Roger:

Yes, two deep cycle batteries should easily start a two cylinder Yanmar. But don't you want to separate the batteries so you can't run them both down at the same time? I am pretty sure that one deep cycle Group 27 will also start your Yanmar easily. So set up two deep cycle batteries; each on one side of a 1, 2, all, off switch so you can always have one battery fully topped off after sailing all day after using the house loads. You can then alternate your "house" and "starting" batteries to keep them equally charged up.

David
"Roger Long" wrote in message ...
Is there any reason to consider using dual purpose or a one starting, one deep cycle set up with a 20 hp Yanmar diesel? I would think the starting loads on the small engine are low enough that two deep cycle batteries would do fine.

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Roger Long