Electrical grounding strip for flexible shaft coupling

[Kite Runner]

I'm installing an R & D flexible shaft coupling to a Yanmar 3MY30 on my 2009 Hunter 36. My question...has anyone else out there installed this item on a newer Hunter such as my 36 and does it require the installation of the electrical grounding strip? I have like most, the galvanic isolator system and I figure if I'm correct, that without the connector the isolator cant do anybody good for the prop shaft and prop. Any input on this install is appreciated.

 

[chuckwayne]

you definitely want the grounding strap. measure carefully how much clearance you have between the stuffing box and the motor flange on the shaft. We have essentially the same setup on our 356-3GM30- and we shortened the stuffing box hose for more clearance- you need to be able to remove the nut to restuff the box.
Well worth the effort, runs really smooth, much less vibration

 

[Bill Roosa]

Without the grounding strap you have effectively isolated your shaft and prop from the rest of the boat. Put a zinc on the shaft and your protected.
Course none of the rest of the boat is protected by that zinc so you would want to consider how you are going to do that.
Additionally, if you put a static grounding strap (rotates with the shaft) you will be effectively grounding the boat through the motor bearings. While a lot of boats have this setup it is not a great idea. A strap that attaches to the transmission case and has a carbon brush (like an alternator rotor brush on a slip ring) that contacts the shaft is a better setup. Think about the path lightning takes to ground and you can see that you could get some welding of the bearings with a static grounding strap.
FWIW

 

[Kite Runner]

Without the grounding strap you have effectively isolated your shaft and prop from the rest of the boat. Put a zinc on the shaft and your protected.
Course none of the rest of the boat is protected by that zinc so you would want to consider how you are going to do that.
Additionally, if you put a static grounding strap (rotates with the shaft) you will be effectively grounding the boat through the motor bearings. While a lot of boats have this setup it is not a great idea. A strap that attaches to the transmission case and has a carbon brush (like an alternator rotor brush on a slip ring) that contacts the shaft is a better setup. Think about the path lightning takes to ground and you can see that you could get some welding of the bearings with a static grounding strap.
FWIW

Thanks for your input!
Gord

 

[Kite Runner]

you definitely want the grounding strap. measure carefully how much clearance you have between the stuffing box and the motor flange on the shaft. We have essentially the same setup on our 356-3GM30- and we shortened the stuffing box hose for more clearance- you need to be able to remove the nut to restuff the box.
Well worth the effort, runs really smooth, much less vibration

Thanks for your input!
Gord

 

[Maine Sail]

Without the grounding strap you have effectively isolated your shaft and prop from the rest of the boat. Put a zinc on the shaft and your protected.
Course none of the rest of the boat is protected by that zinc so you would want to consider how you are going to do that.
Additionally, if you put a static grounding strap (rotates with the shaft) you will be effectively grounding the boat through the motor bearings. While a lot of boats have this setup it is not a great idea. A strap that attaches to the transmission case and has a carbon brush (like an alternator rotor brush on a slip ring) that contacts the shaft is a better setup. Think about the path lightning takes to ground and you can see that you could get some welding of the bearings with a static grounding strap.
FWIW

The engine, on perhaps 90+% of the boats in the water is the main ground point. The ABYC refers to the engine as the "ship ground".

I've never heard of nor seen engine bearings welded by lightning on a sailboat? Do you have any references to this? I don't doubt that it could happen but decoupling the shaft won't necessarily prevent lightning from getting to the engine, and could actually make it worse by changing from a low resistance path to earth vs. a high resistance path? I've seen lots of boats hit by lightning, including my own, and even alternators fried, including my own, but never welded bearings or engine damage beyond electric items.... Our strike was over 25K in damage and the engine was perfect and is the "ship ground"...

Even if you decouple the shaft from the engine, which goes against accepted ABYC safety standards, your engine still has a path to ground via the electrolyte it is filled with, though at a higher resistance. It is still also connected to the ships neg buss via the need for the starter and alternator to have a path back to the battery.. The battery neg is connected to the ships grounding/bonding buss so no matter what your engine is still connected to the electrics and engine & ships earthing system.

If the boat is properly wired the mast & rigging will be bonded to the keel and this should absorb the brunt of the strike if it hits the mast or rigging.

I believe PYI offers a grounding kit for the flexible coupling they sell.

 

[Charles Erwin]

Maine Sail

You mention isolation of the shaft deprives the boat of a path to seawater (thus ground) and that shaft isolation means ABYC rules are transgressed. Seems to me that where the shaft is isolated ABCY rules could be complied with through other means.

