Getting rid of alternator?

[capnorv]

I frequently turn off my alternator output when navigating passes to have the extra response and power from my auxillary. Granted I only have a 27 ton boat with an 80hp motor, but it helps. As a disclosure this is more noticeable after days at anchor where my 500 watts of solar can't keep up with the battery usage. It takes a long time to charge 1100 amp hours of battery.

[capnorv]

I once side towed a 17 ton full keeler 50 miles with my old 8hp yanmar in my 27 Newport. It wasn't fun and it wasn't fast, but we did it. Guess HP was different back then eh.

[sdj]

It depends what your final hybrid setup is going to be.

What is your goal? Fuel efficiency, maximum independance and autonomy?

If you want autonomy, then I'd go all electric 400V DC link propulsion with inverter drive, all the solar you can fit, and 400V LiFepo4 direct on the inverter DC buss. Then I would buy THE most efficient diesel genset you can get your hands on, and use it only when you were forced to. You also get to run your house 230V electrics (including cooking and water heating) directly off your battery system.

Disclaimer: Without a degreed electrical engineer building that, you will be very vulnerable.

[Dockhead]

Originally Posted by a64pilot

I believe it’s the autoprop. Mine anyway and I only have that one to go by seems to load the engine pretty heavy at low RPM, which is good and great for motor sailing.
Loading an engine heavier than what a fixed prop that is chosen to be correct at full throttle does is more along the ideal loading for an engine.
Take a manual transmission car, your cruise gear is quite high and to accelerate you down shift to a much lower ratio.
An autoprop actually operates similarly, during cruise speed through the water drives the prop to quite a high pitch, accelerate the motor and centripetal forces drive the prop to much lower pitch.

In other words I don’t think the thrust output of an Autoprop follows the theoretical curve. It’s very likely using a whole lot more engine power in sustained cruise at lower RPM.
The theoretical curve is a prop that is only correct at full throttle, it’s incorrect at every other throttle setting, the further from full throttle, and the less likely for it to be correct.

The reason why so many people seem to do fine that are way over-propped is that they never go to full throttle, so at their normal cruise speed the engine is fine, it doesn’t get overloaded until the RPM is increased.
An Autoprop from my observation acts at partial throttle once at cruise speed to be over-propped, so at say 1500 RPM a boat will be moving quite a bit faster as the motor is quite a bit more loaded.

Yeah, that's all exactly correct.


The Autoprop pitches up to fill in the gap between the theoretical propeller curve and the max power curve, at lower RPM's. Or when there is little load on, like when motorsailing.

[Dockhead]

Originally Posted by sdj

. . . Disclaimer: Without a degreed electrical engineer building that, you will be very vulnerable.

That's really good advice. And let him also quantify the advantages (if any), so you can put that against the cost and see it it's actually worth it. The numbers don't lie.

[DeValency]

The load reduction on your engines if alternators are removed will be marginal , so you’ll save almost nothing. And you definitely don’t want to trust your single genset for a fast charge when necessary.
Solar is great in maintaining the batteries charge but will be close to useless if your batteries are fully discharged.

[sdj]

Originally Posted by DeValency

Solar is great in maintaining the batteries charge but will be close to useless if your batteries are fully discharged.

Might be with your 1970's liquid filled lead acid, but not so using the modern approach.

[curtis742]

Just for grins the same thing can be accomplished by removing the belts. If it doesn't work or you need the power just put the belts back on.

[curtis742]

The gains under discussion are meager at best. If you want to save fuel work on your sailing skills. If the idea is to save horsepower for propulsion just turn off the alternators. Solar panels rigidly mounted supply max output for only 4 hours a day providing the sun is directly overhead for the three months out of the year that occurs.

[DeValency]

Originally Posted by sdj

Might be with your 1970's liquid filled lead acid, but not so using the modern approach.

Wow! And what’s your “modern approach”?

As an EEE (as part of my day job) and a real sailor with new 600A AGM and lithium array in the bilges, 350W solar and 6.5 KW Northern genset and a portable 2KW Honda, I do not even consider removing my modest 90A/h alternator from my 100HP Volvo - all that on a SAILBOAT that will go anywhere without even using the engine (unlike the OP that has a motor cat). All of it is fully controlled by a central Victron power management with a global remote access, when away from the boat - way too often, unfortunately, but I need to make sure enough $$$ is earned to fill that hole in the ocean....

When out there away from civilization, spare parts and services you want to keep and maintain any power generator you can.

