"So are you saying these alt. are not regulated?"
No, I'm saying something quite the opposite. A 1-wire "generator" or "integral alternator" (the names change every few years) is fully internally regulated. BUT. That regulation is accomplished by taking the output voltage sensing wire, and connecting it directly to the output terminal IN the alternator itself.
This means that the alternator will be very precisely regulated--but it will also substantially ignore the external load and the external voltage drops and the battery condition. And, you often will need to goose the engine (i.e. to 2000 rpm
for a few seconds) to make the alternator turn on, as the excite circuit also is tied back internally. If you just start to idle speed--it may not turn on for quite some time.
It is a great way to make a robust, simple, cheap
circuit. It is not a very nice way to treat your batteries, or optimize your run time, or much of anything else. That's why it is relegated to some industrial, off-road, and cheap
On boats that were set up with two batteries form the factory, it can make sense because two batteries require TWO sense leads and a means of switching them, and instead of running one or two sense leads all the way to the battery compartment, the builder
just ties the sense lead back to the output lead on the "side" of the engine someplace, i.e. at the starter connection, effectively knee-capping a 3-wire system and making it into a 1-wire anyway.
You could certainly break out the wiring on a 1-wire, or bypass the internal regulator and add an external. And Blamar and all will gladly show you how to fit an external regulator that can be switched in/out so the internal one can be used if the external one fails.
But no, I wouldn't use a 1-wire to start with, there's just no excuse for it in this application.
There are many ways to design a charging system, and drawbacks to many of them. For instance, if you read the Delco specs, some of the new alternators have avalanche diodes in them to clamp spikes to 40VDC. A great idea, to protect electronics
from the normal spikes caused by alternators and starters, right?
Well...yeah, but those are consumable parts
(the avalanche diodes) and what happens next is that when they DO fail, the alternator fails. Pick an alternator that's older and cruder and doesn't have them--and it just can't fail that way. (The spikes remain a separate issue but at least the alternator doesn't fail that way.)
ALL conventional internally regulated alternators are designed mainly for car use. That is, to provide one brief shot of high power to make up for what the starter consumed, and then to run all day without overcharging the battery! They are not designed to recharge deep cycle batteries, they are designed to "not cause damage from overcharging".
So unless you match up charing systems and battery capabilities very neatly...an external regulator (which IS usually set up to provide bulk charging for longer periods and IS often programmable to optimize what it does) can cut your run time dramatically. Worth the money
, if you plan to really be using the boat, and the batteries, more extensively.
And personally, I hate lugging batteries, I'd rather lug them fewer times, even if replacing them was free! Every time I get near a wet cell battery, it winds up costing me some piece of clothing
from acid damage. Or the carpet in the car. Or something.