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Jan 6, 2006
3,136
Beneteau 423 Mt. Sinai, NY
Gunni said:
No, Beneteau does not use the Drivesaver. Metal to metal contact at the shaft coupling. Make sure your shaft anode is magnesium and fully bonded to the shaft. You may also have an anode on your prop, that should also be magnesium. Not sure why you need a drivesaver, especially if it is giving you fits, 86 it and drive on.
Click to expand
Gunni why magnesium rather than zinc..... my boat came with zincs. And I don’t see in manual where it specifies magnesium or zinc. Also site that I had previously bought from (boatzinc.com) specifies magnesium is best in fresh water whereas zinc is best in salt.
Thanks!
 
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Hayden Watson

Hayden Watson

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Apr 5, 2009
3,102
Catalina '88 C30 tr/bs Oak Harbor, WA
The OP lists Cheney, KS as homeport. Magnesium is recommended for fresh water boats, aluminum for brackish and zinc for salt water. Most sailing in salt water can use aluminum anodes but just make sure that all anodes on the boat are the same material.
 
Justin_NSA

Justin_NSA

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Jul 7, 2004
8,481
Hunter 30T Cheney, KS
Thanks for the anode comments. Mine is off right now because I have the shaft out. We are in freshwater. It's a watershed reservoir so not the clearest water by far.
 
Gunni

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
NY, What Hayden said. I switched to aluminum anodes a few years ago because they are much more galvanically aggressive and don’t “salt” up with the corrosion byproduct zinc hydroxide. I found my zinc anodes were deactivating with a crust mid season and was concerned I wasn’t getting the protection I needed for my MaxProp. Still use zinc pencil anodes in my genset.
 
Hayden Watson

Hayden Watson

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Apr 5, 2009
3,102
Catalina '88 C30 tr/bs Oak Harbor, WA
Gunni, I read somewhere that all anodes should be the same material. Have you seen any change in anode loss with the zinc pencil and AL shaft?
 
Gunni

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
Hayden Watson said:
Gunni, I read somewhere that all anodes should be the same material. Have you seen any change in anode loss with the zinc pencil and AL shaft?
Click to expand
None. In fact the zinc anode in the genset heat exchanger wears out much quicker, probably because it is ridiculously small. Theory here seems to be that the aluminum anodes would protect it, they don’t seem to make any difference. The Genset connection to the drive train would be through the engine ground. Seems way removed.
 
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