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Old 30-09-2014, 20:01   #1
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Isolating Diesel Engine From Propellar

Hi,
I have a bad electrolisis problem on my steel sailboat , I have Hauled the boat to my yard to repair the damage (holes) and determine why the problem occured in the first place, my diesel engine was grounded to the hull , was this a mistake? I don`t have the isolating connection and bolt sleeves between shaft and and tranny, where could I get one of these? also should my aluminum mast be in contact with my steel hull?
I would also like to thank the people who replied to a previous post for help with this problem, BUT.......I can`tfind that place to thank them
So thank you in advance, you are all great people and very willing to help an old sailor with a problem (don`t do computers very well)

Ed Gushue, sailing Yawl "Estrellita IV "
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Old 01-10-2014, 09:37   #2
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Re: Isolating Diesel Engine From Propellar

To stop a steel boat from wasting away I suggest that you use an isolated ground electrical system. This way the engine is inert electrically and you wont have the problems that you are now having.

Stanley
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Old 03-10-2014, 21:42   #3
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Re: Isolating Diesel Engine From Propellar

Thank you Stanley,yes I have been told that is the thing to do,
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Old 05-10-2014, 04:22   #4
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Re: Isolating Diesel Engine From Propellar

I doubt that this on its own would cause your problem. Our engine is connected to the negative side of our electrical system and has been for over 20 years no problems.
When the boat is not being used, there are switches that isolate the battery at each pole.
I suppose you could use an above ground alternator and also connect the negative line to your starter through a relay but you will still have to replace the oil pressure and temp senders with isolated units if you can get them.
This should not be necessary if you find the current leakage that is causing the problem.

Regards,
Richard.
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Old 05-10-2014, 06:12   #5
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Re: Isolating Diesel Engine From Propellar

Aren't these usually shore power issues?
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Old 05-10-2014, 06:50   #6
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Re: Isolating Diesel Engine From Propellar

Thank You John for the reply, one "expert" told me that 99.9 per cent of the time on boats that he has investigated , the problem was on board,
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Old 05-10-2014, 08:09   #7
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Re: Isolating Diesel Engine From Propellar

Quote:
Originally Posted by roaminraulf View Post
Thank You John for the reply, one "expert" told me that 99.9 per cent of the time on boats that he has investigated , the problem was on board,
yes, the vessel's shore power arrangement. Do you have Calder's Mech/Elec book?
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Old 05-10-2014, 08:24   #8
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Re: Isolating Diesel Engine From Propellar

I also have a steel boat which has a negative floating DC supply . e.g. negative is not connected to sea water.

When we bought the the boat we had electrolysis problems (heat exchangers, propeller, shaft) that we spent a few years sorting out, mainly by rewiring carefully,

We ended up fitting carbon brushes to the prop shaft to ground it out, see Product Catalogue - Marine Cathodic Protection - MGDUFF

I also came across the following link whilst I was looking for the MgMacDuff thing

Grounding Shaft with a DriverSaver

Good luck
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Old 05-10-2014, 09:37   #9
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Re: Isolating Diesel Engine From Propellar

Do you connect to shore power when at the dock and if so do you have an isolation transformer between the shore power and your boat?
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Old 05-10-2014, 10:59   #10
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Re: Isolating Diesel Engine From Propellar

Quote:
Originally Posted by roaminraulf View Post
Hi,
I have a bad electrolisis problem on my steel sailboat , I have Hauled the boat to my yard to repair the damage (holes) and determine why the problem occured in the first place, my diesel engine was grounded to the hull , was this a mistake?
Yes...that is diffenately a mistake. You have essentially created a path from a D.C. negative (ground) to sea water and back to D.C. positive back through the sending units on the engine. the prop shaft is insolated by the cutlass bearing and the engine should be isolated vis the rubber isolatic mounts. So I am assuming you connected a cable from the engine to the hull. If so, remove it and ground the casting of the engine directly to the battery negative gang post. this will isolate the path. To check the system for other grounds to hull, you can put a volt meter from the hull itself to the positive terminal on the batteries. There should be no reading.

Quote:
Originally Posted by boden36 View Post
I doubt that this on its own would cause your problem. Our engine is connected to the negative side of our electrical system and has been for over 20 years no problems.
I am assuming the connection from the engine goes directly back to the negative battery and not through the hull.

Regards,
Richard.
Quote:
Originally Posted by Triumphant View Post
I also have a steel boat which has a negative floating DC supply . e.g. negative is not connected to sea water.
Exactly
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