Question 1. What do you think of a double switch system and this wiring plan in general?
It is my opinion that the underlying problem with the traditional 1-2-Both-Off switches is that many, many, many
owners lack the operational discipline to properly position the multiple switches correctly. I know its hard to believe, but it is true
! Most vessels that I walk on to that are equipped with multiple battery selector switches have defaulted to leaving all of the switches in the Both or All position. I know that is also hard to believe, but it is very true
So, with this preamble, here is a response that I wrote yesterday to a similar question:
I typically do away with the traditional 1-2-both-off switches and install either simple on-off switches (Blue Sea 6006, 9003e or 3000) or remotely operated battery switches (Blue Sea ML7700) for battery isolation and to simplify the system.
Charging sources are generally connected to the house bank and the starting battery or batteries and the bow thruster and/or anchor windlass batteries are charged with either an ACR (Blue Sea 7610 or ML 7620) or a Balmar DuoCharge.
To continue with simplification of the system, the legacy split house bank system on older vessels is combined to become a single house bank. This philosophy, championed by Nigel Calder, has developed and matured over the last several years and is the generally accepted practice now.
I usually upgrade the connections to the batteries or their bus bars through a compact Blue Sea Marine Rated Battery Fuse (MRBF) that provides circuit protection as close to the source (the battery) as is physically possible. MRBF fuse holders are Blue Sea 5191 (single) or 2151 (double) and fuse are from 30A to 300A, have a 10,000A AIC are ignition protected and have an IP rating (susceptibility to water intrusion) that resists water jets.
The main issue I ran into when planning is that our engine came prewired with the starter and alternator connection on a single post on the motor.
This method is favored by production boat builders because it is easy, and less expensive than providing both a charging
path from the alternator and a source path to the starter. Generally the output conductor from the alternator is the bare minimum gauge and will have to be replaced when the alternator is upgraded. There is also the fine point that this arrangement leaves a lot of conductor that is unprotected by an overcurrent protection device (OCPD). To refresh memories, an OCPD is required by ABYC and ISO standards at the conductor's connection to a source. The only exception, for now, is engine starting circuits although some advocate the installation
of a high amperage Class T fuse in these circuits.
When faced with your arrangement, I generally split the two circuits. The alternator output is connected to the house bank via an MRBF and the starter is connected to the starting battery via one of the On/Off switches cited above.
is provided by using another On/Off switch between the house bank and the load side of the starter isolation switch. When emergency
starting is required, the starter isolation switch is turned Off, to disable to the starting battery circuit, and the emergency starting switch is turned On bringing starting current
to the starter without wasting energy attempting to charge the discharged starting battery.
Now, I will happily admit that my scheme has replaced two
, four position switches with three
On/Off switches and an ACR or DuoCharge, but the functionality and safety
of the overall system has been significantly enhanced.
Question 2. Our motor has a flexible shaft coupler that isn't metal and the boat has been grounded to a dynaplate. This was done by the PO and I've left it the same for now. Should I change this?
This is a difficult question. It is also a can of worms on a forum!
There may be legitimate reasons for "grounding" the boat to a dyna-plate, but very, very few and it is usually done for the wrong reason. I would suggest, in an attempt to keep this thread < 150 responses on the pros and cons of "grounding" the boat to the dynaplate, that you contact the previous owner and ask him why he did this.
In the meantime, technically, unless the dyna-plate was installed for some compelling, technically sound reason backed by science and engineering, you can bond the output shaft of the engine to the drive shaft with a jumper around the flex coupling. The engine, and thus the vessel ground, may or may not be electrically bonded to the drive shaft by this method because of inherent electrical
resistance in the transmission
Let the games begin!