[transmitterdan]

Originally Posted by curtis742

The gains under discussion are meager at best. If you want to save fuel work on your sailing skills. If the idea is to save horsepower for propulsion just turn off the alternators. Solar panels rigidly mounted supply max output for only 4 hours a day providing the sun is directly overhead for the three months out of the year that occurs.

Their boat doesn’t have any sails....

[carlwk3c]

Originally Posted by Jim Cate

umm again! I think that 0.13 hp is actually around 0.1% of the rated output of your engine(s).

And BTW, on many engines, the same belt that drives the alternator drives the fresh water cooling pump... whatcha gonna do about that if you remove the alternator?

Jim

Good point. The alternator, swinging on its adjustable bracket, is generally what tensions the belt that also drives the water pump. Without the alternator, some alternative means of tensioning the belt would be required.
Removing the alternators will gain essentially nothing, except removing desirable redundancy in power generation. I wonder if the OP has fully considered strings of cloudy days when solar output will be low?

[Alan green]

Remember the alternaters main perpous is to recharge the battery after starting the engine rapidly once cgarged it doesn't pull on the engine the solar system will take hours or days to replenish them so hoping around engine on engine off wil leave flat batteries

[DeValency]

Originally Posted by carlwk3c

Good point. The alternator, swinging on its adjustable bracket, is generally what tensions the belt that also drives the water pump. Without the alternator, some alternative means of tensioning the belt would be required.
Removing the alternators will gain essentially nothing, except removing desirable redundancy in power generation. I wonder if the OP has fully considered strings of cloudy days when solar output will be low?

Right! Solar (unless the OP has a solar farm towed) will need multiple sunny days to fully charge very low batteries.

That’s considering:
• 300W from the solars = 25A/h at optimal conditions without any use of other electrical devices - no fridges, no electronics - nothing! In reality, what you can get from 3 good solar panels a day is +/- 100-150A. I have a data logger on my Siemens panels array in the Caribbeans at this time - that’s it! - and have been verified it with most neighbors at the Saint Lucia Rodney Bay Marina. Never be impressed with pick numbers.

• battery bank of 600A that needs, say 300A of charge.

Meaning you need two sunny days of stand still to get your very low batteries (worse case scenario) to fully charge - could work somehow for a sail boat/cat but never to the OP motor boat while cruising.

And a generator tend to screw us when we really need it. So for me, a genset is the last device to relay on.

But this is my personal taste in power generation. Yet my first line generator is still the modest simple alternator.

[CatNewBee]

Originally Posted by DeValency

Right! Solar (unless the OP has a solar farm towed) will need multiple sunny days to fully charge very low batteries.

That’s considering:
• 300W from the solars = 25A/h at optimal conditions without any use of other electrical devices - no fridges, no electronics - nothing! In reality, what you can get from 3 good solar panels a day is +/- 100-150A. I have a data logger on my Siemens panels array in the Caribbeans at this time - that’s it! - and have been verified it with most neighbors at the Saint Lucia Rodney Bay Marina. Never be impressed with pick numbers.

• battery bank of 600A that needs, say 300A of charge.

Meaning you need two sunny days of stand still to get your very low batteries (worse case scenario) to fully charge - could work somehow for a sail boat/cat but never to the OP motor boat while cruising.

And a generator tend to screw us when we really need it. So for me, a genset is the last device to relay on.

But this is my personal taste in power generation. Yet my first line generator is still the modest simple alternator.

Dont mess up the units please, it hurts people with basic electric knowledge.

A (Amps) is the unit of current flowing actually.
A/h Amps per hour is nothing.
Ah is the capacity of a battery of known voltage, better use Wh or kWh for comparison

There is no battery of 600A, if you short a 100Ah start battery you may get even 1000A for a second. What you mean is 600Ah. And it needs maybe 300Ah of charge, 300A is only the current, I doubt your battery would accept a 300A current (0.5C) under normal conditions.

300W from solar at 14V would end up to a charge current of 21A, if you have 300Wp panels, only in perpendicular radiation at noon and cold ambient temperature you may get 300W out. But your rule of thumb is ok, solar peek Watt (Wp) of the panels * 4 is the average Wh harvested per day for flat panels you can expect. 1200Wh or about 90..100Ah per day at 12V would be an average output for a 300Wp solar array.

It really depends on the radiation (clouds, shading from mast, lines, boom), ambient temperature, used voltages and controller (PWM vs. MPPT), type of battery (FLA or LFP) if you can squeeze every electron out of your panels.

And dont forget your running loads while charging, they tend to chew up a lot of the incomming energy before it even reaches the battery.