Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 28-05-2020, 09:37   #1
Registered User

Join Date: Nov 2015
Location: Arlington, VA
Posts: 93
DC system and flexible shaft coupling

I installed a flexible shaft coupling which essentially isolated my entire boat. I didn't realize this until I hauled the boat and the sacrificial prop-shaft zinc was 99% intact. Usually, it's about 60% after a normal season.



Do I need to buy a strap (or make one) to reconnect my engine to seawater via the prop shaft like it used to be?


Here are some considerations: I have only DC on my boat, no AC. None of the seacocks are bonded together - they are all isolated.



Essentially, I just have about 90AH of power for simple things like chartplotter, depth, nav lights and a 12v plug to charge my cell phone and bluetooth speaker. It's a closed system -from batteries / panel / electrical items / back to batteries.



What is the compelling reason to reconnect my system to the seawater? Can I just keep it like a car, which is totally isolated from the outside world?



My only concern is lightening grounding, but I think that's a whole separate issue and probably shouldn't be gounded through the engine out the shaft. I'm not sure how to crack that, because I have an encapsulated keel and I'm not liking the prospect of a massive copper bar and more things going through my fiberglass. But that may be the right answer for that. Anyway. Separate issue. (i think!)



What say you?
__________________

ArmySailor is offline   Reply With Quote
Old 28-05-2020, 10:46   #2
Registered User

Join Date: Apr 2020
Boat: Amel 53, Super Maramu
Posts: 430
Re: DC system and flexible shaft coupling

Ah... a subject (bonding) that generates almost as much smoke as anchors and guns...


Fully bonded boats work fine (mostly). Fully unbonded boats work fine (mostly). Boats that are partially bonded frequently have problems.

And you have discovered one of the problems with an unbonded boat... they are frequently partially bonded, if unintentionally so.

In your case, I would guess you have an engine that does not have an isolated ground, i.e.; the battery negative is permanently connected to the engine block. This is by far the most commmon, although not optimum, way of connecting an engine to battery power.

This means that your engine and driveshaft (and formally, your propeller) are effectively bonded to every piece of electrical gear aboard the boat through the battery negative cables. This can allow stray currents and accelerated zinc consumption. The more complex the boat, and the more electrical systems in contact with sea water, the more likely a problem is in this situation.

It sounds like you have a pretty simple boat, and not bonding should continue to work well for you. If you intend to keep your boat unbonded, I would keep the isolation of the prop that was created when you added the flexible coupling. You have effectively made your boat "less bonded" than it was before. Many people doing mechanical and electrical work on an unbonded boat go the opposite way by ignorance and accident.

If you DO bond your underwater metals, and rely on the shaft zinc to protect them from galvanic corrosion, then you MUST bridge the insulating gap in the prop shaft.
__________________

SVHarmonie is offline   Reply With Quote
Old 28-05-2020, 11:59   #3
Registered User

Join Date: Nov 2015
Location: Arlington, VA
Posts: 93
Re: DC system and flexible shaft coupling

Thank you for your reply! Yes, I've read a number of articles on it but it's never cut and dry, owing to the unique situations of each boat. This creates room for a lot of opinions, some based on fact, some not.



I'm not sure exactly how my engine is connected. I'll investigate that tomorrow.

I'm still thrown off as to why a battery would be connected to an engine block in the first place. Why isn't the engine treated as any other electrical need? Like a fan? Positive, negative, plug in, done. I think that's a piece of understanding I lack.



I did rip out all of the green wire on this boat because like you alluded to, it was dodgy and "half bonding" the boat. Some seacocks were connected, some chainplates were / were not, and some of those connections were just terrible.



So it's essentially a car now. I'd love to keep it that way.



I'm going to kick myself in the butt later if I eventually want AC...but so far if I need to use a powertool I just use a shore power cord and and a 110 adaptor with a built in GCFI thing in case I drop it in the water. It's fine for now.



Thanks again!
ArmySailor is offline   Reply With Quote
Old 28-05-2020, 12:23   #4
Registered User
 
Cheechako's Avatar

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 22,553
Re: DC system and flexible shaft coupling

I'm not sure you need to bond your engine, Your shaft zinc is for the prop and shaft is it not?
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard











Cheechako is offline   Reply With Quote
Old 28-05-2020, 12:57   #5
Registered User

Join Date: Nov 2019
Posts: 1,599
Re: DC system and flexible shaft coupling

Quote:
Originally Posted by ArmySailor View Post
I installed a flexible shaft coupling which essentially isolated my entire boat. I didn't realize this until I hauled the boat and the sacrificial prop-shaft zinc was 99% intact. Usually, it's about 60% after a normal season.



Do I need to buy a strap (or make one) to reconnect my engine to seawater via the prop shaft like it used to be?


