My motor is the Elco motor w 6 deka 8D AGM glass matte wet cell batteries.
Here's the vision: I'm cruising in choppy swells & I'm 30 minutes away from my destination but my batteries are low cuz of rough seas. The portable generator will charge my batteries as I'm cruising to avoid running out of power before I can get to my destination. It's just an extra charge, just in case I run low.
If you're not too far into it... you might investigate a big bank of 6V deep cycle golf cart batteries, instead of 12V 8D batteries.
A single Lifeline 8D (for example) will give you approx. 255 Ah. A bank of 6 will give you approx. 1530 Ah. (Many manufacturers spec that at closer to 245 Ah for an 8D, or 1470 Ah for a bank of 6.)
A pair of 6V GCs will give you at least 220 Ah, but taller versions can get you to 300 or even 400 Ah per pair. You should be able to fit at least 6 pairs of GCs in the same space as 6 8Ds... so with taller GCs you could get to 1800 or 2400 Ah in the same footprint.
Two additional advantages: each individual 6V battery weighs less than an 8D, so you can dispense with some of the labor (maybe one less hulk, and you won't need the mule and the small boy)... and golf cart batteries are a true deep cycle design, unlike many of the 8Ds (although I think the Lifeline 8Ds are spec'd as "deep cycle").
Check here for comparisons:
Lifeline Batteries - Marine & RV Deep Cycle Batteries
The golf cart batteries are the GPL-4CT (220 Ah/pair), 6CT (300 Ah), and L16T (400 Ah).
The portable generator is a fair enough idea, although as far as I know the only manageable
portable products -- for your purposes -- are like the small Honda and Yamaha gasoline models. (Refilling a small-ish gasoline tank while sloshing around in rough seas could be an issue... There is a way to run these on propane, should that interest you.)
Anyway, they convert energy from gas to electricity. Unlike a battery pack as used for emergency auto starting; those simply bring some additional pre-stored electricity to the scene.
You may eventually want some solar, but probably can't get enough energy from that fast enough to make much difference in your "choppy seas" scenario. Might be very nice for recharging batteries at anchor, though.
-Chris