Question on battery fixes

[Rich]

I just purchased a 1988 ComPac 27 and am working through the list of recommendations from the boat surveyor.  Since I'm new to boats with engines, I'd like advice on the below two items.  A marine company I'm working with says this work will take 3-4 hours at $100/hour.  Are these two items needed and worth this expense?

--Install over-current protection in positive battery cables from each battery cable going to disconnect
switch in the form of slow blow fuse rated for wire gauge. All other wires should be taking off of buss
bar aft of disconnect switch.
--Install terminal protection for unprotected positive terminals for both batteries and on alternator and
starter motor.

Thanks
Rich

[BobK]

Rich,

I understand the safety implications for the work the surveyor suggested having done ---However -

Over current protection is nothing I have had on my current 1988 CP 27 or any boat I have had prior to this one.  I rely on the fuses or circuit breakers that protect each of the circuits that draw current from the battery's.  The addition of a bus bar is something you can do easily. There are many utube videos and books available for 12 volt wiring.

The terminal protection (rubber boots) for the batteries and starter motor and alternator are available at any auto parts store.  Again with the location of the batteries under the step and knowledge of where the terminals are on both the alternator and starter plus knowing it is a diesel not gas engine my boat again has neither.  I have been sailing for 60+ years and have never had a problem due to shorting the electrical system,

BobK

[kevin27]

The new fuse is to protect you from a dead short of a battery cable. Blue Seas 5191 MRBF terminal block is easy to add, 90A would be the fuse value to use for 105 deg C #4 AWG but I don't know the temperature rating of your cable. House loads are probably supplied by a wire off of the battery switch which probably doesn't have protection though. Starter will pull way more than 90A, probably something like 250A but only for a couple of seconds, see time/current curve here:

https://www.bluesea.com/products/5182/MRBF_Terminal_Fuse_-_90A

If you can find the right fuse value for your cable temperature rating and your starter will cooperate, these are just bolt on parts that will likely work fine with your current lug sizes. If the starter blows the biggest fuse that protects your cable, you have a problem because you may only protect battery #2 but sooner or later, you're going to start on #2 by accident.

[NateD]

As the other posters have said, pretty straight forward to add rubber boots to terminals/alternator/starter and to get some fuses on those wires.

To BobK's point, the odds of one of these drawing enough current to overheat and start a fire is pretty low, but I think it is worth doing. If the nuts that hold the positive cables onto the alternator or starter were to work their way loose and the hot cable fell off and laid on the block or some other ground, they would overheat and likely start a fire. On my CP23 the starter wire got caught in the adjustable motor mount when I was lowering it once and shorted out the cable. It's amazing how fast the insulation starts melting.

Personally I'm cheap and pretty competent with DIY, so I wouldn't pay $300-$400 for that, but stuff always takes longer than I think. It's worth doing eventually, but I wouldn't make it a priority if there are other safety related things to repair/improve.

[Rich]

Many thanks to all for your advice.  I will put on the to do list once I become more comfortable doing such work myself.  My main take-away is I don't need to spend $300-400 to have it done!

[wes]

I'll add that fusing the battery cables near the battery wasn't a standard practice back in the 1980s and 1990s when most of the CP 27s were built. The ABYC has added this requirement in recent years because so many boat fires start in this area. It's a good idea. ABYC requires the fuses be located no further than 7" from the battery, but in practice this can be difficult to achieve. Just get them as close as you can. The most challenging issue is borrowing or buying a proper crimp tool and lugs for the bug 6 ga. battery cables. If you don't want to bother, you could properly measure what you need and have a well equipped boatyard or marine electrician make the cables for you.

Wes

[moonlight]

The 7" rule can be extended if you shield the cable in a protective sleeve to eventual overcurrent protection.

Starter cables are exempt due to their high loads albeit for short periods of time; fusing just doesn't work.  Shield them if you can as well.

The "post caps" are a "dropped tool preventer". 

I once had a Group 27 battery in the back of GMC Yukon.  And a pile of tools next to it.  Drove MILES with no problem.  Turned onto a friends rutted and potholed driveway ... and looked in the mirror to watch the spark show.  A hacksaw slipped off the top of the tool pile and connected both terminals.  The hacksaw blade burnt clean through like a fuse, disconnecting the "circuit".

But not before melting the cap on the can of WD-40 standing by the battery.

And igniting those contents in a vicious fireball.

You know, I pulled in the middle of the field, away from any structures, opened the back of the Yukon, and pitched that WD-40 can still flaming farther than I've ever thrown anything else before or since.

Except maybe that Group 27 battery, which, in the presence of the flaming WD-40, burned a hole in the battery case and the plastic was burning too.  I threw that battery a good ways in the opposite direction.

My friend operated a B&B at that place.  Real nice place.  It was 9AM, just after breakfast service.  When I walked in the door, they asked "Hey Dave, want some breakfast?"  I just showed them my outstretched, upright hand as I rounded the bar... after a couple quick shots, then I rested upon the bar top and relayed the story!  Then went to clean up the yard.