Hi!

Iḿ building now a 73" tug and have very much space in the hull.
the electrical question I have are as follow:

Is it possible to use power from main engine battery pack while its charging from a onboard generator? Using a 12V netfeed charger to charge the leadbatteries.

Taking power from a nitroengine running a generator @12V

Thanksfor any help!

You would need some sort of regulator , but i do know someone that
runs a gas engine in his tug to supply electric power for the boat.

Like Umi says, with appropriate regulation, no problem.  I would just add that suppression is vital as well.  Telephone systems have been working like this for many, many years.

Okej, how would a regulator look like or make one?

Oh my Lord!
Save yourself a whole lot of trouble and use the space for more battery capacity.
You are going to need a lot of ballast anyway.

Perhaps a regulator that is tyically used in an automobile could be used?

A boat that big can take a 12-volt deep-cycle battery and run almost all day long. You're going to need the weight for ballast anyway so why not usable weight? I've seen smaller tugs that used one and rode at the waterline so I know that you'd need more weight than what one of those provide.

Basically, I go along with the bigger battery school of thought, but in the interests of pushing the boundary a bit - what were you thinking of using for a generator?  If it is a mains electricity type (eek!), then a battery charger for your type of battery will do the job.  If it has an auto-mobile type alternator, it might well have the regulator built in.  The normal rules for charging lead acid apply, voltage limiting to avoid over charging, and current limited to the maximum that the battery allows.  It assumes that if the motor wants more than the charger can give, the battery makes up the difference until the demand is removed, when the alternator recharges the battery.

so awesome!