"You do not mention which boat
"You do not mention which boat, which size nor which year. (Is it safe to assume with twin 140's we're talking 26/28' or so????)
Many of the smaller twin engine boats offer the House Bank as being on the Stbd Engine side.
Don, I perform all types of marine electrical work..... along with the Volvo Penta work. I am very anal about it.
I also own a smaller 28 foot SDN F/B twin engine boat. So I am very familiar with the separation of Port/Stbd 12 volt systems.
I'll share this with you and for what it's worth.
What I like to see is this;
a) a dedicated Cranking Battery on your # 1 position of your MBSS (Main Battery Selector Switch) for each engine.
b) a <font color=""0000ff"">**group of batteries</font> for the House Bank of which would be on the # 2 position of the MBSS.... and typically (not exclusively) on the Stbd engine side!
c) occasionally the Stbd engine can share the Port engine cranking battery! (or visa-versa)
d) or..... have it's own dedicated Cranking type battery.
(*see note on combining)
<font color=""0000ff"">** (I might add that these should be "LIKE" batteries. I.E., Like in age, size, group, condition, etc... best to not mix them for charging reasons!)</font>
IMO, it is preferable to use "cranking" or "starting" type batteries on your # 1 MBSS position (the selection for cranking your engines).
House Banks (# 2 MBSS) are preferable if Deep Cycle's are used!
Whether Port or Stbd:
**Your MBSS position #1 is typically a single cranking battery..... (# 1 = one battery.... an easy way to remember)
**Your MBSS position #2 is typically a multiple bank........ (# 2 = two or more batteries.... an easy way to remember)
That being said...... on my own 28 footer, I have twin 5.7L's
My Stbd engine has a large group of <font color=""aa00aa"">*** 6 volt golf cart</font> type batteries only......(no single cranking battery)
So I do not use the # 1 position on this MBSS!
I crank on that bank of multiple Deep Cycle Golf Cart batteries. (been doing this for years... no issues! Have buddies who also do this... no issues!)
My Port engine has a single dedicated "Cranking" type battery..... I crank Port engine on that bank.
*Combining:
I also have a very simple solenoid "Combining" system operated by the flip of a single momentary helm switch!
It is nothing more than a heavy duty solenoid switch that momentarily connects both "Common" terminals of the two MBSS's! Very simple!
If my House Bank were to be "Low" or "DOA" in the morning...... a flip of the switch... and WELLA..... it momentarily combines Port to Stbd banks and the Stbd engine has full 12 vdc to fire up on.
You can see that this provides a very reliable and inexpensive means of redundancy!
You definitely want redundancy!
(my further redundancy is a Kohler marine gen, of which has it's own cranking battery)
<font color=""aa00aa""> *** 6 volt golf cart</font> batteries are used in groups of 2 in "series" to create 12 volts, but for increased Amp Hours!
Amp Hours are what you want for your House Bank! "