Can you comment on the following proposition:

Assume the shaft is isolated - and that one is not willing to jumper or use a shaft brush. Can one provide path to seawater (thus ground) via a Dynaplate. That is -- AC safety green, DC ground, radar ground, DC charger ground, and motor block to DynaPlate?

Charles

 

[Don12364]

Gordon,
Since the flex coupling will occupy more length than normal, this is your opportunity to install a rope cutter at the other end of the shaft - as I did.
Just make sure your prop clears the rudder if it is a folding type - as I did not on a previous boat.
There I was, between tides, icy water up to my waist and rising whilst I frantically tried to saw and file 1/4" off the prop tips. Amazing how hard that alum bronze is they make props out of
Didn't make it - drat!

 

[Maine Sail]

Maine Sail

You mention isolation of the shaft deprives the boat of a path to seawater (thus ground) and that shaft isolation means ABYC rules are transgressed. Seems to me that where the shaft is isolated ABCY rules could be complied with through other means.

Can you comment on the following proposition:

Assume the shaft is isolated - and that one is not willing to jumper or use a shaft brush. Can one provide path to seawater (thus ground) via a Dynaplate. That is -- AC safety green, DC ground, radar ground, DC charger ground, and motor block to DynaPlate?

Charles

A submersed copper strip is a better approach or an external lead or iron keel that has not been barrier coated. Dynaplates have been known to explode from a lightning strike, I've seen one. It compromised the hull integrity when it did and the boat was slowly leaking.

Dynaplates are syntered or porous bronze (think of a rice cake) and they use entrapped water in the little chunks of bronze to increase grounding surface area. This works great for SSB radios. When hit by lightning the water entrapped in the "rice cake" or porosity flashes to steam and can literally blast the bronze plate apart. Dyna plates can also cause some added drag in addition to that of the engine drive line..

This is a ground plate that also serves as the ships lightning ground. It is 1/4" X 2" copper about 7-8 feet long.

 

[Charles Erwin]

Gentlemen

The original question did not concern itself with those 90% of boats that do not have shaft isolation. The question concerns the other 10%. In addition, the original question did not ask advice concerning lightning suppression.

The original question involves how one meets the ABYC safety/ground rules - in those cases where the shaft is isolated from the transmission/motor.

With such an isolated shaft there is no (efficient - low resistance) path to ground. Thus- for example - AC safety green cannot shunt an AC short via the safety green - through seawater - and back to shore ground.

Lightning rules aside - the question seems to be - whether the ABYC safety rules are met if AC green (as well as other grounding) are connected to sea water/ground via a DynaPlate - in cases where the shaft is electrically isolated from the motor block.

 

[Maine Sail]

Gentlemen

The original question did not concern itself with those 90% of boats that do not have shaft isolation. The question concerns the other 10%. In addition, the original question did not ask advice concerning lightning suppression.

Unless your lightning bonding is 100% isolated from the ships ground then you can't effectively answer one question without the other. It can be quite difficult to 100% isolate the lightning protection from the ships ground but it can be done.

The original question involves how one meets the ABYC safety/ground rules - in those cases where the shaft is isolated from the transmission/motor.

Technically, you don't meet ABYC, if you have a "ship ground", which you'd need if you had an on board AC system.. Small boats can run "isolated ground" systems where the battery is the ship / system ground but only in a DC boat..


"11.16.1 DC Grounding

If a DC grounding system is installed, the DC grounding conductor shall be used to connect metallic non-current-carrying parts of those direct current devices identified in 11.15.2.1 to the engine negative terminal or its bus for the purpose of minimizing stray current corrosion and ensuring a fault current path in the event of a short circuit."



There is also no way to "isolate the shaft" and meet ABYC standards.


"6.5.5.2

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

Lightning rules aside - the question seems to be - whether the ABYC safety rules are met if AC green (as well as other grounding) are connected to sea water/ground via a DynaPlate - in cases where the shaft is electrically isolated from the motor block.

The short answer, as taken from the standards, is no because you can not "electrically isolate" the shaft and still be ABYC compliant. The ABYC also considers the engine as the only ship ground referenced in the standards.

Of course as a private boat owner you can always do what ever you want on your boat until you need an insurance survey..

A Dynaplate is better than no ground at all but I would not personally wire one so that it was tied in with the ships lightning bonding, but, some people do.