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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #11  
Old 05-03-2013
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Re: Electrical kill switch

"on a boat or a plane, redundancy is a good thing."

Perhaps you've never heard of the KISS principle.

Long distance aircraft used to have four engines, for redundancy. The accepted logic was that you might lose one engine, but three were still more than you needed. Except...

The thinking changed. Four engines means four major failure nodes and now you are 16x more likely to have a failure because they compound, they don't just add up. So now all the airliners use just TWO engines. One, and the minimum number of spares, to provide some extended glide time if one fails.

Same thing on a small boat. The more stuff you've got, the more stuff that finds a way to fail. Infest it with switches, and they will all corrode and wear. Even if you buy the really expensive waterproof and vaportight kind, and then there goes the budget.

Need to cut a power line in a hurry? No problem, one damage control axe can do all sorts of good work fast. (VBG)

You may notice, you don't see THOSE around very much anymore either, do you?

No, you let the battery primary fuse work, the power goes out before you could hit a switch, and then you just attend to the problem. KISS.
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  #12  
Old 05-08-2013
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Re: Electrical kill switch

Quote:
Originally Posted by Dog Ship View Post
The only thing I don't like about my set up is you can start the engine with the battery selector switch in it's off position.
It would be nice to have a night switch/kill switch somewhere so I can shut off the engines battery from inside the boat somewhere. Not being able to start the boats engine so easily would make it a little more secure.
ABYC requires a main switch on any battery with a CCA rating of 800 amps or more. (E11.7.1.2.1) Even with a smaller battery it would be foolish not to have one. It is also something a survey should flag.

Who installed the engine and left the wiring without a switch?

I would also fuse the start battery even though ABYC considers it optional on batteries dedicated to starting.
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  #13  
Old 05-08-2013
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Re: Electrical kill switch

Quote:
Originally Posted by mitiempo View Post
ABYC requires a main switch on any battery with a CCA rating of 800 amps or more. (E11.7.1.2.1) Even with a smaller battery it would be foolish not to have one. It is also something a survey should flag.

Who installed the engine and left the wiring without a switch?

I would also fuse the start battery even though ABYC considers it optional on batteries dedicated to starting.
Gartside Marine installed the engine in 2008.
There is no mention of this switch being required in a Ken Rorison survey that was done prior to purchase by the p/o in 2010. I'm not sure of the size of the battery but yah at 800 amps, a hundred amps one way or the other doesn't make much difference, it would still be the same issue.
Update: I just took a look at the old survey and athough it shows the new motor it only shows the boat having two batteries, not three. The third and dedicated engine battery is mounted beside the engine near the starter, accessed through the port side sheet locker.
I would probably have never known this was wired like this until one day I started the engine and then my wife yelled up to me, "Do you want the batteries turned on?" WTF
And may I add that here is a perfect situation of a tradesmen knowing his job and a surveyor not.
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Last edited by Dog Ship; 05-08-2013 at 09:16 AM.
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  #14  
Old 05-08-2013
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Re: Electrical kill switch

I'm not sure I would say the tradesman knew his job any better than the surveyor did. In theory when the main swtich is off, everything (except perhaps the automatic bilge switch) is OFF to make sure you can't blow yourself up from a spark, among other things.

With a third dedicated engine battery, installed with no consideration for the electrical controls, that's just been skipped because it would have been an extra complication and expense. In the least there should have been another battery switch added next to the house switch, i.e "START off/on....HOUSE off/a/both/b". No matter how they did it, it would have added materials and time to the job.

And if the same a/b type switch was used for the engine battery, the "b" position could be an emergency combiner adding it to the house/both position. Why? For emergency starting, or emergency radio power, etc. Easy enough while you're working there.
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Last edited by hellosailor; 05-08-2013 at 04:53 PM.
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