Here are some considerations: I have only DC on my boat, no AC. None of the seacocks are bonded together - they are all isolated.



Essentially, I just have about 90AH of power for simple things like chartplotter, depth, nav lights and a 12v plug to charge my cell phone and bluetooth speaker. It's a closed system -from batteries / panel / electrical items / back to batteries.



What is the compelling reason to reconnect my system to the seawater? Can I just keep it like a car, which is totally isolated from the outside world?



My only concern is lightening grounding, but I think that's a whole separate issue and probably shouldn't be gounded through the engine out the shaft. I'm not sure how to crack that, because I have an encapsulated keel and I'm not liking the prospect of a massive copper bar and more things going through my fiberglass. But that may be the right answer for that. Anyway. Separate issue. (i think!)



What say you?
Your prop-shaft , regardless of flex coupling , makes a very poor , high resistance earth

The oil film , interrupting metal to metal contact in your transmission , is the issue

If you feel that you need to overcome this then you must use a prop shaft brush

These are not common on yachts , only ships

Expensive , high maintenance

If you feel that you must add your engine to your lightning protection earth grid , simply run a copper conductor from the engine block to a wet piece of metal....thru hull, keel ....
slug is online now   Reply With Quote
Old 29-05-2020, 12:02   #6
Registered User

Join Date: Sep 2013
Location: Alert Bay, Vancouver Island
Boat: 35ft classic ketch/yawl.
Posts: 1,807
Images: 4
Send a message via Skype™ to roland stockham
Re: DC system and flexible shaft coupling

The missing piece is the seawater intake. Seawater is a conductor so anytime the engine is running it is connected via it's intake. Electrolysis only occurs when you have dissimilar metals immersed in a conductor. In this case you may have a S/S shaft and bronze prop so you need a shaft zinc. All other sea-cocks are isolated and have the same metal unless you attached them with S/S bolts so they are fine. The engine has a rich variety of susceptible metals in the cooling system so is normally fitted with it's own zincs. Usually the indication of problems is either going through zincs to fast, they should last more than a season or no loss at all. If the zincs show no errosion they are either not working or not needed!
roland stockham is offline   Reply With Quote
Old 29-05-2020, 12:08   #7
Marine Service Provider
 
boatpoker's Avatar

Join Date: Nov 2008
Location: Whitby, Ontario or Bahamas
Boat: Benford 38 Fantail Cruiser
Posts: 4,186
Re: DC system and flexible shaft coupling

Quote:
Originally Posted by SVHarmonie View Post
Ah... a subject (bonding) that generates almost as much smoke as anchors and guns...


Fully bonded boats work fine (mostly). Fully unbonded boats work fine (mostly). Boats that are partially bonded frequently have problems.

And you have discovered one of the problems with an unbonded boat... they are frequently partially bonded, if unintentionally so.

In your case, I would guess you have an engine that does not have an isolated ground, i.e.; the battery negative is permanently connected to the engine block. This is by far the most commmon, although not optimum, way of connecting an engine to battery power.

This means that your engine and driveshaft (and formally, your propeller) are effectively bonded to every piece of electrical gear aboard the boat through the battery negative cables. This can allow stray currents and accelerated zinc consumption. The more complex the boat, and the more electrical systems in contact with sea water, the more likely a problem is in this situation.

It sounds like you have a pretty simple boat, and not bonding should continue to work well for you. If you intend to keep your boat unbonded, I would keep the isolation of the prop that was created when you added the flexible coupling. You have effectively made your boat "less bonded" than it was before. Many people doing mechanical and electrical work on an unbonded boat go the opposite way by ignorance and accident.

If you DO bond your underwater metals, and rely on the shaft zinc to protect them from galvanic corrosion, then you MUST bridge the insulating gap in the prop shaft.
As a Certified Marine Corrosion Analyst ...... this is a very common sense approach.

PS. No one trained in these matters will ever use the word "electrolysis" thats a different process that is irrelevant to boats.
__________________
That hysterical laughter you hear as you sail a way in your "new" boat ..... is the seller.
boatpoker is online now   Reply With Quote
Old 29-05-2020, 13:35   #8
Registered User

Join Date: Jan 2015
Location: SoCal
Boat: Formosa 30 ketch
Posts: 655
Re: DC system and flexible shaft coupling

As to isolating the engine from the battery negative:
Where are you going to find a starter motor with a floating ground?
I suppose you could use two relays, with one on the neg cable, but then how abut the alternator?
Sounds like a whole can of worms.
Bill Seal is online now   Reply With Quote
Old 29-05-2020, 15:58   #9
Registered User
 
Oceanride007's Avatar

Join Date: Jun 2013
Location: Gladstone Qld.
Boat: Custom Perry Passport 41, steel
Posts: 464
Re: DC system and flexible shaft coupling

If previously you used the shaft Zinc to protect some under water metals, and now due to this new coupling you have isolated that action from happening. Then something underwater is no longer being protected. Should not be using shaft zinc for that purpose anyway as its too small (Meant only to protect Prop and shaft from each other). A slip ring on ships is there to prevent arching across bearings, not your concern, and another thing to maintain).
.
Earthing of Engine got a mention here, yes I like the Amel method. I use a switch myself, You seem to like your car system. No can't agree suggest you do not want hull, engine, or skin fittings connected to Battery Negative.



