Battery question

shemandr

shemandr

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Jan 1, 2006
7,586
Slickcraft 26 Sailfish
Hi
My 4d AGM's are toast. The boat is up on the Mystic River for repairs and is almost ready. For the trip back to Long Island, could I take a new group 24 or 27 wet cell cranking battery up by car and use it to start the engine (Yanmar 3GMF) for the trip home? I could then deal with replacing the 4d's with the Sam's Duracell brand at my regular slip, as I have been reading about. Would I be able to use the instruments (Speed, depth, GPS) while underway with the engine (35 Amp Alternator) with unduly running the battery down? Radar Scanner? Engineless while sailing? Other pitfalls? The 4d's would be disconnected and only the new cranking battery would be wired. Suggestions?
 
Don S/V ILLusion

Don S/V ILLusion

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Sep 25, 2008
7,435
Alden 50 Sarasota, Florida
You could but if you deplete the start battery while sailing sufficient to not be able to crank the engine, hope for a favorable breeze for docking.

A very rough "guesstimate" of your chances could be made by subtracting the amps expected to be used for the duration of the trip from the CCA rating of the start battery to see if there is any margin left for starting.
 
petersea

petersea

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Sep 26, 2008
566
- - Noank CT.
I would just replace all batteries be for the trip and be done with it. Especially if the new wet cell battery is just for this trip only.That being said you should be able to get away with a new battery for the trip. Should not be a problem with or with out the engine running. As I recall it is not that long a trip and you most likely will need to run engine a good part of it anyway. Make sure your sea tow or boats us towing package is up to-date and may want to consider having one of those emergency battery pack/jumpers with you. Also in a pinch a low battery will spin the 3GM over with the compression levers open and close the compression release with the engine still spinning to start the engine. In an extreme case you could hand crank that engine ! (I have never done this but in theory it can be done) Good Luck !
 
Rich Stidger

Rich Stidger

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Feb 10, 2004
4,134
Hunter 40.5 Warwick, RI
Starting-type batteries DO NOT like to be deeply discharged. Taking a starting battery to near flat will reduce it's life by many months. Do it 5-6 times and you have a worthless battery.

If you limit your discharge to maybe 20% at most and recharge as soon as you can you can minimize the damage.

Instruments, GPS, and VHF will probably draw only 3A or less. Eight hours would be 24Ah or about 25% of your battery capacity. Nav lights will take considerably more power. My Raymarine LCD radar pulls about 5A.

Do you have any use for this new battery once you reach home? Can you get to a Sam's near Mystic and get the batteries the you want now?
 
J

JohnShannon

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Jan 4, 2010
1,037
Farr 30 San Francisco
Yes, if your engine is running (which is what I read) then no problem, the instruments will use far less power than the alternator is putting out. So you will arrive at your destination with a battery more charged up then when you left.
 
catsailor

catsailor

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Jan 10, 2009
590
PDQ 32 Deale, MD
JohnShannon said:
Yes, if your engine is running (which is what I read) then no problem, the instruments will use far less power than the alternator is putting out. So you will arrive at your destination with a battery more charged up then when you left.
Click to expand
Just like driving a car. The instruments are little compared to headlights. But like a car, better lighten the load when the engine is off!

And yes, I've done this.
 
Stu Jackson

Stu Jackson

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Feb 26, 2004
23,047
Catalina 34 224 Maple Bay, BC, Canada
Rich & John are right. Gets to the heart of your issue. Go for it.
 
shemandr

shemandr

.
Jan 1, 2006
7,586
Slickcraft 26 Sailfish
Rich Stidger said:
Do you have any use for this new battery once you reach home? Can you get to a Sam's near Mystic and get the batteries the you want now?
Click to expand
It will become the new dedicated starting battery charged by the alternator and echo charger.
I considered a Sam's in CT. I think I'd rather do it at my slip. Getting the beasts on/off the boat will be a snap at the right tide. And, I'm going to wire them as one bank. I don't want to rush the job trying to depart. This doesn't come naturally to me and if my boat has to stay in the slip for a few days whilst I sort it out, it's no big deal.
 
seadaddler

seadaddler

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Dec 19, 2006
5,832
Hunter 36 Punta Gorda
Sure

I think I remember around 5 or 6 hours depending on weather, I have a start battery just for Radar and chartplotter and instruments with out a problem,I am sure you will need to motor part of the way or motor sail.
If wind is good and you do sail most of the trip just start the motor after 2 hours or so to play it safe and just run the Yanmar as needed.
Nick
 
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