Re: [Amel Yacht Owners] Re: Repower

sailormon <kimberlite@...>

Hi Kent,

Would you please send me a copy of the isolation schematics ?

Fair Winds


Kimberlite Amel Super Maramu #376




From: amelyachtowners@... [mailto:amelyachtowners@...]
Sent: Friday, June 26, 2015 2:10 PM
To: amelyachtowners@...
Subject: Re: [Amel Yacht Owners] Re: Repower



The 12v alternator that came on my Yanmar110 has a ground wire, but it is grounded to the block.  I think I will be able to use it.  The 24v alternator that was in the old Volvo is also an isolated ground, but has been grounded to the non-isolated Yanmar ground wire thus far.  Once I get the harness built, install the new switches, senders, and solenoids, both alternators and the senders will be grounded back to the negative on the battery side of the solenoid.  The solenoid will make the connection of the engine block to the negative battery post only when the engine is cranked or when the STOP button is pushed.  When the engine is stopped or running, the connection is interrupted by the solenoid.

It'll make more sense when I get the isolation schematics to you.

Good luck,




On Jun 26, 2015, at 12:53 PM, Steve Davis flyboyscd@... [amelyachtowners] <amelyachtowners@...> wrote:


Thanks Kent. You are a wealth of knowledge on this subject, and a great resource for the group. I'm curious, is your alternator an isolated ground alternator? Also, what gadget do you have to measure hull potential, as I need one. I will admit that your experience has scared me a bit. 


On another subject, do you happen to know the pitch marks for your max prop? I've got the same prop, and suspect I'll need to adjust the pitch for the higher revving Yanmar. 


Steve and Liz

Aloha SM72

On Jun 26, 2015, at 12:36, Kent Robertson karkauai@... [amelyachtowners] <amelyachtowners@...> wrote:


It's my understanding that it shouldn't cause a problem unless there is a fault in the engine's electrical system.  If there is, it can eat up your zincs almost overnight, then start working on the CDrive.

In my case I hauled out to paint the bottom, and discovered the prop zinc gone and rudder zincs almost gone.  While changing the prop shaft seals I discovered the shaft was about 1/3 eaten away as if a blow torch had been used on it.

I discovered a poorly installed charger/inverter that also had a fault, and poorly connected bonding system when I repowered with a Yanmar a few years ago.  I didn't understand the Amel grounding systems well enough at that time and the Yanmar was not isolated as Amel recommends.  I felt certain that the cause of my shaft problem was the charger/inverter and/or poorly bonded CDrive after re powering. 

 Isolating the new Yanmar is more complicated than it should be, and all hull potential readings were normal, so I elected to do the isolation later when I had all the necessary parts assembled.


After being back in the water only 5 weeks, I dove on the prop and discovered that the zincs were half gone.  This was in spite of all hull potential readings being in the "safe" range...but I never checked hull potential with the Yanmar or ONAN running.

When I get back to the boat next week, I expect to find a faulty alternator on the Yanmar.  If not, I'll let you know what I do find.  If that's what it is, the fault is grounded to the bonding system and would have destroyed my prop shaft again!

Before going back in the water I will have the Yanmar electrically isolated.

I will check hull potential monthly and weekly when on the dock with both the Yanmar and ONAN running,  the AC on, and the DC chargers running.

I won't stay connected to shore power unless I am on the boat.


I understand that the Amel system of isolating the bonding system from all AC and DC systems is what is done with metal-hulled boats, but can't confirm that.  It makes a lot more sense to me that that ABYC system of connecting all AC and DC systems to the bonding system.  It's another way that Capn Amel has good reason for designing his boats as he did.  Don't make changes without fully understanding why your boat is designed as it is.


More in a week or so!




On Jun 26, 2015, at 11:19 AM, Richard03801 richard03801@... [amelyachtowners] <amelyachtowners@...> wrote:


Take a look at posts Kent has on this site. Not isolating the engine will over a very short time cause a issues with the Amel drive and engine. The old saying an once of prevention.    

Fair Winds Smooth Sailing To All

Capt Richard 

RP Yacht Brokerage

Newport RI 

We list sell and service fine yachts including Amel's

Cell 603 767 5330

On Jun 26, 2015, at 07:51, alex.paquin@... [amelyachtowners] <amelyachtowners@...> wrote:


So what would be the consequences on not isolating the engine ´s negative on all electrical sensors, actuators and alternators?

Alex Paquin

Simpatico Hull 94

Older Maramu 1981

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