I suggest you leave shaft Zinc alone, use another zinc, can have Anode that you can throw over when vessel stopped, connected on the inside to parts you intend to protect.
__________________
Oceanrider.
"The floggings will continue until morale improves"
Oceanride007 is offline   Reply With Quote
Old 30-05-2020, 04:44   #10
Registered User

Join Date: Nov 2015
Location: Arlington, VA
Posts: 93
Re: DC system and flexible shaft coupling

Quote:
Originally Posted by roland stockham View Post
The missing piece is the seawater intake. Seawater is a conductor so anytime the engine is running it is connected via it's intake. Electrolysis only occurs when you have dissimilar metals immersed in a conductor. In this case you may have a S/S shaft and bronze prop so you need a shaft zinc. All other sea-cocks are isolated and have the same metal unless you attached them with S/S bolts so they are fine. The engine has a rich variety of susceptible metals in the cooling system so is normally fitted with it's own zincs. Usually the indication of problems is either going through zincs to fast, they should last more than a season or no loss at all. If the zincs show no errosion they are either not working or not needed!

The cooling system has it's own zinc, in the heat exchanger. I change that once a season and it goes from 100% to about 50%. No issues or indications of anything out of the ordinary there. But I totally forgot about seawater contact with the engine.



It's almost as if there are two zincs completely separately protection isolated parts - one is the engine-cooling-seawater, the other is the zine on the prop shaft protecting the prop-shaft combo.
ArmySailor is offline   Reply With Quote
Old 30-05-2020, 16:27   #11
Registered User
 
Dougtiff's Avatar

Join Date: Jul 2015
Location: San Rafael, Ca.
Boat: Gaff rigged Ketch[Spray]37' on deck
Posts: 449
Re: DC system and flexible shaft coupling

Just a note regarding your worry about lighting protection, you can carry some chain that can be attached to the rigging wire, and hung in the water when necessary, I.E, attach when needed, not permanently attached.
Dougtiff is offline   Reply With Quote
Old 31-05-2020, 04:59   #12
Registered User

Join Date: Nov 2015
Location: Arlington, VA
Posts: 93
Re: DC system and flexible shaft coupling

Quote:
Originally Posted by Dougtiff View Post
Just a note regarding your worry about lighting protection, you can carry some chain that can be attached to the rigging wire, and hung in the water when necessary, I.E, attach when needed, not permanently attached.

I'm not sure that's the solution for me. That either means hanging chain over the side of my boat 24/7, when I'm not at the marina (because I can't rush over during a storm).


Or hanging chain over while out IN a storm, sailing. Neither of which appeal to me. Unless there was some kind of proven efficacy of that tactic. But it seems like a little witch-doctor-y to be honest.
ArmySailor is offline   Reply With Quote
Old 31-05-2020, 05:54   #13
Registered User

Join Date: Nov 2019
Posts: 1,599
Re: DC system and flexible shaft coupling

Quote:
Originally Posted by Bill Seal View Post
As to isolating the engine from the battery negative:
Where are you going to find a starter motor with a floating ground?
I suppose you could use two relays, with one on the neg cable, but then how abut the alternator?
Sounds like a whole can of worms.
No problem

Two pole ...isolated alternators , starters , engine sensors are widely available

Only glow plugs are single pole and this earth on engine condition only exists momentarily what preheat is used
Attached Thumbnails
Click image for larger version

Name:	08E2FAA9-4CA1-4D37-BFF5-EDA238C0369F.jpg
Views:	5
Size:	165.0 KB
ID:	216275  
__________________

slug is online now   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Shaft alignment with flexible coupling Wayfarer111 Engines and Propulsion Systems 26 09-10-2019 15:44
flexible shaft coupling for short shaft melemakani Propellers & Drive Systems 6 22-12-2015 06:16
DC ground with a flexible coupling on the drive shaft ReMetau Electrical: Batteries, Generators & Solar 10 25-01-2015 15:54
Prop Shaft Flexible Coupling Question bryan and wendy Propellers & Drive Systems 3 06-01-2011 15:45
Flexible Shaft Coupling SkiprJohn Propellers & Drive Systems 51 25-12-2006 07:39

Advertise Here


All times are GMT -7. The time now is 21:28.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.