Starboard motor died

We have a 2009 350 Sundancer. Twin I/O Mercruisers 496 B3 AXIUS
The boat is typically plugged into shore power. Both motors fired up fine. We took the boat to a local harbor for dinner and decided to stay the night.
Since we didn’t have shore power that night, I thought it best to turn the batteries off at night. Next morning turned the batteries on and fired up both engines no problem.
About 30 min into our cruise we stopped the boat to take in the views about a mile offshore. As soon as the boat came to idle the starboard shut down. Tried to restart but would barely turn over seemed like the battery was dead. I turned on the generator thinking it would charge the battery.
After about 10 min the engine fired up. Then turned off the generator and decided to head back our marina. As I approached our slip and brought the rpm’s down to idle, the starboard motor died again. It wouldn't start even with the generator on this time. Btw, I’m not sure the generator even charges the engine batteries.
Needless to say, I was a mess docking with one engine.
Any thoughts on what my problem is? Hopefully it’s just a bad battery.
Thanks
Dave

I do not know your year/make/model detail, however the genny I would think powers up the battery charger, assuming you have the breaker switched to on at the panel. I would test the alternator first, or an easy test would be to switch the cables on the engine crank/starting batteries and see if the port engine then exhibits the same symptoms. If it does, replace the battery.

Pick up a volt meter and check battery/alternator output as well. It will become one of your best friends ;-)

mrsrobinson said:

I do not know your year/make/model detail, however the genny I would think powers up the battery charger, assuming you have the breaker switched to on at the panel. I would test the alternator first, or an easy test would be to switch the cables on the engine crank/starting batteries and see if the port engine then exhibits the same symptoms. If it does, replace the battery.

Pick up a volt meter and check battery/alternator output as well. It will become one of your best friends ;-)

Click to expand...

djcfo said:

We have a 2009 350 Sundancer. Twin I/O Mercruisers 496 B3 AXIUS
The boat is typically plugged into shore power. Both motors fired up fine. We took the boat to a local harbor for dinner and decided to stay the night.
Since we didn’t have shore power that night, I thought it best to turn the batteries off at night. Next morning turned the batteries on and fired up both engines no problem.
About 30 min into our cruise we stopped the boat to take in the views about a mile offshore. As soon as the boat came to idle the starboard shut down. Tried to restart but would barely turn over seemed like the battery was dead. I turned on the generator thinking it would charge the battery.
After about 10 min the engine fired up. Then turned off the generator and decided to head back our marina. As I approached our slip and brought the rpm’s down to idle, the starboard motor died again. It wouldn't start even with the generator on this time. Btw, I’m not sure the generator even charges the engine batteries.
Needless to say, I was a mess docking with one engine.
Any thoughts on what my problem is? Hopefully it’s just a bad battery.
Thanks
Dave

Click to expand...

Smartcraft will report an error/alarm (and deactivate the push button start) if any of your starting batteries are not up to the task of starting the engines. Since you didn’t have this occur, it seems like perhaps one or more bad cells that cause issues when under load (i.e. starting).

I have experienced this behavior of SmartCraft first-hand when I purposefully ran a battery down. Also, SmartCraft/VesselView will display each engines’ alternator output when running so you should easily be able to identify a failed alternator.

I’m not certain of your exact battery configuration but typically the generator will power the battery charger which will in turn charge your battery banks (including the starting batteries).

What is the age/type/size of your starting batteries?

The smartcraft/vessel View did show an amp alert.

We just bought the boat. I’ll check on battery types tonight.

Thank you so much!

If your batteries are lead acid with removable covers for each cell, check the water level and using a tester, each cell's condition.

A voltmeter just gives you part of the picture - a load test on the batteries rounds out the info.

I think the clue is the engines was running fine until brought down to idle. That, to me, indicates the alternator was probably charging and that the batteries for that engine are toast. Of course it could be a multitude of other things too.

I would have left the generator running after needing it to start the first time - but hindsight is 20-20.

Did you try to start with the Emergency start switch?